7.4. Built-in Module thread

The module is optional and supported on SGI IRIX 4.x and 5.x and Sun Solaris 2.x systems, as well as on systems that have a PTHREAD implementation (e.g. KSR).

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 terminates with an unhandled exception, a stack trace is printed and then the thread exits (but other threads continue to run).

exit () -- function of module thread

This is a shorthand for thread.exit_thread().

exit_thread () -- function of module thread

Raise the SystemExit exception. When not caught, this will cause the thread to exit silently.

allocate_lock () -- function of module thread

Return a new lock object. Methods of locks are described below. The lock is initially unlocked.

get_ident () -- function of module thread

Return the `thread identifier' of the current thread. This is a nonzero integer. Its value has no direct meaning; it is intended as a magic cookie to be used e.g. to index a dictionary of thread-specific data. Thread identifiers may be recycled when a thread exits and another thread is created.

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. (When the signal module is available, interrupts always go to the main thread.)

• Calling sys.exit() or raising the SystemExit is equivalent to calling thread.exit_thread().

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