RFR: 8294370: Fix allocation bug in java_lang_Thread::async_get_stack_trace()

[David Holmes]

On Mon, 26 Sep 2022 14:23:38 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

> Please review this small fix in async_get_stack_trace(). The GrowableArrays created to store the bci and Method* of each frame found while traversing the stack are allocated in the resource area of the thread that calls async_get_stack_trace(). But if the handshake is executed by the target and if the number of frames in the stack exceeds the initial size of the GrowableArrays then we will hit an assertion when trying to grow the size of the arrays (see bug description).
> Currently we don't see any issues because the initial size of the GrowableArrays is 512 and our tests don't test beyond that (the maximum value of DEPTH in the vmTestbase/nsk/stress/strace/ tests is 500). The issue can be easily reproduced by either decreasing the initial size of the GrowableArrays or by increasing the value of DEPTH in those strace tests.
> To fix it I allocated the arrays in the C heap instead. Also I lowered the initial size of the arrays since 512 seemed too much to start with.
> Tested it by running all tests in the vmTestbase/nsk/stress/strace/ directory.
> 
> Thanks,
> Patricio

Good find! Looks good! A couple of queries at this stage.

Thanks.

src/hotspot/share/classfile/javaClasses.cpp line 2004:

> 2002:       const bool skip_hidden = !ShowHiddenFrames;
> 2003: 
> 2004:       // Pick some initial length

The comment should at least hint at there being some reasonable reason for choosing the value that follows. :)

src/hotspot/share/classfile/javaClasses.cpp line 2008:

> 2006:       _methods = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Method*>(init_length, mtInternal);
> 2007:       _bcis = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<int>(init_length, mtInternal);
> 2008: 

Couldn't you just do this in the constructor? I'm not clear if there is a subtle reason for needing lazy-init as well as moving to the C_Heap.

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PR: https://git.openjdk.org/jdk/pull/10424