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pthread_mutex.c
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pthread_mutex.c
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/*
Expected outcome:
- works with mutex
- fails without
# PTHREAD_MUTEX_INITIALIZER
New pthread_mutex_t should be initialized to it.
# pthread_mutex_lock
Acquire mutex: from now one no one else can enter.
The mutex is required because:
global++
is not atomic.
There are no non-locking atomic types in POSIX:
http://stackoverflow.com/questions/1130018/unix-portable-atomic-operations
# pthread_mutex_unlock
Release mutex: from now one others can enter.
# volatile
We don't need:
volatile global
because `pthread_mutex_lock` and many other pthread functions
already enforce cross thread memory synchronization:
http://stackoverflow.com/questions/3208060/does-guarding-a-variable-with-a-pthread-mutex-guarantee-its-also-not-cached
*/
#include "common.h"
enum CONSTANTS {
NUM_THREADS = 1000,
NUM_ITERS = 1000
};
int global = 0;
pthread_mutex_t main_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
void* main_thread(void *arg) {
int i;
for (i = 0; i < NUM_ITERS; ++i) {
#ifndef FAIL
pthread_mutex_lock(&main_thread_mutex);
#endif
global++;
#ifndef FAIL
pthread_mutex_unlock(&main_thread_mutex);
#endif
}
return NULL;
}
int main(void) {
pthread_t threads[NUM_THREADS];
int i;
for (i = 0; i < NUM_THREADS; ++i)
pthread_create(&threads[i], NULL, main_thread, NULL);
for (i = 0; i < NUM_THREADS; ++i)
pthread_join(threads[i], NULL);
assert(global == NUM_THREADS * NUM_ITERS);
return EXIT_SUCCESS;
}