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5.8. Built-in Module thread

This module provides low-level primitives for working with multiple threads (a.k.a. light-weight processes or tasks) --- multiple threads of control sharing their global data space. For synchronization, simple locks (a.k.a. mutexes or binary semaphores) are provided.

The module is optional and supported on SGI and Sun Sparc systems only.

It defines the following constant and functions:

error -- exception of module thread
Raised on thread-specific errors.
start_new_thread (func, arg) -- function of module thread
Start a new thread. The thread executes the function func with the argument list arg (which must be a tuple). When the function returns, the thread silently exits. When the function raises terminates with an unhandled exception, a stack trace is printed and then the thread exits (but other threads continue to run).
exit_thread () -- function of module thread
Exit the current thread silently. Other threads continue to run. Caveat: code in pending finally clauses is not executed.
exit_prog (status) -- function of module thread
Exit all threads and report the value of the integer argument status as the exit status of the entire program. Caveat: code in pending finally clauses, in this thread or in other threads, is not executed.
allocate_lock () -- function of module thread
Return a new lock object. Methods of locks are described below. The lock is initially unlocked.
Lock objects have the following methods:

acquire (waitflag) -- Method on lock
Without the optional argument, this method acquires the lock unconditionally, if necessary waiting until it is released by another thread (only one thread at a time can acquire a lock --- that's their reason for existence), and returns None. If the integer waitflag argument is present, the action depends on its value: if it is zero, the lock is only acquired if it can be acquired immediately without waiting, while if it is nonzero, the lock is acquired unconditionally as before. If an argument is present, the return value is 1 if the lock is acquired successfully, 0 if not.
release () -- Method on lock
Releases the lock. The lock must have been acquired earlier, but not necessarily by the same thread.
locked () -- Method on lock
Return the status of the lock: 1 if it has been acquired by some thread, 0 if not.
Caveats: