New Java-style threading module. The doc strings are in a separate module.

1 files changed, 638 insertions, 0 deletions

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