Terminating a thread

A thread can terminate itself by using the thr_exit(S) function

   void thr_exit(
   	void *status
   );

status

is the address returned to another thread that has called thr_join(S).

• Recovery of stack allocated by the Threads Library (see above).

  ---

  NOTE: The stack for a non-detached thread will not be recovered until after another thread calls thr_join to obtain the status for the thread, which is stored on the stack. Likewise, an explicitly-allocated stack should not be recovered until after another thread calls thr_join.

  ---

• Invocation of the ``destructor'' function for each ``key value'' that the thread has used (see ``Thread-specific data'').

The Threads Library arranges for a simple return from the start_routine to be equivalent to a call to thr_exit(S) (except for the initial thread, see ``Termination of the process'').

The thr_exit(S) function allows one thread to return a value called status to another; however, this mechanism is more general than the exit status returned by a child process to its parent. The argument to exit(S) is limited to a small range of integers. The status returned by thr_exit(S) is a general pointer that can be used (with type casts) to direct the receiver to objects of greater complexity such as structures, arrays, and linked lists. Of course, both the terminating and receiving threads should be coded to employ the same convention.

Termination of the process

There are three ways to terminate a threads process.

• The termination of the last ``non-daemon thread'' of the process will terminate the process (with status used as exit(S) status to the parent process). The Threads Library categorizes a thread as either a ``daemon thread'' or a ``non-daemon thread''. In practice, daemon threads are used to provide services for other threads. Although they can terminate themselves or be terminated, there is no need to do so. By being distinguished as daemons, they will be implicitly terminated when there are no other threads (non-daemons) that might need their services.

  A thread is categorized as a daemon thread at the time of its creation by use of the THR_DAEMON flag to thr_create(S).

• There are some special semantics for the initial thread. If the initial thread executes a return statement or if it implicitly returns from main, the process will be terminated. However, a thr_exit(S) by the initial thread will terminate only the initial thread. The process continues to execute as long as there are other non-daemon threads.

• Finally, any thread can terminate the process by calling the exit(S) system call.