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
On a Mac, the command gcc is a symlink to Clang. So by calling gcc -fopenmp -o your_program your_program.c you are in fact using Clang, which until now has not had built-in support for OpenMP. The newer versions of Clang do have support for OpenMP according to this post (where you can also find instructions … Read more
The message basically tells you that you have to provide the path to the libraries and the names of the libraries. The following example should fix your problem (see also find_package(OpenMP)). Note that I use the brew installation using the command “brew install llvm”. The first four lines are just for completeness. set(CMAKE_C_COMPILER “/usr/local/Cellar/llvm/5.0.1/bin/clang”) set(CMAKE_CXX_COMPILER … Read more
The code posted by the OP will never execute in parallel, because the parallel keyword does not appear. The fact that the OP got ids different from 0 shows that probably his code was embedded in a parallel directive. However, this is not clear from his post, and might confuse beginners. The minimum sensible example … Read more
You’ll hit a couple of speed-bumps if OpenMP is on your radar. OpenMP is a multi-threading library for unmanaged C/C++, it requires compiler support to be effective. Not an option in C#. Let’s take a step back. What you’ve got now is as bad as you can possibly get. Get/SetPixel() is dreadfully slow. A major … Read more
This command can help you brew install libomp brew info libomp libomp: stable 6.0.1 (bottled) LLVM’s OpenMP runtime library https://openmp.llvm.org/ /usr/local/Cellar/libomp/6.0.1 (12 files, 1.2MB) * Poured from bottle on 2018-11-20 at 16:12:22 From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/libomp.rb ==> Dependencies Build: cmake ✘ ==> Requirements Required: macOS >= 10.10 ✔ ==> Caveats On Apple Clang, you need to add … Read more
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
Besides calling omp_get_num_threads() outside of the parallel region in your case, calling omp_set_num_threads() still doesn’t guarantee that the OpenMP runtime will use exactly the specified number of threads. omp_set_num_threads() is used to override the value of the environment variable OMP_NUM_THREADS and they both control the upper limit of the size of the thread team that … 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
private variables are not initialised, i.e. they start with random values like any other local automatic variable (and they are often implemented using automatic variables on the stack of each thread). Take this simple program as an example: #include <stdio.h> #include <omp.h> int main (void) { int i = 10; #pragma omp parallel private(i) { … Read more