The following tests timeout in the Valhalla CI on windows-x64 when the -XX:+UseCompactObjectHeaders option is used:

com/sun/jdi/valhalla/FieldWatchpointsTest.java
com/sun/jdi/valhalla/ValueArrayReferenceTest.java
com/sun/jdi/valhalla/ValueClassTypeTest.java
sun/jvmstat/monitor/MonitoredVm/MonitorVmStartTerminate.java

Here's a snippet from the FieldWatchpointsTest.java log file:

#section:main
----------messages:(12/875)----------
command: main FieldWatchpointsTest -XX:+UseArrayFlattening -XX:+UseFieldFlattening -XX:+UseAtomicValueFlattening -XX:+UseNullableValueFlattening -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlineLayout -XX:+PrintFlatArrayLayout
reason: User specified action: run main/othervm FieldWatchpointsTest -XX:+UseArrayFlattening -XX:+UseFieldFlattening -XX:+UseAtomicValueFlattening -XX:+UseNullableValueFlattening -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlineLayout -XX:+PrintFlatArrayLayout
started: Tue Jan 13 00:15:25.448 UTC 2026
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules jdk.jdi
Process id: 12496
Timeout information:
[00:23:25.459] starting timeout handler action(s)
[00:40:41.981] timeout handler action(s) completed
--- Timeout information end.
finished: Tue Jan 13 00:40:41.983 UTC 2026
elapsed time (seconds): 1516.535
----------configuration:(3/38)----------
Boot Layer
  add modules: jdk.jdi

----------System.out:(3/426)*----------
vmOpts: '-Xmx768m -XX:MaxRAMPercentage=4.16667 -Dtest.boot.jdk=c:\\ade\\mesos\\work_dir\\jib-master\\install\\jdk\\25\\37\\bundles\\windows-x64\\jdk-25_windows-x64_bin.zip\\jdk-25 -Djava.io.tmpdir=c:\\sb\\prod\\1768263144\\testoutput\\test-support\\jtreg_open_test_jdk_jdk_svc\\tmp -XX:+CreateCoredumpOnCrash -ea -esa'
javaOpts: '-XX:+UseZGC -XX:+UseCompactObjectHeaders'
[00:23:25.458] Timeout signalled after 480 seconds
----------System.err:(1/237)----------
[2ms] run args: [-XX:+UseArrayFlattening, -XX:+UseFieldFlattening, -XX:+UseAtomicValueFlattening, -XX:+UseNullableValueFlattening, -XX:+UnlockDiagnosticVMOptions, -XX:+PrintInlineLayout, -XX:+PrintFlatArrayLayout, FieldWatchpointsTarg]
----------rerun:(50/6897)*----------


Here's a snippet from the ValueArrayReferenceTest.java log file:

#section:main
----------messages:(12/1096)----------
command: main ValueArrayReferenceTest --add-modules java.base --add-exports java.base/jdk.internal.value=ALL-UNNAMED -XX:+UseArrayFlattening -XX:+UseFieldFlattening -XX:+UseAtomicValueFlattening -XX:+UseNullableValueFlattening -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlineLayout -XX:+PrintFlatArrayLayout
reason: User specified action: run main/othervm ValueArrayReferenceTest --add-modules java.base --add-exports java.base/jdk.internal.value=ALL-UNNAMED -XX:+UseArrayFlattening -XX:+UseFieldFlattening -XX:+UseAtomicValueFlattening -XX:+UseNullableValueFlattening -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlineLayout -XX:+PrintFlatArrayLayout
started: Tue Jan 13 00:15:26.415 UTC 2026
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules java.base --add-exports java.base/jdk.internal.value=ALL-UNNAMED
Process id: 83352
Timeout information:
[00:23:26.432] starting timeout handler action(s)
[00:40:38.098] timeout handler action(s) completed
--- Timeout information end.
finished: Tue Jan 13 00:40:38.103 UTC 2026
elapsed time (seconds): 1511.688
----------configuration:(4/117)----------
Boot Layer
  add modules: java.base
  add exports: java.base/jdk.internal.value ALL-UNNAMED

----------System.out:(3/426)*----------
vmOpts: '-Xmx768m -XX:MaxRAMPercentage=4.16667 -Dtest.boot.jdk=c:\\ade\\mesos\\work_dir\\jib-master\\install\\jdk\\25\\37\\bundles\\windows-x64\\jdk-25_windows-x64_bin.zip\\jdk-25 -Djava.io.tmpdir=c:\\sb\\prod\\1768263144\\testoutput\\test-support\\jtreg_open_test_jdk_jdk_svc\\tmp -XX:+CreateCoredumpOnCrash -ea -esa'
javaOpts: '-XX:+UseZGC -XX:+UseCompactObjectHeaders'
[00:23:26.431] Timeout signalled after 480 seconds
----------System.err:(1/323)----------
[2ms] run args: [--add-modules, java.base, --add-exports, java.base/jdk.internal.value=ALL-UNNAMED, -XX:+UseArrayFlattening, -XX:+UseFieldFlattening, -XX:+UseAtomicValueFlattening, -XX:+UseNullableValueFlattening, -XX:+UnlockDiagnosticVMOptions, -XX:+PrintInlineLayout, -XX:+PrintFlatArrayLayout, ValueArrayReferenceTarg]
----------rerun:(51/7099)*----------


Here's a snippet from the ValueClassTypeTest.java log file:

#section:main
----------messages:(12/871)----------
command: main ValueClassTypeTest -XX:+UseArrayFlattening -XX:+UseFieldFlattening -XX:+UseAtomicValueFlattening -XX:+UseNullableValueFlattening -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlineLayout -XX:+PrintFlatArrayLayout
reason: User specified action: run main/othervm ValueClassTypeTest -XX:+UseArrayFlattening -XX:+UseFieldFlattening -XX:+UseAtomicValueFlattening -XX:+UseNullableValueFlattening -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlineLayout -XX:+PrintFlatArrayLayout
started: Tue Jan 13 00:15:26.773 UTC 2026
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules jdk.jdi
Process id: 77200
Timeout information:
[00:23:26.785] starting timeout handler action(s)
[00:40:42.604] timeout handler action(s) completed
--- Timeout information end.
finished: Tue Jan 13 00:40:42.606 UTC 2026
elapsed time (seconds): 1515.833
----------configuration:(3/38)----------
Boot Layer
  add modules: jdk.jdi

----------System.out:(3/426)*----------
vmOpts: '-Xmx768m -XX:MaxRAMPercentage=4.16667 -Dtest.boot.jdk=c:\\ade\\mesos\\work_dir\\jib-master\\install\\jdk\\25\\37\\bundles\\windows-x64\\jdk-25_windows-x64_bin.zip\\jdk-25 -Djava.io.tmpdir=c:\\sb\\prod\\1768263144\\testoutput\\test-support\\jtreg_open_test_jdk_jdk_svc\\tmp -XX:+CreateCoredumpOnCrash -ea -esa'
javaOpts: '-XX:+UseZGC -XX:+UseCompactObjectHeaders'
[00:23:26.785] Timeout signalled after 480 seconds
----------System.err:(1/235)----------
[2ms] run args: [-XX:+UseArrayFlattening, -XX:+UseFieldFlattening, -XX:+UseAtomicValueFlattening, -XX:+UseNullableValueFlattening, -XX:+UnlockDiagnosticVMOptions, -XX:+PrintInlineLayout, -XX:+PrintFlatArrayLayout, ValueClassTypeTarg]
----------rerun:(50/6875)*----------


Here's a snippet from the MonitoredVm/MonitorVmStartTerminate.java

#section:main
----------messages:(12/681)----------
command: main MonitorVmStartTerminate
reason: User specified action: run main/othervm/timeout=240 MonitorVmStartTerminate
started: Tue Jan 13 00:40:02.903 UTC 2026
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules java.management,jdk.internal.jvmstat --add-exports jdk.internal.jvmstat/sun.jvmstat.monitor=ALL-UNNAMED --add-exports jdk.internal.jvmstat/sun.jvmstat.monitor.event=ALL-UNNAMED
Process id: 17076
Timeout information:
[00:56:02.918] starting timeout handler action(s)
[01:13:25.681] timeout handler action(s) completed
--- Timeout information end.
finished: Tue Jan 13 01:13:25.683 UTC 2026
elapsed time (seconds): 2002.78
----------configuration:(5/228)----------
Boot Layer
  add modules: java.management jdk.internal.jvmstat
  add exports: jdk.internal.jvmstat/sun.jvmstat.monitor ALL-UNNAMED
               jdk.internal.jvmstat/sun.jvmstat.monitor.event ALL-UNNAMED

----------System.out:(1887/100397)*----------
started=0, terminated=0
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_0
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_1
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_2
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_3
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_4
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_5
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_6
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_7
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_8
Starting fe5134ed-01d9-42eb-9419-a97b9cbcede4_9
Waiting for all processes to get started notification

<snip>

This test generates so much output that the log is elided.
There may be something important hiding in there...

<snip>

releaseStarted([99952])
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
hasMainArgs(99952): has main args: 'jstack --pid 17076'
releaseStarted: not a test pid: 99952
releaseTerminated([])
started=0, terminated=8
----------System.err:(24/1760)----------
Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_6 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_6 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_6 has been removed in 1503374962320 ns

Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_0 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_0 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_0 has been removed in 1504392137070 ns

Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_7 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_7 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_7 has been removed in 1503429512140 ns

Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_5 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_5 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_5 has been removed in 1503366624630 ns

Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_2 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_2 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_2 has been removed in 1503680418730 ns

Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_1 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_1 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_1 has been removed in 1503345979040 ns

Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_3 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_3 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_3 has been removed in 1503273039030 ns

Java Process fe5134ed-01d9-42eb-9419-a97b9cbcede4_4 stdout:Waiting for fe5134ed-01d9-42eb-9419-a97b9cbcede4_4 to be removed
waitForRemoval: fe5134ed-01d9-42eb-9419-a97b9cbcede4_4 has been removed in 1503577652990 ns

----------rerun:(50/7075)*----------


I don't know the details about this test, but there are number
of lines like this in the output:

hasMainArgs(99952): has main args: 'jstack --pid 17076'
releaseStarted: not a test pid: 99952
releaseTerminated([])
started=0, terminated=8

releaseStarted reports "ot a test pid: 99952", but that value
is reported in the previous "hasMainArgs(NNNN)" output lines.
What does that mean?

Each group always ends with "started=0, terminated=8"
and those values don't seem to change.

Why does this test only fail on windows-x64 and only when
the -XX:+UseCompactObjectHeaders option is used?

I recommend getting a complete passing log from another
platform, generating a complete failing log on windows-x64
and checking for any glaring differences.


Since this appears to be an issue with -XX:+UseCompactObjectHeaders
I'm starting this issue off in hotspot/runtime for initial triage.