[LLVMdev] IR code generation and JIT execution in a multithread environment

[Edgar Geisler]

Hi Gordon,

> Module and Value are unsafe for concurrent access--even disjoint
> instances thereof. So you'll need to hold a global mutex while
> loading, building, or transforming IR. 

>From my (limited) point of view it would be nice to have some
fine grained lock mechanisms for IR/JIT generation. AFAIK the
critical sections during IR (Module) generation are the alteration 
or access to the static/global Type-/ValueMaps. Wouldn't it be
sufficient to protect them by some kind of 'null'-mutex and leaving the
implemtation to the particular project?

> I think serializing code generation in a JIT will usually be adequate,
> since presumably the compiled program (rather than the compiler)
> should dominate runtime. However, if your project truly needs
> concurrent JIT compilation, LLVM doesn't yet meet your needs. 

I am using LLVM as a kind of glue between a controlling process (exe) and 
some services (lib). Within my mentioned scenario IR/JIT generation
dominates 
runtime with an average factor of 5-10. Simply speaking, executing a
service needs ~ 10 ms while IR/JIT generation for this service needs 
~ 40 - 100 ms on the average. So, if the controller gets a bulk
of service requests, it can be expected that the requests will be lined up
at a global Module generator or at the global JIT generator mutex. 

Edgar