How to use lock in OpenMP?

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You want the OMP_SET_LOCK/OMP_UNSET_LOCK functions:
https://hpc.llnl.gov/tuts/openMP/#OMP_SET_LOCK

Basically:

omp_lock_t writelock;

omp_init_lock(&writelock);

#pragma omp parallel for
for ( i = 0; i < x; i++ )
{
    // some stuff
   omp_set_lock(&writelock);
    // one thread at a time stuff
    omp_unset_lock(&writelock);
    // some stuff
}

omp_destroy_lock(&writelock);

Most locking routines such as pthreads semaphores and sysv semaphores work on that sort of logic, although the specific API calls are different.

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