/* The classic producer-consumer example, implemented with semaphores. 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" #include "semaphore.h" #define BUFFER_SIZE 16 /* Circular buffer of integers. */ struct prodcons { int buffer[BUFFER_SIZE]; /* the actual data */ int readpos, writepos; /* positions for reading and writing */ sem_t sem_read; /* number of elements available for reading */ sem_t sem_write; /* number of locations available for writing */ }; /* Initialize a buffer */ static void init(struct prodcons * b) { sem_init(&b->sem_write, 0, BUFFER_SIZE - 1); sem_init(&b->sem_read, 0, 0); b->readpos = 0; b->writepos = 0; } /* Store an integer in the buffer */ static void put(struct prodcons * b, int data) { /* Wait until buffer is not full */ sem_wait(&b->sem_write); /* 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 contains one more element for reading */ sem_post(&b->sem_read); } /* Read and remove an integer from the buffer */ static int get(struct prodcons * b) { int data; /* Wait until buffer is not empty */ sem_wait(&b->sem_read); /* 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 has now one more location for writing */ sem_post(&b->sem_write); 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; static void * producer(void * data) { int n; for (n = 0; n < 10000; n++) { printf("%d --->\n", n); put(&buffer, n); } put(&buffer, OVER); return NULL; } static 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; }