Multithreaded Programming Guide

pthread_key_create Syntax

int pthread_key_create(pthread_key_t *key,
    void (*destructor) (void *));
#include <pthread.h>

pthread_key_t key;
int ret;

/* key create without destructor */
ret = pthread_key_create(&key, NULL);

/* key create with destructor */
ret = pthread_key_create(&key, destructor); 

Use pthread_key_create(3C) to allocate a key that is used to identify thread-specific data in a process. The key is global to all threads in the process. When the thread-specific data is created, all threads initially have the value NULL associated with the key.

Call pthread_key_create() once for each key before using the key. No implicit synchronization exists for the keys shared by all threads in a process.

Once a key has been created, each thread can bind a value to the key. The values are specific to the threads and are maintained for each thread independently. The per-thread binding is deallocated when a thread terminates if the key was created with a destructor function.

When pthread_key_create() returns successfully, the allocated key is stored in the location pointed to by key. The caller must ensure that the storage and access to this key are properly synchronized.

An optional destructor function, destructor, can be used to free stale storage. If a key has a non-NULL destructor function and the thread has a non-NULL value associated with that key, the destructor function is called with the current associated value when the thread exits. The order in which the destructor functions are called is unspecified.