Unix IPC之Posix信号量实现生产者消费者

采用多生产者，多消费者模型。

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/**  * 生产者  */ P(nempty); P(mutex); // 写入一个空闲位置 V(mutex); V(nstored);   /**  * 消费者  */ P(nstored); P(mutex): // 清空一个非空闲位置 V(mutex); V(nempty);

全局性说明：

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#include    "unpipc.h"   #define NBUFF        10 #define MAXNTHREADS 100   int     nitems, nproducers, nconsumers;     /* read-only */   struct      /* data shared by producers and consumers */ {     int   buff[NBUFF];     int   nput;           /* item number: 0, 1, 2, ... */     int   nputval;        /* value to store in buff[] */     int   nget;           /* item number: 0, 1, 2, ... */     int   ngetval;        /* value fetched from buff[] */     sem_t mutex, nempty, nstored;     /* semaphores, not pointers */ } shared;   void    *produce(void *); void    *consume(void *); /* end globals */

主函数：

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/* include main */ int main(int argc, char **argv) {     int     i, prodcount[MAXNTHREADS], conscount[MAXNTHREADS];     pthread_t   tid_produce[MAXNTHREADS], tid_consume[MAXNTHREADS];        if (argc != 4)         err_quit("usage: prodcons4 <#items> <#producers> <#consumers>");     nitems = atoi(argv[1]);     nproducers = min(atoi(argv[2]), MAXNTHREADS);     nconsumers = min(atoi(argv[3]), MAXNTHREADS);       /* 4initialize three semaphores */     Sem_init(&shared.mutex, 0, 1);     Sem_init(&shared.nempty, 0, NBUFF);     Sem_init(&shared.nstored, 0, 0);       /* 4create all producers and all consumers */     Set_concurrency(nproducers + nconsumers);     for (i = 0; i < nproducers; i++)     {         prodcount[i] = 0;         Pthread_create(&tid_produce[i], NULL, produce, &prodcount[i]);     }     for (i = 0; i < nconsumers; i++)     {         conscount[i] = 0;         Pthread_create(&tid_consume[i], NULL, consume, &conscount[i]);     }       /* 4wait for all producers and all consumers */     for (i = 0; i < nproducers; i++)     {         Pthread_join(tid_produce[i], NULL);         printf("producer count[%d] = %d\n", i, prodcount[i]);     }     for (i = 0; i < nconsumers; i++)     {         Pthread_join(tid_consume[i], NULL);         printf("consumer count[%d] = %d\n", i, conscount[i]);     }       Sem_destroy(&shared.mutex);     Sem_destroy(&shared.nempty);     Sem_destroy(&shared.nstored);     exit(0); } /* end main */

生产者线程：

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/* include produce */ void * produce(void *arg) {     for ( ; ; )     {         Sem_wait(&shared.nempty);   /* wait for at least 1 empty slot */         Sem_wait(&shared.mutex);           if (shared.nput >= nitems)         {             Sem_post(&shared.nstored);  /* let consumers terminate */             Sem_post(&shared.nempty);             Sem_post(&shared.mutex);             return(NULL);           /* all done */         }           shared.buff[shared.nput % NBUFF] = shared.nputval;         shared.nput++;         shared.nputval++;           Sem_post(&shared.mutex);         Sem_post(&shared.nstored);  /* 1 more stored item */         *((int *) arg) += 1;     } } /* end produce */

消费者线程：

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/* include consume */ void * consume(void *arg) {     int     i;       for ( ; ; )     {         Sem_wait(&shared.nstored);  /* wait for at least 1 stored item */         Sem_wait(&shared.mutex);           if (shared.nget >= nitems)         {             Sem_post(&shared.nstored);             Sem_post(&shared.mutex);             return(NULL);           /* all done */         }           i = shared.nget % NBUFF;         if (shared.buff[i] != shared.ngetval)             printf("error: buff[%d] = %d\n", i, shared.buff[i]);         shared.nget++;         shared.ngetval++;           Sem_post(&shared.mutex);         Sem_post(&shared.nempty);   /* 1 more empty slot */         *((int *) arg) += 1;     } } /* end consume */

 

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