Earlier this year I had trouble connecting to the VPN on one of my devices (Windows 11 Pro 24H2). I also got this error from Teams: We Couldn’t authenticate you. This could be due to a device or network problem, or Teams could be experiencing a technical issue – Microsoft Q&A. It was an interesting learning experience, getting to see parts of the OS/networking stack in action that I don’t usually even think about. The troubleshooting process started with the usual tasks: install all Windows updates, including the optional updates. That option (from my desktop) is shown below:
The Azure VPN Client had this error message: Failure in acquiring Microsoft Entra Token: Provider Error <number>: The server or proxy was not found. Someone else ran into this issue in Azure P2S VPN Disconnecting – Microsoft Q&A. This was unusual in my case because the Access work or school pane said that I was connected.
Next, we examined this registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters\DnsPolicyConfig. Here is a screenshot from my desktop (not the device in question).
It turned out that there was a subkey with outdated configuration information! Deleting that subkey resolved all the connectivity issues. This was interesting to me because I assumed that general internet connectivity meant that there shouldn’t be any DNS issues whatsoever. I clearly didn’t have a good picture of how DNS is set up in these configurations and how these setups can go wrong.
Last month, I investigated OpenJDK gtest failures on Windows. The error message was that the gtests Caught std::exception-derived exception escaping the death test statement. I tracked the commit responsible for the failures to 8343756: CAN_SHOW_REGISTERS_ON_ASSERT for Windows · openjdk/jdk@0054bbe.
// Asserts that a given `statement` causes the program to exit, with an
// integer exit status that satisfies `predicate`, and emitting error output
// that matches `matcher`.
#define ASSERT_EXIT(statement, predicate, matcher) \
GTEST_DEATH_TEST_(statement, predicate, matcher, GTEST_FATAL_FAILURE_)
I was trying to ensure my understanding of the exit code being an exact match is correct. The line EXPECT_EXIT(_exit(1), testing::ExitedWithCode(1), ""); from googletest/googletest/test/googletest-death-test-test.cc at v1.14.0 · google/googletest supports this hypothesis. The EXPECT_EXIT macro comment (below) left me wondering how ASSERT_EXIT does not continue on to successive tests. The difference between these two macros is in the final parameter, which is GTEST_NONFATAL_FAILURE_ for the EXPECT_EXIT macro.
// Like `ASSERT_EXIT`, but continues on to successive tests in the
// test suite, if any:
#define EXPECT_EXIT(statement, predicate, matcher) \
GTEST_DEATH_TEST_(statement, predicate, matcher, GTEST_NONFATAL_FAILURE_)
creates a child process with the same executable as the current process to run the death test. The child process is given the –gtest_filter and –gtest_internal_run_death_test flags such that it knows to run the current death test only.
The question now became, why were we catching this std::exception? I asked copilot: how does a windows access violation turn into a std::exception? Part of its answer mentioned the /EHsc compiler flag so I decided to examine the flags used to compile the JVM binaries. I searched for the regex out:[^\s]+jvm.dll in the build logs and found this jvm.dll linker command. Note that 2 separate jvm.dll files get built, one for the product and another for the gtests. The /IMPLIB (Name Import Library) | Microsoft Learn flag was present, but didn’t look relevant.
checking for apk... [not found]
checking for pandoc... [not found]
/cygdrive/d/java/forks/openjdk/jdk/build/.configure-support/generated-configure.sh: line 64028: syntax error: unexpected end of file
configure exiting with result code 2
That file appeared to be truncated??? VSCode was doing something related to building the Java projects in the repo. It is possible that something in VSCode could have interrupted this but I just removed the build folder then reexamined the change.
My include path didn’t appear in the include paths for gtestLauncher.obj! I searched the repo for googlemock and the only place that path could be coming from was CompileGtest.gmk. However, I then noticed that the gtest launcher has its own configuration section. Sheesh. Here is the diff that I used to definitively see how these includes work:
gtestLauncher.exe was now being compiled with -EHsc but the gtests still failed. Since jvm.dll is compiled without -EHsc, I added it to see if the test behavior would change. I started by searching for libjvm in the codebase. This is the additional change I made:
At this point, I looked at the exception handler and it looked like what was happening was that returning EXCEPTION_CONTINUE_EXECUTION let the SEH handler in the gtests continue instead of the code down the report_vm_error path! I decided to create my own handler but needed to look up the syntax. I used Structured Exception Handling (C/C++) | Microsoft Learn.
diff --git a/src/hotspot/share/utilities/debug.hpp b/src/hotspot/share/utilities/debug.hpp
index 12724153659..e40c16c1c59 100644
--- a/src/hotspot/share/utilities/debug.hpp
+++ b/src/hotspot/share/utilities/debug.hpp
@@ -39,7 +39,21 @@ class oopDesc;
#define CAN_SHOW_REGISTERS_ON_ASSERT
extern char* g_assert_poison;
extern const char* g_assert_poison_read_only;
+#if (defined(_WINDOWS))
+// We use structured exception handling when writing to the poison variable.
+// This allows us to continue execution and perform error reporting instead of
+// bailing out to other SEH handlers such as those in the googletest code.
+#include <excpt.h>
+#define TOUCH_ASSERT_POISON \
+do { \
+ __try { \
+ (*g_assert_poison) = 'X'; \
+ } __except (EXCEPTION_CONTINUE_EXECUTION) { \
+ } \
+} while (0)
+#else
#define TOUCH_ASSERT_POISON (*g_assert_poison) = 'X';
+#endif // _WINDOWS
void initialize_assert_poison();
void disarm_assert_poison();
bool handle_assert_poison_fault(const void* ucVoid);
...\jdk\src\hotspot\share\utilities/growableArray.hpp(81): error C2712: Cannot use __try in functions that require object unwinding
...\jdk\src\hotspot\share\classfile/vmClassID.hpp(41): error C3615: constexpr function 'EnumeratorRangeImpl::end_value' cannot result in a constant expression
...\jdk\src\hotspot\share\utilities/enumIterator.hpp(97): note: failure was caused by a statement or an expression that is not valid in a constexpr context
...\jdk\src\hotspot\share\utilities/unsigned5.hpp(190): error C3615: constexpr function 'UNSIGNED5::max_encoded_in_length' cannot result in a constant expression
...\jdk\src\hotspot\share\utilities/unsigned5.hpp(191): note: failure was caused by a statement or an expression that is not valid in a constexpr context
...\jdk\src\hotspot\cpu\x86\register_x86.hpp(61): error C3615: constexpr function 'Register::RegisterImpl::encoding' cannot result in a constant expression
...\jdk\src\hotspot\cpu\x86\register_x86.hpp(61): note: failure was caused by a statement or an expression that is not valid in a constexpr context
...\jdk\src\hotspot\cpu\x86\register_x86.hpp(233): error C3615: constexpr function 'XMMRegister::XMMRegisterImpl::encoding' cannot result in a constant expression
...\jdk\src\hotspot\cpu\x86\register_x86.hpp(233): note: failure was caused by a statement or an expression that is not valid in a constexpr context
...\jdk\src\hotspot\share\runtime/park.hpp(131): error C2712: Cannot use __try in functions that require object unwinding
...\jdk\src\hotspot\share\runtime/mutexLocker.hpp(235): error C2712: Cannot use __try in functions that require object unwinding
...\jdk\src\hotspot\share\runtime/mutexLocker.hpp(240): error C2712: Cannot use __try in functions that require object unwinding
...\jdk\src\hotspot\share\runtime/mutexLocker.hpp(250): error C2712: Cannot use __try in functions that require object unwinding
...\jdk\src\hotspot\share\runtime/mutexLocker.hpp(255): error C2712: Cannot use __try in functions that require object unwinding
At this point, I realized that I needed to disable SEH at the gtest level. I turned off GTEST_HAS_SEH with this change and finally got the gtests to pass!
What was not sure of was whether the JVM reporting code was running (vs the JVM just exiting) and whether there was a narrower way to pass the GTEST_HAS_SEH define – I noticed it in thousands of lines in the compilation log, which might also explain why I was getting error C2712: Cannot use __try in functions that require object unwinding in many more places than I expected when I added the -EHsc flag when compiling jvm.obj. Therefore, it was logical to try to find the minimal diff that would fix the gtests. Here’s one I tried:
This manual approach of finding the minimal change needed was tedious so I decided to add my own defines to see which portions of the gmk files are used and for which compile/link commands:
For location 2, there were 214 lines matching the regex DMYTEST_LOCATION2.+.cpp and 213 lines matching the regex DMYTEST_LOCATION2.+/test/hotspot/gtest/.+.cpp. The location 2 define was therefore correctly scoped to the gtests only. These 213 lines compiled files like test_blocktree.cpp and test_vmerror.cpp. The line that was different between the 2 regexes was the one compiling build/windows-x86_64-server-slowdebug/hotspot/variant-server/libjvm/gtest/objs/BUILD_GTEST_LIBJVM_pch.cpp. Location 3 was only used for compiling test/hotspot/gtest/gtestLauncher.cpp. The challenging case was location 0, which seemed to appear for way more files than it should. Was it really necessary? No it wasn’t! That made life much easier for me.
Inspecting gTest Code Coverage
In the course of this investigation, I considered using time travel debugging to see which code paths were executed. An alternative was to see whether the exception filter code was covered at the end of the gtest execution! The path to the code coverage tool is C:\Program Files\Microsoft Visual Studio\2022\Enterprise\Common7\IDE\Extensions\Microsoft\CodeCoverage.Console\Microsoft.CodeCoverage.Console.exe – it should be in the path by default in the Developer Command Prompt. I kicked it off with these commands:
Search for “exceptionfilter” in the Code Coverage Results pane to view the code coverage for the exception filter.
Verifying Execution Path
The first time I paused execution of the gtests in the debugger, stopped in jdk/src/hotspot/share/utilities/bitMap.cpp. I set a breakpoint there. I liked this location because I could move execution into the failure path (in the assembly view). This was how I saw the gtest structured exception handler kicking in without the JVM’s failure reporting code executing. With the tests now passing, I found the write to the poison location just going through without interruption. Did this mean the test was broken? Or did it mean that the exception filter ran and successfully said to continue execution? I think it has to be the latter but I’ll need time travel debugging to verify this. In the meantime, I sought to at least ensure there were multiple test processes involved.
Verifying Multiple Processes are Started
I started Process Monitor and added a filter for path containing “slowdebug”. Notice tons of PIDs for gtestlauncher.exe in the process monitor screenshot below (as expected).
I could successfully execute the error handling path by manually moving the program counter (RIP) after skipping into the failure path of BitMap::verify_range. Why didn’t the PID change in the debugger? Oh wait, was I was still stepping thereby causing recursion? This callstack did not support that hypothesis. Looks like it was just error reporting continuing to execute.
> jvm.dll!BitMap::verify_range(unsigned __int64 beg, unsigned __int64 end) Line 212 C++
jvm.dll!BitMap::clear_range(unsigned __int64 beg, unsigned __int64 end) Line 280 C++
jvm.dll!JVMFlag::printFlags(outputStream * out, bool withComments, bool printRanges, bool skipDefaults) Line 706 C++
jvm.dll!VMError::report(outputStream * st, bool _verbose) Line 1260 C++
jvm.dll!VMError::report_and_die(int id, const char * message, const char * detail_fmt, char * detail_args, Thread * thread, unsigned char * pc, const void * siginfo, const void * context, const char * filename, int lineno, unsigned __int64 size) Line 1847 C++
jvm.dll!report_vm_error(const char * file, int line, const char * error_msg, const char * detail_fmt, ...) Line 195 C++
jvm.dll!CompressedKlassPointers::check_init<int>(int var) Line 154 C++
jvm.dll!CompressedKlassPointers::shift() Line 218 C++
jvm.dll!CompressedKlassPointers::print_mode(outputStream * st) Line 301 C++
jvm.dll!VMError::report(outputStream * st, bool _verbose) Line 1196 C++
jvm.dll!VMError::report_and_die(int id, const char * message, const char * detail_fmt, char * detail_args, Thread * thread, unsigned char * pc, const void * siginfo, const void * context, const char * filename, int lineno, unsigned __int64 size) Line 1847 C++
jvm.dll!report_vm_error(const char * file, int line, const char * error_msg, const char * detail_fmt, ...) Line 195 C++
jvm.dll!BitMap::verify_limit(unsigned __int64 bit) Line 206 C++
jvm.dll!BitMap::to_words_align_down(unsigned __int64 bit) Line 94 C++
jvm.dll!BitMap::word_addr(unsigned __int64 bit) Line 144 C++
jvm.dll!BitMap::set_bit(unsigned __int64 bit) Line 37 C++
jvm.dll!JfrEventVerifier::set_field_bit(unsigned __int64 field_idx) Line 41 C++
jvm.dll!JfrEvent<EventTenuringDistribution>::set_field_bit(unsigned __int64 field_idx) Line 267 C++
jvm.dll!EventObjectAllocationOutsideTLAB::set_objectClass(const Klass * new_value) Line 7304 C++
jvm.dll!trace_flag_changed<bool,EventBooleanFlagChanged>(JVMFlag * flag, const bool old_value, const bool new_value, const JVMFlagOrigin origin) Line 39 C++
jvm.dll!TypedFlagAccessImpl<bool,EventBooleanFlagChanged>::check_constraint_and_set(JVMFlag * flag, void * value_addr, JVMFlagOrigin origin, bool verbose) Line 78 C++
jvm.dll!FlagAccessImpl_bool::set_impl(JVMFlag * flag, void * value_addr, JVMFlagOrigin origin) Line 98 C++
jvm.dll!FlagAccessImpl::set(JVMFlag * flag, void * value, JVMFlagOrigin origin) Line 49 C++
jvm.dll!JVMFlagAccess::set_impl(JVMFlag * flag, void * value, JVMFlagOrigin origin) Line 307 C++
jvm.dll!JVMFlagAccess::set_or_assert(JVMFlagsEnum flag_enum, int type_enum, void * value, JVMFlagOrigin origin) Line 353 C++
jvm.dll!JVMFlagAccess::set<bool,0>(JVMFlagsEnum flag_enum, bool value, JVMFlagOrigin origin) Line 101 C++
jvm.dll!Flag_UseLargePagesIndividualAllocation_set(bool value, JVMFlagOrigin origin) Line 69 C++
jvm.dll!os::init() Line 4436 C++
jvm.dll!Threads::create_vm(JavaVMInitArgs * args, bool * canTryAgain) Line 463 C++
jvm.dll!JNI_CreateJavaVM_inner(JavaVM_ * * vm, void * * penv, void * args) Line 3589 C++
jvm.dll!JNI_CreateJavaVM(JavaVM_ * * vm, void * * penv, void * args) Line 3680 C++
jvm.dll!init_jvm(int argc, char * * argv, bool disable_error_handling, JavaVM_ * * jvm_ptr) Line 94 C++
jvm.dll!JVMInitializerListener::OnTestStart(const testing::TestInfo & test_info) Line 124 C++
jvm.dll!testing::internal::TestEventRepeater::OnTestStart(const testing::TestInfo & parameter) Line 3858 C++
jvm.dll!testing::TestInfo::Run() Line 2821 C++
jvm.dll!testing::TestSuite::Run() Line 3015 C++
jvm.dll!testing::internal::UnitTestImpl::RunAllTests() Line 5920 C++
jvm.dll!testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl,bool>(testing::internal::UnitTestImpl * object, bool(testing::internal::UnitTestImpl::*)() method, const char * location) Line 2614 C++
jvm.dll!testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl,bool>(testing::internal::UnitTestImpl * object, bool(testing::internal::UnitTestImpl::*)() method, const char * location) Line 2648 C++
jvm.dll!testing::UnitTest::Run() Line 5484 C++
jvm.dll!RUN_ALL_TESTS() Line 2317 C++
jvm.dll!runUnitTestsInner(int argc, char * * argv) Line 290 C++
jvm.dll!runUnitTests(int argc, char * * argv) Line 371 C++
gtestLauncher.exe!main(int argc, char * * argv) Line 40 C++
[Inline Frame] gtestLauncher.exe!invoke_main() Line 78 C++
gtestLauncher.exe!__scrt_common_main_seh() Line 288 C++
kernel32.dll!00007ffdcbdce8d7() Unknown
ntdll.dll!00007ffdcc97c34c() Unknown
One advantage of the stack above is that it showed how the os::init code gets executed (which I was curious about when wondering whether the exception filter was being set up). Disabling the breakpoint just before skipping into the failure path and resuming execution now led to the JVM dying:
[==========] Running 1197 tests from 205 test suites.
[----------] Global test environment set-up.
[----------] 3 tests from AltHashingTest
[ RUN ] AltHashingTest.halfsiphash_test_ByteArray
[ OK ] AltHashingTest.halfsiphash_test_ByteArray (0 ms)
[ RUN ] AltHashingTest.halfsiphash_test_CharArray
[ OK ] AltHashingTest.halfsiphash_test_CharArray (0 ms)
[ RUN ] AltHashingTest.halfsiphash_test_FromReference
[ OK ] AltHashingTest.halfsiphash_test_FromReference (0 ms)
[----------] 3 tests from AltHashingTest (2 ms total)
[----------] 1 test from ThreadsListHandle
[ RUN ] ThreadsListHandle.sanity_vm
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (d:\java\forks\openjdk\jdk\src\hotspot\share\utilities\bitMap.cpp:208), pid=39132, tid=109872
# assert(bit <= _size) failed: BitMap limit out of bounds: 0 > 64
#
# JRE version: ((uninitialized)) (slowdebug build )
# Java VM: OpenJDK 64-Bit Server VM (slowdebug 26-internal-adhoc.saint.jdk, mixed mode, sharing, tiered, compressed class ptrs, unknown gc, windows-amd64)
# Core dump will be written. Default location: D:\java\forks\openjdk\jdk\build\windows-x86_64-server-slowdebug\images\test\hotspot\gtest\server\hs_err_pid39132.mdmp
#
# An error report file with more information is saved as:
# D:\java\forks\openjdk\jdk\build\windows-x86_64-server-slowdebug\images\test\hotspot\gtest\server\hs_err_pid39132.log
#
#
D:\java\forks\openjdk\jdk\build\windows-x86_64-server-slowdebug\images\test\hotspot\gtest\server\gtestLauncher.exe (process 39132) exited with code 1 (0x1).
To automatically close the console when debugging stops, enable Tools->Options->Debugging->Automatically close the console when debugging stops.
Press any key to close this window . . .
c:\progra~1\mib055~1\2022\enterprise\vc\tools\msvc\14.44.35207\include\__msvc_ostream.hpp(781): error C2220: the following warning is treated as an error
c:\progra~1\mib055~1\2022\enterprise\vc\tools\msvc\14.44.35207\include\__msvc_ostream.hpp(781): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
c:\progra~1\mib055~1\2022\enterprise\vc\tools\msvc\14.44.35207\include\__msvc_ostream.hpp(781): note: the template instantiation context (the oldest one first) is
c:\repos\googletest\googletest\include\gtest/gtest-message.h(118): note: see reference to function template instantiation 'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const char *)' being compiled
I bought new toner for my Brother printer. It’s been a while since I replaced it, but I knew I could count on someone on YouTube to walk me through the process again. The folks that upload these videos deserve an award for their service – I would have wasted time fidgeting around.
I was reviewing jtreg test failures in some GitHub actions last week. Since I was only interested in the failures, I decided to write a script to extract the failure details from the log files I had downloaded from GitHub. This looked like another task for the VS Code agent so I wrote the algorithm for extracting the failure details into individual text files, which would be easier to review. Below is the prompt I used.
write a python script that processes all the text files in a user-specified folder. For each text file:
- split it into sections using "--------------------------------------------------" as a separator
- generate a filename for the section from the first line after the separator. To do so, use the text after "TEST: " and replace /, #, and . with underscores and append the ".txt" extension.
- if the section contains the string "test jdk:" then write the content of the entire section to a file with the generated name.
I thought I would need to do at least some debugging of the script but I did not! The script worked flawlessly. I didn’t even need to execute it myself because the flow of using the agent included running the script on my raw folder and then generating a README file! See the script and the README at Add scripts generated by Claude Sonnet 4 VS Code agent · swesonga/scratchpad@f5e8057. The agent was using the Claude Sonnet 4 model.
delete all lines from ":: jdk21u x64"
replace 2025-07 with a variable called psu
replace aarch64 and x64 with a variable called arch
replace jdk21u with a variable called jdkrepo
replace jdk-21.0.6+7 with a variable called jdktag
replace D:\java\binaries\jdk\%arch%\%psu%\windows-%jdkrepo% with a variable called psudir
output a message showing the psudir after setting it
make the variables user-specified variables
make the variables command line arguments instead
I pasted the screenshots of the result of each prompt into the slideshow below. Notice that I was using Agent mode with Anthropic’s Claude Sonnet 4 model. I was not exactly saving much time in this scenario using the VSCode agent, but I was certainly understanding its capabilities.
I created a duplicate directory with the initial .bat file then used a single prompt with all the lines above. I was pleased that I got the same result!
I was a bit confused the 2nd time I worked through these prompts because the behavior of the agent was different! I didn’t notice that I had somehow switched from Agent mode to Ask mode but I have now learned the difference between these two modes.
What is the torch.varkeepDim parameter used for? p101
What about the correction parameter (formerly unbiased)? How does it relate to Bessel’s_correction? p103
Explain the difference between layer normalization and batch normalization. p104
When is layer normalization advantageous? p105
What is a GELU? How can it lead to better optimization properties during training (compared to a ReLU)?
What is one advantage of small non-zero outputs on negative inputs to a GELU? p106
Explain the role of a FeedForward module in enhancing the model’s ability to learn from and generalize data. Compare with Feedforward neural network. p108
Why were shortcut connections originally proposed for deep networks in computer vision? p109
Which PyTorch method computes loss gradients? p112
Explain Pre-LayerNorm and Post-LayerNorm. p115
What does preservation of shape throughout the transformer block architecture enable? p116
Explain weight-tying as used in the original GPT-2 architecture and its advantages. p121
This is the author’s video corresponding to chapter 4 of the book.
Build an LLM from Scratch 4: Implementing a GPT model from Scratch To Generate Text
Math Concepts
The author mentioned that OpenAI used the biased variance option when training their GPT-2 model. The reasons why Bessel’s correction is usually used in statistics is explained well in this video:
Why We Divide by N-1 in the Sample Variance (The Bessel’s Correction)
I didn’t think the reason we need activation functions was expounded upon. This final video provides a great explanation.
Why Do We Need Activation Functions in Neural Networks?
As part of the jdk11u release process, I needed to run some shell tests on my Windows desktop to determine whether they failed due to a product issue or an environment issue. I defaulted to using my Git Bash environment instead of Cygwin. This post shares some errors I ran into as a result of the different shell environment. The key takeaway was to run such tests in Cygwin whenever I encountered path errors.
I confirmed that rmic.exe exists in the bin directory of the jdk.
$ ls -1 /d/java/binaries/jdk/x64/2025-07/windows-jdk11u/jdk-11.0.28+6/bin/rmic*
/d/java/binaries/jdk/x64/2025-07/windows-jdk11u/jdk-11.0.28+6/bin/rmic.exe*
Changing the test to directly refer to rmic.exe instead of rmic (as shown in the diff below) resulted in the test passing on my machine. I concluded that this specific issue must therefore be a test bug (i.e. the test should avoid this issue on Windows). See Shell Tests in jtreg for possible ways to fix this. This is one reason why shell scripts are being discouraged for OpenJDK testing.
STDOUT:
Warning: generation and use of skeletons and static stubs for JRMP
is deprecated. Skeletons are unnecessary, and static stubs have
been superseded by dynamically generated stubs. Users are
encouraged to migrate away from using rmic to generate skeletons and static
stubs. See the documentation for java.rmi.server.UnicastRemoteObject.
This warning is output by the sun.rmi.rmic.Main.compile method. The arguments to rmic.exe are parsed by Main.parseArgs. The -v1.2 argument specifies the non-default generator to use. My local machine must be using a different default generator (or so I thought).
So what does the failing line do? I asked Copilot: what does this command do in a bash script? . ${TESTSRC-.}/common.sh
. (dot command) This is shorthand for source, which executes the contents of a file in the current shell environment rather than in a subshell. This means any variables, functions, or changes made by the script will persist in the current shell.
${TESTSRC-.} This is a parameter expansion. It means:
Use the value of the TESTSRC environment variable if it is set.
If TESTSRC is not set, use . (the current directory) as the default.
/common.sh This appends /common.sh to the path determined above.
This error was a Windows path issue again. Notepad++ could open D:/java/ms/openjdk-jdk11u/test/jdk/sun/tools/jrunscript/common.sh so the path itself was fine. I used this workaround:
diff --git a/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh b/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh
index 6a3d4e76ff..94001967b0 100644
--- a/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh
+++ b/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh
@@ -30,10 +30,11 @@
# @run shell jrunscript-eTest.sh
# @summary Test that output of 'jrunscript -e' matches the dash-e.out file
-. ${TESTSRC-.}/common.sh
+comn=`/mnt/c/software/msys64/usr/bin/cygpath.exe ${TESTSRC-.}/common.sh`
+. "/mnt$comn"
setup
-${JAVA} ${TESTVMOPTS} ${TESTJAVAOPTS} -cp ${TESTCLASSES} CheckEngine
+${JAVA}.exe ${TESTVMOPTS} ${TESTJAVAOPTS} -cp ${TESTCLASSES} CheckEngine
if [ $? -eq 2 ]; then
echo "No js engine found and engine not required; test vacuously passes."
exit 0
This got me to the actual test error:
STDOUT:
Output of jrunscript -e differ from expected output. Failed.
STDERR:
Warning: Nashorn engine is planned to be removed from a future JDK release
diff: D:/java/ms/openjdk-jdk11u/test/jdk/sun/tools/jrunscript/dash-e.out: No such file or directory
I couldn’t see which command generated the output though, so I added set -ex to the top of the script (like run.sh in the previous test). This was the resulting output:
Aha! Notice the root cause of the filename issues: OS=Linux! This also confirmed that I was using the same diff command. I didn’t get the error message at jdk11u/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh at jdk-11.0.28+5 · openjdk/jdk11u because because of set -ex (the e means exit immediately if any command fails, which does not match the behavior this test requires). After removing the e, I got this output:
$ ls -1 `cygpath D:/java/ms/openjdk-jdk11u/test/jdk/sun/tools/jrunscript/dash-e.out`
/d/java/ms/openjdk-jdk11u/test/jdk/sun/tools/jrunscript/dash-e.out
I patched the script as shown in the next diff:
diff --git a/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh b/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh
index 6a3d4e76ff..4c7130857e 100644
--- a/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh
+++ b/test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh
@@ -30,10 +30,13 @@
# @run shell jrunscript-eTest.sh
# @summary Test that output of 'jrunscript -e' matches the dash-e.out file
-. ${TESTSRC-.}/common.sh
+set -x
+
+comn=`/mnt/c/software/msys64/usr/bin/cygpath.exe ${TESTSRC-.}/common.sh`
+. "/mnt$comn"
setup
-${JAVA} ${TESTVMOPTS} ${TESTJAVAOPTS} -cp ${TESTCLASSES} CheckEngine
+${JAVA}.exe ${TESTVMOPTS} ${TESTJAVAOPTS} -cp ${TESTCLASSES} CheckEngine
if [ $? -eq 2 ]; then
echo "No js engine found and engine not required; test vacuously passes."
exit 0
@@ -44,7 +47,9 @@ fi
rm -f jrunscript-eTest.out 2>/dev/null
${JRUNSCRIPT} -J-Dnashorn.args.prepend=--no-deprecation-warning -J-Djava.awt.headless=true -l nashorn -e "println('hello')" > jrunscript-eTest.out 2>&1
-$golden_diff jrunscript-eTest.out ${TESTSRC}/dash-e.out
+diffarg=`/mnt/c/software/msys64/usr/bin/cygpath.exe ${TESTSRC}/dash-e.out`
+
+$golden_diff jrunscript-eTest.out "/mnt$diffarg"
if [ $? != 0 ]
then
echo "Output of jrunscript -e differ from expected output. Failed."
Avoiding Path Issues
This madness (in the diff above) that made me realize that I needed to fix the path issues and that perhaps Cygwin was the better environment for these tests. Sure enough, the test passed the first time I executed it in Cygwin:
Executing: D:/java/binaries/jdk/x64/2025-07/windows-jdk11u/jdk-11.0.28+6/bin/java -Xmx512m -jar C:/java/binaries/jtreg/jtreg-7.4+1/lib/jtreg.jar -agentvm -ignore:quiet -automatic -xml -vmoption:-Xmx512m -timeoutFactor:4 -concurrency:1 -testjdk:D:/java/binaries/jdk/x64/2025-07/windows-jdk11u/jdk-11.0.28+6 -verbose:fail,error,summary -nativepath:D:/java/binaries/jdk/x64/2025-07/windows-jdk11u/jdk-11.0.28+6-test-image/hotspot/jtreg/native test/jdk/sun/tools/jrunscript/jrunscript-eTest.sh
XML output to D:\java\ms\dups\openjdk-jdk11u\JTwork
Passed: sun/tools/jrunscript/jrunscript-eTest.sh
Test results: passed: 1
Moral of the story: run OpenJDK shell tests on Windows in the Cygwin environment! At this point, the only outstanding question is about the difference between the local machine and the test environment the build was executed in. I thought that the fact that I didn’t get the rmic.jrmp.stubs.deprecated warning meant that a different default generator was used on my machine. However, I realized that the stdout messages were not being displayed! That warning was present in the output but I needed to open JTwork\sun\rmi\rmic\defaultStubVersion\run.jtr to see it!
----------System.out:(11/743)----------
Warning: generation and use of skeletons and static stubs for JRMP
is deprecated. Skeletons are unnecessary, and static stubs have
been superseded by dynamically generated stubs. Users are
encouraged to migrate away from using rmic to generate skeletons and static
stubs. See the documentation for java.rmi.server.UnicastRemoteObject.
Warning: generation and use of skeletons and static stubs for JRMP
is deprecated. Skeletons are unnecessary, and static stubs have
been superseded by dynamically generated stubs. Users are
encouraged to migrate away from using rmic to generate skeletons and static
stubs. See the documentation for java.rmi.server.UnicastRemoteObject.
TEST PASSED: default output identical to -v1.2 output
----------System.err:(8/706)----------
+ defdir=./default_output
+ refdir=./reference_output
+ rm -rf ./default_output ./reference_output
+ mkdir ./default_output ./reference_output
+ D:/java/binaries/jdk/x64/2025-07/windows-jdk11u/jdk-11.0.28+6/bin/rmic -classpath D:/java/ms/openjdk-jdk11u/JTwork/classes/sun/rmi/rmic/defaultStubVersion/run.d -keep -nowrite -d ./default_output G1Impl
+ D:/java/binaries/jdk/x64/2025-07/windows-jdk11u/jdk-11.0.28+6/bin/rmic -classpath D:/java/ms/openjdk-jdk11u/JTwork/classes/sun/rmi/rmic/defaultStubVersion/run.d -keep -nowrite -d ./reference_output -v1.2 G1Impl
+ diff -r ./default_output ./reference_output
+ echo 'TEST PASSED: default output identical to -v1.2 output'
This was sufficient for me to confirm that the build behaves as expected in this scenario.
Once I had finished Setting up my First 3D Printer, I wanted to design and print custom models. The Anycubic Slicer Next software can only open 3mf files. Being new to this space means that I had never even heard of this format before. Here are some useful resources for learning more about it:
Download the latest release from the releases page. This is a .zip archive.
In Blender, go to Edit -> Preferences and open the Add-ons tab on the left.
Click on the Install… button at the top. Navigate to the .zip you downloaded.
Under the “Community” category, find the add-on called “Import-Export: 3MF format”. Make sure that it’s enabled. (Note: If searching with the search box, exclude the “Import-Export” text since this is the category, not part of the add-on name. Just search for “3MF” instead.)
As promised on the plugins page, the export option is now available:
Note that there is a “Scale” option on the export dialog. I just ensured my dimensions were real world dimensions. Here is the simple blender model I made in the Anycubic Slicer Next software. I was able to successfully print it.
Anycubic Slicer Next with a 3mf exported from Blender
The AI advances of the past couple of years have streamlined many mundane tasks. A recent example for me was having Copilot generate scripts to crop images. I wanted to crop the top portion of my screenshots of the Anycubic app (which I used in my post on Setting up my First 3D Printer). I figured I might as well have one post showing my evolution of prompts for this task:
Prompt 1 – Crop my PNGs
Write a python script that takes a number p and crops the top p pixels from a PNG
copilot:
Sure thing! Here's a Python script that uses the Pillow library to crop the top p pixels from a PNG image:
Setup Tip: You'll need to install Pillow if you haven’t already:
pip install pillow
Let me know if you'd like to expand it—for example, batch processing multiple images or adding a GUI.
from PIL import Image
def crop_top_pixels(image_path, p, output_path):
# Open the image
img = Image.open(image_path)
# Ensure p isn't larger than the image height
width, height = img.size
p = min(p, height)
# Define the crop box (left, upper, right, lower)
crop_box = (0, p, width, height)
# Crop and save
cropped_img = img.crop(crop_box)
cropped_img.save(output_path)
print(f"Cropped image saved to {output_path}")
# Example usage
crop_top_pixels("input.png", 50, "output.png")
Pillow Installation
The only notable thing about installing pillow is that I still need this --break-system-packages flag. I will save that investigation for another day. I will upgrade pip though!
saint@MacBookPro Kobra3-app % pip3 install pillow
[notice] A new release of pip is available: 24.3.1 -> 25.1.1
[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.
...
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 Kobra3-app % pip3 install pillow --break-system-packages
Collecting pillow
Downloading pillow-11.2.1-cp313-cp313-macosx_11_0_arm64.whl.metadata (8.9 kB)
Downloading pillow-11.2.1-cp313-cp313-macosx_11_0_arm64.whl (3.0 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 3.0/3.0 MB 27.0 MB/s eta 0:00:00
Installing collected packages: pillow
Successfully installed pillow-11.2.1
[notice] A new release of pip is available: 24.3.1 -> 25.1.1
[notice] To update, run: python3.13 -m pip install --upgrade pip
Prompt 2 – Invoking via Bash
write a bash script to pass all PNG images to the Python script
copilot:
You got it! Here's a simple Bash script that loops through all .png files in a directory and passes each one to the Python script you created:
#!/bin/bash
# Number of pixels to crop from the top
CROP_HEIGHT=50
# Directory containing PNG images (current directory)
IMAGE_DIR="."
# Python script name
PYTHON_SCRIPT="crop.py"
# Output directory
OUTPUT_DIR="./cropped"
# Create output directory if it doesn't exist
mkdir -p "$OUTPUT_DIR"
# Loop through all PNG files
for img in "$IMAGE_DIR"/*.png; do
filename=$(basename "$img")
output_path="$OUTPUT_DIR/$filename"
echo "Cropping $img..."
python3 "$PYTHON_SCRIPT" "$img" "$CROP_HEIGHT" "$output_path"
done
copilot (continued):
To use this setup:
- Make sure your Python script (crop.py) accepts arguments like this:
- Save the Bash script to a file like batch_crop.sh, make it executable with chmod +x batch_crop.sh, and run it from the terminal:
./batch_crop.sh
Prompt 3 – User Configurable Crop Dimensions
make bash script take number of pixels as a command line argument
copilot:
You got it, Saint. Here's the updated Bash script that takes the number of pixels to crop (CROP_HEIGHT) as a command-line argument:
#!/bin/bash
# Check for a crop height argument
if [ $# -lt 1 ]; then
echo "Usage: $0 <crop_height>"
exit 1
fi
CROP_HEIGHT=$1
IMAGE_DIR="."
PYTHON_SCRIPT="crop.py"
OUTPUT_DIR="./cropped"
mkdir -p "$OUTPUT_DIR"
for img in "$IMAGE_DIR"/*.png; do
filename=$(basename "$img")
output_path="$OUTPUT_DIR/$filename"
echo "Cropping $img by $CROP_HEIGHT pixels..."
python3 "$PYTHON_SCRIPT" "$img" "$CROP_HEIGHT" "$output_path"
done
copilot (continued):
How to run it:
./batch_crop.sh 50
Let me know if you want it to support additional flags (like input/output dirs or image formats) to make it more flexible!
Prompt 4 – Scale Down the Images
modify python script to support scaling each image down to a configurable width
copilot:
Absolutely! Here's how you can update your Python script to not only crop the top p pixels but also scale each image down to a configurable target width while preserving the aspect ratio:
import sys
from PIL import Image
def crop_and_scale(image_path, crop_pixels, output_path, target_width=None):
# Open the image
img = Image.open(image_path)
width, height = img.size
# Crop the top p pixels
crop_pixels = min(crop_pixels, height)
cropped_img = img.crop((0, crop_pixels, width, height))
# Resize while maintaining aspect ratio
if target_width is not None and target_width < cropped_img.width:
aspect_ratio = cropped_img.height / cropped_img.width
target_height = int(target_width * aspect_ratio)
cropped_img = cropped_img.resize((target_width, target_height), Image.LANCZOS)
# Save the result
cropped_img.save(output_path)
if __name__ == "__main__":
if len(sys.argv) < 4:
print("Usage: python crop.py <input_path> <crop_pixels> <output_path> [target_width]")
sys.exit(1)
img_path = sys.argv[1]
crop_amount = int(sys.argv[2])
output_path = sys.argv[3]
width = int(sys.argv[4]) if len(sys.argv) > 4 else None
crop_and_scale(img_path, crop_amount, output_path, width)
copilot (continued):
Example command to run it:
python3 crop.py input.png 50 output.png 300
This will crop the top 50 pixels, then scale the image to 300px wide while maintaining the aspect ratio.
Let me know if you want to add height constraints or enforce padding for uniform size outputs!
Prompt 5 – No Bash Required
merge the functionality of the bash script into the python script
copilot:
You got it, Saint. Here's a standalone Python script that handles batch processing of all PNGs in the current directory, crops the top p pixels, and optionally scales them to a target width—all from the command line:
import os
import sys
from PIL import Image
def crop_and_scale(image_path, crop_pixels, output_path, target_width=None):
img = Image.open(image_path)
width, height = img.size
# Crop top p pixels
crop_pixels = min(crop_pixels, height)
cropped = img.crop((0, crop_pixels, width, height))
# Resize if target width is specified
if target_width is not None and target_width < cropped.width:
aspect_ratio = cropped.height / cropped.width
new_height = int(target_width * aspect_ratio)
cropped = cropped.resize((target_width, new_height), Image.LANCZOS)
cropped.save(output_path)
def process_directory(crop_pixels, target_width=None):
input_dir = "."
output_dir = "./cropped"
os.makedirs(output_dir, exist_ok=True)
for filename in os.listdir(input_dir):
if filename.lower().endswith(".png"):
input_path = os.path.join(input_dir, filename)
output_path = os.path.join(output_dir, filename)
print(f"Processing {filename}...")
crop_and_scale(input_path, crop_pixels, output_path, target_width)
if __name__ == "__main__":
if len(sys.argv) < 2:
print("Usage: python batch_crop.py <crop_pixels> [target_width]")
sys.exit(1)
crop_pixels = int(sys.argv[1])
target_width = int(sys.argv[2]) if len(sys.argv) > 2 else None
process_directory(crop_pixels, target_width)
copilot (continued):
Example usage:
python batch_crop.py 50 # Crop top 50 pixels only
python batch_crop.py 50 300 # Crop top 50 pixels and scale to 300px wide
Want to add input/output directory flags, process JPGs too, or make it a little GUI app for drag-and-drop convenience? I’d be glad to help with any of that.
Prompt 6 – Renaming Files
modify the script to replace user specified filename prefix with a custom user specified prefix
copilot:
Sure thing! Here's the updated Python script that allows the user to specify:
- The number of pixels to crop (crop_pixels)
- An optional scaling width (target_width)
- A filename prefix to replace
- A new prefix to substitute in its place
import os
import sys
from PIL import Image
def crop_and_scale(image_path, crop_pixels, output_path, target_width=None):
img = Image.open(image_path)
width, height = img.size
# Crop
crop_pixels = min(crop_pixels, height)
cropped = img.crop((0, crop_pixels, width, height))
# Scale
if target_width is not None and target_width < cropped.width:
aspect_ratio = cropped.height / cropped.width
new_height = int(target_width * aspect_ratio)
cropped = cropped.resize((target_width, new_height), Image.LANCZOS)
cropped.save(output_path)
def process_directory(crop_pixels, target_width, old_prefix, new_prefix):
input_dir = "."
output_dir = "./cropped"
os.makedirs(output_dir, exist_ok=True)
for filename in os.listdir(input_dir):
if filename.lower().endswith(".png"):
if not filename.startswith(old_prefix):
continue # Skip files that don't match the prefix
# Replace old prefix with new
new_filename = new_prefix + filename[len(old_prefix):]
input_path = os.path.join(input_dir, filename)
output_path = os.path.join(output_dir, new_filename)
print(f"Processing {filename} → {new_filename}")
crop_and_scale(input_path, crop_pixels, output_path, target_width)
if __name__ == "__main__":
if len(sys.argv) < 4:
print("Usage: python batch_crop.py <crop_pixels> <old_prefix> <new_prefix> [target_width]")
sys.exit(1)
crop_pixels = int(sys.argv[1])
old_prefix = sys.argv[2]
new_prefix = sys.argv[3]
target_width = int(sys.argv[4]) if len(sys.argv) > 4 else None
process_directory(crop_pixels, target_width, old_prefix, new_prefix)
Example usage:
python batch_crop.py 40 IMG_ thumb_ 300
If you have files like IMG_001.png, the output will be named thumb_001.png.
Let me know if you’d like suffix support, regex matching, or nested folder traversal next!
This final script enabled me to crop, scale down, and renamed all the PNGs from my phone with minimal effort. Here is an example of how I used it:
