Overhead of pthread mutexes?

Question

I\'m trying to make a C++ API (for Linux and Solaris) thread-safe, so that its functions can be called from different threads without breaking internal data structures. In m

Answer 1

I was curious about the expense of using a pthred_mutex_lock/unlock. I had a scenario where I needed to either copy anywhere from 1500-65K bytes without using a mutex or to use a mutex and do a single write of a pointer to the data needed.

I wrote a short loop to test each

gettimeofday(&starttime, NULL)
COPY DATA
gettimeofday(&endtime, NULL)
timersub(&endtime, &starttime, &timediff)
print out timediff data

or

ettimeofday(&starttime, NULL)
pthread_mutex_lock(&mutex);
gettimeofday(&endtime, NULL)
pthread_mutex_unlock(&mutex);
timersub(&endtime, &starttime, &timediff)
print out timediff data

If I was copying less than 4000 or so bytes, then the straight copy operation took less time. If however I was copying more than 4000 bytes, then it was less costly to do the mutex lock/unlock.

The timing on the mutex lock/unlock ran between 3 and 5 usec long including the time for the gettimeofday for the currentTime which took about 2 usec