RFR: 8284828: Use `os::ThreadCrashProtection` to protect AsyncGetCallTrace from crashing

[Thomas Stuefe]

On Wed, 13 Apr 2022 15:11:41 GMT, Jaroslav Bachorik <jbachorik at openjdk.org> wrote:

>> Move the AsyncGetCallTrace method implementation into a separate method and wrap its call in non-assert compilation mode in `os::ThreadCrashProtection` like it is done in [JFR](https://github.com/openjdk/jdk/blob/965ea8d9cd29aee41ba2b1b0b0c67bb67eca22dd/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp#L165).
>> This prevents AsyncGetCallTrace from crashing on segmentation faults (but not on `guarantee`s).
>> 
>> If a crash is observed, then the `num_frames` field of the trace is set to `ticks_unknown_state` (-7) to signal a state that cannot be properly handled. `ticks_unknown_state` is currently also used for signaling unknown thread states but this should not be a problem, as the semantic is the same. If `num_frames` already has an error code then this error code is not changed. This helps to distinguish between errors in walking threads in Java and non-Java mode, as `num_frames` is set there before the walking to the appropriate error code.
>> 
>> _Thanks for @tstuefe for suggesting this._
>
> src/hotspot/share/prims/forte.cpp line 671:
> 
>> 669: #ifndef ASSERT
>> 670:   trace->num_frames = ticks_unknown_state;
>> 671:   AsyncGetCallTraceCallBack cb(trace, depth, ucontext);
> 
> ~Isn't [this assert](https://github.com/openjdk/jdk/blob/e245f9d2007b0a6c9962b6bf4488ba4d4ce47e92/src/hotspot/os/posix/os_posix.cpp#L1158) failing? It seems like the crash protection is only for the JFR sampler thread.~
> 
> OIC - this is only when asserts are not enabled.

I think if we start using ThreadCrashProtection like a general-purpose class, we should make it one and remove the JFR dependencies.

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PR: https://git.openjdk.java.net/jdk/pull/8225