1 /********************************************************
2 * An example source module to accompany...
3 *
4 * "Using POSIX Threads: Programming with Pthreads"
5 * by Brad nichols, Dick Buttlar, Jackie Farrell
6 * O'Reilly & Associates, Inc.
7 *
8 ********************************************************
9 * once_exam.c
10 *
11 * An example of using the pthreads_once() call to execute an
12 * initialization procedure.
13 *
14 * A program spawns multiple threads and each one tries to
15 * execute the routine welcome() using the once call. Only
16 * the first thread into the once routine will actually
17 * execute welcome().
18 *
19 * The program's main thread synchronizes its exit with the
20 * exit of the threads using the pthread_join() operation.
21 *
22 */
23
24 #include <stdlib.h>
25 #include <stdio.h>
26 #include <unistd.h>
27 #include <sys/types.h>
28
29 #include <pthread.h>
30
31 #define NUM_THREADS 10
32
33 static pthread_once_t welcome_once_block = PTHREAD_ONCE_INIT;
34
welcome(void)35 void welcome(void)
36 {
37 printf("welcome: Welcome\n");
38 }
39
identify_yourself(void * arg)40 void *identify_yourself(void *arg)
41 {
42 int rtn;
43
44 if ((rtn = pthread_once(&welcome_once_block,
45 welcome)) != 0) {
46 fprintf(stderr, "pthread_once failed with %d",rtn);
47 pthread_exit((void *)NULL);
48 }
49 printf("identify_yourself: Hi, I'm a thread\n");
50 return(NULL);
51 }
52
53 extern int
main(void)54 main(void)
55 {
56 int *id_arg, thread_num, rtn;
57 pthread_t threads[NUM_THREADS];
58
59 id_arg = (int *)malloc(NUM_THREADS*sizeof(int));
60
61 for (thread_num = 0; thread_num < NUM_THREADS; (thread_num)++) {
62
63 id_arg[thread_num] = thread_num;
64
65 if (( rtn = pthread_create(&threads[thread_num],
66 NULL,
67 identify_yourself,
68 (void *) &(id_arg[thread_num])))
69 != 0) {
70 fprintf(stderr, "pthread_create failed with %d",rtn);
71 exit(1);
72 }
73 }
74
75 for (thread_num = 0; thread_num < NUM_THREADS; thread_num++) {
76 pthread_join(threads[thread_num], NULL);
77 //printf("main: joined to thread %d\n", thread_num);
78 }
79 printf("main: Goodbye\n");
80 return 0;
81 }
82