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 … Read more
Just imagine, how the processor would execute a typical spin-wait loop: 1 Spin_Lock: 2 CMP lockvar, 0 ; Check if lock is free 3 JE Get_Lock 4 JMP Spin_Lock 5 Get_Lock: After a few iterations the branch predictor will predict that the conditional branch (3) will never be taken and the pipeline will fill with … Read more
The effect on g_qCount is the same, but what’s done is different. An OpenMP critical section is completely general – it can surround any arbitrary block of code. You pay for that generality, however, by incurring significant overhead every time a thread enters and exits the critical section (on top of the inherent cost of … Read more