The previous post introduced different types of networks and some of their architectural details. In this post, we look at the biggest problem network engineers work on: congestion. How are networks designed to address it? The professor starts tackling this area with a discussion of Quality of Service (QoS). Quality is defined in terms of the underlying requirements e.g. throughput, delay, jitter, packet loss, service availability, and per-flow sequence preservation. Services can be best effort, or other classes like gold service. Cisco’s Quality of Service (QoS) document discusses four levels of metal policy (platinum, gold, silver, and bronze), for example.
Class of Service (CoS) is a traffic classification that enables different actions to be taken on individual classes of traffic. Contrast this to type of service (ToS), which is a specific field in the IPv4 header (used to implement CoS). Juniper Networks post on Understanding Class of Service (CoS) Profiles equates QoS and CoS, but the professor explains that QoS is a more abstract concept than CoS.
QoS is a set of actions that the network takes to deliver the right delay, throughput, etc. QoS timeframes affect the way congestion is handled. For example, scheduling and dropping techniques and per-hop queuing are useful for the low millisecond time regime common in web traffic. Congestion over hundreds of milliseconds typically affects TCP (e.g. round trip times, closed-loop feedback) and this is addressed via methods like active queue management (AQM) and congestion control techniques like random early detection (RED). Congestion that occurs in the tens of seconds to minutes range is addressed by capacity planning.
How is QoS achieved in the data and control planes? By queuing, scheduling, policing, and dropping. The roles of the data and control planes are quite extensive as per the router diagram used to describe them. This is without getting into the details of the management plane e.g. the element management systems (per node) and the network management systems they communicate with. Control plane QoS mechanisms handle admission control and resource reservation and are typically implemented in software. Resource Reservation Protocol (RSVP) is the protocol mostly used in practice for control plane QoS. There are many explanations on RSVP, e.g. this Introduction to RSVP and this RSVP Overview. The primary QoS architectures are integrated services (Intserv) and differentiated services (Diffserv). Intserv uses RSVP and although it doesn’t scale, it is useful when guaranteed service is required.
We start a deep dive into the QoS techniques with queuing. There are different types of queues: first come first served (FCFS/FIFO), priority queues, and weighted queues. Packet schedulers can have a mix of these approches, e.g. 1 priority queue and N other weighted queues. Performance modeling can be done on queues. For voice traffic, the distribution of the arrival rate of traffic is a Poisson distribution. Therefore, the delay of packets and the length of the queue can be accurately modeled/predicted! See M/M/1 queues as a starting point (M/M/1 is Kendall notation and is more fully described in the next video).
Queuing Theory Tutorial – Queues/Lines, Characteristics, Kendall Notation, M/M/1 Queues
Data Plane QoS Mechanisms
These data plane QoS mechanisms are applied at each network node: classification, marking, policing and shaping, prioritization, minimum rate assurance. Below are more details about each.
Classification
This is the process of identifying flows of packets and grouping individual traffic flows into aggregated streams such that actions can be applied to those flow streams. Up to this point, I have had a vague idea of what a flow is but not a proper definition. The instructor defines a flow as a 5-tuple of source & destination IP addresses and TCP/UDP ports and a transport protocol. What is a Network Traffic Flow? discusses various ways of defining a flow, and this is just one of many. Classification needs to avoid fragmentation because the 5-tuple information is only in the first packet. There are 4 ways of classifying traffic:
Simple classification – the use of fields designed for QoS classification in IP headers e.g. the type of service (TOS) byte in IPv4. There are complications with using the DTRM bits of the TOS (e.g. minimizing delay and maximizing throughput could conflict).
Implicit classification – done without inspecting packet header or content, e.g. by examining layer 1 or 2 identifiers.
Complex classification – using fields not designed for QoS classification or layer 2 criteria like MAC addresses.
This is simply setting the fields assigned for QoS classification in IP packet headers (DSCP field) or MPLS packet headers (EXP field).
Source marking is applied at the source of the packets
Ingress marking: used when source cannot mark correctly or cannot be trusted to do so.
Rate Enforcement
This is done to avoid congestion. Policing is a mechanism to ensure that a traffic stream does not exceed a defined maximum rate. It stands in constrast to shaping, which is typically accomplished by queuing (delays traffic, never drops it). One type of policer is the token bucket policer. It never delays traffic and cannot reorder or reprioritize traffic. See Cisco’s Policing and Shaping Overview and QoS Policing documents for details. This is one of the rate limiting algorithms discussed in the video below (I found this video’s explanation more intuitive).
Five Rate Limiting Algorithms ~ Key Concepts in System Design
The next stage is prioritization of the traffic. 4 possible approaches: with prioritiy queues, e.g. where VoIP traffic always has highest priority, other queues can be starved by the scheduler. Weighted round robbin will take more packets from the high priority queues but still cycle through the other queues, taking fewer packets from them. Weighted bandwidth scheduling considers the packet sizes instead of just packet counts per queue (e.g. just taking 1 packet from a low priority queue can have negative impact if the packet is huge). Deficit round robbin is the one used in practice. It keeps track of the history of the number of packets services, and not just instantaneous values. I found the next video to expand on these brief explanations of scheduling algorithms.
How Do Schedulers in Routers Work? Understanding RR, WRR, WFQ, and DRR Through Simple Examples
One of the points that came up in discussion was that the schedulers use Run-to-completion scheduling, which means that a packet must be fully processed before starting on another packet. Routers have an interface FIFO (Tx buffer) on the physical link. When it fills up, this signals to the scheduler that there may be congestion downstream, thereby allowing for back pressure flow control. There is also multi-level strict policy queuing which allows for multiple priority queues instead of just 1 (e.g. voice & video) but not as common today.
Routers also drop packets to prevent unacceptable delays caused by buffering too many packets. There are different dropping strategies, e.g. tail dropping (dropping from the back of the queue), weighted tail dropping (>1 queue limit via heuristics), and head dropping (rare).
Active queue management (AQM) is a congestion avoidance technique. It works by detecting congestion before queues overflow. These are some techniques for AQM:
These QoS mechanisms operate in the context of an overriding architecture, integrated services (Intserv) or differentiated services (Diffserv). IntServ can be used in the financial industry or medical health facilities, for example. These are delay sensitive applications where unbounded scaling is not a real requirement. IntServ explicitly manages bandwidth resources on a per flow basis. DiffServ was developed to support (as the name suggests) differentiated treatment of packets in large scale environments. It does this using a 6-bit differentiated services code point (DSCP) in the IPv4 ToS header or the IPv6 traffic class octet. Classification and conditioning happen at the edge of the DiffServ domain. Actions are performed on behavior aggregates (contrast this to the per flow actions of IntServ). The next technology we learn about is Multiprotocol Label Switching, defined as follows on Wikipedia:
MPLS is similar to IntServ in that it lets you define an end-to-end path through the network for traffic but without reserving resources. It is a hop by hop forwarding mechanism, which stands in contrast to IP which works by making next hop routing decisions without regard to the end-to-end path taken by the packets. MPLS can be deployed on any layer 2 technology (multiprotocol). Benefits of MPLS include fast rerouting in case of failures and providing QoS support. One of the settings in which MPLS is used is in SD-WAN. This article provides a helpful contrast: What is the difference between SD-WAN and MPLS? These are the main applications of MPLS:
Traffic Engineering: allows network administrator to make the path deterministic (normal hop-by-hop routing is not). In other words, a frame forwarding policy can be used instead of relying on dynamic routing protocols.
QoS: the MPLS EXP bits are used for marking traffic per the labels.
This is quite the array of topics, especially for an introduction to networks course. I have a greater appreciation of how broad this space is.
I’m taking an online introductory course on networks. I have been surprised by how much ground this course is covering. I didn’t expect to cover wireless (mobile) networks, for example. I looked for videos on some of the topics to learn more, e.g. 4g network architecture – YouTube. Networking is turning out to be much cooler and more interesting than I thought possible. This post is a compilation of all the key topics introduced in the course (in the general order they were introduced, but not particularly organized into a coherent story).
My main takeaway from this first video is that 4G networks are entirely packet switched (basic, but new to me).
4G LTE Network Architecture Simplified
The next video on how messages are transmitted to the cell phone tower is insightful as well. I appreciated the high-level discussion of antennas.
How WiFi and Cell Phones Work | Wireless Communication Explained
The concept of control plane and data plane came up as well. One advantage of this separation as per the overview below are independent evolution and development of each (e.g. control software can be upgraded without changing the hardware).
M2.1: Overview of Control and Data Plane Separation
5G Service Based Architecture | Telecoms Bytes – Mpirical
Then of course there are the fundamental concepts of throughput, delay, and packet loss error. Jim Kurose’s book (and video below) covers these topics but it’s been a while since I read that book.
The professor also clarified the difference between bandwidth and throughput. The next video briefly touches on this distinction:
The course has also introduced me to the concept of spectral efficiency as part of understanding the difference between bandwidth and throughput. There is no shortage of concepts to learn about, from the different types of lines like T1 and T3 to bit robbing to the existence of network interface devices. The video below is good intro to T1.
DS1 (T1) Fundamentals
There was also a discussion about cable networks, with an onslaught of concepts like Hybrid fiber-coaxial. This Cable 101 video is a helpful resource.
The HFC Cable Systems Introduction video below starts out with a comparison of coax and fiber then explains the flow of signals from the core network to the home.
HFC Cable Systems Introduction
I still need to learn more information about the Cable modem termination system (CMTS) and the next resource is perfect. It mentions CMTS vendors like Arris, Cisco, and Motorola, which inspires me to look up the Cisco CMTS.
Cable Modem Termination System Tutorial (CMTS)
I have never researched how most of these systems work so I am greatly appreciating this introduction to networks course! Here’s a video on how cable modems work, including their interactions with the CMTS.
How Cable Modems Work
The communication between the CMTS and the CMs is done via DOCSIS. Here is the reference I found with insight into DOCSIS.
DOCSIS® 3.1 – An Overview
Something I picked up is that CableLabs does a lot of the research for these systems. Other concepts to know include wavelength-division multiplexing (WDM), which was used in the traditional coax networks. The following explanation is an example of WDM in fiber.
Next, we get into the 7-layer OSI model. The example given for the physical layer is SONET technology. Another foray into T1 technology reveals the fact that bipolar transmission is used for T1 since it is more power efficient.
Multiplexing is the next interesting topic introduced. I have included some videos below on the different types of multiplexing employed in communications.
FDM involves modulating message signals over carrier frequencies then using bandpass filters to extract the individual signals.
The course also addresses transmission fundamentals like the difference between bit rate and baud rate, the Shannon–Hartley theorem, the Nyquist–Shannon sampling theorem, modulation, modems, and codecs. I have compiled a few videos covering these topics below.
Here is an explanation of the Shannon–Hartley theorem:
Channel Capacity by Shannon-Hartley | Basics, Proof & Maximum Bandwidth Condition
We then start getting into network addressing. One of the important concepts here is how the exhaustion of IPv4 addresses is handled: private IP addresses, DHCP, subnetting, and IPv6. One particularly interesting point was the difference between IPv4 and IPv6 headers:
In a discussion of the impact of TCP on throughput, the professor called out TCP global synchronization as an issue that networks need to avoid. Here’s one video about it.
Avoiding packet reordering is another important aspect of TCP. The contrast with UDP is especially interesting when other protocols like Google’s QUIC are designed. The RTP protocol (a relative of UDP, informally speaking) is used for VoIP. This is a good description of RTP:
I mentioned in my last post (Learning about Large Language Models) that I recently started going through Sebastian Raschka’s Build a Large Language Model from Scratch book. It had been a while since I ran python code on my laptop so I needed to do some cleanup to restore my environment. I cloned the repo and started executing the first cell in Chapter 2:
from importlib.metadata import version
print("torch version:", version("torch"))
print("tiktoken version:", version("tiktoken"))
I got this error: PackageNotFoundError: No package metadata was found for torch".
{
"name": "PackageNotFoundError",
"message": "No package metadata was found for torch",
"stack": "---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
File /opt/homebrew/Cellar/python@3.11/3.11.1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/importlib/metadata/__init__.py:563, in Distribution.from_name(cls, name)
562 try:
--> 563 return next(cls.discover(name=name))
564 except StopIteration:
StopIteration:
During handling of the above exception, another exception occurred:
PackageNotFoundError Traceback (most recent call last)
Cell In[2], line 7
3 print(sys.version)
5 from importlib.metadata import version
----> 7 print(\"torch version:\", version(\"torch\"))
8 print(\"tiktoken version:\", version(\"tiktoken\"))
File /opt/homebrew/Cellar/python@3.11/3.11.1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/importlib/metadata/__init__.py:1008, in version(distribution_name)
1001 def version(distribution_name):
1002 \"\"\"Get the version string for the named package.
1003
1004 :param distribution_name: The name of the distribution package to query.
1005 :return: The version string for the package as defined in the package's
1006 \"Version\" metadata key.
1007 \"\"\"
-> 1008 return distribution(distribution_name).version
File /opt/homebrew/Cellar/python@3.11/3.11.1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/importlib/metadata/__init__.py:981, in distribution(distribution_name)
975 def distribution(distribution_name):
976 \"\"\"Get the ``Distribution`` instance for the named package.
977
978 :param distribution_name: The name of the distribution package as a string.
979 :return: A ``Distribution`` instance (or subclass thereof).
980 \"\"\"
--> 981 return Distribution.from_name(distribution_name)
File /opt/homebrew/Cellar/python@3.11/3.11.1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/importlib/metadata/__init__.py:565, in Distribution.from_name(cls, name)
563 return next(cls.discover(name=name))
564 except StopIteration:
--> 565 raise PackageNotFoundError(name)
PackageNotFoundError: No package metadata was found for torch"
}
How is this showing version 3.10.9 but VS Code is using 3.11 from brew (per the file paths in the error messages? This is how to print the version from a python script as per Printing Python version in output – Stack Overflow
Since I have brew installed, this might be what I need: the comment that “If you brew-install Python, but pip is still not in your path, you might need to re-link, like this brew unlink python && brew link python” at python – How do I install pip on macOS or OS X? – Stack Overflow.
saint@MacBookPro LLMs-from-scratch % brew update
==> Downloading https://ghcr.io/v2/homebrew/portable-ruby/portable-ruby/blobs/sha256:d9faa506c014dedc0b034a68103ba75c9a58242f4d6c67b6ca0f649c39602bcf
######################################################################################################################################################################################################################################### 100.0%
==> Pouring portable-ruby-3.3.7.arm64_big_sur.bottle.tar.gz
==> Homebrew collects anonymous analytics.
Read the analytics documentation (and how to opt-out) here:
https://docs.brew.sh/Analytics
No analytics have been recorded yet (nor will be during this `brew` run).
==> homebrew/core is old and unneeded, untapping to save space...
Untapping homebrew/core...
Untapped 3 commands and 7398 formulae (7,130 files, 1GB).
==> homebrew/cask is old and unneeded, untapping to save space...
Untapping homebrew/cask...
Untapped 7333 casks (4,415 files, 487.2MB).
==> Downloading https://formulae.brew.sh/api/formula_tap_migrations.jws.json
Updated 4 taps (microsoft/git, homebrew/cask-versions, homebrew/core and homebrew/cask).
==> New Formulae
...<hundreds of lines omitted but included python entries below>
python-argcomplete
python-freethreading
python-gdbm@3.12
python-gdbm@3.13
python-matplotlib
python-packaging
python-setuptools
python-tk@3.12
python-tk@3.13
python@3.12
python@3.13
pyupgrade
...
==> Deleted Installed Formulae
icu4c ✘
==> Deleted Installed Casks
git-credential-manager-core ✘ microsoft-openjdk11 ✘
Error: Unexpected method 'appcast' called on Cask adoptopenjdk16.
Follow the instructions here:
https://github.com/Homebrew/homebrew-cask#reporting-bugs
==> Downloading https://formulae.brew.sh/api/cask_tap_migrations.jws.json
==> Outdated Formulae
aom fb303 fribidi gnuplot jasper libheif libtool lua openblas pstoedit sqlite xorgproto
arpack fbthrift gcc graphicsmagick jbig2dec libidn libunistring lz4 openexr pyqt@5 suite-sparse xz
autoconf fig2dev gd harfbuzz jpeg-turbo libidn2 libvmaf maven openjdk python@3.10 sundials zstd
boost fizz gdbm hdf5 jpeg-xl liblqr libx11 mpdecimal openjpeg python@3.11 tcl-tk
brotli flac gettext highway libaec libomp libxau mpfr openssl@1.1 python@3.9 texinfo
ca-certificates fltk ghostscript hwloc libavif libpng libxcb mpg123 openssl@3 qscintilla2 wangle
cairo fmt giflib icu4c@76 libcerf libraw libxdmcp netpbm opus qt@5 watchman
cmake folly git-gui imagemagick libde265 libsndfile libxext ninja pango readline webp
double-conversion fontconfig glib imath libevent libsodium libxrender octave pcre2 shared-mime-info wget
edencommon freetype gmp isl libffi libtiff little-cms2 open-mpi pixman snappy x265
==> Outdated Casks
git-credential-manager microsoft-openjdk microsoft-openjdk@11
You have 113 outdated formulae and 3 outdated casks installed.
You can upgrade them with brew upgrade
or list them with brew outdated.
Error: Unexpected method 'appcast' called on Cask adoptopenjdk16.
Follow the instructions here:
https://github.com/Homebrew/homebrew-cask#reporting-bugs
==> Migrating cask git-credential-manager-core to git-credential-manager
Error: inreplace failed
/opt/homebrew/Caskroom/git-credential-manager/.metadata/2.1.2/20230703191748.675/Casks/git-credential-manager.rb:
expected replacement of /\A\s*cask\s+"git\-credential\-manager\-core"/ with "cask \"git-credential-manager\""
python3 --version is still 3.10.9 after this. I tried running pip but zsh sayd command not found. Unfortunately, linking or unlinking of either python or python3 fails with the errors below (despite ls -l `which python3` showing the same path as before).
saint@MacBookPro LLMs-from-scratch % brew unlink python3
Error: Unexpected method 'appcast' called on Cask adoptopenjdk16.
Follow the instructions here:
https://github.com/Homebrew/homebrew-cask#reporting-bugs
Error: No such keg: /opt/homebrew/Cellar/python3
I decided to install python3 again.
saint@MacBookPro LLMs-from-scratch % brew install python3
==> Downloading https://formulae.brew.sh/api/formula.jws.json
==> Downloading https://formulae.brew.sh/api/cask.jws.json
==> Downloading https://ghcr.io/v2/homebrew/core/python/3.13/manifests/3.13.1
######################################################################################################################################################################################################################################### 100.0%
==> Fetching dependencies for python@3.13: mpdecimal, ca-certificates, openssl@3, readline, sqlite and xz
==> Downloading https://ghcr.io/v2/homebrew/core/mpdecimal/manifests/4.0.0-1
######################################################################################################################################################################################################################################### 100.0%
==> Fetching mpdecimal
==> Downloading https://ghcr.io/v2/homebrew/core/mpdecimal/blobs/sha256:0f5f269bed0e6be2de3edfc4b52867e656f993e5bcff40717f26ee94dd0d2211
######################################################################################################################################################################################################################################### 100.0%
==> Downloading https://ghcr.io/v2/homebrew/core/ca-certificates/manifests/2024-12-31
######################################################################################################################################################################################################################################### 100.0%
==> Fetching ca-certificates
...
<lots of omitted lines>
...
==> Fetching harfbuzz
==> Downloading https://ghcr.io/v2/homebrew/core/harfbuzz/blobs/sha256:2f892566c02b3c8c61aed6f7867b4405e5c814df8500ef4bc4ca91a9e40205a9
######################################################################################################################################################################################################################################### 100.0%
==> Fetching openjdk
==> Downloading https://ghcr.io/v2/homebrew/core/openjdk/blobs/sha256:1285eadf2b5998cda49e4470ee3875e855b0be199765401ad77dc38aea573f49
######################################################################################################################################################################################################################################### 100.0%
Error: can't modify frozen String: "The bottle needs the Xcode Command Line Tools to be installed at /Library/Developer/CommandLineTools.\nDevelopment tools provided by Xcode.app are not sufficient.\n\nYou can install the Xcode Command Line Tools, if desired, with:\n xcode-select --install\n"
This was the new state of affairs is that command (failed):
saint@MacBookPro LLMs-from-scratch % python3 --version
Python 3.13.1
saint@MacBookPro LLMs-from-scratch % which python3
/opt/homebrew/bin/python3
saint@MacBookPro LLMs-from-scratch % ls -l `which python3`
lrwxr-xr-x 1 saint admin 40 Feb 4 17:02 /opt/homebrew/bin/python3 -> ../Cellar/python@3.13/3.13.1/bin/python3
saint@MacBookPro LLMs-from-scratch % which pip
pip not found
Ah, all that agonizing and look at this – did I need to be using pip3 all this time?
saint@MacBookPro LLMs-from-scratch % which pip3
/opt/homebrew/bin/pip3
saint@MacBookPro LLMs-from-scratch % ls -l `which pip3`
lrwxr-xr-x 1 saint admin 37 Feb 4 17:02 /opt/homebrew/bin/pip3 -> ../Cellar/python@3.13/3.13.1/bin/pip3
saint@MacBookPro LLMs-from-scratch %
Interestingly, I still can’t install pytorch using pip3?
saint@MacBookPro LLMs-from-scratch % pip3 install pytorch
[notice] A new release of pip is available: 24.3.1 -> 25.0
[notice] To update, run: python3.13 -m pip install --upgrade pip
error: externally-managed-environment
× This environment is externally managed
╰─> To install Python packages system-wide, try brew install
xyz, where xyz is the package you are trying to
install.
If you wish to install a Python library that isn't in Homebrew,
use a virtual environment:
python3 -m venv path/to/venv
source path/to/venv/bin/activate
python3 -m pip install xyz
If you wish to install a Python application that isn't in Homebrew,
it may be easiest to use 'pipx install xyz', which will manage a
virtual environment for you. You can install pipx with
brew install pipx
You may restore the old behavior of pip by passing
the '--break-system-packages' flag to pip, or by adding
'break-system-packages = true' to your pip.conf file. The latter
will permanently disable this error.
If you disable this error, we STRONGLY recommend that you additionally
pass the '--user' flag to pip, or set 'user = true' in your pip.conf
file. Failure to do this can result in a broken Homebrew installation.
Read more about this behavior here: <https://peps.python.org/pep-0668/>
note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.
saint@MacBookPro LLMs-from-scratch % xcode-select --install
xcode-select: note: install requested for command line developer tools
I installed the command line developer tools when prompted below.
Trying to run the first cell in VS Code with the updated setup now gave this error:
{
"name": "",
"message": "",
"stack": "Running cells with 'Python 3.13.1' requires the ipykernel package.
Run the following command to install 'ipykernel' into the Python environment.
Command: '/opt/homebrew/bin/python3 -m pip install ipykernel -U --user --force-reinstall'"
}
saint@MacBookPro LLMs-from-scratch % /opt/homebrew/bin/python3 -m pip install ipykernel -U --user --force-reinstall
[notice] A new release of pip is available: 24.3.1 -> 25.0
[notice] To update, run: python3.13 -m pip install --upgrade pip
error: externally-managed-environment
× This environment is externally managed
╰─> To install Python packages system-wide, try brew install
xyz, where xyz is the package you are trying to
install.
If you wish to install a Python library that isn't in Homebrew,
use a virtual environment:
python3 -m venv path/to/venv
source path/to/venv/bin/activate
python3 -m pip install xyz
If you wish to install a Python application that isn't in Homebrew,
it may be easiest to use 'pipx install xyz', which will manage a
virtual environment for you. You can install pipx with
brew install pipx
You may restore the old behavior of pip by passing
the '--break-system-packages' flag to pip, or by adding
'break-system-packages = true' to your pip.conf file. The latter
will permanently disable this error.
If you disable this error, we STRONGLY recommend that you additionally
pass the '--user' flag to pip, or set 'user = true' in your pip.conf
file. Failure to do this can result in a broken Homebrew installation.
Read more about this behavior here: <https://peps.python.org/pep-0668/>
note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.
saint@MacBookPro LLMs-from-scratch % brew install ipykernel
==> Downloading https://formulae.brew.sh/api/formula.jws.json
==> Downloading https://formulae.brew.sh/api/cask.jws.json
Warning: No available formula with the name "ipykernel".
==> Searching for similarly named formulae and casks...
Error: No formulae or casks found for ipykernel.
I override the warning using the --break-system-packages flag and the VS Code notebook now runs.
saint@MacBookPro LLMs-from-scratch % python3 -m pip install ipykernel -U --user --force-reinstall --break-system-package
Collecting ipykernel
Downloading ipykernel-6.29.5-py3-none-any.whl.metadata (6.3 kB)
Collecting appnope (from ipykernel)
Downloading appnope-0.1.4-py2.py3-none-any.whl.metadata (908 bytes)
Collecting comm>=0.1.1 (from ipykernel)
Downloading comm-0.2.2-py3-none-any.whl.metadata (3.7 kB)
Collecting debugpy>=1.6.5 (from ipykernel)
Downloading debugpy-1.8.12-cp313-cp313-macosx_14_0_universal2.whl.metadata (1.3 kB)
Collecting ipython>=7.23.1 (from ipykernel)
Downloading ipython-8.32.0-py3-none-any.whl.metadata (5.0 kB)
Collecting jupyter-client>=6.1.12 (from ipykernel)
Downloading jupyter_client-8.6.3-py3-none-any.whl.metadata (8.3 kB)
Collecting jupyter-core!=5.0.*,>=4.12 (from ipykernel)
Downloading jupyter_core-5.7.2-py3-none-any.whl.metadata (3.4 kB)
Collecting matplotlib-inline>=0.1 (from ipykernel)
Downloading matplotlib_inline-0.1.7-py3-none-any.whl.metadata (3.9 kB)
Collecting nest-asyncio (from ipykernel)
Downloading nest_asyncio-1.6.0-py3-none-any.whl.metadata (2.8 kB)
Collecting packaging (from ipykernel)
Downloading packaging-24.2-py3-none-any.whl.metadata (3.2 kB)
Collecting psutil (from ipykernel)
Downloading psutil-6.1.1-cp36-abi3-macosx_11_0_arm64.whl.metadata (22 kB)
Collecting pyzmq>=24 (from ipykernel)
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Collecting six>=1.5 (from python-dateutil>=2.8.2->jupyter-client>=6.1.12->ipykernel)
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Downloading tornado-6.4.2-cp38-abi3-macosx_10_9_universal2.whl (436 kB)
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Downloading pexpect-4.9.0-py2.py3-none-any.whl (63 kB)
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Installing collected packages: wcwidth, pure-eval, ptyprocess, traitlets, tornado, six, pyzmq, pygments, psutil, prompt_toolkit, platformdirs, pexpect, parso, packaging, nest-asyncio, executing, decorator, debugpy, asttokens, appnope, stack_data, python-dateutil, matplotlib-inline, jupyter-core, jedi, comm, jupyter-client, ipython, ipykernel
WARNING: The script pygmentize is installed in '/Users/saint/Library/Python/3.13/bin' which is not on PATH.
Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.
WARNING: The script debugpy is installed in '/Users/saint/Library/Python/3.13/bin' which is not on PATH.
Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.
WARNING: The scripts jupyter, jupyter-migrate and jupyter-troubleshoot are installed in '/Users/saint/Library/Python/3.13/bin' which is not on PATH.
Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.
WARNING: The scripts jupyter-kernel, jupyter-kernelspec and jupyter-run are installed in '/Users/saint/Library/Python/3.13/bin' which is not on PATH.
Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.
WARNING: The scripts ipython and ipython3 are installed in '/Users/saint/Library/Python/3.13/bin' which is not on PATH.
Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.
Successfully installed appnope-0.1.4 asttokens-3.0.0 comm-0.2.2 debugpy-1.8.12 decorator-5.1.1 executing-2.2.0 ipykernel-6.29.5 ipython-8.32.0 jedi-0.19.2 jupyter-client-8.6.3 jupyter-core-5.7.2 matplotlib-inline-0.1.7 nest-asyncio-1.6.0 packaging-24.2 parso-0.8.4 pexpect-4.9.0 platformdirs-4.3.6 prompt_toolkit-3.0.50 psutil-6.1.1 ptyprocess-0.7.0 pure-eval-0.2.3 pygments-2.19.1 python-dateutil-2.9.0.post0 pyzmq-26.2.1 six-1.17.0 stack_data-0.6.3 tornado-6.4.2 traitlets-5.14.3 wcwidth-0.2.13
[notice] A new release of pip is available: 24.3.1 -> 25.0
[notice] To update, run: python3.13 -m pip install --upgrade pip
saint@MacBookPro LLMs-from-scratch %
First cell now fails because the torch package cannot be found:
{
"name": "PackageNotFoundError",
"message": "No package metadata was found for torch",
"stack": "---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
File /opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/importlib/metadata/__init__.py:407, in Distribution.from_name(cls, name)
406 try:
--> 407 return next(iter(cls.discover(name=name)))
408 except StopIteration:
StopIteration:
During handling of the above exception, another exception occurred:
PackageNotFoundError Traceback (most recent call last)
Cell In[1], line 3
1 from importlib.metadata import version
----> 3 print(\"torch version:\", version(\"torch\"))
4 print(\"tiktoken version:\", version(\"tiktoken\"))
File /opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/importlib/metadata/__init__.py:987, in version(distribution_name)
980 def version(distribution_name: str) -> str:
981 \"\"\"Get the version string for the named package.
982
983 :param distribution_name: The name of the distribution package to query.
984 :return: The version string for the package as defined in the package's
985 \"Version\" metadata key.
986 \"\"\"
--> 987 return distribution(distribution_name).version
File /opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/importlib/metadata/__init__.py:960, in distribution(distribution_name)
954 def distribution(distribution_name: str) -> Distribution:
955 \"\"\"Get the ``Distribution`` instance for the named package.
956
957 :param distribution_name: The name of the distribution package as a string.
958 :return: A ``Distribution`` instance (or subclass thereof).
959 \"\"\"
--> 960 return Distribution.from_name(distribution_name)
File /opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/importlib/metadata/__init__.py:409, in Distribution.from_name(cls, name)
407 return next(iter(cls.discover(name=name)))
408 except StopIteration:
--> 409 raise PackageNotFoundError(name)
PackageNotFoundError: No package metadata was found for torch"
}
These are the commands I tried to install pytorch before finding the correct one: pip3 install torch --break-system-packages.
saint@MacBookPro LLMs-from-scratch % brew install torch
==> Downloading https://formulae.brew.sh/api/formula.jws.json
==> Downloading https://formulae.brew.sh/api/cask.jws.json
Warning: No available formula with the name "torch". Did you mean tor, pytorch or orc?
==> Searching for similarly named formulae and casks...
==> Formulae
pytorch ✔ torchvision tor orc
To install pytorch ✔, run:
brew install pytorch ✔
saint@MacBookPro LLMs-from-scratch % brew install pytorch
Warning: pytorch 2.5.1_4 is already installed and up-to-date.
To reinstall 2.5.1_4, run:
brew reinstall pytorch
saint@MacBookPro LLMs-from-scratch % pip3 install torch
[notice] A new release of pip is available: 24.3.1 -> 25.0
[notice] To update, run: python3.13 -m pip install --upgrade pip
error: externally-managed-environment
× This environment is externally managed
╰─> To install Python packages system-wide, try brew install
xyz, where xyz is the package you are trying to
install.
If you wish to install a Python library that isn't in Homebrew,
use a virtual environment:
python3 -m venv path/to/venv
source path/to/venv/bin/activate
python3 -m pip install xyz
If you wish to install a Python application that isn't in Homebrew,
it may be easiest to use 'pipx install xyz', which will manage a
virtual environment for you. You can install pipx with
brew install pipx
You may restore the old behavior of pip by passing
the '--break-system-packages' flag to pip, or by adding
'break-system-packages = true' to your pip.conf file. The latter
will permanently disable this error.
If you disable this error, we STRONGLY recommend that you additionally
pass the '--user' flag to pip, or set 'user = true' in your pip.conf
file. Failure to do this can result in a broken Homebrew installation.
Read more about this behavior here: <https://peps.python.org/pep-0668/>
note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.
saint@MacBookPro LLMs-from-scratch %
saint@MacBookPro LLMs-from-scratch % pip3 install torch --break-system-packages
Collecting torch
Downloading torch-2.6.0-cp313-none-macosx_11_0_arm64.whl.metadata (28 kB)
Collecting filelock (from torch)
Downloading filelock-3.17.0-py3-none-any.whl.metadata (2.9 kB)
Collecting typing-extensions>=4.10.0 (from torch)
Downloading typing_extensions-4.12.2-py3-none-any.whl.metadata (3.0 kB)
Collecting networkx (from torch)
Downloading networkx-3.4.2-py3-none-any.whl.metadata (6.3 kB)
Collecting jinja2 (from torch)
Downloading jinja2-3.1.5-py3-none-any.whl.metadata (2.6 kB)
Collecting fsspec (from torch)
Downloading fsspec-2025.2.0-py3-none-any.whl.metadata (11 kB)
Collecting setuptools (from torch)
Downloading setuptools-75.8.0-py3-none-any.whl.metadata (6.7 kB)
Collecting sympy==1.13.1 (from torch)
Downloading sympy-1.13.1-py3-none-any.whl.metadata (12 kB)
Collecting mpmath<1.4,>=1.1.0 (from sympy==1.13.1->torch)
Downloading mpmath-1.3.0-py3-none-any.whl.metadata (8.6 kB)
Collecting MarkupSafe>=2.0 (from jinja2->torch)
Downloading MarkupSafe-3.0.2-cp313-cp313-macosx_11_0_arm64.whl.metadata (4.0 kB)
Downloading torch-2.6.0-cp313-none-macosx_11_0_arm64.whl (66.5 MB)
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Downloading sympy-1.13.1-py3-none-any.whl (6.2 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 6.2/6.2 MB 75.0 MB/s eta 0:00:00
Downloading typing_extensions-4.12.2-py3-none-any.whl (37 kB)
Downloading filelock-3.17.0-py3-none-any.whl (16 kB)
Downloading fsspec-2025.2.0-py3-none-any.whl (184 kB)
Downloading jinja2-3.1.5-py3-none-any.whl (134 kB)
Downloading networkx-3.4.2-py3-none-any.whl (1.7 MB)
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Downloading setuptools-75.8.0-py3-none-any.whl (1.2 MB)
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Downloading MarkupSafe-3.0.2-cp313-cp313-macosx_11_0_arm64.whl (12 kB)
Downloading mpmath-1.3.0-py3-none-any.whl (536 kB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 536.2/536.2 kB 27.9 MB/s eta 0:00:00
Installing collected packages: mpmath, typing-extensions, sympy, setuptools, networkx, MarkupSafe, fsspec, filelock, jinja2, torch
Successfully installed MarkupSafe-3.0.2 filelock-3.17.0 fsspec-2025.2.0 jinja2-3.1.5 mpmath-1.3.0 networkx-3.4.2 setuptools-75.8.0 sympy-1.13.1 torch-2.6.0 typing-extensions-4.12.2
[notice] A new release of pip is available: 24.3.1 -> 25.0
[notice] To update, run: python3.13 -m pip install --upgrade pip
saint@MacBookPro LLMs-from-scratch %
The pytorch import finally works! The next error is also a PackageNotFoundError: "No package metadata was found for tiktoken" which I addressed with the same installation steps:
saint@MacBookPro LLMs-from-scratch % pip3 install tiktoken
[notice] A new release of pip is available: 24.3.1 -> 25.0
[notice] To update, run: python3.13 -m pip install --upgrade pip
error: externally-managed-environment
× This environment is externally managed
╰─> To install Python packages system-wide, try brew install
xyz, where xyz is the package you are trying to
install.
If you wish to install a Python library that isn't in Homebrew,
use a virtual environment:
python3 -m venv path/to/venv
source path/to/venv/bin/activate
python3 -m pip install xyz
If you wish to install a Python application that isn't in Homebrew,
it may be easiest to use 'pipx install xyz', which will manage a
virtual environment for you. You can install pipx with
brew install pipx
You may restore the old behavior of pip by passing
the '--break-system-packages' flag to pip, or by adding
'break-system-packages = true' to your pip.conf file. The latter
will permanently disable this error.
If you disable this error, we STRONGLY recommend that you additionally
pass the '--user' flag to pip, or set 'user = true' in your pip.conf
file. Failure to do this can result in a broken Homebrew installation.
Read more about this behavior here: <https://peps.python.org/pep-0668/>
note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.
saint@MacBookPro LLMs-from-scratch %
saint@MacBookPro LLMs-from-scratch % pip3 install tiktoken --break-system-packages
Collecting tiktoken
Downloading tiktoken-0.8.0-cp313-cp313-macosx_11_0_arm64.whl.metadata (6.6 kB)
Collecting regex>=2022.1.18 (from tiktoken)
Downloading regex-2024.11.6-cp313-cp313-macosx_11_0_arm64.whl.metadata (40 kB)
Collecting requests>=2.26.0 (from tiktoken)
Downloading requests-2.32.3-py3-none-any.whl.metadata (4.6 kB)
Collecting charset-normalizer<4,>=2 (from requests>=2.26.0->tiktoken)
Downloading charset_normalizer-3.4.1-cp313-cp313-macosx_10_13_universal2.whl.metadata (35 kB)
Collecting idna<4,>=2.5 (from requests>=2.26.0->tiktoken)
Downloading idna-3.10-py3-none-any.whl.metadata (10 kB)
Collecting urllib3<3,>=1.21.1 (from requests>=2.26.0->tiktoken)
Downloading urllib3-2.3.0-py3-none-any.whl.metadata (6.5 kB)
Collecting certifi>=2017.4.17 (from requests>=2.26.0->tiktoken)
Downloading certifi-2025.1.31-py3-none-any.whl.metadata (2.5 kB)
Downloading tiktoken-0.8.0-cp313-cp313-macosx_11_0_arm64.whl (982 kB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 982.8/982.8 kB 24.2 MB/s eta 0:00:00
Downloading regex-2024.11.6-cp313-cp313-macosx_11_0_arm64.whl (284 kB)
Downloading requests-2.32.3-py3-none-any.whl (64 kB)
Downloading certifi-2025.1.31-py3-none-any.whl (166 kB)
Downloading charset_normalizer-3.4.1-cp313-cp313-macosx_10_13_universal2.whl (195 kB)
Downloading idna-3.10-py3-none-any.whl (70 kB)
Downloading urllib3-2.3.0-py3-none-any.whl (128 kB)
Installing collected packages: urllib3, regex, idna, charset-normalizer, certifi, requests, tiktoken
Successfully installed certifi-2025.1.31 charset-normalizer-3.4.1 idna-3.10 regex-2024.11.6 requests-2.32.3 tiktoken-0.8.0 urllib3-2.3.0
[notice] A new release of pip is available: 24.3.1 -> 25.0
[notice] To update, run: python3.13 -m pip install --upgrade pip
saint@MacBookPro LLMs-from-scratch %
Finally, my machine is in a state that can run the code in the Jupyter notebook! This is such a brittle environment. I need to switch to a managed environment to avoid this type of mess.
These shortcomings aside, the ASRock > B550M-C motherboard in that desktop had more than enough SATA ports. I mounted the hard disk in my HPZ4 desktop (now there’s a well-designed case) and plugged one of the HP case power connectors to it. I then connected the SATA cable from the hard disk to my Skytech motherboard. Talk about a cowboy setup. Here’s the Disk Management view after starting Windows.
I use the “New Simple Volume” command to do an NTFS quick format on the 7630868 MB volume:
With my 8TB hard ddrive set up, I searched for how to move onedrive folder to different drive. This Microsoft Support result had directions on how to Change the location of your OneDrive folder. I set up OneDrive to download everything on OneDrive and to always keep the files locally. I disabled sleep mode on my desktop to let OneDrive download continuously. After downloading 896.5GB, I got this error.
Syncing did not resume until later the next day (it had been over 24hours by the time I tried again). It had never crossed my mind that there are such limits for these services – I just expect them to be available when I needed them, which is another reason to have a local copy of everything I have in the cloud. In the process of setting all this up, I realized that 200GB of the videos I had on OneDrive didn’t really need to be there, so I was able to free up enough space to meet my needs for some time into the foreseeable future.
I have seen many platforms playing multiple videos where the presenter and their screen are separate streams but they are kept in sync. Native HTML5 video support was relatively new when I last worked on web development so I decided to experiment with multiple videos in an HTML5 document. Here is the basic HTML page:
I ran this through the W3C Markup Validation Service and this snippet passed the check. My initial attempt closed the video tag using the <video ... /> style. The validator complained that “Self-closing syntax (/>) used on a non-void HTML element.” A search engine led me to Mozilla’s Void element page.
A void element is an element in HTML that cannot have any child nodes (i.e., nested elements or text nodes). Void elements only have a start tag; end tags must not be specified for void elements.
This means that non-void elements should have a closing tag. It’s also strange to me that the controls attribute is required to show controls but I guess it makes sense to let that be, well, controllable.
To synchronize the videos, we need to ensure that playing one video results in the other playing as well. Likewise for pausing, seeking, and changing the playback speed. My first attempt at this was to add JavaScript to the head of the HTML document. I’m not using jQuery or any other libraries. Therefore, I ran into exceptions because the DOM wasn’t ready when my script was running. Vanilla JavaScript equivalent of jQuery’s $.ready() – how to call a function when the page/DOM is ready for it [duplicate] suggested putting the script after all the HTML elements. All this was once second nature to me back in the IE6 days but this suggestion is good enough for my experiment. The final page now looks like this (with links to the relevant events, properties, and methods):
<!DOCTYPE html>
<html lang="en">
<title>Two Video Synchronization Demo</title>
<body>
<!-- https://developer.mozilla.org/en-US/docs/Web/HTML/Element/video -->
<videocontrols id="video1" src="flower.mp4"></video>
<videocontrols id="video2" src="nature.mp4"></video>
<script>
const video1 = document.getElementById("video1");
const video2 = document.getElementById("video2");
// Handle the play event on each video to ensure that
// when one video is played the other plays as well.
video1.addEventListener("play", (event) => {
video2.play();
});
video2.addEventListener("play", (event) => {
video1.play();
});
// Handle the pause event on each video to ensure that
// when one video is paused the other is paused as well.
video1.addEventListener("pause", (event) => {
video2.pause();
});
video2.addEventListener("pause", (event) => {
video1.pause();
});
// Handle the ratechange event on each video to ensure that
// when the playback rate of one video is changed,
// the other is set to use the same rate.
video1.addEventListener("ratechange", (event) => {
video2.playbackRate = video1.playbackRate;
});
video2.addEventListener("ratechange", (event) => {
video1.playbackRate = video2.playbackRate;
});
// Handle the seek event on each video to ensure that
// when one video is seeked the other seeks to the same location.
video1.addEventListener("seeked", (event) => {
// Do not use fastSeek since we need precision.
if (video1.paused && video2.paused) {
video2.currentTime = video1.currentTime;
}
});
video2.addEventListener("seeked", (event) => {
if (video1.paused && video2.paused) {
video1.currentTime = video2.currentTime;
}
});
</script>
</body>
</html>
Notice that the last requirement on seeking is implemented slightly differently: I synchronized the current time in the videos only if they were both paused. This prevents weird behavior where the videos keep syncing to each other interrupting playback.
The last thing I wanted to do was lay out the videos so that one overlaps the other (in the top left or bottom right). I needed to add a style tag to the head of the document. I searched for how to put a div in the bottom right and the StackOverflow question How can I position my div at the bottom of its container? suggests absolute positioning in a container div. See the CSS in the final page below.
<!DOCTYPE html>
<html lang="en">
<title>Two Video Synchronization Demo</title>
<style>
#video-container {
position: relative;
}
#video1 {
width: 20%;
position:absolute;
top: 0px;
left: 0px;
}
#video2 {
width: 100%;
}
</style>
<body>
<div id="video-container">
<videocontrols id="video1" src="flower.mp4"></video>
<videocontrols id="video2" src="nature.mp4"></video>
</div>
<script>
const video1 = document.getElementById("video1");
const video2 = document.getElementById("video2");
// Handle the play event on each video to ensure that
// when one video is played the other plays as well.
video1.addEventListener("play", (event) => {
video2.play();
});
video2.addEventListener("play", (event) => {
video1.play();
});
// Handle the pause event on each video to ensure that
// when one video is paused the other is paused as well.
video1.addEventListener("pause", (event) => {
video2.pause();
});
video2.addEventListener("pause", (event) => {
video1.pause();
});
// Handle the ratechange event on each video to ensure that
// when the playback rate of one video is changed,
// the other is set to use the same rate.
video1.addEventListener("ratechange", (event) => {
video2.playbackRate = video1.playbackRate;
});
video2.addEventListener("ratechange", (event) => {
video1.playbackRate = video2.playbackRate;
});
// Handle the seek event on each video to ensure that
// when one video is seeked the other seeks to the same location.
video1.addEventListener("seeked", (event) => {
// Do not use fastSeek since we need precision.
if (video1.paused && video2.paused) {
video2.currentTime = video1.currentTime;
}
});
video2.addEventListener("seeked", (event) => {
if (video1.paused && video2.paused) {
video1.currentTime = video2.currentTime;
}
});
</script>
</body>
</html>
This was a useful HTML, JavaScript, and CSS refresher!
I want to evaluate the OpenJDK serial collector using a Java program I wrote to factorize natural numbers by trial division. This post is about how to set up the app to run in a Docker container on a Linux host. Since the host is a shared machine, I put all my work under ~/swesonga (my own custom home directory). The directory structure for the container will be under ~/swesonga/container/.
Set up the Factorization App
First, log into Linux machine and download the Java binaries to test:
ssh user@IPaddress
mkdir -p ~/swesonga/container/java/binaries/jdk/x64/
cd ~/swesonga/container/java/binaries/jdk/x64/
curl -Lo microsoft-jdk-21.0.5-linux-x64.tar.gz https://aka.ms/download-jdk/microsoft-jdk-21.0.5-linux-x64.tar.gz
tar xzf microsoft-jdk-21.0.5-linux-x64.tar.gz
cd ~/swesonga/container/
git clone https://github.com/swesonga/factorize
cd ~/swesonga/container/java
curl -Lo commons-cli-1.9.0-bin.tar.gz https://dlcdn.apache.org//commons/cli/binaries/commons-cli-1.9.0-bin.tar.gz
tar xzf commons-cli-1.9.0-bin.tar.gz
Verify that docker is up by running docker version. I got this output:
user@machine:~/swesonga$ docker version
Client: Docker Engine - Community
Version: 23.0.1
API version: 1.42
Go version: go1.19.5
Git commit: a5ee5b1
Built: Thu Feb 9 19:46:56 2023
OS/Arch: linux/amd64
Context: default
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
One error I ran into initially was that docker was unable to start the container process. I had missed the COPY command in the Dockerfile so the file couldn’t be found:
user@machine:~/swesonga$ docker run -i -t swesonga-jdk21-testapp
docker: Error response from daemon: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: exec: "/home/<user>/swesonga/java/binaries/jdk/x64/jdk-21.0.5+11/bin/java": stat /home/<user>/swesonga/java/binaries/jdk/x64/jdk-21.0.5+11/bin/java: no such file or directory: unknown.
ERRO[0000] error waiting for container:
user@machine:~/swesonga$ docker system df
TYPE TOTAL ACTIVE SIZE RECLAIMABLE
Images 2 2 1.22GB 443.1MB (36%)
Containers 3 0 0B 0B
Local Volumes 0 0 0B 0B
Build Cache 9 0 776.9MB 776.9MB
user@machine:~/swesonga$ docker system df -v
Images space usage:
REPOSITORY TAG IMAGE ID CREATED SIZE SHARED SIZE UNIQUE SIZE CONTAINERS
swesonga-jdk21-testapp latest 682fedf54071 11 minutes ago 1.22GB 443.1MB 776.9MB 2
<none> <none> 4c068055cad5 26 minutes ago 443.1MB 443.1MB 0B 1
Containers space usage:
CONTAINER ID IMAGE COMMAND LOCAL VOLUMES SIZE CREATED STATUS NAMES
c77b69082a8a swesonga-jdk21-testapp "/home/<user>/swesonga/…" 0 0B 6 minutes ago Created awesome_chatelet
58c723638dd2 swesonga-jdk21-testapp "/home/<user>/swesonga/…" 0 0B 8 minutes ago Created sharp_lamport
4a3be55725b5 4c068055cad5 "/home/<user>/swesonga/…" 0 0B 17 minutes ago Created lucid_tharp
Local Volumes space usage:
VOLUME NAME LINKS SIZE
Build cache usage: 776.9MB
...
I tried pruning the build cache as suggested in that post.
user@machine:~/swesonga$ docker builder prune --all
WARNING! This will remove all build cache. Are you sure you want to continue? [y/N] y
ID RECLAIMABLE SIZE LAST ACCESSED
te4o8rbj7s6nh6pluquzummzz true 0B 8 minutes ago
n2wbz4gf448fluw4uuogiqxdo* true 776.9MB 8 minutes ago
...
Total: 1.554GB
I realized that pruning wasn’t what I needed because now the cache was empty but the containers were still there based on the next output:
user@machine:~/swesonga$ docker system df -v
Images space usage:
REPOSITORY TAG IMAGE ID CREATED SIZE SHARED SIZE UNIQUE SIZE CONTAINERS
swesonga-jdk21-testapp latest 682fedf54071 18 minutes ago 1.22GB 443.1MB 776.9MB 2
<none> <none> 4c068055cad5 33 minutes ago 443.1MB 443.1MB 0B 1
Containers space usage:
CONTAINER ID IMAGE COMMAND LOCAL VOLUMES SIZE CREATED STATUS NAMES
c77b69082a8a swesonga-jdk21-testapp "/home/<user>/swesonga/…" 0 0B 13 minutes ago Created awesome_chatelet
58c723638dd2 swesonga-jdk21-testapp "/home/<user>/swesonga/…" 0 0B 15 minutes ago Created sharp_lamport
4a3be55725b5 4c068055cad5 "/home/<user>/swesonga/…" 0 0B 24 minutes ago Created lucid_tharp
Local Volumes space usage:
VOLUME NAME LINKS SIZE
Build cache usage: 0B
CACHE ID CACHE TYPE SIZE CREATED LAST USED USAGE SHARED
user@machine:~/swesonga$
I should have been using docker ps -a instead! The -a shows the existing containers (regardless of whether they are running).
user@machine:~/swesonga$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c77b69082a8a 682fedf54071 "/home/<user>/swesonga/…" 16 minutes ago Created awesome_chatelet
58c723638dd2 682fedf54071 "/home/<user>/swesonga/…" 18 minutes ago Created sharp_lamport
4a3be55725b5 4c068055cad5 "/home/<user>/swesonga/…" 27 minutes ago Created lucid_tharp
user@machine:~/swesonga$
I started displaying the Dockerfile before building and one of the errors I ran into was because I hadn’t saved the Dockerfile. Sheesh.
cat Dockerfile
docker build -t swesonga-jdk21-testapp .
docker ps -a
docker run -i -t swesonga-jdk21-testapp
docker ps -a
docker run -i --memory 2GB -t swesonga-jdk21-testapp
Observe the head of the jdk21 GC log below. The total memory is now reported as 2048M. The maximum heap size is 25% of this total, as expected. The initial heap is 32MB and the minimum heap is 8MB.
The test passed on x64 but I wanted to see how to step into the test code itself so I tried this setup in Visual Studio 2022. Unfortunately, it was not straightforward to break into the correct process when launching the test in Visual Studio 2022.
I decided to try to understand the test execution sequence and started by looking at the output generated when running the jtreg test. Notice that the CreateCoredumpOnCrash product flag is disabled. The first thing I did was to enable it so that there is a core dump to examine.
The core dump wasn’t particularly helpful. I worked on simplifying the test so that only the failing scenarios remained. The log in the JBS issue was interpreted code only so I added the -Xint argument and could still reproduce the failure on Windows AArch64.
I came back to the idea of capturing the full command line for the final java.exe process that runs the test. Is there a way to log process start on Windows to capture all command lines? Copilot cited PowerShell and Command Line Logging | LogRhythm, which suggested enabling the use of Event ID 4688: a new process has been created.
However, the event viewer didn’t have command line arguments when I did this, which is what I needed. I just looked up Event ID 4688 and found 4688(S) A new process has been created. – Windows 10 | Microsoft Learn, which explains that you must enable “Administrative Templates\System\Audit Process Creation\Include command line in process creation events” group policy to include command line in process creation events. Hmm, I definitely didn’t do that when I was investigating this issue. I just tried this and it does the trick!
In the midst of all this wrangling, I decide to write a simple test to spit out the value of the sun.jnu.encoding property. That test runs fine so next step is to use the same flags as the failing jtreg test. However, as I added the ZGC flags to the test command line, I realized that I hadn’t even tried those flags with the java -version. What an oversight! The bug reproduces without running any specific program!
Since the assert happens when cloning an array, I decided to find the native implementation of the clone method. Searched for “clone_” and the only relevant hit (from a quick glance) appeared to be in the LinkResolver::check_method_accessability method.
Command: C:/java/forks/openjdk/jdk/build/windows-aarch64-server-slowdebug/jdk/bin/java.exe
Arguments: -XX:+UseZGC -XX:+ZGenerational -XX:+ZVerifyOops -version
Working Dir: C:/java/forks/openjdk/jdk
The failure appeared to be happening in this statement: HeapAccess<>::clone(obj(), new_obj_oop, size). I got this callstack by stepping into the calls in the slowdebug build because the is_valid function is inlined in the fastdebug build, preventing me from setting a breakpoint in it.
jvm.dll!is_valid(zaddress addr, bool assert_on_failure) Line 298 C++
jvm.dll!assert_is_valid(zaddress addr) Line 321 C++
jvm.dll!to_zaddress(unsigned __int64 value) Line 339 C++
jvm.dll!to_zaddress(oopDesc * o) Line 345 C++
jvm.dll!ZBarrierSet::AccessBarrier<270432,ZBarrierSet>::clone_in_heap(oopDesc * src, oopDesc * dst, unsigned __int64 size) Line 433 C++
jvm.dll!AccessInternal::PostRuntimeDispatch<ZBarrierSet::AccessBarrier<270400,ZBarrierSet>,9,270400>::access_barrier(oopDesc * src, oopDesc * dst, unsigned __int64 size) Line 200 C++
jvm.dll!AccessInternal::RuntimeDispatch<270400,oopDesc *,9>::clone_init(oopDesc * src, oopDesc * dst, unsigned __int64 size) Line 349 C++
jvm.dll!AccessInternal::RuntimeDispatch<270400,oopDesc *,9>::clone(oopDesc * src, oopDesc * dst, unsigned __int64 size) Line 533 C++
jvm.dll!AccessInternal::PreRuntimeDispatch::clone<270400>(oopDesc * src, oopDesc * dst, unsigned __int64 size) Line 890 C++
jvm.dll!AccessInternal::clone<262144>(oopDesc * src, oopDesc * dst, unsigned __int64 size) Line 1181 C++
jvm.dll!Access<262144>::clone(oopDesc * src, oopDesc * dst, unsigned __int64 size) Line 212 C++
jvm.dll!JVM_Clone(JNIEnv_ * env, _jobject * handle) Line 698 C++
00000298b2bbf056() Unknown
00000298a2ee5590() Unknown
000000c053dfe908() Unknown
Here’s the stack from stepping into the fastdebug assembly (note that line numbers might be off since this is not slowdebug):
I looked at this and searched for UTF-8 byte 0xBD meaning – Search (bing.com) but that didn’t turn up anything meaningful. I noticed that count is 3 on my Aarch64 device so we are copying 3 oops. Was this expected given that the count is 4 on Windows x64? More importantly though, the big question I have now is why doesn’t slowdebug step into the oop checking code when pressing F11 on line 120 in the screenshot? I expected the behavior of oop::on_usage to be different, not that it wouldn’t be called at all! When browsing the sources in VSCode on my x64 desktop, I clicked on the oop type (of the src argument) and it took me to a typedef of class oopDesc*. That’s when I spotted the CHECK_UNHANDLED_OOPS ifndef. The fastdebug build must have this defined! The only non-cpp/hpp file that contains CHECK_UNHANDLED_OOPS is jdk/make/hotspot/lib/JvmFlags.gmk. Sure enough, it is only defined for fastdebug. This means that I should be able to enable it for slowdebug and release and verify whether the behavior is present there. We can therefore configure a slowdebug build with the --with-extra-cflags=-DCHECK_UNHANDLED_OOPS option.
date; time bash configure --with-jtreg=/cygdrive/c/java/binaries/jtreg-7.4+1 --with-gtest=/cygdrive/c/repos/googletest --with-boot-jdk=/cygdrive/c/java/binaries/jdk/x64/jdk-22.0.1+8 --openjdk-target=aarch64-unknown-cygwin --with-debug-level=slowdebug --with-extra-cflags=-DCHECK_UNHANDLED_OOPS
time /cygdrive/c/repos/scratchpad/scripts/java/cygwin/build-jdk.sh windows aarch64 0 slowdebug
Looking at the actual pointer, I noticed that its value is the data “cp1252..”. After further investigation, I conclude that the bug is that we’re calling oops::operator= instead of just copying the values! I test a fix that simply copies the values directly and it works! The test passes even with the -DCHECK_UNHANDLED_OOPS option!
On to the next question: is there anything else using the pd_conjoint_oops_atomic function (and will it be negatively affected by my change)? While searching for “pd_conjoint_oops_atomic”, I notice that some platforms have an assert that oops == long or smth like that. There are 2 users of pd_conjoint_oops_atomic:
One idea is to run Java programs on a build linked with /PROFILE (Performance Tools Profiler) i.e. configured via --with-extra-ldflags=-profile to enable collection of code coverage data then confirming that those functions are executed. That seems cumbersome though so I try to create some array copying code to see if I can get to those functions (using breakpoints but none are hit). After taking a break: I wonder if I can just search from the bottom instead? Looking in jvm.cpp for copy reveals the JVM_ArrayCopy function. Here is my Java program:
public class CopyArray {
public static void main(String[] args) {
int length = 0xdeadc0d;
int srcPos = 0;
if (args.length > 0) {
try {
int userLength = Integer.parseInt(args[0]);
length = userLength;
}
catch (Throwable e) {
System.err.println("Ignoring invalid user arguments.");
}
}
byte[] src = new byte[length];
for (int i = 0; i < src.length; i++) {
src[i] = (byte)(i % 256);
}
byte[] dest = new byte[length];
System.arraycopy(src, srcPos, dest, 0, length);
}
}
I debugged the JVM running this program on my x64 machine. This hits the target function, JVM_ArrayCopy but there are so many callers. I have to set a condition on the breakpoint (hence the magic value of the length above) before I can step in to see where my call goes. Here are the source paths (note the different commit)
jvm.dll!Copy::pd_conjoint_bytes_atomic(const void * from, void * to, unsigned __int64 count) Line 119 C++
jvm.dll!Copy::conjoint_memory_atomic(const void * from, void * to, unsigned __int64 size) Line 53 C++
jvm.dll!AccessInternal::arraycopy_conjoint_atomic<void>(void * src, void * dst, unsigned __int64 length) Line 164 C++
jvm.dll!RawAccessBarrierArrayCopy::arraycopy<136585312,void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, void * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, void * dst_raw, unsigned __int64 length) Line 298 C++
jvm.dll!RawAccessBarrier<136585312>::arraycopy<void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, void * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, void * dst_raw, unsigned __int64 length) Line 308 C++
jvm.dll!AccessInternal::PreRuntimeDispatch::arraycopy<136587328,void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, void * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, void * dst_raw, unsigned __int64 length) Line 834 C++
jvm.dll!AccessInternal::PreRuntimeDispatch::arraycopy<136585280,void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, void * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, void * dst_raw, unsigned __int64 length) Line 867 C++
jvm.dll!AccessInternal::arraycopy_reduce_types<136585280,void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, void * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, void * dst_raw, unsigned __int64 length) Line 1008 C++
jvm.dll!AccessInternal::arraycopy<136577024,void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, const void * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, void * dst_raw, unsigned __int64 length) Line 1172 C++
jvm.dll!Access<136577024>::arraycopy<void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, const void * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, void * dst_raw, unsigned __int64 length) Line 147 C++
jvm.dll!ArrayAccess<134217728>::arraycopy<void>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, unsigned __int64 length) Line 301 C++
jvm.dll!TypeArrayKlass::copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, JavaThread * __the_thread__) Line 170 C++
jvm.dll!JVM_ArrayCopy(JNIEnv_ * env, _jclass * ignored, _jobject * src, int src_pos, _jobject * dst, int dst_pos, int length) Line 307 C++
00000244ea690702() Unknown
Copy::conjoint_memory_atomic is interesting because it has a comment indicating that copying bytes is not aligned and so there is no need to be atomic. The if statements in that method indicate that I can change the size of elements in the array to call different paths. Looks like I need to create an array of objects.
/**
export JAVA_HOME=~/java/binaries/jdk/x64/jdk-21.0.2+13
$JAVA_HOME/bin/javac CopyArray.java
$JAVA_HOME/bin/java CopyArray
*/
public class CopyArray {
public static void main(String[] args) {
int length = 0xdead;
int srcPos = 0;
if (args.length > 0) {
try {
int userLength = Integer.parseInt(args[0]);
length = userLength;
}
catch (Throwable e) {
System.err.println("Ignoring invalid user arguments.");
}
}
Object[] src = new Object[length];
for (int i = 0; i < src.length; i++) {
src[i] = new Object();
}
Object[] dest = new Object[length];
System.arraycopy(src, srcPos, dest, 0, length);
}
}
Now we are closer to the array_oops code I was trying to hit:
jvm.dll!Copy::pd_conjoint_jints_atomic(const int * from, int * to, unsigned __int64 count) Line 52 C++
jvm.dll!Copy::conjoint_oops_atomic(const narrowOop * from, narrowOop * to, unsigned __int64 count) Line 155 C++
jvm.dll!AccessInternal::arraycopy_conjoint_oops(narrowOop * src, narrowOop * dst, unsigned __int64 length) Line 54 C++
jvm.dll!RawAccessBarrierArrayCopy::arraycopy<50331750,HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 234 C++
jvm.dll!RawAccessBarrier<52715622>::arraycopy<enum narrowOop>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, narrowOop * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, narrowOop * dst_raw, unsigned __int64 length) Line 308 C++
jvm.dll!RawAccessBarrier<52715622>::oop_arraycopy<enum narrowOop>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, narrowOop * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, narrowOop * dst_raw, unsigned __int64 length) Line 130 C++
jvm.dll!ModRefBarrierSet::AccessBarrier<35938406,CardTableBarrierSet>::oop_arraycopy_in_heap<enum narrowOop>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, narrowOop * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, narrowOop * dst_raw, unsigned __int64 length) Line 109 C++
jvm.dll!AccessInternal::PostRuntimeDispatch<CardTableBarrierSet::AccessBarrier<35938406,CardTableBarrierSet>,8,35938406>::oop_access_barrier<HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 142 C++
jvm.dll!AccessInternal::RuntimeDispatch<35938374,HeapWordImpl *,8>::arraycopy(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 517 C++
jvm.dll!AccessInternal::PreRuntimeDispatch::arraycopy<35938374,HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 871 C++
jvm.dll!AccessInternal::arraycopy_reduce_types<35938372>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 1018 C++
jvm.dll!AccessInternal::arraycopy<35913732,HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * const * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 1172 C++
jvm.dll!Access<35913728>::oop_arraycopy<HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * const * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 136 C++
jvm.dll!ArrayAccess<33554432>::oop_arraycopy(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, unsigned __int64 length) Line 327 C++
jvm.dll!ObjArrayKlass::do_copy(arrayOop s, unsigned __int64 src_offset, arrayOop d, unsigned __int64 dst_offset, int length, JavaThread * __the_thread__) Line 197 C++
jvm.dll!ObjArrayKlass::copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, JavaThread * __the_thread__) Line 282 C++
jvm.dll!JVM_ArrayCopy(JNIEnv_ * env, _jclass * ignored, _jobject * src, int src_pos, _jobject * dst, int dst_pos, int length) Line 307 C++
00000202d3f00502() Unknown
00000202cc269950() Unknown
In this call stack, the arraycopy_conjoint_oops(narrowOop* src, narrowOop* dst, size_t length) implementation that is called has narrow oops because of the branch in ObjArrayKlass::copy_array. Launch the application using these arguments instead:
Now the code block of interest is hit! Hmm, I’m realizing that I should have been explicit about the collector to use. This was debugging the G1 collector (chosen ergonomically).
jvm.dll!ZBarrierSet::AccessBarrier<52715590,ZBarrierSet>::oop_arraycopy_in_heap_no_check_cast(zpointer * dst, zpointer * src, unsigned __int64 length) Line 371 C++
jvm.dll!ZBarrierSet::AccessBarrier<35938374,ZBarrierSet>::oop_arraycopy_in_heap(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, zpointer * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, zpointer * dst_raw, unsigned __int64 length) Line 403 C++
jvm.dll!ZBarrierSet::AccessBarrier<35938374,ZBarrierSet>::oop_arraycopy_in_heap(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, oop * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, oop * dst_raw, unsigned __int64 length) Line 128 C++
jvm.dll!AccessInternal::PostRuntimeDispatch<ZBarrierSet::AccessBarrier<35938374,ZBarrierSet>,8,35938374>::oop_access_barrier<HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 142 C++
jvm.dll!AccessInternal::RuntimeDispatch<35938374,HeapWordImpl *,8>::arraycopy(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 517 C++
jvm.dll!AccessInternal::PreRuntimeDispatch::arraycopy<35938374,HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 871 C++
jvm.dll!AccessInternal::arraycopy_reduce_types<35938372>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 1018 C++
jvm.dll!AccessInternal::arraycopy<35913732,HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * const * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 1172 C++
jvm.dll!Access<35913728>::oop_arraycopy<HeapWordImpl *>(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, HeapWordImpl * const * src_raw, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, HeapWordImpl * * dst_raw, unsigned __int64 length) Line 136 C++
jvm.dll!ArrayAccess<33554432>::oop_arraycopy(arrayOop src_obj, unsigned __int64 src_offset_in_bytes, arrayOop dst_obj, unsigned __int64 dst_offset_in_bytes, unsigned __int64 length) Line 327 C++
jvm.dll!ObjArrayKlass::do_copy(arrayOop s, unsigned __int64 src_offset, arrayOop d, unsigned __int64 dst_offset, int length, JavaThread * __the_thread__) Line 198 C++
jvm.dll!ObjArrayKlass::copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, JavaThread * __the_thread__) Line 290 C++
jvm.dll!JVM_ArrayCopy(JNIEnv_ * env, _jclass * ignored, _jobject * src, int src_pos, _jobject * dst, int dst_pos, int length) Line 308 C++
000002602e8c06a8() Unknown
I need to turn off compressed oops with the serial collector as well but it looks like there is no check_oop_function for the serial collector. That said, this exploration of array copying code was insightful, showing how the data type sizes determine which path is taken for copying primitives and objects. There didn’t appear to be any red flags about removing the oop::operator= usage so I opened 8334475: UnsafeIntrinsicsTest.java#ZGenerationalDebug assert(!assert_on_failure) failed: Has low-order bits set by swesonga · Pull Request #20390 · openjdk/jdk (github.com) to fix the assertion failure. The most interesting part of this investigation was that the bad address was a data value (cp1252) staring right at me and I missed it. This was quite educational for me though.
One of the downsides of horse ownership is the cost. The cost of the horse is just the starting point. Transporting the horse is a non-trivial cost. We needed to buy a trailer and many of the trailers we looked at are heavy enough that we needed to buy a truck as well. This raised the question of what the minimum required towing capacity would be. It’s strange that these trucks are classified using tons. What Does Half-Ton, Three-Quarter-Ton, One-Ton Mean When Talking About Pickup Trucks? | Cars.com gives me the impression that tonnage is a historical artifact of payload measurement. A ton seems to be a reference to a Short ton – Wikipedia. It is also interesting that Toyota and Nissan don’t really have offerings above the half-ton classification. The approximate weight of the trailer (and the horse) that I want to transport (or alternatively, our camper) requires at least a 3/4-ton truck.
One of the trucks we considered is the 2012 F 150 Towing Capacity Full Guide (with Charts) (truckauxiliary.com). The concern here was that even though it had a towing package, it was still a half-ton truck. It was also likely to be outside our budget, so we didn’t really wait for that seller to give us a price. We also looked at a 2006 RAM 2500. Our mechanic took a look at it and exclaimed that everything that could possibly leak on that vehicle was leaking (transmission, power steering, etc). That was an easy pass given that it was already at the top of our price range.
Fortunately, the next truck we looked at worked out. Cylinder 6 was misfiring on this truck (we could hear the tick) and this was confirmed by the digital codes from the vehicle. We decided to buy a new spark plug and coil for that cylinder to see if we could fix it before driving off with the truck but neither AutoZone nor Oreilly Autoparts had the right coil in stock. We walked out with just the spark plug and our mechanic replaced it. In the process of pulling out the old spark plug, the spark plug wire came apart, and we had to buy an entire Duralast Silicone Spark Plug Wire Set. Thankfully, that was all that was needed to address the cylinder misfiring. We were glad to have our mechanic available to fix that problem before we drove off with our “new” 2002 truck (through a private sale). We had also confirmed with our insurance company that the new vehicle was covered as we drove it away and that we had up to 5 days to add it to our insurance plan.
Ironically, the towing hitch was significantly damaged on this truck (one of our most important requirements). However, the mechanic pointed out that it can be readily replaced (just don’t do any welding on the existing setup since its integrity cannot be guaranteed). The only question I have remaining is how to compute the tongue weight (came up when we were looking up new hitches online). What is Tongue Weight and What Does it Mean for Safe Towing? explains various ways to determine the tongue weight. They also recommend their weigh-safe hitch, which has a built-in scale (I like how convenient this hitch makes it). This is the video they linked discussing this option.
Behind the scenes of the Ike Gauntlet: How to measuring Tongue Weight for Safe Towing
I have been learning about the SFrame tracing effort and figured I should document the resources I have reviewed. Indu Bhagat has been actively involved in the development of SFrame. This is one of her talks giving an overview of the objectives of SFrame. The overall idea is that profiling tools (e.g. perf) usually need to generate stack traces. She lists some methods used to generate stack traces, e.g. using frame pointers, EH frame, last branch record (LBR), and other heuristics. Each of these have their own advantages and pitfalls. SFrame encodes the minimal info required for stack tracing.
I found additional videos by searching for sframe indu (there are lots of unrelated sframe results out there). This one by Steven and Indu covers potential issues that need to be addressed for JITted code.
