Practical example to barriers (pthread_barrier)
main.c
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#define THREAD_NUM 8
int dice_values[THREAD_NUM];
int status[THREAD_NUM] = { 0 };
pthread_barrier_t barrierRolledDice;
pthread_barrier_t barrierCalculated;
void* roll(void* args) {
int index = *(int*)args;
while (1) {
dice_values[index] = rand() % 32 + 1;
pthread_barrier_wait(&barrierRolledDice);
pthread_barrier_wait(&barrierCalculated);
if (status[index] == 1) {
printf("(%d rolled %d) I won\n", index, dice_values[index]);
} else {
printf("(%d rolled %d) I lost\n", index, dice_values[index]);
}
}
free(args);
}
int main(int argc, char *argv[]) {
srand(time(NULL));
pthread_t th[THREAD_NUM];
int i;
pthread_barrier_init(&barrierRolledDice, NULL, THREAD_NUM + 1);
pthread_barrier_init(&barrierCalculated, NULL, THREAD_NUM + 1);
for (i = 0; i < THREAD_NUM; i++) {
int* a = malloc(sizeof(int));
*a = i;
if (pthread_create(&th[i], NULL, &roll, (void*) a) != 0) {
perror("Failed to create thread");
}
}
while (1) {
pthread_barrier_wait(&barrierRolledDice);
// Calculate winner
int max = 0;
for (i = 0; i < THREAD_NUM; i++) {
if (dice_values[i] > max) {
max = dice_values[i];
}
}
for (i = 0; i < THREAD_NUM; i++) {
if (dice_values[i] == max) {
status[i] = 1;
} else {
status[i] = 0;
}
}
sleep(1);
printf("==== New round starting ====\n");
pthread_barrier_wait(&barrierCalculated);
}
for (i = 0; i < THREAD_NUM; i++) {
if (pthread_join(th[i], NULL) != 0) {
perror("Failed to join thread");
}
}
pthread_barrier_destroy(&barrierRolledDice);
pthread_barrier_destroy(&barrierCalculated);
return 0;
}
Unix Threads in C
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