75 lines
3 KiB
C
75 lines
3 KiB
C
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// odd/even thread coordination on incrementing an global
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// variable. This version uses a condition variable to efficiently
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// notify threads of changes to the global variable.
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#include "odds_evens.h"
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int count = 0; // global variable all threads are modifiying
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pthread_mutex_t count_mutex; // mutex to check count
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pthread_cond_t count_condv; // condition variable to receive wake-ups
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// Run by even child threads, increment count when it is even
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void *even_work(void *t) {
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int tid = *( (int *) t);
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for(int i=0; i<THREAD_ITERS; i++){
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pthread_mutex_lock(&count_mutex);
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while(count % 2 != 0){ // wait until count is even
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VPRINTF("%d iter %d: count %d, NOT EVEN, sleeping\n",
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tid, i, count);
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pthread_cond_wait(&count_condv, &count_mutex); // await notification to check again, gets lock on wakeup
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}
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printf("%d iter %d: count %d, IS EVEN, proceeding\n",
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tid, i, count);
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update(&count); // now have lock and condition is correct can safely increment
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pthread_mutex_unlock(&count_mutex); // release lock
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pthread_cond_broadcast(&count_condv); // notify all others waiting
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}
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printf("%d FINISHED %d iterations\n", tid, THREAD_ITERS);
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return NULL;
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}
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// Run by odd child threads, increment count when it is odd
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void *odd_work(void *t) {
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int tid = *( (int *) t);
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for(int i=0; i<THREAD_ITERS; i++){
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pthread_mutex_lock(&count_mutex);
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while(count % 2 != 1){ // wait until count is odd
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VPRINTF("%d iter %d: count %d, NOT ODD, sleeping\n",
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tid, i, count);
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pthread_cond_wait(&count_condv, &count_mutex); // await notification to check again, gets lock on wakeup
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}
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printf("%d iter %d: count %d, IS ODD, proceeding\n",
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tid, i, count);
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update(&count); // now have lock can safely increment
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pthread_mutex_unlock(&count_mutex); // release lock
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pthread_cond_broadcast(&count_condv); // notify all others waiting, pthread_cond_signal() only notifies single thread
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}
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printf("%d FINISHED %d iterations\n", tid, THREAD_ITERS);
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return NULL;
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}
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int main(int argc, char *argv[]) {
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pthread_t threads[TOT_THREADS];
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int tids[TOT_THREADS];
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pthread_mutex_init(&count_mutex, NULL); // Initialize mutex and condition variable
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pthread_cond_init (&count_condv, NULL);
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for(int i=0; i<TOT_THREADS; i+=2){
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tids[i] = i;
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pthread_create(&threads[i], NULL, even_work, (void *) &(tids[i]));
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tids[i+1] = i+1;
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pthread_create(&threads[i+1], NULL, odd_work, (void *) &(tids[i+1]));
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}
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for(int i=0; i<TOT_THREADS; i++) { // Wait for all threads to complete
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pthread_join(threads[i], NULL);
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}
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printf("main: count is %d\n",count);
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pthread_mutex_destroy(&count_mutex); // Clean up and exit
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pthread_cond_destroy(&count_condv);
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exit(0);
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}
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