pth_once.c revision e739ac0589b4fb43561f801c4faba8c1b89f8680 
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
33static pthread_once_t welcome_once_block = PTHREAD_ONCE_INIT;
34
35void welcome(void)
36{
37	printf("welcome: Welcome\n");
38}
39
40void *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
53extern int
54main(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