81 lines
2.8 KiB
C
81 lines
2.8 KiB
C
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// odd/even thread coordination on incrementing an global
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// variable. This version involves busy waiting on the odd/even
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// condition by checking odd/even first, then locking, then
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// re-checking.
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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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// 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; ){ // no increment here
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if(count % 2 == 0){
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pthread_mutex_lock(&count_mutex);
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if(count % 2 == 0){ // check for evenness
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printf("%d iter %d: count %d, IS EVEN, proceeding\n", tid, i, count);
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update(&count); // now have lock and condition is correct can safely increment
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i++;
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}
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else{
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VPRINTF("%d iter %d: count %d, LOCKED NOT EVEN\n", tid, i, count);
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}
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pthread_mutex_unlock(&count_mutex); // release lock allowing others to look/change count
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}
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else{
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VPRINTF("%d iter %d: count %d, NOT LOCKED NOT EVEN\n", tid, i, count);
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}
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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; ){ // no increment here
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if(count % 2 == 1){
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pthread_mutex_lock(&count_mutex);
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if(count % 2 == 1){ // check for evenness
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printf("%d iter %d: count %d, IS ODD, proceeding\n", tid, i, count);
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update(&count); // now have lock and condition is correct can safely increment
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i++;
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}
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else{
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VPRINTF("%d iter %d: count %d, LOCKED NOT ODD\n", tid, i, count);
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}
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pthread_mutex_unlock(&count_mutex); // release lock allowing others to look/change count
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}
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else{
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VPRINTF("%d iter %d: count %d, NOT LOCKED NOT ODD\n", tid, i, count);
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}
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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
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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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exit(0);
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}
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