pthread_key_setspecific和pthread_key_getspecific 用法

 #include <pthread.h>

void *pthread_getspecific(pthread_key_t key);

int pthread_setspecific(pthread_key_t key,
const void *value);

设置线程共享数据的函数。

在线程中调用

英文说明如下：pthread_setspecific 将数据绑定到pthread_key_t 类型的key上面(key作为一个全局变量)。

可以不同的线程都绑定到key上面，但是各自线程在调用pthread_getspecific函数时，获取的是该线程绑定的数据。

其中key是通过下面的函数创建

通过该函数提供的功能，可以提供线程通用的函数，而各线程通过pthread_getspecific获取的就是其所需的数据。

即代码一致，获取的数据确实各自所需。

#include <pthread.h>

int pthread_key_create(pthread_key_t *key, void (*destructor)(void*));

DESCRIPTION

The pthread_getspecific() function shall return the value currently bound to the specified key on behalf of the calling thread.

The pthread_setspecific() function shall associate a thread-specific value with a key obtained via a previous call to pthread_key_create().
Different threads may bind different values to the same key. These values are typically pointers to blocks of dynamically allocated memory that have been reserved for use by the calling thread.

The effect of calling pthread_getspecific() or pthread_setspecific() with a key value not obtained from pthread_key_create() or
after key has been deleted with pthread_key_delete() is undefined.

Both pthread_getspecific() and pthread_setspecific() may be called from a thread-specific data destructor function. A call to pthread_getspecific() for the thread-specific data key being destroyed shall return the value NULL, unless
the value is changed (after the destructor starts) by a call to pthread_setspecific(). Calling pthread_setspecific() from a thread-specific data destructor routine may result either in lost storage (after at least PTHREAD_DESTRUCTOR_ITERATIONS
attempts at destruction) or in an infinite loop.

Both functions may be implemented as macros.

RETURN VALUE

The pthread_getspecific() function shall return the thread-specific data value associated with the given key. If no thread-specific data value is associated with key, then the value NULL shall be returned.

If successful, the pthread_setspecific() function shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

No errors are returned from pthread_getspecific().

The pthread_setspecific() function shall fail if:

[ENOMEM]Insufficient memory exists to associate the non-NULL value with the key.The pthread_setspecific() function may fail if:

[EINVAL]The key value is invalid.These functions shall not return an error code of [EINTR].

refer : 

http://pubs.opengroup.org/onlinepubs/009696699/functions/pthread_key_create.html

http://pubs.opengroup.org/onlinepubs/009696699/functions/pthread_setspecific.html