_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. The threading module provides an easier to use and higher-level threading API built on top of this module.

3.7 版更變: This module used to be optional, it is now always available.

This module defines the following constants and functions:

exception _thread.error

Raised on thread-specific errors.

3.3 版更變: This is now a synonym of the built-in RuntimeError.

_thread.LockType

This is the type of lock objects.

_thread.start_new_thread(function, args[, kwargs])

开启一个新线程并返回其标识。 线程执行函数 function 并附带参数列表 args (必须是元组)。 可选的 kwargs 参数指定一个关键字参数字典。

当函数返回时,线程会静默地退出。

当函数因某个未处理异常而终结时,sys.unraisablehook() 会被调用以处理异常。 钩子参数的 object 属性为 function。 在默认情况下,会打印堆栈回溯然后该线程将退出(但其他线程会继续运行)。

当函数引发 SystemExit 异常时,它会被静默地忽略。

3.8 版更變: 现在会使用 sys.unraisablehook() 来处理未处理的异常。

_thread.interrupt_main()

模拟一个 signal.SIGINT 信号到达主线程的效果。 线程可以使用这个函数来中断主线程。

如果 Python 没有处理 signal.SIGINT (将它设为 signal.SIG_DFLsignal.SIG_IGN),此函数将不做任何事。

_thread.exit()

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

_thread.allocate_lock()

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

_thread.get_ident()

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.

_thread.get_native_id()

返回内核分配给当前线程的原生集成线程 ID。 这是一个非负整数。 它的值可被用来在整个系统中唯一地标识这个特定线程(直到线程终结,在那之后该值可能会被 OS 回收再利用)。

可用性: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD, AIX。

3.8 版新加入.

_thread.stack_size([size])

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 unsupported, a RuntimeError is raised. If the specified stack size is invalid, a 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).

可用性: Windows,具有 POSIX 线程的系统。

_thread.TIMEOUT_MAX

The maximum value allowed for the timeout parameter of Lock.acquire(). Specifying a timeout greater than this value will raise an OverflowError.

3.2 版新加入.

Lock objects have the following methods:

lock.acquire(waitflag=1, timeout=-1)

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.

3.2 版更變: The timeout parameter is new.

3.2 版更變: Lock acquires can now be interrupted by signals on POSIX.

lock.release()

Releases the lock. The lock must have been acquired earlier, but not necessarily by the same thread.

lock.locked()

Return the status of the lock: True if it has been acquired by some thread, False if not.

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")

Caveats:

  • 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 exception is equivalent to calling _thread.exit().

  • 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 most systems, they are killed without executing try ... finally clauses or executing object destructors.

  • 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.