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Commit 9f7e247a authored by Raymond Hettinger's avatar Raymond Hettinger
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Issue #17375: Add docstrings to the threading module.

parent 3d08f25a
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Showing with 346 additions and 5 deletions
Lib/threading.py
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......@@ -87,10 +87,22 @@ _profile_hook = None
_trace_hook = None
def setprofile(func):
"""Set a profile function for all threads started from the threading module.
The func will be passed to sys.setprofile() for each thread, before its
run() method is called.
"""
global _profile_hook
_profile_hook = func
def settrace(func):
"""Set a trace function for all threads started from the threading module.
The func will be passed to sys.settrace() for each thread, before its run()
method is called.
"""
global _trace_hook
_trace_hook = func
......@@ -99,9 +111,22 @@ def settrace(func):
Lock = _allocate_lock
def RLock(*args, **kwargs):
"""Factory function that returns a new reentrant lock.
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.
"""
return _RLock(*args, **kwargs)
class _RLock(_Verbose):
"""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.
"""
def __init__(self, verbose=None):
_Verbose.__init__(self, verbose)
......@@ -119,6 +144,26 @@ class _RLock(_Verbose):
self.__class__.__name__, owner, self.__count)
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 an argument would block, return false immediately;
otherwise, do the same thing as when called without arguments, and
return true.
"""
me = _get_ident()
if self.__owner == me:
self.__count = self.__count + 1
......@@ -139,6 +184,21 @@ class _RLock(_Verbose):
__enter__ = acquire
def release(self):
"""Release a lock, decrementing 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.
Only call this method when the calling thread owns the lock. A
RuntimeError is raised if this method is called when the lock is
unlocked.
There is no return value.
"""
if self.__owner != _get_ident():
raise RuntimeError("cannot release un-acquired lock")
self.__count = count = self.__count - 1
......@@ -179,9 +239,22 @@ class _RLock(_Verbose):
def Condition(*args, **kwargs):
"""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.
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.
"""
return _Condition(*args, **kwargs)
class _Condition(_Verbose):
"""Condition variables allow one or more threads to wait until they are
notified by another thread.
"""
def __init__(self, lock=None, verbose=None):
_Verbose.__init__(self, verbose)
......@@ -233,6 +306,28 @@ class _Condition(_Verbose):
return True
def wait(self, timeout=None):
"""Wait until notified or until a timeout occurs.
If the calling thread has not acquired the lock when this method is
called, a RuntimeError is raised.
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.
"""
if not self._is_owned():
raise RuntimeError("cannot wait on un-acquired lock")
waiter = _allocate_lock()
......@@ -275,6 +370,15 @@ class _Condition(_Verbose):
self._acquire_restore(saved_state)
def notify(self, n=1):
"""Wake up one or more threads waiting on this condition, if any.
If the calling thread has not acquired the lock when this method is
called, a RuntimeError is raised.
This method wakes up at most n of the threads waiting for the condition
variable; it is a no-op if no threads are waiting.
"""
if not self._is_owned():
raise RuntimeError("cannot notify on un-acquired lock")
__waiters = self.__waiters
......@@ -293,15 +397,35 @@ class _Condition(_Verbose):
pass
def notifyAll(self):
"""Wake up all threads waiting on this condition.
If the calling thread has not acquired the lock when this method
is called, a RuntimeError is raised.
"""
self.notify(len(self.__waiters))
notify_all = notifyAll
def Semaphore(*args, **kwargs):
"""A factory function that returns a new semaphore.
Semaphores manage 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. If not given, value defaults to 1.
"""
return _Semaphore(*args, **kwargs)
class _Semaphore(_Verbose):
"""Semaphores manage 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. If not given, value defaults to 1.
"""
# After Tim Peters' semaphore class, but not quite the same (no maximum)
......@@ -313,6 +437,25 @@ class _Semaphore(_Verbose):
self.__value = value
def acquire(self, blocking=1):
"""Acquire a semaphore, decrementing the internal counter by one.
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 blocking set to true, do the same thing as when called
without arguments, and return true.
When invoked with blocking set to false, do not block. If a call without
an argument would block, return false immediately; otherwise, do the
same thing as when called without arguments, and return true.
"""
rc = False
self.__cond.acquire()
while self.__value == 0:
......@@ -334,6 +477,12 @@ class _Semaphore(_Verbose):
__enter__ = acquire
def release(self):
"""Release a semaphore, incrementing the internal counter by one.
When the counter is zero on entry and another thread is waiting for it
to become larger than zero again, wake up that thread.
"""
self.__cond.acquire()
self.__value = self.__value + 1
if __debug__:
......@@ -347,24 +496,64 @@ class _Semaphore(_Verbose):
def BoundedSemaphore(*args, **kwargs):
"""A factory function that returns a new bounded semaphore.
A bounded semaphore checks to make sure its current value doesn't exceed its
initial value. If it does, ValueError is raised. In most situations
semaphores are used to guard resources with limited capacity.
If the semaphore is released too many times it's a sign of a bug. If not
given, value defaults to 1.
Like regular semaphores, bounded semaphores manage 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. If not given, value defaults to 1.
"""
return _BoundedSemaphore(*args, **kwargs)
class _BoundedSemaphore(_Semaphore):
"""Semaphore that checks that # releases is <= # acquires"""
"""A bounded semaphore checks to make sure its current value doesn't exceed
its initial value. If it does, ValueError is raised. In most situations
semaphores are used to guard resources with limited capacity.
"""
def __init__(self, value=1, verbose=None):
_Semaphore.__init__(self, value, verbose)
self._initial_value = value
def release(self):
"""Release a semaphore, incrementing the internal counter by one.
When the counter is zero on entry and another thread is waiting for it
to become larger than zero again, wake up that thread.
If the number of releases exceeds the number of acquires,
raise a ValueError.
"""
if self._Semaphore__value >= self._initial_value:
raise ValueError, "Semaphore released too many times"
raise ValueError("Semaphore released too many times")
return _Semaphore.release(self)
def Event(*args, **kwargs):
"""A factory function that returns a new event.
Events manage 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.
"""
return _Event(*args, **kwargs)
class _Event(_Verbose):
"""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.
"""
# After Tim Peters' event class (without is_posted())
......@@ -378,11 +567,18 @@ class _Event(_Verbose):
self.__cond.__init__()
def isSet(self):
'Return true if and only if the internal flag is true.'
return self.__flag
is_set = isSet
def set(self):
"""Set the internal flag to true.
All threads waiting for the flag to become true are awakened. Threads
that call wait() once the flag is true will not block at all.
"""
self.__cond.acquire()
try:
self.__flag = True
......@@ -391,6 +587,12 @@ class _Event(_Verbose):
self.__cond.release()
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.
"""
self.__cond.acquire()
try:
self.__flag = False
......@@ -398,6 +600,20 @@ class _Event(_Verbose):
self.__cond.release()
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).
This method returns the internal flag on exit, so it will always return
True except if a timeout is given and the operation times out.
"""
self.__cond.acquire()
try:
if not self.__flag:
......@@ -422,7 +638,11 @@ _limbo = {}
# Main class for threads
class Thread(_Verbose):
"""A class that represents a thread of control.
This class can be safely subclassed in a limited fashion.
"""
__initialized = False
# Need to store a reference to sys.exc_info for printing
# out exceptions when a thread tries to use a global var. during interp.
......@@ -435,6 +655,27 @@ class Thread(_Verbose):
def __init__(self, group=None, target=None, name=None,
args=(), kwargs=None, verbose=None):
"""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* is the callable object to be invoked by the run()
method. Defaults to None, meaning nothing is called.
*name* is the thread name. By default, a unique name is constructed of
the form "Thread-N" where N is a small decimal number.
*args* is the argument tuple for the target invocation. Defaults to ().
*kwargs* is a dictionary of keyword arguments for the target
invocation. Defaults to {}.
If a subclass overrides the constructor, it must make sure to invoke
the base class constructor (Thread.__init__()) before doing anything
else to the thread.
"""
assert group is None, "group argument must be None for now"
_Verbose.__init__(self, verbose)
if kwargs is None:
......@@ -483,6 +724,15 @@ class Thread(_Verbose):
return "<%s(%s, %s)>" % (self.__class__.__name__, self.__name, status)
def start(self):
"""Start the thread's activity.
It 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.
This method will raise a RuntimeError if called more than once on the
same thread object.
"""
if not self.__initialized:
raise RuntimeError("thread.__init__() not called")
if self.__started.is_set():
......@@ -500,6 +750,14 @@ class Thread(_Verbose):
self.__started.wait()
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 to the object's constructor as the
target argument, if any, with sequential and keyword arguments taken
from the args and kwargs arguments, respectively.
"""
try:
if self.__target:
self.__target(*self.__args, **self.__kwargs)
......@@ -651,6 +909,29 @@ class Thread(_Verbose):
raise
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). As join() always returns None, you must call
isAlive() after join() to decide whether a timeout happened -- if the
thread is still alive, the join() call timed out.
When the timeout argument is not present or None, the operation will
block until the thread terminates.
A thread can be join()ed many times.
join() raises a RuntimeError if an attempt is made to join the current
thread as that would cause a deadlock. It is also an error to join() a
thread before it has been started and attempts to do so raises the same
exception.
"""
if not self.__initialized:
raise RuntimeError("Thread.__init__() not called")
if not self.__started.is_set():
......@@ -685,6 +966,12 @@ class Thread(_Verbose):
@property
def name(self):
"""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.
"""
assert self.__initialized, "Thread.__init__() not called"
return self.__name
......@@ -695,10 +982,24 @@ class Thread(_Verbose):
@property
def ident(self):
"""Thread identifier of this thread or None if it has not been started.
This is a nonzero integer. See the thread.get_ident() function. Thread
identifiers may be recycled when a thread exits and another thread is
created. The identifier is available even after the thread has exited.
"""
assert self.__initialized, "Thread.__init__() not called"
return self.__ident
def isAlive(self):
"""Return whether the thread is alive.
This method returns True just before the run() method starts until just
after the run() method terminates. The module function enumerate()
returns a list of all alive threads.
"""
assert self.__initialized, "Thread.__init__() not called"
return self.__started.is_set() and not self.__stopped
......@@ -706,6 +1007,17 @@ class Thread(_Verbose):
@property
def daemon(self):
"""A boolean value indicating whether this thread is a daemon thread (True) or not (False).
This must be set before start() is called, otherwise RuntimeError is
raised. Its initial value is inherited from the creating thread; the
main thread is not a daemon thread and therefore all threads created in
the main thread default to daemon = False.
The entire Python program exits when no alive non-daemon threads are
left.
"""
assert self.__initialized, "Thread.__init__() not called"
return self.__daemonic
......@@ -732,14 +1044,24 @@ class Thread(_Verbose):
# The timer class was contributed by Itamar Shtull-Trauring
def Timer(*args, **kwargs):
"""Factory function to create a Timer object.
Timers call a function after a specified number of seconds:
t = Timer(30.0, f, args=[], kwargs={})
t.start()
t.cancel() # stop the timer's action if it's still waiting
"""
return _Timer(*args, **kwargs)
class _Timer(Thread):
"""Call a function after a specified number of seconds:
t = Timer(30.0, f, args=[], kwargs={})
t.start()
t.cancel() # stop the timer's action if it's still waiting
t = Timer(30.0, f, args=[], kwargs={})
t.start()
t.cancel() # stop the timer's action if it's still waiting
"""
def __init__(self, interval, function, args=[], kwargs={}):
......@@ -828,6 +1150,12 @@ class _DummyThread(Thread):
# Global API functions
def currentThread():
"""Return the current 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.
"""
try:
return _active[_get_ident()]
except KeyError:
......@@ -837,6 +1165,12 @@ def currentThread():
current_thread = currentThread
def activeCount():
"""Return the number of Thread objects currently alive.
The returned count is equal to the length of the list returned by
enumerate().
"""
with _active_limbo_lock:
return len(_active) + len(_limbo)
......@@ -847,6 +1181,13 @@ def _enumerate():
return _active.values() + _limbo.values()
def enumerate():
"""Return a list of all Thread objects currently alive.
The list includes daemonic threads, dummy thread objects created by
current_thread(), and the main thread. It excludes terminated threads and
threads that have not yet been started.
"""
with _active_limbo_lock:
return _active.values() + _limbo.values()
......
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