使用 线程 和 pxsem 实现多个生产者和一个消费者
《Unix 进程间通信》中一个使用信号量实现多个生产者和一个消费者的例子，相比使用线程锁和条件更为简单，源码如下：
unpv22e\pxsem\prodcons3.c
1 #include <unistd.h> 2 #include <pthread.h> 3 #include <semaphore.h> // no name semaphore 4 #include <stdio.h> 5 #include <stdlib.h> 6 7 #define NBUFF 10 8 #define MAXNTHREADS 100 9 10 #define min(X,Y) ((X) < (Y) ? (X) : (Y)) 11 12 int nitems, nproducers; /* read-only by producer and consumer */ 13 14 struct { /* data shared by producers and consumer */ 15 int buff[NBUFF]; 16 int nput; 17 int nputval; 18 sem_t mutex, nempty, nstored; /* semaphores, not pointers */ 19 } shared; 20 21 void *produce(void *), *consume(void *); 22 void err_quit(char *ptr); 23 void err_sys(char *ptr); 24 25 int 26 main(int argc, char **argv) 27 { 28 int i, count[MAXNTHREADS]; // record how many resource were created by each producter 29 pthread_t tid_produce[MAXNTHREADS], tid_consume; 30 31 if (argc != 3) 32 err_quit("usage: prodcons3 <#items> <#producers>"); // items 指生产多少个产品，producers表示有几个生产者 33 nitems = atoi(argv[1]); // resource number 34 nproducers = min(atoi(argv[2]), MAXNTHREADS); 35 36 /* 4initialize three semaphores */ 37 sem_init(&shared.mutex, 0, 1); // just a lock 38 sem_init(&shared.nempty, 0, NBUFF); // record idle space 39 sem_init(&shared.nstored, 0, 0); // record already stored space 40 41 /* 4create all producers and one consumer */ 42 pthread_setconcurrency(nproducers + 1); 43 for (i = 0; i < nproducers; i++) { 44 count[i] = 0; 45 pthread_create(&tid_produce[i], NULL, produce, &count[i]); //&count[i]为整形数组成员地址，即int型指针 46 } 47 pthread_create(&tid_consume, NULL, consume, NULL); 48 49 /* 4wait for all producers and the consumer */ 50 for (i = 0; i < nproducers; i++) { 51 pthread_join(tid_produce[i], NULL); 52 printf("count[%d] = %d\n", i, count[i]); // 打印各个生产者生产的多少产品 53 } 54 pthread_join(tid_consume, NULL); 55 56 sem_destroy(&shared.mutex); 57 sem_destroy(&shared.nempty); 58 sem_destroy(&shared.nstored); 59 exit(0); 60 } 61 /* end main */ 62 63 /* include produce */ 64 void * 65 produce(void *arg) 66 { 67 for ( ; ; ) { 68 sem_wait(&shared.nempty); /* wait for at least 1 empty slot */ 69 sem_wait(&shared.mutex); 70 71 if (shared.nput >= nitems) { 72 sem_post(&shared.nempty); 73 sem_post(&shared.mutex); 74 return(NULL); /* all done */ 75 } 76 77 shared.buff[shared.nput % NBUFF] = shared.nputval; // 循环存放 78 printf("produce buff[%d] = %d\n", shared.nput % NBUFF, shared.buff[shared.nput % NBUFF]); 79 shared.nput++; 80 shared.nputval++; // 产品数值始终是累加的 81 82 sem_post(&shared.mutex); 83 sem_post(&shared.nstored); /* 1 more stored item */ 84 *((int *) arg) += 1; // 先转换为int型地址，之后解引用加一 85 } 86 } 87 /* end produce */ 88 89 /* include consume */ 90 void * 91 consume(void *arg) 92 { 93 int i; 94 95 for (i = 0; i < nitems; i++) { 96 sem_wait(&shared.nstored); /* wait for at least 1 stored item */ 97 sem_wait(&shared.mutex); 98 99 if (shared.buff[i % NBUFF] != i) 100 printf("error: buff[%d] = %d\n", i, shared.buff[i % NBUFF]); 101 printf("consume shared.buff[%d] = %d\n", i % NBUFF, shared.buff[i % NBUFF]); 102 103 sem_post(&shared.mutex); 104 sem_post(&shared.nempty); /* 1 more empty slot */ 105 } 106 return(NULL); 107 } 108 /* end consume */ 109 110 void 111 err_quit(char *ptr) 112 { 113 fprintf(stderr, "%s\n", ptr); 114 exit(1); 115 } 116 117 void 118 err_sys(char *ptr) 119 { 120 fprintf(stderr, "%s\n", ptr); 121 exit(1); 122 }
