/* The classic producer-consumer example. Illustrates mutexes and conditions. All integers between 0 and 9999 should be printed exactly twice, once to the right of the arrow and once to the left. */ #include <stdio.h> #include "pthread.h" #define BUFFER_SIZE 16 /* Circular buffer of integers. */ struct prodcons { int buffer[BUFFER_SIZE]; /* the actual data */ pthread_mutex_t lock; /* mutex ensuring exclusive access to buffer */ int readpos, writepos; /* positions for reading and writing */ pthread_cond_t notempty; /* signaled when buffer is not empty */ pthread_cond_t notfull; /* signaled when buffer is not full */ }; /* Initialize a buffer */ void init(struct prodcons * b) { pthread_mutex_init(&b->lock, NULL); pthread_cond_init(&b->notempty, NULL); pthread_cond_init(&b->notfull, NULL); b->readpos = 0; b->writepos = 0; } /* Store an integer in the buffer */ void put(struct prodcons * b, int data) { pthread_mutex_lock(&b->lock); /* Wait until buffer is not full */ while ((b->writepos + 1) % BUFFER_SIZE == b->readpos) { pthread_cond_wait(&b->notfull, &b->lock); /* pthread_cond_wait reacquired b->lock before returning */ } /* Write the data and advance write pointer */ b->buffer[b->writepos] = data; b->writepos++; if (b->writepos >= BUFFER_SIZE) b->writepos = 0; /* Signal that the buffer is now not empty */ pthread_cond_signal(&b->notempty); pthread_mutex_unlock(&b->lock); } /* Read and remove an integer from the buffer */ int get(struct prodcons * b) { int data; pthread_mutex_lock(&b->lock); /* Wait until buffer is not empty */ while (b->writepos == b->readpos) { pthread_cond_wait(&b->notempty, &b->lock); } /* Read the data and advance read pointer */ data = b->buffer[b->readpos]; b->readpos++; if (b->readpos >= BUFFER_SIZE) b->readpos = 0; /* Signal that the buffer is now not full */ pthread_cond_signal(&b->notfull); pthread_mutex_unlock(&b->lock); return data; } /* A test program: one thread inserts integers from 1 to 10000, the other reads them and prints them. */ #define OVER (-1) struct prodcons buffer; void * producer(void * data) { int n; for (n = 0; n < 10000; n++) { printf("%d --->\n", n); put(&buffer, n); } put(&buffer, OVER); return NULL; } void * consumer(void * data) { int d; while (1) { d = get(&buffer); if (d == OVER) break; printf("---> %d\n", d); } return NULL; } int main(void) { pthread_t th_a, th_b; void * retval; init(&buffer); /* Create the threads */ pthread_create(&th_a, NULL, producer, 0); pthread_create(&th_b, NULL, consumer, 0); /* Wait until producer and consumer finish. */ pthread_join(th_a, &retval); pthread_join(th_b, &retval); return 0; }