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639 lines
22 KiB
Python
639 lines
22 KiB
Python
"""Proposed new higher-level threading interfaces.
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This module is safe for use with 'from threading import *'. It
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defines the following objects:
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Lock()
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A factory function that returns a new primitive lock object. Once
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a thread has acquired it, subsequent attempts to acquire it block,
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until it is released; any thread may release it.
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RLock()
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A factory function that returns a new reentrant lock object.
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A reentrant lock must be released by the thread that acquired it.
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Once a thread has acquired a reentrant lock, the same thread may
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acquire it again without blocking; the thread must release it once
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for each time it has acquired it.
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Condition()
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A factory function that returns a new condition variable object.
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A condition variable allows one or more threads to wait until they
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are notified by another thread.
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Semaphore()
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A factory function that returns a new semaphore object. A
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semaphore manages a counter representing the number of release()
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calls minus the number of acquire() calls, plus an initial value.
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The acquire() method blocks if necessary until it can return
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without making the counter negative.
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Event()
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A factory function that returns a new event object. An event
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manages a flag that can be set to true with the set() method and
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reset to false with the clear() method. The wait() method blocks
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until the flag is true.
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Thread
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A class that represents a thread of control -- subclassable.
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currentThread()
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A function that returns the Thread object for the caller's thread.
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activeCount()
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A function that returns the number of currently active threads.
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enumerate()
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A function that returns a list of all currently active threads.
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Detailed interfaces for each of these are documented below in the form
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of pseudo class definitions. Note that the classes marked as ``do not
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subclass'' are actually implemented as factory functions; classes are
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shown here as a way to structure the documentation only.
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The design of this module is loosely based on Java's threading model.
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However, where Java makes locks and condition variables basic behavior
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of every object, they are separate objects in Python. Python's Thread
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class supports a subset of the behavior of Java's Thread class;
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currently, there are no priorities, no thread groups, and threads
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cannot be destroyed, stopped, suspended, resumed, or interrupted. The
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static methods of Java's Thread class, when implemented, are mapped to
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module-level functions.
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All methods described below are executed atomically.
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"""
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class Lock:
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"""Primitive lock object.
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*** DO NOT SUBCLASS THIS CLASS ***
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A primitive lock is a synchronization primitive that is not owned
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by a particular thread when locked. In Python, it is currently
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the lowest level synchronization primitive available, implemented
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directly by the thread extension module.
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A primitive lock is in one of two states, ``locked'' or
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``unlocked''. It is created in the unlocked state. It has two
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basic methods, acquire() and release(). When the state is
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unlocked, acquire() changes the state to locked and returns
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immediately. When the state is locked, acquire() blocks until a
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call to release() in another thread changes it to unlocked, then
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the acquire() call resets it to locked and returns. The release()
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method should only be called in the locked state; it changes the
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state to unlocked and returns immediately. When more than one
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thread is blocked in acquire() waiting for the state to turn to
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unlocked, only one thread proceeds when a release() call resets
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the state to unlocked; which one of the waiting threads proceeds
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is not defined, and may vary across implementations.
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All methods are executed atomically.
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"""
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def acquire(self, blocking=1):
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"""Acquire a lock, blocking or non-blocking.
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When invoked without arguments, block until the lock is
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unlocked, then set it to locked, and return. There is no
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return value in this case.
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When invoked with the 'blocking' argument set to true, do the
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same thing as when called without arguments, and return true.
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When invoked with the 'blocking' argument set to false, do not
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block. If a call without argument would block, return false
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immediately; otherwise, do the same thing as when called
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without arguments, and return true.
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"""
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def release(self):
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"""Release a lock.
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When the lock is locked, reset it to unlocked, and return. If
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any other threads are blocked waiting for the lock to become
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unlocked, allow exactly one of them to proceed.
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Do not call this method when the lock is unlocked.
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There is no return value.
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"""
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class RLock:
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"""Reentrant lock object.
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*** DO NOT SUBCLASS THIS CLASS ***
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A reentrant lock is a synchronization primitive that may be
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acquired multiple times by the same thread. Internally, it uses
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the concepts of ``owning thread'' and ``recursion level'' in
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addition to the locked/unlocked state used by primitive locks. In
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the locked state, some thread owns the lock; in the unlocked
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state, no thread owns it.
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To lock the lock, a thread calls its acquire() method; this
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returns once the thread owns the lock. To unlock the lock, a
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thread calls its release() method. acquire()/release() call pairs
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may be nested; only the final release() (i.e. the release() of the
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outermost pair) resets the lock to unlocked and allows another
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thread blocked in acquire() to proceed.
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"""
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def acquire(self, blocking=1):
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"""Acquire a lock, blocking or non-blocking.
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When invoked without arguments: if this thread already owns
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the lock, increment the recursion level by one, and return
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immediately. Otherwise, if another thread owns the lock,
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block until the lock is unlocked. Once the lock is unlocked
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(not owned by any thread), then grab ownership, set the
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recursion level to one, and return. If more than one thread
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is blocked waiting until the lock is unlocked, only one at a
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time will be able to grab ownership of the lock. There is no
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return value in this case.
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When invoked with the 'blocking' argument set to true, do the
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same thing as when called without arguments, and return true.
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When invoked with the 'blocking' argument set to false, do not
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block. If a call without argument would block, return false
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immediately; otherwise, do the same thing as when called
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without arguments, and return true.
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"""
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def release(self):
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"""Release a lock.
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Only call this method when the calling thread owns the lock.
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Decrement the recursion level. If after the decrement it is
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zero, reset the lock to unlocked (not owned by any thread),
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and if any other threads are blocked waiting for the lock to
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become unlocked, allow exactly one of them to proceed. If
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after the decrement the recursion level is still nonzero, the
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lock remains locked and owned by the calling thread.
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Do not call this method when the lock is unlocked.
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There is no return value.
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"""
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class Condition:
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"""Synchronized condition variable object.
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*** DO NOT SUBCLASS THIS CLASS ***
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A condition variable is always associated with some kind of lock;
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this can be passed in or one will be created by default. (Passing
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one in is useful when several condition variables must share the
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same lock.)
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A condition variable has acquire() and release() methods that call
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the corresponding methods of the associated lock.
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It also has a wait() method, and notify() and notifyAll() methods.
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These three must only be called when the calling thread has
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acquired the lock.
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The wait() method releases the lock, and then blocks until it is
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awakened by a notifiy() or notifyAll() call for the same condition
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variable in another thread. Once awakened, it re-acquires the
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lock and returns. It is also possible to specify a timeout.
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The notify() method wakes up one of the threads waiting for the
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condition variable, if any are waiting. The notifyAll() method
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wakes up all threads waiting for the condition variable.
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Note: the notify() and notifyAll() methods don't release the
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lock; this means that the thread or threads awakened will not
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return from their wait() call immediately, but only when the
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thread that called notify() or notifyAll() finally relinquishes
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ownership of the lock.
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Tip: the typical programming style using condition variables uses
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the lock to synchronize access to some shared state; threads that
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are interested in a particular change of state call wait()
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repeatedly until they see the desired state, while threads that
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modify the state call notify() or notifyAll() when they change the
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state in such a way that it could possibly be a desired state for
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one of the waiters. For example, the following code is a generic
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producer-consumer situation with unlimited buffer capacity:
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# Consume one item
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cv.acquire()
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while not an_item_is_available():
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cv.wait()
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get_an_available_item()
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cv.release()
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# Produce one item
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cv.acquire()
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make_an_item_available()
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cv.notify()
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cv.release()
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To choose between notify() and notifyAll(), consider whether one
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state change can be interesting for only one or several waiting
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threads. E.g. in a typical producer-consumer situation, adding
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one item to the buffer only needs to wake up one consumer thread.
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"""
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def __init__(self, lock=None):
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"""Constructor.
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If the lock argument is given and not None, it must be a Lock
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or RLock object, and it is used as the underlying lock.
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Otherwise, a new RLock object is created and used as the
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underlying lock.
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"""
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def acquire(self, *args):
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"""Acquire the underlying lock.
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This method calls the corresponding method on the underlying
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lock; the return value is whatever that method returns.
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"""
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def release(self):
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"""Release the underlying lock.
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This method calls the corresponding method on the underlying
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lock; there is no return value.
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"""
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def wait(self, timeout=None):
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"""Wait until notified or until a timeout occurs.
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This must only be called when the calling thread has acquired
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the lock.
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This method releases the underlying lock, and then blocks
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until it is awakened by a notify() or notifyAll() call for the
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same condition variable in another thread, or until the
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optional timeout occurs. Once awakened or timed out, it
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re-acquires the lock and returns.
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When the timeout argument is present and not None, it should
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be a floating point number specifying a timeout for the
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operation in seconds (or fractions thereof).
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When the underlying lock is an RLock, it is not released using
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its release() method, since this may not actually unlock the
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lock when it was acquired() multiple times recursively.
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Instead, an internal interface of the RLock class is used,
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which really unlocks it even when it has been recursively
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acquired several times. Another internal interface is then
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used to restore the recursion level when the lock is
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reacquired.
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"""
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def notify(self):
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"""Wake up a thread waiting on this condition, if any.
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This must only be called when the calling thread has acquired
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the lock.
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This method wakes up one of the threads waiting for the
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condition variable, if any are waiting; it is a no-op if no
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threads are waiting.
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The current implementation wakes up exactly one thread, if any
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are waiting. However, it's not safe to rely on this behavior.
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A future, optimized implementation may occasionally wake up
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more than one thread.
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Note: the awakened thread does not actually return from its
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wait() call until it can reacquire the lock. Since notify()
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does not release the lock, its caller should.
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"""
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def notifyAll(self):
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"""Wake up all threads waiting on this condition.
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This method acts like notify(), but wakes up all waiting
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threads instead of one.
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"""
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class Semaphore:
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"""Semaphore object.
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This is one of the oldest synchronization primitives in the
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history of computer science, invented by the early Dutch computer
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scientist Edsger W. Dijkstra (he used P() and V() instead of
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acquire() and release()).
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A semaphore manages an internal counter which is decremented by
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each acquire() call and incremented by each release() call. The
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counter can never go below zero; when acquire() finds that it is
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zero, it blocks, waiting until some other thread calls release().
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"""
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def __init__(self, value=1):
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"""Constructor.
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The optional argument gives the initial value for the internal
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counter; it defaults to 1.
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"""
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def acquire(self, blocking=1):
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"""Acquire a semaphore.
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When invoked without arguments: if the internal counter is
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larger than zero on entry, decrement it by one and return
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immediately. If it is zero on entry, block, waiting until
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some other thread has called release() to make it larger than
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zero. This is done with proper interlocking so that if
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multiple acquire() calls are blocked, release() will wake
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exactly one of them up. The implementation may pick one at
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random, so the order in which blocked threads are awakened
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should not be relied on. There is no return value in this
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case.
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When invoked with the 'blocking' argument set to true, do the
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same thing as when called without arguments, and return true.
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When invoked with the 'blocking' argument set to false, do not
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block. If a call without argument would block, return false
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immediately; otherwise, do the same thing as when called
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without arguments, and return true.
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"""
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def release(self):
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"""Release a semaphore.
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Increment the internal counter by one. When it was zero on
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entry and another thread is waiting for it to become larger
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than zero again, wake up that thread.
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"""
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class Event:
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"""Event object.
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This is one of the simplest mechanisms for communication between
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threads: one thread signals an event and another thread, or
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threads, wait for it.
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An event object manages an internal flag that can be set to true
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with the set() method and reset to false with the clear() method.
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The wait() method blocks until the flag is true.
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"""
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def __init__(self):
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"""Constructor.
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The internal flag is initially false.
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"""
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def isSet(self):
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"""Return true iff the internal flag is true."""
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def set(self):
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"""Set the internal flag to true.
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All threads waiting for it to become true are awakened.
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Threads that call wait() once the flag is true will not block
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at all.
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"""
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def clear(self):
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"""Reset the internal flag to false.
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Subsequently, threads calling wait() will block until set() is
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called to set the internal flag to true again.
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"""
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def wait(self, timeout=None):
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"""Block until the internal flag is true.
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If the internal flag is true on entry, return immediately.
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Otherwise, block until another thread calls set() to set the
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flag to true, or until the optional timeout occurs.
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When the timeout argument is present and not None, it should
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be a floating point number specifying a timeout for the
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operation in seconds (or fractions thereof).
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"""
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class Thread:
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"""Thread class.
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*** ONLY OVERRIDE THE __init__() AND run() METHODS OF THIS CLASS ***
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This class represents an activity that is run in a separate thread
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of control. There are two ways to specify the activity: by
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passing a callable object to the constructor, or by overriding the
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run() method in a subclass. No other methods (except for the
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constructor) should be overridden in a subclass.
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Once a thread object is created, its activity must be started by
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calling the thread's start() method. This invokes the run()
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method in a separate thread of control.
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Once the thread's activity is started, the thread is considered
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'alive' and 'active' (these concepts are almost, but not quite
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exactly, the same; their definition is intentionally somewhat
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vague). It stops being alive and active when its run() method
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terminates -- either normally, or by raising an unhandled
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exception. The isAlive() method tests whether the thread is
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alive.
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Other threads can call a thread's join() method. This blocks the
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calling thread until the thread whose join() method is called
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is terminated.
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A thread has a name. The name can be passed to the constructor,
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set with the setName() method, and retrieved with the getName()
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method.
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A thread can be flagged as a ``daemon thread''. The significance
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of this flag is that the entire Python program exits when only
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daemon threads are left. The initial value is inherited from the
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creating thread. The flag can be set with the setDaemon() method
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and retrieved with the getDaemon() method.
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There is a ``main thread'' object; this corresponds to the
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initial thread of control in the Python program. It is not a
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daemon thread.
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There is the possibility that ``dummy thread objects'' are
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created. These are thread objects corresponding to ``alien
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threads''. These are threads of control started outside the
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threading module, e.g. directly from C code. Dummy thread objects
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have limited functionality; they are always considered alive,
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active, and daemonic, and cannot be join()ed. They are never
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deleted, since it is impossible to detect the termination of alien
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threads.
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"""
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def __init__(self, group=None, target=None, name=None,
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args=(), kwargs={}):
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"""Thread constructor.
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This constructor should always be called with keyword
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arguments. Arguments are:
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group
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Should be None; reserved for future extension when a
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ThreadGroup class is implemented.
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target
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Callable object to be invoked by the run() method.
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Defaults to None, meaning nothing is called.
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name
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The thread name. By default, a unique name is constructed
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of the form ``Thread-N'' where N is a small decimal
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number.
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args
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Argument tuple for the target invocation. Defaults to ().
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kwargs
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Keyword argument dictionary for the target invocation.
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Defaults to {}.
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If the subclass overrides the constructor, it must make sure
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to invoke the base class constructor (Thread.__init__())
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before doing anything else to the thread.
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"""
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def start(self):
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"""Start the thread's activity.
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This must be called at most once per thread object. It
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arranges for the object's run() method to be invoked in a
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separate thread of control.
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"""
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def run(self):
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"""Method representing the thread's activity.
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You may override this method in a subclass. The standard
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run() method invokes the callable object passed as the
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'target' argument, if any, with sequential and keyword
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arguments taken from the 'args' and 'kwargs' arguments,
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respectively.
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"""
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def join(self, timeout=None):
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"""Wait until the thread terminates.
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This blocks the calling thread until the thread whose join()
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method is called terminates -- either normally or through an
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unhandled exception -- or until the optional timeout occurs.
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When the timeout argument is present and not None, it should
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be a floating point number specifying a timeout for the
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operation in seconds (or fractions thereof).
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A thread can be join()ed many times.
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A thread cannot join itself because this would cause a
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deadlock.
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It is an error to attempt to join() a thread before it has
|
|
been started.
|
|
|
|
"""
|
|
|
|
def getName(self):
|
|
"""Return the thread's name."""
|
|
|
|
def setName(self, name):
|
|
"""Set the thread's name.
|
|
|
|
The name is a string used for identification purposes only.
|
|
It has no semantics. Multiple threads may be given the same
|
|
name. The initial name is set by the constructor.
|
|
|
|
"""
|
|
|
|
def isAlive(self):
|
|
"""Return whether the thread is alive.
|
|
|
|
Roughly, a thread is alive from the moment the start() method
|
|
returns until its run() method terminates.
|
|
|
|
"""
|
|
|
|
def isDaemon(self):
|
|
"""Return the thread's daemon flag."""
|
|
|
|
def setDaemon(self, daemonic):
|
|
"""Set the thread's daemon flag (a Boolean).
|
|
|
|
This must be called before start() is called.
|
|
|
|
The initial value is inherited from the creating thread.
|
|
|
|
The entire Python program exits when no active non-daemon
|
|
threads are left.
|
|
|
|
"""
|
|
|
|
|
|
# Module-level functions:
|
|
|
|
|
|
def currentThread():
|
|
"""Return the current Thread object.
|
|
|
|
This function returns the Thread object corresponding to the
|
|
caller's thread of control.
|
|
|
|
If the caller's thread of control was not created through the
|
|
threading module, a dummy thread object with limited functionality
|
|
is returned.
|
|
|
|
"""
|
|
|
|
|
|
def activeCount():
|
|
"""Return the number of currently active Thread objects.
|
|
|
|
The returned count is equal to the length of the list returned by
|
|
enumerate().
|
|
|
|
"""
|
|
|
|
|
|
def enumerate():
|
|
"""Return a list of all currently active Thread objects.
|
|
|
|
The list includes daemonic threads, dummy thread objects created
|
|
by currentThread(), and the main thread. It excludes terminated
|
|
threads and threads that have not yet been started.
|
|
|
|
"""
|