RFR: 8271931: Make AbortVMOnVMOperationTimeout more resilient to OS scheduling [v4]

[Albert Mingkun Yang]

On Mon, 9 Aug 2021 05:22:23 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   disarm
>
> src/hotspot/share/runtime/vmThread.cpp line 84:
> 
>> 82:   // The two stores to `_armed` are counted in VM-op, but they should be
>> 83:   // insignificant compared to the actual VM-op duration.
>> 84:   jlong vm_op_duration = nanos_to_millis(os::javaTimeNanos() - _arm_time);
> 
> You could move this ahead of the store. And then you only need a small comment in arm().

You previously commented on slack: "Also disarm before getting the end time just to shorten the race with the watcher thread". I agree with that; for non-stuck VM-ops, checking timeout on VM thread is more reliable.

> src/hotspot/share/runtime/vmThread.cpp line 89:
> 
>> 87:   // VMOperationTimeoutTask might miss the arm-disarm window depending on
>> 88:   // the scheduling.
>> 89:   assert(Thread::current()->is_VM_thread(), "Check timeout on VM thread");
> 
> Seems unnecessary to assert this.

Removed.

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PR: https://git.openjdk.java.net/jdk/pull/5016