82 lines
2.1 KiB
C
82 lines
2.1 KiB
C
/*
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* tsd_once.c
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*
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* Demonstrate use of pthread_once to initialize something
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* exactly once within a multithreaded program.
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*
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* Note that it is often easier to use a statically initialized
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* mutex to accomplish the same result.
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*/
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#include <pthread.h>
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#include "errors.h"
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/*
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* Structure used as the value for thread-specific data key.
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*/
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typedef struct tsd_tag {
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pthread_t thread_id;
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char *string;
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} tsd_t;
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pthread_key_t tsd_key; /* Thread-specific data key */
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pthread_once_t key_once = PTHREAD_ONCE_INIT;
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/*
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* One-time initialization routine used with the pthread_once
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* control block.
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*/
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void once_routine (void)
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{
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int status;
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printf ("initializing key\n");
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status = pthread_key_create (&tsd_key, NULL);
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if (status != 0)
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err_abort (status, "Create key");
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}
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/*
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* Thread start routine that uses pthread_once to dynamically
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* create a thread-specific data key.
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*/
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void *thread_routine (void *arg)
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{
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tsd_t *value;
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int status;
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status = pthread_once (&key_once, once_routine);
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if (status != 0)
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err_abort (status, "Once init");
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value = (tsd_t*)malloc (sizeof (tsd_t));
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if (value == NULL)
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errno_abort ("Allocate key value");
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status = pthread_setspecific (tsd_key, value);
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if (status != 0)
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err_abort (status, "Set tsd");
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printf ("%s set tsd value %p\n", arg, value);
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value->thread_id = pthread_self ();
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value->string = (char*)arg;
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value = (tsd_t*)pthread_getspecific (tsd_key);
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printf ("%s starting...\n", value->string);
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sleep (2);
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value = (tsd_t*)pthread_getspecific (tsd_key);
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printf ("%s done...\n", value->string);
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return NULL;
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}
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void main (int argc, char *argv[])
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{
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pthread_t thread1, thread2;
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int status;
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status = pthread_create (
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&thread1, NULL, thread_routine, "thread 1");
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if (status != 0)
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err_abort (status, "Create thread 1");
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status = pthread_create (
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&thread2, NULL, thread_routine, "thread 2");
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if (status != 0)
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err_abort (status, "Create thread 2");
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pthread_exit (NULL);
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}
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