Parallelization: pthreads or OpenMP?

Question

Most people in scientific computing use OpenMP as a quasi-standard when it comes to shared memory parallelization.

Is there any reason (other than readability) to u

Answer 1

OpenMP requires a compiler that supports it, and works with pragmas. The advantage to this is that when compiling without OpenMP-support (e.g. PCC or Clang/LLVM as of now), the code will still compile. Also, have a look at what Charles Leiserson wrote about DIY multithreading.

Pthreads is a POSIX standard (IEEE POSIX 1003.1c) for libraries, while OpenMP specifications are to be implemented on compilers; that being said, there are a variety of pthread implementations (e.g. OpenBSD rthreads, NPTL), and a number of compilers that support OpenMP (e.g. GCC with the -fopenmp flag, MSVC++ 2008).

Pthreads are only effective for parallelization when multiple processors are available, and only when the code is optimized for the number of processors available. Code for OpenMP is more-easily scalable as a result. You can mix code that compiles with OpenMP with code using pthreads, too.