Creating and Destroying Thread-Specific Storage

The tss_create() function creates a new thread-specific data key. The key space is opaque and global to all threads in the process. Each thread has its own value-space which can be manipulated with the tss_get() and tss_set() functions. A given key persists until tss_delete() is called.

When a key is created, the value NULL is associated with all current threads. When a thread is created, the value NULL is assigned as the value for the entire key-space.

A key may optionally be created with a destructor function dtor. The function dtor will run when the thread exits (see thrd_exit(3C)) if the value for the key is not NULL. The key space's destructors may be run in any order. When the destructor is run due to a thread exiting, all signals will be blocked.

The tss_delete() function deletes the key identified by key from the global name-space. When a key is deleted, no registered destructor is called, it is up to the calling program to free any storage that was associated with key across all threads. Because of this property, it is legal to call tss_delete() from inside a destructor. Any destructors that had been associated with key will no longer be called when a thread terminates.

Obtaining Values

The tss_get() function may be used to obtain the value associated with key for the calling thread. Note that if the calling thread has never set a value, then it will receive the default value, NULL. tss_get() may be called from a tss destructor.

Setting Values

The tss_set() function sets the value of the key key for the calling thread to value, which may be obtained by subsequent calls to tss_get. To remove a value for a specific thread, one may pass NULL in as value. Changing the value of a key with tss_set() does not cause any destructors to be invoked. This means that tss_set() may be used in the context of a destructor, but special care must be taken to avoid leaking storage or causing an infinite loop.