Questions tagged [openmp]

OpenMP is a cross-platform multi-threading API which allows fine-grained task parallelization and synchronization using special compiler directives.

OpenMP is a cross-platform multi-threading API which allows fine-grained task parallelization and synchronization using special compiler directives. OpenMP offers easy access to multi-threading without requiring knowledge of system-dependent details. At the same time, it is reasonably efficient compared to fine-tuned implementations with the bonus of being easiest to write multi-threads code. Forums and complete information on OpenMP is at https://openmp.org/.

OpenMP is based on multi-thread model, and offers Shared Memory parallelism and heterogeneous programming for coprocessors through compiler directives, library routines and environment variables. It is restricted to C/C++ and Fortran applications, however provides portability across different Shared Memory architectures.

It is through directives, added by the programmer to the code, that the compiler adds parallelism in the application. OpenMP can be used in single or multi-cores machines, in the first architecture the compiler directives are ignored, thus the application is executed in a sequential manner, promoting portability between the two architectures.

Latest version is 5.2 (November 2021): Official OpenMP specifications.

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C++11 Thread safety of Random number generators

In C++11 there are a bunch of new Random number generator engines and distribution functions. Are they thread safe? If you share a single random distribution and engine among multiple threads, is it safe and will you still receive random numbers?…
user1139069
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GCC does not honor 'pragma GCC diagnostic' to silence warnings

We recently enabled -Wall for a project. Its enabled when GCC is at 4.7 or above (or Clang) because we can use GCC diagnostic to manage the output from the elevated warnings. We want to manage them from the source code, and not via command line…
jww
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Ignore OpenMP on machine that does not have it

I have a C++ program using OpenMP, which will run on several machines that may have or not have OpenMP installed. How could I make my program know if a machine has no OpenMP and ignore those #include , OpenMP directives (like #pragma omp…
Tim
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Parallel for loop in openmp

I'm trying to parallelize a very simple for-loop, but this is my first attempt at using openMP in a long time. I'm getting baffled by the run times. Here is my code: #include #include using namespace std; int main () { …
dsign
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Measure execution time in C++ OpenMP code

I am running a .cpp code (i) in sequential style and (ii) using OpenMP statements. I am trying to see the time difference. For calculating time, I use this: #include ..... main() { clock_t start, finish; start = clock(); . . . …
Benny
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Installing OpenMP on Mac OS X 10.11

How can I get OpenMP to run on Mac OSX 10.11, so that I can execute scripts via terminal? I have installed OpenMP: brew install clang-omp. When I run, for example: gcc -fopenmp -o Parallel.b Parallel.c the following expression returns: fatal error:…
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How to include omp.h in OS X?

I'm new in C and have some problems compiling my code in OS X. I code Java a lot both in Eclipse and use terminal to compile my code. However now I'm learning openMP and have troubles with it. First I downloaded Xcode to write openMP code but it…
user3928256
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How to compile openmp using g++

I have a problem about the openmp compiling. Like the following code: #include #include #include #include #include using namespace std; sem_t empty,full; stack stk; void produce(int i) { …
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Can OpenMP be used for GPUs?

I've been searching the web but I'm still very confused about this topic. Can anyone explain this more clearly? I come from an Aerospace Engineering background (not from a Computer Science one), so when I read online about OpenMP/CUDA/etc. and…
André Almeida
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How to use lock in OpenMP?

I have two pieces of C++ code running on 2 different cores. Both of them write to the same file. How to use OpenMP and make sure there is no crash?
MainID
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Error enabling openmp - "ld: library not found for -lgomp" and Clang errors

I'm trying to get openmp to run in my program on Mavericks, however when I try to compile using the flag -fopenmp I get the following error: ld: library not found for -lgomp clang: error: linker command failed with exit code 1 (use -v to see…
Davy Li
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Specify OpenMP to GCC

For OpenMP, when my code is using the functions in its API (for example, omp_get_thread_num()) without using its directives (such as those #pragma omp ...), why directly specifying libgomp.a to gcc instead of using -fopenmp doesn't work, such as…
Tim
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Getting started with openMP. install on windows

I want to write parallel program in C++ using OpenMP, so I am getting started with OpenMP. On the other words I am a beginner and I need good OpenMP guide telling how to install it. Does someone know how to install OpenMP on Windows, then compile…
Nurlan
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Parallel OpenMP loop with break statement

I know that you cannot have a break statement for an OpenMP loop, but I was wondering if there is any workaround while still the benefiting from parallelism. Basically I have 'for' loop, that loops through the elements of a large vector looking for…
Jeanno
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Python and OpenMP C Extensions

I have a C extension in which I'd like to use OpenMP. When I import my module, though, I get an import error: ImportError: /home/.../_entropysplit.so: undefined symbol: GOMP_parallel_end I've compiled the module with -fopenmp and -lgomp. Is this…
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