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This article mainly explains "how to carry out openmp multithread programming on the Linux system". The content of the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "how to carry out openmp multithreading programming on the Linux system".

OpenMP is a multiprocessor and multithreaded programming language, which can support multiple platforms, including Linux systems, so how to do openmp multithreading programming under Linux? Let's get to know it.

Key syntax:

The code is as follows:

# inlcude "omp.h"

# pragma omp parallel for

# pragma omp for reduction (+: variable)

# pragma omp critical// lock

{

}

# pragma omp parallel for private (XMague y) / / each thread copies the xQuery variable independently and does not interfere with each other. If it is not set, it is a shared variable by default

# pragma omp parallel for schedule (static/dynamic/guided, k) / / the total workload is divided into nmax k blocks, and then multi-thread scheduling

# pragma omp parallel sections

{

# pragma omp section// to ensure that there are no variable dependencies between functions under several section

.

# pragma omp section

.

}

# pragma omp parallel

{

. ()

# pragma omp master/single / / ensure that only the main thread / a thread can access the following function. The difference is that there is no barrier barrier for using master. If single is used, the thread that finishes first waits for the thread that has not finished.

{

}

.

} "/ p"p" # pragma omp barrier/nowait / / forcibly set a mountain barrier / do not need to wait, if the subsequent function does not depend on the previous multithreading, you can use nowait

# pragma omp parallel for firstprivate (variable) / lastprivate (variable) / / assign an initial value to each multithread / assign a value for the main thread to use when the multithread returns to the main thread

And then there is OpenMP's API:

The code is as follows:

Int omp_get_num_threads (); / / get the number of threads currently in use

Int omp_get_num_threads (2Accord 3 /. ) / / set the number of threads to be used

Nt omp_get_thread_num (void); / / returns the current thread number

Int omp_get_num_procs (void); / / returns the number of available processing cores

Under ubuntu, there is no need to add a "omp.h" header file, just add-fopenmp when compiling.

For example, the emacs operation command is as follows

The code is as follows:

Emacs omp.c "/ p"p" # include "stdio.h"

Int main ()

{

Int rank, size

# pragma omp parallel num_thread (3) private (rank) / / num_threads to control the number of threads

/ / or use omp_set_num_threads (3); "/ p"p" {

Rank = omp_get_thread_num ()

Size = omp_get_num_threads ()

Printf ("using% d of% d now.\ n", rank, size)

}

Return 0

} "/ p"p" ctrl+x s

Alt+x compile

Gcc-fopenmp-o omp omp.c

Alt+shift+1 . / omp

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