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 synchronisation, simple locks (also called mutexes or binary semaphores) are provided.

When a thread specific error occurs a RuntimeError exception is raised.

Quick Usage Example

import _thread
import time

def th_func(delay, id):
    while True:
        time.sleep(delay)
        print('Running thread %d' % id)

for i in range(2):
    _thread.start_new_thread(th_func, (i + 1, i))

Functions

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

Start a new thread and return its identifier. The thread executes the 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).

#####_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.stack_size([size])

Return the thread stack size (in bytes) 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 4096 (4KiB). 4KiB is currently the minimum supported stack size value to guarantee sufficient stack space for the interpreter itself.

Objects

_thread.LockType

This is the type of lock objects.

class Lock – used for synchronisation between threads

Methods

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.

#####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")

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