Parallel OpenMP loop with break statement

Question

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 one element that satisfies a certain condition. However there is only one element that will satisfy the condition so once that is found we can break out of the loop, Thanks in advance

for(int i = 0; i <= 100000; ++i)   {     if(element[i] ...)      {           ....           break;       }    } 

Answer 1

See this snippet:

volatile bool flag=false;  #pragma omp parallel for shared(flag) for(int i=0; i<=100000; ++i) {         if(flag) continue;     if(element[i] ...)     {           ...           flag=true;     } } 

This situation is more suitable for pthread.

Answer 2

You could try to manually do what the openmp for loop does, using a while loop:

const int N = 100000; std::atomic<bool> go(true); uint give = 0;  #pragma omp parallel {     uint i, stop;      #pragma omp critical     {         i = give;         give += N/omp_get_num_threads();         stop = give;          if(omp_get_thread_num() == omp_get_num_threads()-1)             stop = N;     }        while(i < stop && go)     {         ...         if(element[i]...)         {             go = false;         }         i++;     } } 

This way you have to test "go" each cycle, but that should not matter that much. More important is that this would correspond to a "static" omp for loop, which is only useful if you can expect all iterations to take a similar amount of time. Otherwise, 3 threads may be already finished while one still has halfway to got...