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. It is supported on Windows NT and '95, SGI
IRIX, Solaris 2.x, as well as on systems that have a POSIX thread
(a.k.a. ``pthread'') implementation.
Start a new thread and return its identifier. The thread executes the function
function with the argument list args (which must be a tuple). The
optional kwargs argument specifies a dictionary of keyword arguments.
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).
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.
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.
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 signalmodule is available, interrupts always go to the main thread.)
Calling sys.exit() or raising the SystemExit
exception is equivalent to calling exit().
Not all built-in functions that may block waiting for I/O allow other
threads to run. (The most popular ones (time.sleep(),
file.read(), select.select()) work as
It is not possible to interrupt the acquire() method on a lock
-- the KeyboardInterrupt exception will happen after the
lock has been acquired.
When the main thread exits, it is system defined whether the other
threads survive. On SGI IRIX using the native thread implementation,
they survive. On most other systems, they are killed without
executing try ... finally clauses or executing
When the main thread exits, it does not do any of its usual cleanup
(except that try ... finally clauses are honored),
and the standard I/O files are not flushed.