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 int buffer[BUFFER_SIZE]; /* the actual data */
15 int readpos, writepos; /* positions for reading and writing */
16 sem_t sem_read; /* number of elements available for reading */
17 sem_t sem_write; /* number of locations available for writing */
18 };
19
20 /* Initialize a buffer */
21
init(struct prodcons * b)22 void init(struct prodcons * b)
23 {
24 sem_init(&b->sem_write, 0, BUFFER_SIZE - 1);
25 sem_init(&b->sem_read, 0, 0);
26 b->readpos = 0;
27 b->writepos = 0;
28 }
29
30 /* Store an integer in the buffer */
31
put(struct prodcons * b,int data)32 void put(struct prodcons * b, int data)
33 {
34 /* Wait until buffer is not full */
35 sem_wait(&b->sem_write);
36 /* Write the data and advance write pointer */
37 b->buffer[b->writepos] = data;
38 b->writepos++;
39 if (b->writepos >= BUFFER_SIZE) b->writepos = 0;
40 /* Signal that the buffer contains one more element for reading */
41 sem_post(&b->sem_read);
42 }
43
44 /* Read and remove an integer from the buffer */
45
get(struct prodcons * b)46 int get(struct prodcons * b)
47 {
48 int data;
49 /* Wait until buffer is not empty */
50 sem_wait(&b->sem_read);
51 /* Read the data and advance read pointer */
52 data = b->buffer[b->readpos];
53 b->readpos++;
54 if (b->readpos >= BUFFER_SIZE) b->readpos = 0;
55 /* Signal that the buffer has now one more location for writing */
56 sem_post(&b->sem_write);
57 return data;
58 }
59
60 /* A test program: one thread inserts integers from 1 to 10000,
61 the other reads them and prints them. */
62
63 #define OVER (-1)
64
65 struct prodcons buffer;
66
producer(void * data)67 static void *producer(void * data)
68 {
69 int n;
70 for (n = 0; n < 10000; n++) {
71 printf("%d --->\n", n);
72 put(&buffer, n);
73 }
74 put(&buffer, OVER);
75 return NULL;
76 }
77
consumer(void * data)78 static void *consumer(void * data)
79 {
80 int d;
81 while (1) {
82 d = get(&buffer);
83 if (d == OVER) break;
84 printf("---> %d\n", d);
85 }
86 return NULL;
87 }
88
libc_ex5(void)89 int libc_ex5(void)
90 {
91 pthread_t th_a, th_b;
92 void * retval;
93
94 init(&buffer);
95 /* Create the threads */
96 pthread_create(&th_a, NULL, producer, 0);
97 pthread_create(&th_b, NULL, consumer, 0);
98 /* Wait until producer and consumer finish. */
99 pthread_join(th_a, &retval);
100 pthread_join(th_b, &retval);
101 return 0;
102 }
103 #include <finsh.h>
104 FINSH_FUNCTION_EXPORT(libc_ex5, example 5 for libc);
105
106