RFR: 8330846: Add stacks of mounted virtual threads to the HotSpot thread dump

[David Holmes]

On Fri, 31 May 2024 02:07:25 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Print the stack traces of mounted virtual threads when calling `jcmd <pid> Thread.print`.
>
> I'd probably give preference to the stack of the virtual thread, as the stack of the carrier when a vthread is mounted is generally quite uninteresting:
> 
> "ForkJoinPool-1-worker-1" #25 [33795] daemon prio=5 os_prio=31 cpu=46574.42ms elapsed=47.15s tid=0x00007f81670d1a00  [0x000070000e9a4000]
>        Carrying virtual thread #24
>              at Main.lambda$main$0(Main.java:7)
>              at java.lang.VirtualThread.run(java.base/VirtualThread.java:381)
> 	at jdk.internal.vm.Continuation.run(java.base/Continuation.java:262)
> 	at java.lang.VirtualThread.runContinuation(java.base/VirtualThread.java:283)
> 	at java.lang.VirtualThread$$Lambda/0x00000001220b2868.run(java.base/Unknown Source)
> 	at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.compute(java.base/ForkJoinTask.java:1726)
> 	at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.compute(java.base/ForkJoinTask.java:1717)
> 	at java.util.concurrent.ForkJoinTask$InterruptibleTask.exec(java.base/ForkJoinTask.java:1641)
> 	at java.util.concurrent.ForkJoinTask.doExec(java.base/ForkJoinTask.java:507)
> 	at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(java.base/ForkJoinPool.java:1455)
> 	at java.util.concurrent.ForkJoinPool.runWorker(java.base/ForkJoinPool.java:2031)
> 	at java.util.concurrent.ForkJoinWorkerThread.run(java.base/ForkJoinWorkerThread.java:189)

> > * The format proposed by @dholmes-ora definitely makes sense
> 
> You will different get different opinions on how it is presented. Can you also try putting a new section that lists the mounted virtual threads and their stack trace. If the virtual thread has a name then it can be shown too.

That suggests to me that we have to iterate the list of all threads twice ?? If so that seems not ideal.

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PR Comment: https://git.openjdk.org/jdk/pull/19482#issuecomment-2144602366