[LLVMdev] multithreaded use of llvm::sys::RemoveFileOnSignal

[Dmitri Gribenko]

On Thu, Feb 27, 2014 at 12:50 AM, Vikas Bhargava
<vikasbhargava at gmail.com> wrote:
> Hi,
> I am using clang::ToolInvocation class to compile some code in-memory:
>
>    clang::tooling::ToolInvocation ti
>       (
>        compilerArgs,
>        new clang::EmitBCAction(),
>        new clang::FileManager(clang::FileSystemOptions())
>       );
>    //filename is the name of the source file, e.g. "Somefile.cpp"
>    //sourcecode contains the source of the file
>    ti.mapVirtualFile( filename, sourcecode );
>    bool ret = ti.run();
>
> In order to speed up compilation of several sources, I call the above code
> concurrently in separate threads, with each thread compiling its own source
> code. However, this does not work because clang::CompilerInstance calls
> llvm::Sys::RemoveFileOnSignal which in turn calls RegisterHandlers() which
> is not re-entrant.
>
> Is there a way to make RegisterHandlers() re-entrant? I do call
> llvm::start_multi_threaded() before any of this, hoping that it will make
> llvm routines thread-safe, but to no avail.

Seems like it is a bug in either RemoveFileOnSignal().  For some
reason, the first one releases the mutex before calling the
RegisterHandlers().

bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
                                   std::string* ErrMsg) {
  SignalsMutex.acquire();
...
  SignalsMutex.release();

  RegisterHandlers();
  return false;
}

CC'ing Argyrios because this is important for libclang.

Argyrios: what do you think -- should we call RegisterHandlers() under a mutex?

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/