5-Pthreads.pdf

Pthreads High Performance Computing Master in Applied Artificial Intelligence Nuno Lopes Motivation u Library for developing parallel applications using shared memory. u Assumes a POSIX-compliant operating system as its base. u Library ca...

Pthreads High Performance Computing Master in Applied Artificial Intelligence Nuno Lopes Motivation u Library for developing parallel applications using shared memory. u Assumes a POSIX-compliant operating system as its base. u Library can be embedded in any programming language, usually C. u The use of threads is achieved by invoking functions from the library. Compilation and Execution of Pthreads Programs u Include library headers: u #include u Linker option: u -lpthread u gcc - lpthread hello.c -o hello Pthread API to create and join threads pthread_create( pthread_t* thread_p const pthread_attr_t* attr_p void* (*start_routine)(void*) void* arg_p ); u thread_p: thread object reference, u attr_p: creation attributes, NULL u start_routine: function to execute u arg_p: function argument u Generic function header: void* start_routine(void* args_p); Pthread API to create and join threads pthread_join( pthread_t thread , void** ret_val_p ); Example Incremental Application // global vars long long n; // set to number of iterations long long thread_count; // set to number threads long long sum;// global sum value // thread operation void* Increment(void* rank) { long my_rank = (long) rank; long long my_n = n/thread count; // even division long long my_first_i = my_n * my_rank; long long my_last_i = my_first_i + my_n; printf(“Thread %ld range: %ld to %ld\n”, rank, my_first_i, my_last_i); for( i=my_first_i; i