The C++11 standard library is broadly thread safe. The thread safety guarantees on PRNG objects are the same as on containers. More specifically, since the PRNG classes are all pseudo-random, i.e. they generate a deterministic sequence based on a definite current state, there is really no room to be peeking or poking at anything outside … Read more
OpenMP compilation adds the preprocessor definition “_OPENMP”, so you can do: #if defined(_OPENMP) #pragma omp … #endif For some examples, see http://bisqwit.iki.fi/story/howto/openmp/#Discussion and the code which follows.
What affects the runtime of guided scheduling? There are three effects to consider: 1. Load balance The whole point of dynamic/guided scheduling is to improve the distribution of work in the case where not each loop iteration contains the same amount of work. Fundamentally: schedule(dynamic, 1) provides optimal load balancing dynamic, k will always have … Read more
Sorry to put this in as an answer since it’s more of a comment, but it’s too long to fit in as a comment, so here goes: From the site you referenced. Runtime support library for GNU OpenMP (part of GCC), at least for GCC versions 4.2 and 4.3. The GNU OpenMP runtime library (libgomp.so) … Read more
Ok, picked up the bait. This is on a system with Intel(R) Core(TM)2 Quad CPU Q9550 @ 2.83GHz 4×5666.59 bogomips Linux meerkat 2.6.35-28-generic-pae #50-Ubuntu SMP Fri Mar 18 20:43:15 UTC 2011 i686 GNU/Linux gcc version 4.4.5 total used free shared buffers cached Mem: 8127172 4220560 3906612 0 374328 2748796 -/+ buffers/cache: 1097436 7029736 Swap: 0 … Read more
Yes it is possible to do an array reduction with OpenMP. In Fortran it even has construct for this. In C/C++ you have to do it yourself. Here are two ways to do it. The first method makes private version of S for each thread, fill them in parallel, and then merges them into S … Read more
With gcc, you need to compile and link with -fopenmp to enable OpenMP. Other compilers have different options; with intel it’s -openmp, with pgi it’s -mp, etc.
The problem with your code is that the iterations of the inner loop depend on the outer loop. According to the OpenMP specification under the description of the section on binding and the collapse clause: If execution of any associated loop changes any of the values used to compute any of the iteration counts, then … Read more
Walter, I believe I not only told you the current state of things in that other discussion, but also provided you with information directly from the source (i.e. from my colleague who is part of the OpenMP language committee). OpenMP was designed as a lightweight data-parallel addition to FORTRAN and C, later extended to C++ … Read more
It basically boils down to what level of control you want over your parallelization. OpenMP is great if all you want to do is add a few #pragma statements and have a parallel version of your code quite quickly. If you want to do really interesting things with MIMD coding or complex queueing, you can … Read more