llvm dev - Feb 2008 - [LLVMdev] JITted code in multiple threads

I just thought of something that scared me, and I'm hoping there is a
happy ending.  I realized recently that the JITter does not
necessarily finish JITting inside of getPointerToFunction.  Instead,
it often generates stubs which get a final JIT only upon jumping to
them.  Now--I am in the situation where I'd like to do a
getPointerToFunction, and then take the pointer and pass it out to
multiple cores to execute the code I've generated in parallel.  This
seems like a problem--if jumping to an address means code will be
munged, then two or more cores trying to jump to that address at the
same time might all try to JIT the stubs, resulting in a barrage of
random code!!

This seems like a very obvious issue, so I'm guessing there is a
simple answer for this.  What are peoples' thoughts?  Any and all are
appreciated.

Aaron

On Feb 27, 2008, at 1:10 AM, Aaron Dwyer wrote:
> I just thought of something that scared me, and I'm hoping there is a
> happy ending.  I realized recently that the JITter does not
> necessarily finish JITting inside of getPointerToFunction.  Instead,
> it often generates stubs which get a final JIT only upon jumping to
> them.  Now--I am in the situation where I'd like to do a
> getPointerToFunction, and then take the pointer and pass it out to
> multiple cores to execute the code I've generated in parallel.  This
> seems like a problem--if jumping to an address means code will be
> munged, then two or more cores trying to jump to that address at the
> same time might all try to JIT the stubs, resulting in a barrage of
> random code!!
>
> This seems like a very obvious issue, so I'm guessing there is a
> simple answer for this.  What are peoples' thoughts?  Any and all are
> appreciated.
The JIT is thread safe: it uses a pthread mutex to prevent multiple  
threads from clobbering each other, even if lazy compilation is  
happening.

-Chris