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

[Argyrios Kyrtzidis]

On Feb 27, 2014, at 3:23 AM, Dmitri Gribenko <gribozavr at gmail.com> wrote:

> 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?

That, or get RegisterHandlers to use the mutex.
Also access to CallBacksToRun is not thread-safe (the whole file probably needs reviewing..)

But it's not so clear to me what is the exact symptom, is there a crash occurring ? Vika, could you explain ?

> 
> 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>*/

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