_thread— Low-level threading API
This module provides low-level primitives for working with multiple threads
(also called light-weight processes or tasks) — multiple threads of
control sharing their global data space. For synchronization, simple locks
(also called mutexes or binary semaphores) are provided.
threading module provides an easier to use and higher-level
threading API built on top of this module.
Changed in version 3.7: This module used to be optional, it is now always available.
This module defines the following constants and functions:
Raised on thread-specific errors.
Changed in version 3.3: This is now a synonym of the built-in
start_new_thread(function, args[, kwargs])
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,
sys.unraisablehook() is called to handle the exception. The object
attribute of the hook argument is function. By default, a stack trace is
printed and then the thread exits (but other threads continue to run).
When the function raises a
SystemExit exception, it is silently
Changed in version 3.8:
sys.unraisablehook() is now used to handle unhandled exceptions.
Simulate the effect of a
signal.SIGINT signal arriving in the main
thread. A thread can use this function to interrupt the main thread.
SystemExitexception. When not caught, this will cause the thread to exit silently.
Return the native integral Thread ID of the current thread assigned by the kernel. This is a non-negative integer. Its value may be used to uniquely identify this particular thread system-wide (until the thread terminates, after which the value may be recycled by the OS).
Availability: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD, AIX.
New in version 3.8.
Return the thread stack size used when creating new threads. The optional
size argument specifies the stack size to be used for subsequently created
threads, and must be 0 (use platform or configured default) or a positive
integer value of at least 32,768 (32 KiB). If size is not specified,
0 is used. If changing the thread stack size is
RuntimeError is raised. If the specified stack size is
ValueError is raised and the stack size is unmodified. 32 KiB
is currently the minimum supported stack size value to guarantee sufficient
stack space for the interpreter itself. Note that some platforms may have
particular restrictions on values for the stack size, such as requiring a
minimum stack size > 32 KiB or requiring allocation in multiples of the system
memory page size - platform documentation should be referred to for more
information (4 KiB pages are common; using multiples of 4096 for the stack size is
the suggested approach in the absence of more specific information).
Availability: Windows, systems with POSIX threads.
The maximum value allowed for the timeout parameter of
Lock.acquire(). Specifying a timeout greater than this value will
New in version 3.2.
Lock objects have the following methods:
Without any 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).
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 above.
If the floating-point timeout argument is present and positive, it specifies the maximum wait time in seconds before returning. A negative timeout argument specifies an unbounded wait. You cannot specify a timeout if waitflag is zero.
The return value is
True if the lock is acquired successfully,
False if not.
Changed in version 3.2: The timeout parameter is new.
Changed in version 3.2: Lock acquires can now be interrupted by signals on POSIX.
Trueif it has been acquired by some thread,
In addition to these methods, lock objects can also be used via the
with statement, e.g.:
import _thread a_lock = _thread.allocate_lock() with a_lock: print("a_lock is locked while this executes")
KeyboardInterruptexception will be received by an arbitrary thread. (When the
signalmodule is available, interrupts always go to the main thread.)
sys.exit()or raising the
SystemExitexception is equivalent to calling
acquire()method on a lock — the
KeyboardInterruptexception will happen after the lock has been acquired.
finallyclauses or executing object destructors.
finallyclauses are honored), and the standard I/O files are not flushed.