linuxthreads/Examples/ex5.c

   1 /* The classic producer-consumer example, implemented with semaphores.
   2    All integers between 0 and 9999 should be printed exactly twice,
   3    once to the right of the arrow and once to the left. */
   4
   5 #include <stdio.h>
   6 #include "pthread.h"
   7 #include "semaphore.h"
   8
   9 #define BUFFER_SIZE 16
  10
  11 /* Circular buffer of integers. */
  12
  13 struct prodcons
  14 {
  15   int buffer[BUFFER_SIZE];      /* the actual data */
  16   int readpos, writepos;        /* positions for reading and writing */
  17   sem_t sem_read;               /* number of elements available for reading */
  18   sem_t sem_write;              /* number of locations available for writing */
  19 };
  20
  21 /* Initialize a buffer */
  22
  23 static void
  24 init (struct prodcons *b)
  25 {
  26   sem_init (&b->sem_write, 0, BUFFER_SIZE - 1);
  27   sem_init (&b->sem_read, 0, 0);
  28   b->readpos = 0;
  29   b->writepos = 0;
  30 }
  31
  32 /* Store an integer in the buffer */
  33
  34 static void
  35 put (struct prodcons *b, int data)
  36 {
  37   /* Wait until buffer is not full */
  38   sem_wait (&b->sem_write);
  39   /* Write the data and advance write pointer */
  40   b->buffer[b->writepos] = data;
  41   b->writepos++;
  42   if (b->writepos >= BUFFER_SIZE)
  43     b->writepos = 0;
  44   /* Signal that the buffer contains one more element for reading */
  45   sem_post (&b->sem_read);
  46 }
  47
  48 /* Read and remove an integer from the buffer */
  49
  50 static int
  51 get (struct prodcons *b)
  52 {
  53   int data;
  54   /* Wait until buffer is not empty */
  55   sem_wait (&b->sem_read);
  56   /* Read the data and advance read pointer */
  57   data = b->buffer[b->readpos];
  58   b->readpos++;
  59   if (b->readpos >= BUFFER_SIZE)
  60     b->readpos = 0;
  61   /* Signal that the buffer has now one more location for writing */
  62   sem_post (&b->sem_write);
  63   return data;
  64 }
  65
  66 /* A test program: one thread inserts integers from 1 to 10000,
  67    the other reads them and prints them. */
  68
  69 #define OVER (-1)
  70
  71 struct prodcons buffer;
  72
  73 static void *
  74 producer (void *data)
  75 {
  76   int n;
  77   for (n = 0; n < 10000; n++)
  78     {
  79       printf ("%d --->\n", n);
  80       put (&buffer, n);
  81     }
  82   put (&buffer, OVER);
  83   return NULL;
  84 }
  85
  86 static void *
  87 consumer (void *data)
  88 {
  89   int d;
  90   while (1)
  91     {
  92       d = get (&buffer);
  93       if (d == OVER)
  94         break;
  95       printf ("---> %d\n", d);
  96     }
  97   return NULL;
  98 }
  99
 100 int
 101 main (void)
 102 {
 103   pthread_t th_a, th_b;
 104   void *retval;
 105
 106   init (&buffer);
 107   /* Create the threads */
 108   pthread_create (&th_a, NULL, producer, 0);
 109   pthread_create (&th_b, NULL, consumer, 0);
 110   /* Wait until producer and consumer finish. */
 111   pthread_join (th_a, &retval);
 112   pthread_join (th_b, &retval);
 113   return 0;
 114 }