[cfe-dev] llvm::CrashRecoveryContext (in libclang)

[Vedant Kumar via cfe-dev]

> On Oct 1, 2015, at 12:25 PM, John Sully <john at csquare.ca> wrote:
> 
> A multiprocess model is workable for major operations like reparsing but too much overhead for some of the smaller query type operations that libclang provides.

Yes, I was worried about that.


> In an ideal world clang would never crash and clean up all of its resources so this wouldn't be necessary. My experience shows its about 99% there if you don't use the precompiled options. 

Are you having issues with pre-compiled headers?


> I have a set of patches that will enable this as an option.  I think libclang should take them, and support this mode.

I'm curious about what you mean by 'clean up all of its resources'. Is that something we rely on CrashRecoveryContext to do?

At any rate, it'd be great to have these patches up on reviews.llvm.org! Please tag me as a reviewer.

thanks
vedant


> On Thursday, October 1, 2015, Vedant Kumar <vsk at apple.com> wrote:
> 
> 
> > On Sep 27, 2015, at 8:13 PM, John Sully via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> >
> > I'm writing a client application that uses libclang and uses it to parse documents on multiple threads.  I've been debugging a memory corruption bug and traced it to the CrashRecoveryContext destructor deleting other thread's Parser objects out from under it.
> >
> > Looking at the CrashRecoveryContext code it appears no effort is made to make this thread safe, specifically it heavily relies on static members which is how pointers are making their way across threads.
> >
> > There are two questions here:
> > 1) Is libclang intended to be thread safe?  (I.e. would a patch be accepted to fix this or is this behavior by design)
> 
> I'd be very happy to see patches geared towards making libclang more thread safe. There seem to be important use cases for this.
> 
> 
> > 2) Generally "recovering" from unknown crashes is considered to be bad practice, is there a recommended way to prevent use of the crash recovery mechanism?
> 
> The clang driver uses process isolation. E.g, a monitor process can wait on the compile process and emit diagnostics if it crashes. Does that work for your project?
> 
> vedant