c_cpp/pthreadtest/05bounded.c

   1 /* bounded.c                                                              */
   2 /* Code for Producer/Consumer problem using mutex and condition variables */
   3 /* To compile me for Unix, type:  gcc -o filename filename.c -lpthread */
   4
   5 #include <pthread.h>
   6 #include <stdio.h>
   7
   8 #define BSIZE 4
   9 #define NUMITEMS 30
  10
  11 typedef struct {
  12   char buf[BSIZE];
  13   int occupied;
  14   int nextin, nextout;
  15   pthread_mutex_t mutex;
  16   pthread_cond_t more;
  17   pthread_cond_t less;
  18 } buffer_t;
  19
  20 buffer_t buffer;
  21
  22 void * producer(void *);
  23 void * consumer(void *);
  24
  25
  26 #define NUM_THREADS 2
  27 pthread_t tid[NUM_THREADS];      /* array of thread IDs */
  28
  29 main( int argc, char *argv[] )
  30 {
  31   int i;
  32
  33   pthread_cond_init(&(buffer.more), NULL);
  34   pthread_cond_init(&(buffer.less), NULL);
  35
  36   pthread_create(&tid[1], NULL, consumer, NULL);
  37   pthread_create(&tid[0], NULL, producer, NULL);
  38   for ( i = 0; i < NUM_THREADS; i++)
  39     pthread_join(tid[i], NULL);
  40
  41   printf("\nmain() reporting that all %d threads have terminated\n", i);
  42
  43 }  /* main */
  44
  45
  46
  47 void * producer(void * parm)
  48 {
  49   char item[NUMITEMS]="IT'S A SMALL WORLD, AFTER ALL.";
  50   int i;
  51
  52   printf("producer started.\n");
  53
  54   for(i=0;i<NUMITEMS;i++)
  55     { /* produce an item, one character from item[] */
  56
  57       if (item[i] == '\0') break;  /* Quit if at end of string. */
  58
  59       pthread_mutex_lock(&(buffer.mutex));
  60
  61       if (buffer.occupied >= BSIZE) printf("producer waiting.\n");
  62       while (buffer.occupied >= BSIZE)
  63         pthread_cond_wait(&(buffer.less), &(buffer.mutex) );
  64       printf("producer executing.\n");
  65
  66       buffer.buf[buffer.nextin++] = item[i];
  67       buffer.nextin %= BSIZE;
  68       buffer.occupied++;
  69
  70       /* now: either buffer.occupied < BSIZE and buffer.nextin is the index
  71          of the next empty slot in the buffer, or
  72          buffer.occupied == BSIZE and buffer.nextin is the index of the
  73          next (occupied) slot that will be emptied by a consumer
  74          (such as buffer.nextin == buffer.nextout) */
  75
  76       pthread_cond_signal(&(buffer.more));
  77       pthread_mutex_unlock(&(buffer.mutex));
  78     }
  79   printf("producer exiting.\n");
  80   pthread_exit(0);
  81 }
  82
  83 void * consumer(void * parm)
  84 {
  85   char item;
  86   int i;
  87
  88   printf("consumer started.\n");
  89
  90   for(i=0;i<NUMITEMS;i++){
  91
  92   pthread_mutex_lock(&(buffer.mutex) );
  93
  94   if (buffer.occupied <= 0) printf("consumer waiting.\n");
  95   while(buffer.occupied <= 0)
  96     pthread_cond_wait(&(buffer.more), &(buffer.mutex) );
  97   printf("consumer executing.\n");
  98
  99   item = buffer.buf[buffer.nextout++];
 100   printf("%c\n",item);
 101   buffer.nextout %= BSIZE;
 102   buffer.occupied--;
 103
 104   /* now: either buffer.occupied > 0 and buffer.nextout is the index
 105      of the next occupied slot in the buffer, or
 106      buffer.occupied == 0 and buffer.nextout is the index of the next
 107      (empty) slot that will be filled by a producer (such as
 108      buffer.nextout == buffer.nextin) */
 109
 110   pthread_cond_signal(&(buffer.less));
 111   pthread_mutex_unlock(&(buffer.mutex));
 112   }
 113   printf("consumer exiting.\n");
 114   pthread_exit(0);
 115 }
 116
 117