Programming with POSIX® Threads

27 printf ("thread \"%s\" exiting...\n", private->string);

28 free (value);

29 status = pthread_mutex_lock (&identity_key_mutex);

30 if (status != 0)

31  err_abort (status, "Lock key mutex");

32 identity_key_counter--;

33 if (identity_key_counter <= 0) {

34  status = pthread_key_delete (identity_key);

35  if (status != 0)

36  err_abort (status, "Delete key");

37  printf ("key deleted...\n");

38 }

39 status = pthread_mutex_unlock (&identity_key_mutex);

40 if (status != 0)

41  err_abort (status, "Unlock key mutex");

42 }

43

44 /*

45 * Helper routine to allocate a new value for thread-specific

46 * data key if the thread doesn't already have one.

47 */

48 void *identity_key_get (void)

49 {

50 void *value;

51 int status; 52

53 value = pthread_getspecific (identity_key);

54 if (value == NULL) {

55  value = malloc (sizeof (private_t));

56  if (value == NULL)

57  errno_abort ("Allocate key value");

58  status = pthread_setspecific (identity_key, (void*)value);

59  if (status != 0)

60  err_abort (status, "Set TSD");

61 }

62 return value;

63 }

64

65 /*

66 * Thread start routine to use thread-specific data.

67 */

68 void *thread_routine (void *arg)

69 {

70 private_t *value; 71

72 value = (private_t*)identity_key_get ();

73 value->thread_id = pthread_self ();

74 value->string = (char*)arg;

75 printf ("thread \"%s\" starting...\n", value->string);

76 sleep (2);

77 return NULL;

78 }

79

80 void main (int argc, char *argv[])

81 {

82 pthread_t thread_l, thread_2;

83 private_t *value;

84 int status;

85

86 /*

87 * Create the TSD key, and set the reference counter to

88 * the number of threads that will use it (two thread_routine

89 * threads plus main). This must be done before creating

90 * the threads! Otherwise, if one thread runs the key's

91 * destructor before any other thread uses the key, it will

92 * be deleted.

93 *

94 * Note that there's rarely any good reason to delete a

95 * thread-specific data key.

96 */

97 status = pthread_key_create (

98  &identity_key, identity_key_destructor);

99 if (status != 0)

100  err_abort (status, "Create key");

101 identity_key_counter = 3;

102 value = (private_t*)identity_key_get ();

103 value->thread_id = pthread_self ();

104 value->string = "Main thread";

105 status = pthread_create (&thread_1, NULL,

106 thread_routine, "Thread 1");

107 if (status != 0)

108  err_abort (status, "Create thread 1");

109 status = pthread_create (&thread_2, NULL,

110  thread_routine, "Thread 2");

111 if (status != 0)

112  err_abort (status, "Create thread 2");

113 pthread_exit (NULL);

114 }

5.5 Realtime scheduling