CODEWITHSUNDEEP
copenmpbenchmarkingintel
bad code
bad code

Reputation: 13

In openMP how do I ensure threads are synchronized before continuing?

I am using a #pragma omp barrier to ensure that all my parallel threads meet up at the same point before continuing (no fancy conditionally branching code, just straight loop), but I am surmising that the barrier pragma does not actually guarantee synchronicity, just completion as these are the results I am getting:

0: func() size: 64 Time: 0.000414 Start: 1522116688.801262 End: 1522116688.801676
1: func() size: 64 Time: 0.000828 Start: 1522116688.801263 End: 1522116688.802091

thread 0 is starting about a microsecond faster than thread 1, giving it the somewhat unrealistic completion time of 0.414 msec, incidentally in a single core/thread run the run time averages around 0.800 msec. (please forgive me if my units are off, it is late).

My Question is: Is there a way to ensure in openMP that threads are all started at the same time? Or would I have to bring in another library like pthread in order to have this functionality?

Upvotes: 1

Views: 1018

Answers (1)

user9478968
user9478968

Reputation:

The barrier statement in OpenMP, as in other languages, ensures no thread progresses until all threads reach the barrier.

It does not specify the order in which threads begin to execute again. As far as I know manually scheduling threads is not possible in OpenMP or Pthread libraries(see comment below).

Upvotes: 1

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