信号量例子
#include <stdio.h>#include <stdlib.h>#include <semaphore.h>#include <errno.h>sem_t remain, apple, pear, mutex;static unsigned int vremain = 20, vapple = 0, vpear = 0;void *father(void *);void *mother(void *);void *son(void *);void *daughter(void *);void print_sem();int main(){ pthread_t fa, ma, so, da; sem_init(&remain, 0 , 20); sem_init(&apple, 0, 0); sem_init(&pear, 0, 0); sem_init(&mutex, 0, 1); pthread_create(&fa, NULL, &father, NULL); pthread_create(&ma, NULL, &mother, NULL); pthread_create(&so, NULL, &son, NULL); pthread_create(&da, NULL, &daughter, NULL); while(1) { sem_wait(&mutex); printf("apple: %u, pear: %u, left: %u\n", vapple, vpear, vremain); sem_post(&mutex); sleep(1); }}void *father(void *arg){ while(1) { sem_wait(&remain); sem_wait(&mutex); printf("father: put before, left = %u, apple = %u\n", vremain, vapple); vremain --; vapple ++; printf("father: put after, left = %u, apple = %u\n\n", vremain, vapple); sem_post(&mutex); sem_post(&apple); sleep(1); }}void *son(void *arg){ while(1) { sem_wait(&apple); sem_wait(&mutex); printf("son: take before, left = %u, apple = %u\n", vremain, vapple); vremain ++; vapple --; printf("son: put after, left = %u, apple = %u\n\n", vremain, vapple); sem_post(&mutex); sem_post(&remain); sleep(3); }}void *mother(void *arg){ while(1) { sem_wait(&remain); sem_wait(&mutex); printf("mother: put before, left = %u, pear = %u\n", vremain, vpear); vremain --; vpear ++; printf("mother: put after, left = %u, pear = %u\n\n", vremain, vpear); sem_post(&mutex); sem_post(&pear); sleep(3); }}void *daughter(void *arg){ while(1) { sem_wait(&pear); sem_wait(&mutex); printf("dau: take before, left = %u, pear = %u\n", vremain, vpear); vremain ++; vpear --; printf("dau: take after, left = %u, pear = %u\n\n", vremain, vpear); sem_post(&mutex); sem_post(&remain); sleep(1); }}