PTHREAD_KEY_CREATE(3) BSD Library Functions Manual PTHREAD_KEY_CREATE(3)NAME
pthread_key_create -- thread-specific data key creation
SYNOPSIS
#include <pthread.h>
int
pthread_key_create(pthread_key_t *key, void (*destructor)(void *));
DESCRIPTION
The pthread_key_create() function creates a thread-specific data key visible to all threads in the process. Key values provided by
pthread_key_create() are opaque objects used to locate thread-specific data. Although the same key value may be used by different threads,
the values bound to the key by pthread_setspecific() are maintained on a per-thread basis and persist for the life of the calling thread.
Upon key creation, the value NULL is associated with the new key in all active threads. Upon thread creation, the value NULL is associated
with all defined keys in the new thread.
An optional destructor function may be associated with each key value. At thread exit, if a key value has a non-NULL destructor pointer, and
the thread has a non-NULL value associated with the key, the function pointed to is called with the current associated value as its sole
argument. The order of destructor calls is unspecified if more than one destructor exists for a thread when it exits.
If, after all the destructors have been called for all non-NULL values with associated destructors, there are still some non-NULL values with
associated destructors, then the process is repeated. If, after at least [PTHREAD_DESTRUCTOR_ITERATIONS] iterations of destructor calls for
outstanding non-NULL values, there are still some non-NULL values with associated destructors, the implementation stops calling destructors.
RETURN VALUES
If successful, the pthread_key_create() function will store the newly created key value at the location specified by key and returns zero.
Otherwise an error number will be returned to indicate the error.
ERRORS
The pthread_key_create() function will fail if:
[EAGAIN] The system lacked the necessary resources to create another thread-specific data key, or the system-imposed limit on the
total number of keys per process [PTHREAD_KEYS_MAX] would be exceeded.
[ENOMEM] Insufficient memory exists to create the key.
SEE ALSO pthread_getspecific(3), pthread_key_delete(3), pthread_setspecific(3)STANDARDS
The pthread_key_create() function conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').
BSD April 4, 1996 BSD
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pthread_key_create(3C) Standard C Library Functions pthread_key_create(3C)NAME
pthread_key_create, pthread_key_create_once_np - create thread-specific data key
SYNOPSIS
cc -mt [ flag... ] file... -lpthread [ library... ]
#include <pthread.h>
int pthread_key_create(pthread_key_t *key,
void (*destructor)(void*));
int pthread_key_create_once_np(pthread_key_t *key,
void (*destructor)(void*));
DESCRIPTION
The pthread_key_create() function creates a thread-specific data key visible to all threads in the process. Key values provided by
pthread_key_create() are opaque objects used to locate thread-specific data. Although the same key value may be used by different threads,
the values bound to the key by pthread_setspecific() are maintained on a per-thread basis and persist for the life of the calling thread.
Upon key creation, the value NULL is associated with the new key in all active threads. Upon thread creation, the value NULL is associ-
ated with all defined keys in the new thread.
An optional destructor function may be associated with each key value. At thread exit, if a key value has a non-NULL destructor pointer,
and the thread has a non-NULL value associated with that key, the function pointed to is called with the current associated value as its
sole argument. Destructors can be called in any order.
If, after all the destructors have been called for all keys with non-NULL values, there are still some keys with non-NULL values, the
process will be repeated. If, after at least PTHREAD_DESTRUCTOR_ITERATIONS iterations of destructor calls for outstanding non-NULL values,
there are still some keys with non-NULL values, the process is continued, even though this might result in an infinite loop.
An exiting thread runs with all signals blocked. All thread termination functions, including thread-specific data destructor functions, are
called with all signals blocked.
The pthread_key_create_once_np() function is identical to the pthread_key_create() function except that the key referred to by *key must be
statically initialized with the value PTHREAD_ONCE_KEY_NP before calling pthread_key_create_once_np(), and the key is created exactly once.
This function call is equivalent to using pthread_once(3C) to call a onetime initialization function that calls pthread_key_create() to
create the data key.
RETURN VALUES
If successful, the pthread_key_create() and pthread_key_create_once_np() functions store the newly created key value at *key and return 0.
Otherwise, an error number is returned to indicate the error.
ERRORS
The pthread_key_create() and pthread_key_create_once_np() functions will fail if:
EAGAIN The system lacked the necessary resources to create another thread-specific data key, or the system-imposed limit on the total
number of keys per process PTHREAD_KEYS_MAX has been exceeded.
ENOMEM Insufficient memory exists to create the key.
The pthread_key_create() and pthread_key_create_once_np() functions will not return an error value of EINTR.
EXAMPLES
Example 1 Call thread-specific data in the function from more than one thread without special initialization.
In the following example, the thread-specific data in the function can be called from more than one thread without special initialization.
For each argument passed to the executable, a thread is created and privately bound to the string-value of that argument.
/* cc -mt thisfile.c */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
static void *thread_function(void *);
static void show_tsd(void);
static void cleanup(void*);
#define MAX_THREADS 20
static pthread_key_t tsd_key = PTHREAD_ONCE_KEY_NP;
int
main(int argc, char *argv[])
{
pthread_t tid[MAX_THREADS];
int num_threads;
int i;
if ((num_threads = argc - 1) > MAX_THREADS)
num_threads = MAX_THREADS;
for (i = 0; i < num_threads; i++)
pthread_create(&tid[i], NULL, thread_function, argv[i+1]);
for (i = 0; i < num_threads; i++)
pthread_join(tid[i], NULL);
return(0);
}
static void *
thread_function(void *arg)
{
char *data;
pthread_key_create_once_np(&tsd_key, cleanup);
data = malloc(strlen(arg) + 1);
strcpy(data, arg);
pthread_setspecific(tsd_key, data);
show_tsd();
return (NULL);
}
static void
show_tsd()
{
void *tsd = pthread_getspecific(tsd_key);
printf("tsd for %d = %s
", pthread_self(), (char *)tsd);
}
/* application-specific clean-up function */
static void
cleanup(void *tsd)
{
printf("freeing tsd for %d = %s
", pthread_self(), (char *)tsd);
free(tsd);
}
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Committed. |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
|Standard |See below. |
+-----------------------------+-----------------------------+
For pthread_key_create(), see standards(5).
SEE ALSO pthread_once(3C), pthread_getspecific(3C), pthread_setspecific(3C), pthread_key_delete(3C), attributes(5), standards(5)SunOS 5.11 2 Nov 2007 pthread_key_create(3C)