threading
--- Thread-based parallelism¶
Code source : Lib/threading.py
This module constructs higher-level threading interfaces on top of the lower
level _thread
module.
Modifié dans la version 3.7: Ce module était auparavant optionnel, il est maintenant toujours disponible.
Voir aussi
concurrent.futures.ThreadPoolExecutor
offers a higher level interface
to push tasks to a background thread without blocking execution of the
calling thread, while still being able to retrieve their results when needed.
queue
provides a thread-safe interface for exchanging data between
running threads.
asyncio
offers an alternative approach to achieving task level
concurrency without requiring the use of multiple operating system threads.
Note
In the Python 2.x series, this module contained camelCase
names
for some methods and functions. These are deprecated as of Python 3.10,
but they are still supported for compatibility with Python 2.5 and lower.
Particularité de l'implémentation CPython : In CPython, due to the Global Interpreter Lock, only one thread
can execute Python code at once (even though certain performance-oriented
libraries might overcome this limitation).
If you want your application to make better use of the computational
resources of multi-core machines, you are advised to use
multiprocessing
or concurrent.futures.ProcessPoolExecutor
.
However, threading is still an appropriate model if you want to run
multiple I/O-bound tasks simultaneously.
Availability: not WASI.
This module does not work or is not available on WebAssembly. See Plateformes WebAssembly for more information.
Ce module définit les fonctions suivantes :
- threading.active_count()¶
Renvoie le nombre d'objets
Thread
actuellement vivants. Le compte renvoyé est égal à la longueur de la liste renvoyée parenumerate()
.The function
activeCount
is a deprecated alias for this function.
- threading.current_thread()¶
Renvoie l'objet
Thread
courant, correspondant au fil de contrôle de l'appelant. Si le fil de contrôle de l'appelant n'a pas été créé via le moduleThread
, un objet thread factice aux fonctionnalités limitées est renvoyé.The function
currentThread
is a deprecated alias for this function.
- threading.excepthook(args, /)¶
Gère les exceptions non-attrapées levées par
Thread.run()
.L'argument arg a les attributs suivants :
exc_type : le type de l'exception ;
exc_value: la valeur de l'exception, peut être
None
;exc_traceback : la pile d'appels pour cette exception, peut être
None
;thread: le fil d'exécution ayant levé l'exception, peut être
None
.
Si exc_type est
SystemExit
, l'exception est ignorée silencieusement. Toutes les autres sont affichées sursys.stderr
.Si cette fonction lève une exception,
sys.excepthook()
est appelée pour la gérer.La fonction
threading.excepthook()
peut être surchargée afin de contrôler comment les exceptions non-attrapées levées parThread.run()
sont gérées.Stocker exc_value en utilisant une fonction de rappel personnalisée peut créer un cycle de références. exc_value doit être nettoyée explicitement pour casser ce cycle lorsque l'exception n'est plus nécessaire.
Stocker thread en utilisant une fonction de rappel personnalisée peut le ressusciter, si c'est un objet en cours de finalisation. Évitez de stocker thread après la fin de la fonction de rappel, pour éviter de ressusciter des objets.
Voir aussi
sys.excepthook()
gère les exceptions qui n'ont pas été attrapées.Ajouté dans la version 3.8.
- threading.__excepthook__¶
Holds the original value of
threading.excepthook()
. It is saved so that the original value can be restored in case they happen to get replaced with broken or alternative objects.Ajouté dans la version 3.10.
- threading.get_ident()¶
Renvoie l'« identifiant de fil » du fil d'exécution courant. C'est un entier non nul. Sa valeur n'a pas de signification directe ; il est destiné à être utilisé comme valeur magique opaque, par exemple comme clef de dictionnaire de données pour chaque fil. Les identificateurs de fils peuvent être recyclés lorsqu'un fil se termine et qu'un autre fil est créé.
Ajouté dans la version 3.3.
- threading.get_native_id()¶
Renvoie l'identifiant natif complet assigné par le noyau du fil d'exécution actuel. C'est un entier non négatif. Sa valeur peut uniquement être utilisée pour identifier ce fil d'exécution à l'échelle du système (jusqu'à ce que le fil d'exécution se termine, après quoi la valeur peut être recyclée par le système d'exploitation).
Availability: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD, AIX, DragonFlyBSD, GNU/kFreeBSD.
Ajouté dans la version 3.8.
Modifié dans la version 3.13: Added support for GNU/kFreeBSD.
- threading.enumerate()¶
Return a list of all
Thread
objects currently active. The list includes daemonic threads and dummy thread objects created bycurrent_thread()
. It excludes terminated threads and threads that have not yet been started. However, the main thread is always part of the result, even when terminated.
- threading.main_thread()¶
Renvoie l'objet fil d'exécution
Thread
principal. Dans des conditions normales, le fil principal est le fil à partir duquel l'interpréteur Python a été lancé.Ajouté dans la version 3.4.
- threading.settrace(func)¶
Attache une fonction de traçage pour tous les fils d'exécution démarrés depuis le module
Thread
. La fonction func est passée àsys.settrace()
pour chaque fil, avant que sa méthoderun()
soit appelée.
- threading.settrace_all_threads(func)¶
Set a trace function for all threads started from the
threading
module and all Python threads that are currently executing.The func will be passed to
sys.settrace()
for each thread, before itsrun()
method is called.Ajouté dans la version 3.12.
- threading.gettrace()¶
Get the trace function as set by
settrace()
.Ajouté dans la version 3.10.
- threading.setprofile(func)¶
Attache une fonction de profilage pour tous les fils d'exécution démarrés depuis le module
Threading
. La fonction func est passée àsys.setprofile()
pour chaque fil, avant que sa méthoderun()
soit appelée.
- threading.setprofile_all_threads(func)¶
Set a profile function for all threads started from the
threading
module and all Python threads that are currently executing.The func will be passed to
sys.setprofile()
for each thread, before itsrun()
method is called.Ajouté dans la version 3.12.
- threading.getprofile()¶
Get the profiler function as set by
setprofile()
.Ajouté dans la version 3.10.
- threading.stack_size([size])¶
Renvoie la taille de la pile d'exécution utilisée lors de la création de nouveaux fils d'exécution. L'argument optionnel size spécifie la taille de pile à utiliser pour les fils créés ultérieurement, et doit être 0 (pour utiliser la taille de la plate-forme ou la valeur configurée par défaut) ou un entier positif supérieur ou égal à 32 768 (32 Kio). Si size n'est pas spécifié, 0 est utilisé. Si la modification de la taille de la pile de fils n'est pas prise en charge, une
RuntimeError
est levée. Si la taille de pile spécifiée n'est pas valide, uneValueError
est levée et la taille de pile n'est pas modifiée. 32 Kio est actuellement la valeur minimale de taille de pile prise en charge pour garantir un espace de pile suffisant pour l'interpréteur lui-même. Notez que certaines plates-formes peuvent avoir des restrictions particulières sur les valeurs de taille de la pile, telles que l'exigence d'une taille de pile minimale > 32 Kio ou d'une allocation en multiples de la taille de page de la mémoire du système – la documentation de la plate-forme devrait être consultée pour plus d'informations (4 Kio sont courantes ; en l'absence de renseignements plus spécifiques, l'approche proposée est l'utilisation de multiples de 4 096 pour la taille de la pile).Availability: Windows, pthreads.
Unix platforms with POSIX threads support.
Ce module définit également la constante suivante :
- threading.TIMEOUT_MAX¶
La valeur maximale autorisée pour le paramètre timeout des fonctions bloquantes (
Lock.acquire()
,RLock.acquire()
,Condition.wait()
, etc.). Spécifier un délai d'attente supérieur à cette valeur lève uneOverflowError
.Ajouté dans la version 3.2.
Ce module définit un certain nombre de classes, qui sont détaillées dans les sections ci-dessous.
La conception de ce module est librement basée sur le modèle des fils d'exécution de Java. Cependant, là où Java fait des verrous et des variables de condition le comportement de base de chaque objet, ils sont des objets séparés en Python. La classe Python Thread
prend en charge un sous-ensemble du comportement de la classe Thread de Java ; actuellement, il n'y a aucune priorité, aucun groupe de fils d'exécution, et les fils ne peuvent être détruits, arrêtés, suspendus, repris ni interrompus. Les méthodes statiques de la classe Thread de Java, lorsqu'elles sont implémentées, correspondent à des fonctions au niveau du module.
Toutes les méthodes décrites ci-dessous sont exécutées de manière atomique.
Données locales au fil d'exécution¶
Les données locales au fil d'exécution (thread-local data) sont des données dont les valeurs sont propres à chaque fil. Pour gérer les données locales au fil, il suffit de créer une instance de local
(ou une sous-classe) et d'y stocker des données :
mydata = threading.local()
mydata.x = 1
Les valeurs dans l'instance sont différentes pour des threads différents.
- class threading.local¶
Classe qui représente les données locales au fil d'exécution.
For more details and extensive examples, see the documentation string of the
_threading_local
module: Lib/_threading_local.py.
Objets Threads¶
The Thread
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. In other words, only override the
__init__()
and run()
methods of this class.
Une fois qu'un objet fil d'exécution est créé, son activité doit être lancée en appelant la méthode start()
du fil. Ceci invoque la méthode run()
dans un fil d'exécution séparé.
Une fois que l'activité du fil d'exécution est lancée, le fil est considéré comme « vivant ». Il cesse d'être vivant lorsque sa méthode run()
se termine – soit normalement, soit en levant une exception non gérée. La méthode is_alive()
teste si le fil est vivant.
D'autres fils d'exécution peuvent appeler la méthode join()
d'un fil. Ceci bloque le fil appelant jusqu'à ce que le fil dont la méthode join()
est appelée soit terminé.
Un fil d'exécution a un nom. Le nom peut être passé au constructeur, et lu ou modifié via l'attribut name
.
Si la méthode run()
lève une exception, threading.excepthook()
est appelée pour s'en occuper. Par défaut, threading.excepthook()
ignore silencieusement SystemExit
.
Un fil d'exécution peut être marqué comme « fil démon ». Un programme Python se termine quand il ne reste plus que des fils démons. La valeur initiale est héritée du fil d'exécution qui l'a créé. Cette option peut être définie par la propriété daemon
ou par l'argument daemon du constructeur.
Note
Les fils d'exécution démons sont brusquement terminés à l'arrêt du programme Python. Leurs ressources (fichiers ouverts, transactions de base de données, etc.) peuvent ne pas être libérées correctement. Si vous voulez que vos fils s'arrêtent proprement, faites en sorte qu'ils ne soient pas démoniques et utilisez un mécanisme de signalisation approprié tel qu'un objet évènement Event
.
Il y a un objet "fil principal", qui correspond au fil de contrôle initial dans le programme Python. Ce n'est pas un fil démon.
There is the possibility that "dummy thread objects" are created. These are thread objects corresponding to "alien threads", which are threads of control started outside the threading module, such as directly from C code. Dummy thread objects have limited functionality; they are always considered alive and daemonic, and cannot be joined. They are never deleted, since it is impossible to detect the termination of alien threads.
- class threading.Thread(group=None, target=None, name=None, args=(), kwargs={}, *, daemon=None)¶
Ce constructeur doit toujours être appelé avec des arguments nommés. Les arguments sont :
group should be
None
; reserved for future extension when aThreadGroup
class is implemented.target est l'objet appelable qui doit être invoqué par la méthode
run()
. La valeur par défaut estNone
, ce qui signifie que rien n'est appelé.name is the thread name. By default, a unique name is constructed of the form "Thread-N" where N is a small decimal number, or "Thread-N (target)" where "target" is
target.__name__
if the target argument is specified.args is a list or tuple of arguments for the target invocation. Defaults to
()
.kwargs est un dictionnaire d'arguments nommés pour l'invocation de l'objet appelable. La valeur par défaut est
{}
.S'il ne vaut pas
None
, daemon définit explicitement si le fil d'exécution est démonique ou pas. S'il vautNone
(par défaut), la valeur est héritée du fil courant.Si la sous-classe réimplémente le constructeur, elle doit s'assurer d'appeler le constructeur de la classe de base (
Thread.__init__()
) avant de faire autre chose au fil d'exécution.Modifié dans la version 3.3: Added the daemon parameter.
Modifié dans la version 3.10: Use the target name if name argument is omitted.
- start()¶
Lance l'activité du fil d'exécution.
Elle ne doit être appelée qu'une fois par objet de fil. Elle fait en sorte que la méthode
run()
de l'objet soit invoquée dans un fil d'exécution.Cette méthode lève une
RuntimeError
si elle est appelée plus d'une fois sur le même objet fil d'exécution.
- run()¶
Méthode représentant l'activité du fil d'exécution.
Vous pouvez remplacer cette méthode dans une sous-classe. La méthode standard
run()
invoque l'objet appelable passé au constructeur de l'objet en tant qu'argument target, le cas échéant, avec des arguments positionnels et des arguments nommés tirés respectivement des arguments args et kwargs.Using list or tuple as the args argument which passed to the
Thread
could achieve the same effect.Example:
>>> from threading import Thread >>> t = Thread(target=print, args=[1]) >>> t.run() 1 >>> t = Thread(target=print, args=(1,)) >>> t.run() 1
- join(timeout=None)¶
Attend que le fil d'exécution se termine. Ceci bloque le fil appelant jusqu'à ce que le fil dont la méthode
join()
est appelée se termine – soit normalement, soit par une exception non gérée – ou jusqu'à ce que le délai optionnel timeout soit atteint.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). Asjoin()
always returnsNone
, you must callis_alive()
afterjoin()
to decide whether a timeout happened -- if the thread is still alive, thejoin()
call timed out.Lorsque l'argument timeout n'est pas présent ou vaut
None
, l'opération se bloque jusqu'à ce que le fil d'exécution se termine.A thread can be joined many times.
join()
lève uneRuntimeError
si une tentative est faite pour attendre le fil d'exécution courant car cela conduirait à un interblocage (deadlock en anglais). Attendre viajoin()
un fil d'exécution avant son lancement est aussi une erreur et, si vous tentez de le faire, lève la même exception.
- name¶
Une chaîne de caractères utilisée à des fins d'identification seulement. Elle n'a pas de sémantique. Plusieurs fils d'exécution peuvent porter le même nom. Le nom initial est défini par le constructeur.
- getName()¶
- setName()¶
Deprecated getter/setter API for
name
; use it directly as a property instead.Obsolète depuis la version 3.10.
- ident¶
« L'identificateur de fil d'exécution » de ce fil ou
None
si le fil n'a pas été lancé. C'est un entier non nul. Voyez également la fonctionget_ident()
. Les identificateurs de fils peuvent être recyclés lorsqu'un fil se termine et qu'un autre fil est créé. L'identifiant est disponible même après que le fil ait terminé.
- native_id¶
The Thread ID (
TID
) of this thread, as assigned by the OS (kernel). This is a non-negative integer, orNone
if the thread has not been started. See theget_native_id()
function. This value may be used to uniquely identify this particular thread system-wide (until the thread terminates, after which the value may be recycled by the OS).Note
Tout comme pour les Process IDs, les Thread IDs ne sont valides (garantis uniques sur le système) uniquement du démarrage du fil à sa fin.
Availability: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD, AIX, DragonFlyBSD.
Ajouté dans la version 3.8.
- is_alive()¶
Renvoie si le fil d'exécution est vivant ou pas.
Cette méthode renvoie
True
depuis juste avant le démarrage de la méthoderun()
et jusqu'à juste après la terminaison de la méthoderun()
. La fonctionenumerate()
du module renvoie une liste de tous les fils d'exécution vivants.
- daemon¶
A boolean value indicating whether this thread is a daemon thread (
True
) or not (False
). This must be set beforestart()
is called, otherwiseRuntimeError
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 todaemon
=False
.Le programme Python se termine lorsqu'il ne reste plus de fils d'exécution non-démons vivants.
Verrous¶
Un verrou primitif n'appartient pas à un fil d'exécution lorsqu'il est verrouillé. En Python, c'est actuellement la méthode de synchronisation la plus bas-niveau qui soit disponible, implémentée directement par le module d'extension _thread
.
Un verrou primitif est soit « verrouillé » soit « déverrouillé ». Il est créé dans un état déverrouillé. Il a deux méthodes, acquire()
et release()
. Lorsque l'état est déverrouillé, acquire()
verrouille et se termine immédiatement. Lorsque l'état est verrouillé, acquire()
bloque jusqu'à ce qu'un appel à release()
provenant d'un autre fil d'exécution le déverrouille. À ce moment acquire()
le verrouille à nouveau et rend la main. La méthode release()
ne doit être appelée que si le verrou est verrouillé, elle le déverrouille alors et se termine immédiatement. Déverrouiller un verrou qui n'est pas verrouillé provoque une RuntimeError
.
Locks also support the context management protocol.
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.
- class threading.Lock¶
The class implementing primitive lock objects. Once a thread has acquired a lock, subsequent attempts to acquire it block, until it is released; any thread may release it.
Modifié dans la version 3.13:
Lock
is now a class. In earlier Pythons,Lock
was a factory function which returned an instance of the underlying private lock type.- acquire(blocking=True, timeout=-1)¶
Acquiert un verrou, bloquant ou non bloquant.
When invoked with the blocking argument set to
True
(the default), block until the lock is unlocked, then set it to locked and returnTrue
.When invoked with the blocking argument set to
False
, do not block. If a call with blocking set toTrue
would block, returnFalse
immediately; otherwise, set the lock to locked and returnTrue
.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. A timeout argument of
-1
specifies an unbounded wait. It is forbidden to specify a timeout when blocking isFalse
.The return value is
True
if the lock is acquired successfully,False
if not (for example if the timeout expired).Modifié dans la version 3.2: Le paramètre timeout est nouveau.
Modifié dans la version 3.2: Lock acquisition can now be interrupted by signals on POSIX if the underlying threading implementation supports it.
- release()¶
Release a lock. This can be called from any thread, not only the thread which has acquired the 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.
When invoked on an unlocked lock, a
RuntimeError
is raised.Il n'y a pas de valeur de retour.
- locked()¶
Return
True
if the lock is acquired.
RLock Objects¶
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.
Threads call a lock's acquire()
method to lock it,
and its release()
method to unlock it.
Note
Reentrant locks support the context management protocol,
so it is recommended to use with
instead of manually calling
acquire()
and release()
to handle acquiring and releasing the lock for a block of code.
RLock's acquire()
/release()
call pairs may be nested,
unlike Lock's acquire()
/release()
. Only the final
release()
(the release()
of the outermost pair) resets
the lock to an unlocked state and allows another thread blocked in
acquire()
to proceed.
acquire()
/release()
must be used in pairs: each acquire
must have a release in the thread that has acquired the lock. Failing to
call release as many times the lock has been acquired can lead to deadlock.
- class threading.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.
Note that
RLock
is actually a factory function which returns an instance of the most efficient version of the concrete RLock class that is supported by the platform.- acquire(blocking=True, timeout=-1)¶
Acquiert un verrou, bloquant ou non bloquant.
Voir aussi
- Using RLock as a context manager
Recommended over manual
acquire()
andrelease()
calls whenever practical.
When invoked with the blocking argument set to
True
(the default):If no thread owns the lock, acquire the lock and return immediately.
If another thread owns the lock, block until we are able to acquire lock, or timeout, if set to a positive float value.
If the same thread owns the lock, acquire the lock again, and return immediately. This is the difference between
Lock
andRLock
;Lock
handles this case the same as the previous, blocking until the lock can be acquired.
When invoked with the blocking argument set to
False
:If no thread owns the lock, acquire the lock and return immediately.
If another thread owns the lock, return immediately.
If the same thread owns the lock, acquire the lock again and return immediately.
In all cases, if the thread was able to acquire the lock, return
True
. If the thread was unable to acquire the lock (i.e. if not blocking or the timeout was reached) returnFalse
.If called multiple times, failing to call
release()
as many times may lead to deadlock. Consider usingRLock
as a context manager rather than calling acquire/release directly.Modifié dans la version 3.2: Le paramètre timeout est nouveau.
- release()¶
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 not acquired.Il n'y a pas de valeur de retour.
Condition Objects¶
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. The lock is part of the condition object: you don't have to track it separately.
A condition variable obeys the context management protocol:
using the with
statement acquires the associated lock for the duration of
the enclosed block. The acquire()
and
release()
methods also call the corresponding methods of
the associated lock.
Other methods must be called with the associated lock held. The
wait()
method releases the lock, and then blocks until
another thread awakens it by calling notify()
or
notify_all()
. Once awakened, wait()
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 notify_all()
method wakes up all threads waiting for the condition variable.
Note: the notify()
and notify_all()
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 notify_all()
finally relinquishes ownership of the lock.
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 notify_all()
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
with cv:
while not an_item_is_available():
cv.wait()
get_an_available_item()
# Produce one item
with cv:
make_an_item_available()
cv.notify()
The while
loop checking for the application's condition is necessary
because wait()
can return after an arbitrary long time,
and the condition which prompted the notify()
call may
no longer hold true. This is inherent to multi-threaded programming. The
wait_for()
method can be used to automate the condition
checking, and eases the computation of timeouts:
# Consume an item
with cv:
cv.wait_for(an_item_is_available)
get_an_available_item()
To choose between notify()
and notify_all()
,
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.
- class threading.Condition(lock=None)¶
This class implements condition variable objects. 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 aLock
orRLock
object, and it is used as the underlying lock. Otherwise, a newRLock
object is created and used as the underlying lock.Modifié dans la version 3.3: changed from a factory function to a class.
- acquire(*args)¶
Acquire the underlying lock. This method calls the corresponding method on the underlying lock; the return value is whatever that method returns.
- release()¶
Release the underlying lock. This method calls the corresponding method on the underlying lock; there is no return value.
- wait(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()
ornotify_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 itsrelease()
method, since this may not actually unlock the lock when it was acquired multiple times recursively. Instead, an internal interface of theRLock
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.The return value is
True
unless a given timeout expired, in which case it isFalse
.Modifié dans la version 3.2: Previously, the method always returned
None
.
- wait_for(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.
This utility method may call
wait()
repeatedly until the predicate is satisfied, or until a timeout occurs. The return value is the last return value of the predicate and will evaluate toFalse
if the method timed out.Ignoring the timeout feature, calling this method is roughly equivalent to writing:
while not predicate(): cv.wait()
Therefore, the same rules apply as with
wait()
: The lock must be held when called and is re-acquired on return. The predicate is evaluated with the lock held.Ajouté dans la version 3.2.
- notify(n=1)¶
By default, wake up one thread 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.
The current implementation wakes up exactly n threads, if at least n threads are waiting. However, it's not safe to rely on this behavior. A future, optimized implementation may occasionally wake up more than n threads.
Note: an awakened thread does not actually return from its
wait()
call until it can reacquire the lock. Sincenotify()
does not release the lock, its caller should.
- notify_all()¶
Wake up all threads waiting on this condition. This method acts like
notify()
, but wakes up all waiting threads instead of one. If the calling thread has not acquired the lock when this method is called, aRuntimeError
is raised.The method
notifyAll
is a deprecated alias for this method.
Semaphore Objects¶
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 the names 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()
.
Semaphores also support the context management protocol.
- class threading.Semaphore(value=1)¶
This class implements semaphore objects. A semaphore manages an atomic counter representing the number of
release()
calls minus the number ofacquire()
calls, plus an initial value. Theacquire()
method blocks if necessary until it can return without making the counter negative. If not given, value defaults to 1.The optional argument gives the initial value for the internal counter; it defaults to
1
. If the value given is less than 0,ValueError
is raised.Modifié dans la version 3.3: changed from a factory function to a class.
- acquire(blocking=True, timeout=None)¶
Acquire a semaphore.
When invoked without arguments:
If the internal counter is larger than zero on entry, decrement it by one and return
True
immediately.If the internal counter is zero on entry, block until awoken by a call to
release()
. Once awoken (and the counter is greater than 0), decrement the counter by 1 and returnTrue
. Exactly one thread will be awoken by each call torelease()
. The order in which threads are awoken should not be relied on.
When invoked with blocking set to
False
, do not block. If a call without an argument would block, returnFalse
immediately; otherwise, do the same thing as when called without arguments, and returnTrue
.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, returnFalse
. ReturnTrue
otherwise.Modifié dans la version 3.2: Le paramètre timeout est nouveau.
- release(n=1)¶
Release a semaphore, incrementing the internal counter by n. When it was zero on entry and other threads are waiting for it to become larger than zero again, wake up n of those threads.
Modifié dans la version 3.9: Added the n parameter to release multiple waiting threads at once.
- class threading.BoundedSemaphore(value=1)¶
Class implementing bounded semaphore objects. 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.Modifié dans la version 3.3: changed from a factory function to a class.
Semaphore
Example¶
Semaphores are often used to guard resources with limited capacity, for example, a database server. In any situation where the size of the resource is fixed, you should use a bounded semaphore. Before spawning any worker threads, your main thread would initialize the semaphore:
maxconnections = 5
# ...
pool_sema = BoundedSemaphore(value=maxconnections)
Once spawned, worker threads call the semaphore's acquire and release methods when they need to connect to the server:
with pool_sema:
conn = connectdb()
try:
# ... use connection ...
finally:
conn.close()
The use of a bounded semaphore reduces the chance that a programming error which causes the semaphore to be released more than it's acquired will go undetected.
Event Objects¶
This is one of the simplest mechanisms for communication between threads: one thread signals an event and other 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.
- class threading.Event¶
Class implementing event objects. An event manages a flag that can be set to true with the
set()
method and reset to false with theclear()
method. Thewait()
method blocks until the flag is true. The flag is initially false.Modifié dans la version 3.3: changed from a factory function to a class.
- is_set()¶
Return
True
if and only if the internal flag is true.The method
isSet
is a deprecated alias for this method.
- set()¶
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.
- clear()¶
Reset the internal flag to false. Subsequently, threads calling
wait()
will block untilset()
is called to set the internal flag to true again.
- wait(timeout=None)¶
Block as long as the internal flag is false and the timeout, if given, has not expired. The return value represents the reason that this blocking method returned;
True
if returning because the internal flag is set to true, orFalse
if a timeout is given and the internal flag did not become true within the given wait time.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.Modifié dans la version 3.1: Previously, the method always returned
None
.
Timer Objects¶
This class represents an action that should be run only after a certain amount
of time has passed --- a timer. Timer
is a subclass of Thread
and as such also functions as an example of creating custom threads.
Timers are started, as with threads, by calling their Timer.start
method. The timer can be stopped (before its action has begun) by calling the
cancel()
method. The interval the timer will wait before
executing its action may not be exactly the same as the interval specified by
the user.
Par exemple :
def hello():
print("hello, world")
t = Timer(30.0, hello)
t.start() # after 30 seconds, "hello, world" will be printed
- class threading.Timer(interval, function, args=None, kwargs=None)¶
Create a timer that will run function with arguments args and keyword arguments kwargs, after interval seconds have passed. If args is
None
(the default) then an empty list will be used. If kwargs isNone
(the default) then an empty dict will be used.Modifié dans la version 3.3: changed from a factory function to a class.
- cancel()¶
Stop the timer, and cancel the execution of the timer's action. This will only work if the timer is still in its waiting stage.
Barrier Objects¶
Ajouté dans la version 3.2.
This class provides a simple synchronization primitive for use by a fixed number
of threads that need to wait for each other. Each of the threads tries to pass
the barrier by calling the wait()
method and will block until
all of the threads have made their wait()
calls. At this point,
the threads are released simultaneously.
The barrier can be reused any number of times for the same number of threads.
As an example, here is a simple way to synchronize a client and server thread:
b = Barrier(2, timeout=5)
def server():
start_server()
b.wait()
while True:
connection = accept_connection()
process_server_connection(connection)
def client():
b.wait()
while True:
connection = make_connection()
process_client_connection(connection)
- class threading.Barrier(parties, action=None, timeout=None)¶
Create a barrier object for parties number of threads. An action, when provided, is a callable to be called by one of the threads when they are released. timeout is the default timeout value if none is specified for the
wait()
method.- wait(timeout=None)¶
Pass the barrier. When all the threads party to the barrier have called this function, they are all released simultaneously. If a timeout is provided, it is used in preference to any that was supplied to the class constructor.
The return value is an integer in the range 0 to parties -- 1, different for each thread. This can be used to select a thread to do some special housekeeping, e.g.:
i = barrier.wait() if i == 0: # Only one thread needs to print this print("passed the barrier")
If an action was provided to the constructor, one of the threads will have called it prior to being released. Should this call raise an error, the barrier is put into the broken state.
If the call times out, the barrier is put into the broken state.
This method may raise a
BrokenBarrierError
exception if the barrier is broken or reset while a thread is waiting.
- reset()¶
Return the barrier to the default, empty state. Any threads waiting on it will receive the
BrokenBarrierError
exception.Note that using this function may require some external synchronization if there are other threads whose state is unknown. If a barrier is broken it may be better to just leave it and create a new one.
- abort()¶
Put the barrier into a broken state. This causes any active or future calls to
wait()
to fail with theBrokenBarrierError
. Use this for example if one of the threads needs to abort, to avoid deadlocking the application.It may be preferable to simply create the barrier with a sensible timeout value to automatically guard against one of the threads going awry.
- parties¶
The number of threads required to pass the barrier.
- n_waiting¶
The number of threads currently waiting in the barrier.
- broken¶
A boolean that is
True
if the barrier is in the broken state.
- exception threading.BrokenBarrierError¶
This exception, a subclass of
RuntimeError
, is raised when theBarrier
object is reset or broken.
Using locks, conditions, and semaphores in the with
statement¶
All of the objects provided by this module that have acquire
and
release
methods can be used as context managers for a with
statement. The acquire
method will be called when the block is
entered, and release
will be called when the block is exited. Hence,
the following snippet:
with some_lock:
# do something...
est équivalente à :
some_lock.acquire()
try:
# do something...
finally:
some_lock.release()
Currently, Lock
, RLock
, Condition
,
Semaphore
, and BoundedSemaphore
objects may be used as
with
statement context managers.