5.8. Built-in Module thread

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.

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.

• • Threads interact strangely with interrupts: the KeyboardInterrupt exception will be received by an arbitrary thread.

• • Calling sys.exit(status) or executing raise SystemExit, status is almost equivalent to calling thread.exit_prog(status), except that the former ways of exiting the entire program do honor finally clauses in the current thread (but not in other threads).

• • Not all built-in functions that may block waiting for I/O allow other threads to run, although the most popular ones (sleep, read, select) work as expected.