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### 34.1 Thread-specific Data

The GNU C Library implements functions to allow users to create and manage data specific to a thread. Such data may be destroyed at thread exit, if a destructor is provided. The following functions are defined:

`int pthread_key_create (pthread_key_t *`key`, void (*`destructor`)(void*))`
  Create a thread-specific data key for the calling thread, referenced by key.

  Objects declared with the C++11 `thread_local` keyword are destroyed before thread-specific data, so they should not be used in thread-specific data destructors or even as members of the thread-specific data, since the latter is passed as an argument to the destructor function.

`int pthread_key_delete (pthread_key_t` key`)`
  Destroy the thread-specific data key in the calling thread. The destructor for the thread-specific data is not called during destruction, nor is it called during thread exit.
`void *pthread_getspecific (pthread_key_t` key`)`
  Return the thread-specific data associated with key in the calling thread.
`int pthread_setspecific (pthread_key_t` key`, const void *`value`)`
  Associate the thread-specific value with key in the calling thread.