- In addition to compiler directives (pragmas),
there are a number of support functions in OpenMP:
Function Name Effect omp_set_num_threads(int nthread) Set size of thread team int omp_get_num_threads( ) return size of thread team int omp_get_max_threads() return max size of thread team (typically equal to the number of processors int omp_get_thread_num( ) return thread ID of the thread that calls this function int omp_get_num_procs() return number of processors boolean omp_in_parallel() return TRUE if currently in a PARALLEL segment omp_init_lock(omp_lock_t *lock) Initialize the mutex lock "lock" omp_set_lock(omp_lock_t *lock) Lock the mutex lock "lock" omp_unset_lock(omp_lock_t *lock) Unlock the mutex lock "lock" omp_test_lock(omp_lock_t *lock) Return true if the mutex lock "lock" is locked, returns false otherwise - Here is a simple OMP program in C++:
#include <iostream.h> #include <omp.h> // Read in OpenMP function prototypes int main(int argc, char *argv[]) { int nthreads, myid; #pragma omp parallel private (nthreads, myid) { /* Every thread does this */ myid = omp_get_thread_num(); cout << "Hello I am thread " << myid << endl; /* Only thread 0 does this */ if (myid == 0) { nthreads = omp_get_num_threads(); cout << "Number of threads = " << nthreads << endl; } } return 0; } -
Example Program:
(OpenMP C++ program) ---
click here
- Compile using the following command:
- g++ -fopenmp hello.C
- Compile using the following command: