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Commit ea6fa4a0 authored by Georg Brandl's avatar Georg Brandl
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Closes #17375: port new threading docstrings from 2.7.

parent 8a4b1ba9
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Lib/threading.py
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......@@ -44,10 +44,22 @@ _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
......@@ -56,11 +68,27 @@ 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.
"""
if _CRLock is None:
return _PyRLock(*args, **kwargs)
return _CRLock(*args, **kwargs)
class _RLock:
"""This class implements reentrant lock objects.
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):
self._block = _allocate_lock()
......@@ -77,6 +105,31 @@ class _RLock:
self.__class__.__name__, owner, self._count)
def acquire(self, blocking=True, timeout=-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.
When invoked with the floating-point timeout argument set to a positive
value, block for at most the number of seconds specified by timeout
and as long as the lock cannot be acquired. Return true if the lock has
been acquired, false if the timeout has elapsed.
"""
me = get_ident()
if self._owner == me:
self._count = self._count + 1
......@@ -90,6 +143,21 @@ class _RLock:
__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
......@@ -123,6 +191,16 @@ _PyRLock = _RLock
class Condition:
"""Class that implements a condition variable.
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.
"""
def __init__(self, lock=None):
if lock is None:
......@@ -173,6 +251,28 @@ class Condition:
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 notify_all() 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()
......@@ -198,6 +298,13 @@ class Condition:
self._acquire_restore(saved_state)
def wait_for(self, predicate, timeout=None):
"""Wait until a condition evaluates to True.
predicate should be a callable which result will be interpreted as a
boolean value. A timeout may be provided giving the maximum time to
wait.
"""
endtime = None
waittime = timeout
result = predicate()
......@@ -214,6 +321,15 @@ class Condition:
return result
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
......@@ -228,12 +344,26 @@ class Condition:
pass
def notify_all(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))
notifyAll = notify_all
class Semaphore:
"""This class implements semaphore objects.
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)
......@@ -244,6 +374,29 @@ class Semaphore:
self._value = value
def acquire(self, blocking=True, timeout=None):
"""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.
When invoked with a timeout other than None, it will block for at
most timeout seconds. If acquire does not complete successfully in
that interval, return false. Return true otherwise.
"""
if not blocking and timeout is not None:
raise ValueError("can't specify timeout for non-blocking acquire")
rc = False
......@@ -268,6 +421,12 @@ class Semaphore:
__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.
"""
with self._cond:
self._value = self._value + 1
self._cond.notify()
......@@ -277,12 +436,36 @@ class Semaphore:
class BoundedSemaphore(Semaphore):
"""Semaphore that checks that # releases is <= # acquires"""
"""Implements a 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.
"""
def __init__(self, value=1):
Semaphore.__init__(self, value)
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.
"""
with self._cond:
if self._value >= self._initial_value:
raise ValueError("Semaphore released too many times")
......@@ -291,6 +474,13 @@ class BoundedSemaphore(Semaphore):
class Event:
"""Class implementing event objects.
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. The flag is initially false.
"""
# After Tim Peters' event class (without is_posted())
......@@ -303,11 +493,18 @@ class Event:
self._cond.__init__()
def is_set(self):
"""Return true if and only if the internal flag is true."""
return self._flag
isSet = is_set
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.
"""
self._cond.acquire()
try:
self._flag = True
......@@ -316,6 +513,12 @@ class Event:
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
......@@ -323,6 +526,20 @@ class Event:
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:
signaled = self._flag
......@@ -345,19 +562,22 @@ class Event:
# similar to 'draining' except that threads leave with a BrokenBarrierError,
# and a 'broken' state in which all threads get the exception.
class Barrier:
"""Implements a Barrier.
Useful for synchronizing a fixed number of threads at known synchronization
points. Threads block on 'wait()' and are simultaneously once they have all
made that call.
"""
Barrier. Useful for synchronizing a fixed number of threads
at known synchronization points. Threads block on 'wait()' and are
simultaneously once they have all made that call.
"""
def __init__(self, parties, action=None, timeout=None):
"""
Create a barrier, initialised to 'parties' threads.
'action' is a callable which, when supplied, will be called
by one of the threads after they have all entered the
barrier and just prior to releasing them all.
If a 'timeout' is provided, it is uses as the default for
all subsequent 'wait()' calls.
"""Create a barrier, initialised to 'parties' threads.
'action' is a callable which, when supplied, will be called by one of
the threads after they have all entered the barrier and just prior to
releasing them all. If a 'timeout' is provided, it is uses as the
default for all subsequent 'wait()' calls.
"""
self._cond = Condition(Lock())
self._action = action
......@@ -367,12 +587,13 @@ class Barrier:
self._count = 0
def wait(self, timeout=None):
"""
Wait for the barrier. When the specified number of threads have
started waiting, they are all simultaneously awoken. If an 'action'
was provided for the barrier, one of the threads will have executed
that callback prior to returning.
"""Wait for the barrier.
When the specified number of threads have started waiting, they are all
simultaneously awoken. If an 'action' was provided for the barrier, one
of the threads will have executed that callback prior to returning.
Returns an individual index number from 0 to 'parties-1'.
"""
if timeout is None:
timeout = self._timeout
......@@ -439,10 +660,11 @@ class Barrier:
self._cond.notify_all()
def reset(self):
"""
Reset the barrier to the initial state.
"""Reset the barrier to the initial state.
Any threads currently waiting will get the BrokenBarrier exception
raised.
"""
with self._cond:
if self._count > 0:
......@@ -458,11 +680,11 @@ class Barrier:
self._cond.notify_all()
def abort(self):
"""
Place the barrier into a 'broken' state.
Useful in case of error. Any currently waiting threads and
threads attempting to 'wait()' will have BrokenBarrierError
raised.
"""Place the barrier into a 'broken' state.
Useful in case of error. Any currently waiting threads and threads
attempting to 'wait()' will have BrokenBarrierError raised.
"""
with self._cond:
self._break()
......@@ -475,16 +697,12 @@ class Barrier:
@property
def parties(self):
"""
Return the number of threads required to trip the barrier.
"""
"""Return the number of threads required to trip the barrier."""
return self._parties
@property
def n_waiting(self):
"""
Return the number of threads that are currently waiting at the barrier.
"""
"""Return the number of threads currently waiting at the barrier."""
# We don't need synchronization here since this is an ephemeral result
# anyway. It returns the correct value in the steady state.
if self._state == 0:
......@@ -493,13 +711,12 @@ class Barrier:
@property
def broken(self):
"""
Return True if the barrier is in a broken state
"""
"""Return True if the barrier is in a broken state."""
return self._state == -2
#exception raised by the Barrier class
class BrokenBarrierError(RuntimeError): pass
# exception raised by the Barrier class
class BrokenBarrierError(RuntimeError):
pass
# Helper to generate new thread names
......@@ -520,6 +737,13 @@ _dangling = WeakSet()
# Main class for threads
class Thread:
"""A class that represents a thread of control.
This class can be safely subclassed in a limited fashion. 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.
"""
__initialized = False
# Need to store a reference to sys.exc_info for printing
......@@ -533,6 +757,27 @@ class Thread:
def __init__(self, group=None, target=None, name=None,
args=(), kwargs=None, *, daemon=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"
if kwargs is None:
kwargs = {}
......@@ -575,6 +820,15 @@ class Thread:
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")
......@@ -591,6 +845,14 @@ class Thread:
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)
......@@ -729,6 +991,29 @@ class Thread:
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():
......@@ -753,6 +1038,12 @@ class Thread:
@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
......@@ -763,10 +1054,24 @@ class Thread:
@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 is_alive(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
......@@ -774,6 +1079,17 @@ class Thread:
@property
def daemon(self):
"""A boolean value indicating whether this thread is a daemon thread.
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
......@@ -805,6 +1121,7 @@ class Timer(Thread):
t = Timer(30.0, f, args=None, kwargs=None)
t.start()
t.cancel() # stop the timer's action if it's still waiting
"""
def __init__(self, interval, function, args=None, kwargs=None):
......@@ -816,7 +1133,7 @@ class Timer(Thread):
self.finished = Event()
def cancel(self):
"""Stop the timer if it hasn't finished yet"""
"""Stop the timer if it hasn't finished yet."""
self.finished.set()
def run(self):
......@@ -885,6 +1202,12 @@ class _DummyThread(Thread):
# Global API functions
def current_thread():
"""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:
......@@ -893,6 +1216,12 @@ def current_thread():
currentThread = current_thread
def active_count():
"""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)
......@@ -903,6 +1232,13 @@ def _enumerate():
return list(_active.values()) + list(_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 list(_active.values()) + list(_limbo.values())
......
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