[Lldb-commits] [lldb] r253086 - Add a null check against the ThreadPlan

[Zachary Turner via lldb-commits]

I'll change it to an assert and next time it happens I'll dig a little
more.  I've only seen this on about 1 or 2 out of 100 runs of the test
suite so I don't know how it happens.

On Fri, Nov 13, 2015 at 1:44 PM Jim Ingham <jingham at apple.com> wrote:

> GetCurrentPlan should never return NULL.  The Thread constructor pushes
> the Base thread plan onto the stack, and pop won't remove the Base plan.
> When we destroy the thread (in ThreadDestroy) we clear the plan stack and
> then push a ThreadPlanNull onto the plan stack.  So if you are seeing a
> GetCurrentPlan returning NULL that means somebody is using it while it is
> in the process of being created or destroyed.  The former shouldn't be
> possible, so you must be accessing it while it is in mid-destroy.
>
> I'd rather not put more code in various places that checks for things that
> should never be true, or if you are doing this check you should assert so
> we can figure out how this is happening.
>
> Note, ThreadDestroy doesn't lock itself against uses of the thread.  That
> hasn't been necessary but if you are seeing crashes here, it might be worth
> doing that.
>
> Jim
>
>
> > On Nov 13, 2015, at 1:28 PM, Zachary Turner via lldb-commits <
> lldb-commits at lists.llvm.org> wrote:
> >
> > Author: zturner
> > Date: Fri Nov 13 15:28:53 2015
> > New Revision: 253086
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=253086&view=rev
> > Log:
> > Add a null check against the ThreadPlan
> >
> > I'm seeing some cases where the ThreadPlan is null.  It could
> > be a sign of a valid race condition, but at least we shouldn't
> > crash.
> >
> > Modified:
> >    lldb/trunk/source/Target/ThreadList.cpp
> >
> > Modified: lldb/trunk/source/Target/ThreadList.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Target/ThreadList.cpp?rev=253086&r1=253085&r2=253086&view=diff
> >
> ==============================================================================
> > --- lldb/trunk/source/Target/ThreadList.cpp (original)
> > +++ lldb/trunk/source/Target/ThreadList.cpp Fri Nov 13 15:28:53 2015
> > @@ -538,7 +538,7 @@ ThreadList::WillResume ()
> >
> >     for (pos = m_threads.begin(); pos != end; ++pos)
> >     {
> > -        if ((*pos)->GetResumeState() != eStateSuspended &&
> > +        if ((*pos)->GetResumeState() != eStateSuspended &&
> (*pos)->GetCurrentPlan() &&
> >                  (*pos)->GetCurrentPlan()->StopOthers())
> >         {
> >             if ((*pos)->IsOperatingSystemPluginThread() &&
> !(*pos)->GetBackingThread())
> >
> >
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>
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