Thread-local data¶

Thread-local data is data whose values are thread specific. If youhave data that you want to be local to a thread, create alocal object and use its attributes:

>>>mydata=local()>>>mydata.number=42>>>mydata.number42

You can also access thelocal-object's dictionary:

>>>mydata.__dict__{'number': 42}>>>mydata.__dict__.setdefault('widgets',[])[]>>>mydata.widgets[]

If we access the data in a different thread:

>>>log=[]>>>deff():...items=sorted(mydata.__dict__.items())...log.append(items)...mydata.number=11...log.append(mydata.number)>>>importthreading>>>thread=threading.Thread(target=f)>>>thread.start()>>>thread.join()>>>log[[], 11]

we get different data. Furthermore, changes made in the other threaddon't affect data seen in this thread:

>>>mydata.number42

Of course, values you get from alocal object, including their__dict__ attribute, are for whatever thread was currentat the time the attribute was read. For that reason, you generallydon't want to save these values across threads, as they apply only tothe thread they came from.

You can create customlocal objects by subclassing thelocal class:

>>>classMyLocal(local):...number=2...def__init__(self,/,**kw):...self.__dict__.update(kw)...defsquared(self):...returnself.number**2

This can be useful to support default values, methods andinitialization. Note that if you define an__init__()method, it will be called each time thelocal object is usedin a separate thread. This is necessary to initialize each thread'sdictionary.

現在如果我們建立一個local 物件：

>>>mydata=MyLocal(color='red')

會有一個預設的數字：

>>>mydata.number2

和一個初始顏色：

>>>mydata.color'red'>>>delmydata.color

和一個操作資料的方法：

>>>mydata.squared()4

As before, we can access the data in a separate thread:

>>>log=[]>>>thread=threading.Thread(target=f)>>>thread.start()>>>thread.join()>>>log[[('color', 'red')], 11]

without affecting this thread's data:

>>>mydata.number2>>>mydata.colorTraceback (most recent call last):...AttributeError:'MyLocal' object has no attribute 'color'

Note that subclasses can define__slots__, but they are notthread local. They are shared across threads:

>>>classMyLocal(local):...__slots__='number'>>>mydata=MyLocal()>>>mydata.number=42>>>mydata.color='red'

So, the separate thread:

>>>thread=threading.Thread(target=f)>>>thread.start()>>>thread.join()

affects what we see:

>>>mydata.number11

classthreading.local¶

A class that represents thread-local data.

Thread objects¶

TheThread class represents an activity that is run in a separatethread of control. There are two ways to specify the activity: by passing acallable object to the constructor, or by overriding therun()method in a subclass. No other methods (except for the constructor) should beoverridden in a subclass. In other words,only override the__init__() andrun() methods of this class.

Once a thread object is created, its activity must be started by calling thethread'sstart() method. This invokes therun()method in a separate thread of control.

Once the thread's activity is started, the thread is considered 'alive'. Itstops being alive when itsrun() method terminates -- eithernormally, or by raising an unhandled exception. Theis_alive()method tests whether the thread is alive.

Other threads can call a thread'sjoin() method. This blocksthe calling thread until the thread whosejoin() method iscalled is terminated.

A thread has a name. The name can be passed to the constructor, and read orchanged through thename attribute.

If therun() method raises an exception,threading.excepthook() is called to handle it. By default,threading.excepthook() ignores silentlySystemExit.

A thread can be flagged as a "daemon thread". The significance of this flag isthat the entire Python program exits when only daemon threads are left. Theinitial value is inherited from the creating thread. The flag can be setthrough thedaemon property or thedaemon constructorargument.

There is a "main thread" object; this corresponds to the initial thread ofcontrol in the Python program. It is not a daemon thread.

There is the possibility that "dummy thread objects" are created. These arethread objects corresponding to "alien threads", which are threads of controlstarted outside the threading module, such as directly from C code. Dummythread objects have limited functionality; they are always considered alive anddaemonic, and cannot bejoined. They are never deleted,since it is impossible to detect the termination of alien threads.

classthreading.Thread(group=None,target=None,name=None,args=(),kwargs={},*,daemon=None)¶

This constructor should always be called with keyword arguments. Argumentsare:

group should beNone; reserved for future extension when aThreadGroup class is implemented.

target is the callable object to be invoked by therun() method.Defaults toNone, meaning nothing is called.

name is the thread name. By default, a unique name is constructedof the form "Thread-N" whereN is a small decimal number,or "Thread-N (target)" where "target" istarget.__name__ if thetarget argument is specified.

args is a list or tuple of arguments for the target invocation. Defaults to().

kwargs is a dictionary of keyword arguments for the target invocation.Defaults to{}.

If notNone,daemon explicitly sets whether the thread is daemonic.IfNone (the default), the daemonic property is inherited from thecurrent thread.

If the subclass overrides the constructor, it must make sure to invoke thebase class constructor (Thread.__init__()) before doing anything else tothe thread.

在 3.3 版的變更:新增daemon 參數。

在 3.10 版的變更:Use thetarget name ifname argument is omitted.

start()¶

Start the thread's activity.

It must be called at most once per thread object. It arranges for theobject'srun() method to be invoked in a separate threadof control.

This method will raise aRuntimeError if called more than onceon the same thread object.

run()¶

Method representing the thread's activity.

You may override this method in a subclass. The standardrun()method invokes the callable object passed to the object's constructor asthetarget argument, if any, with positional and keyword arguments takenfrom theargs andkwargs arguments, respectively.

Using list or tuple as theargs argument which passed to theThreadcould achieve the same effect.

舉例來說：

>>>fromthreadingimportThread>>>t=Thread(target=print,args=[1])>>>t.run()1>>>t=Thread(target=print,args=(1,))>>>t.run()1

join(timeout=None)¶

Wait until the thread terminates. This blocks the calling thread untilthe thread whosejoin() method is called terminates -- eithernormally or through an unhandled exception -- or until the optionaltimeout occurs.

When thetimeout argument is present and notNone, it should be afloating-point number specifying a timeout for the operation in seconds(or fractions thereof). Asjoin() always returnsNone,you must callis_alive() afterjoin() todecide whether a timeout happened -- if the thread is still alive, thejoin() call timed out.

When thetimeout argument is not present orNone, the operation willblock until the thread terminates.

A thread can be joined many times.

join() raises aRuntimeError if an attempt is madeto join the current thread as that would cause a deadlock. It is alsoan error tojoin() a thread before it has been startedand attempts to do so raise the same exception.

name¶

A string used for identification purposes only. It has no semantics.Multiple threads may be given the same name. The initial name is set bythe constructor.

getName()¶

setName()¶

Deprecated getter/setter API forname; use it directly as aproperty instead.

在 3.10 版之後被棄用.

ident¶

The 'thread identifier' of this thread orNone if the thread has notbeen started. This is a nonzero integer. See theget_ident()function. Thread identifiers may be recycled when a thread exits andanother thread is created. The identifier is available even after thethread has exited.

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 notbeen started. See theget_native_id() function.This value may be used to uniquely identify this particular threadsystem-wide (until the thread terminates, after which the valuemay be recycled by the OS).

備註

Similar to Process IDs, Thread IDs are only valid (guaranteed uniquesystem-wide) from the time the thread is created until the threadhas been terminated.

適用: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD, AIX, DragonFlyBSD.

在 3.8 版被加入.

is_alive()¶

Return whether the thread is alive.

This method returnsTrue just before therun() methodstarts until just after therun() method terminates. Themodule functionenumerate() returns a list of all alive threads.

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 inheritedfrom the creating thread; the main thread is not a daemon thread andtherefore all threads created in the main thread default todaemon =False.

The entire Python program exits when no alive non-daemon threads are left.

isDaemon()¶

setDaemon()¶

Deprecated getter/setter API fordaemon; use it directly as aproperty instead.

在 3.10 版之後被棄用.

Lock objects¶

原始鎖 (primitive lock) 是一種同步原語 (synchronization primitive)，在鎖定時不屬於特定執行緒。在 Python 中，它是目前可用的最低階同步原語，直接由_thread 擴充模組實作。

原始鎖會處於兩種狀態之一：「鎖定 (locked)」或「未鎖定 (unclocked)」，建立時會處於未鎖定狀態。它有兩個基本方法acquire() 和release()。當狀態為未鎖定時，acquire() 會將狀態變更為鎖定並立即回傳。當狀態被鎖定時，acquire() 會阻塞 (block)，直到另一個執行緒中對release() 的呼叫將其更改為未鎖定狀態，然後acquire() 呼叫會將其重置為鎖定並回傳。release() 方法只能在鎖定狀態下呼叫；它將狀態更改為未鎖定並立即回傳。如果嘗試釋放未鎖定的鎖，則會引發RuntimeError。

鎖也支援情境管理協定。

當多個執行緒阻塞在acquire() 中等待狀態轉變為未鎖定，此時若呼叫release() 將狀態重置為未鎖定，則只會有一個執行緒繼續進行；哪一個等待執行緒會繼續進行是未定義的，並且可能因實作而異。

所有方法均以最小不可分割的操作方式 (atomically) 執行。

classthreading.Lock¶

實作原始鎖物件的類別。一旦執行緒獲得了鎖，後續再嘗試獲得它就會被阻塞，直到鎖被釋放；任何執行緒都可以去釋放它。

在 3.13 版的變更:Lock 現在是一個類別。在早期的 Python 中，Lock 是一個會回傳底層私有鎖型別實例的工廠函式。

acquire(blocking=True,timeout=-1)¶

阻塞或非阻塞地取得鎖。

當以blocking 引數設為True（預設值）來叫用，將會阻塞直到鎖被解鎖，然後將其設為鎖定並回傳True。

當以blocking 引數設為False 叫用則不會阻塞。如果blocking 設定為True 的呼叫會阻塞，則立即回傳False；否則將鎖設為鎖定並回傳True。

當使用設定為正值的浮點timeout 引數進行叫用，只要持續無法取得鎖，最多會阻塞timeout 指定的秒數。-1 的timeout 引數代表指定為不會停止的等待。當blocking 為False 時禁止指定timeout。

如果成功取得鎖，則回傳值為True，否則回傳值為False（例如像是timeout 已逾期）。

在 3.2 版的變更:新的timeout 參數。

在 3.2 版的變更:如果底層執行緒實作支援的話，鎖的取得現在可以被 POSIX 上的訊號中斷。

release()¶

釋放鎖。這可以從任何執行緒呼叫，而不是只有獲得鎖的執行緒。

當鎖被鎖定時，將其重置為未鎖定然後回傳。如果任何其他執行緒在等待鎖被解鎖時被阻塞，只允許其中一個執行緒繼續進行。

當在未鎖定的鎖上叫用時，會引發RuntimeError

沒有回傳值。

locked()¶

如果有取得了鎖，則回傳True。

RLock objects¶

可重入鎖 (reentrant lock) 是一種同步原語，同一執行緒可以多次取得它。在內部，除了原始鎖使用的鎖定/未鎖定狀態之外，它還使用「所屬執行緒 (owning thread)」和「遞迴等級 (recursion level)」的概念。在鎖定狀態下，某個執行緒會擁有鎖；在未鎖定狀態下則沒有執行緒擁有它。

執行緒呼叫鎖的acquire() 方法來鎖定它，並呼叫它的release() 方法來解鎖它。

RLock 的acquire()/release() 呼叫成對組合可以嵌套使用，這與 Lock 的acquire()/release() 不同。只有最後一個release()（最外面一對的release()）會將鎖重置為未鎖定狀態，並允許在acquire() 中阻塞的另一個執行緒繼續進行。

acquire()/release() 必須成對使用：每次獲得都必須在已獲得鎖的執行緒中有一個釋放。如果鎖釋放的次數不能和取得的次數一樣的話，可能會導致死鎖 (deadlock)。

classthreading.RLock¶

此類別實作了可重入鎖物件。可重入鎖必須由獲得它的執行緒釋放。一旦一個執行緒獲得了可重入鎖，同一個執行緒可以再次獲得它而不會阻塞；執行緒每次獲得它也都必須釋放它一次。

請注意，RLock 實際上是一個工廠函式，它會回傳平台有支援的特定 RLock 類別的最高效率版本的實例。

acquire(blocking=True,timeout=-1)¶

阻塞或非阻塞地取得鎖。

也參考

將 RLock 用作為情境管理器

若是使用場景合理，和手動呼叫acquire() 和release() 相比，會是更為推薦的使用方式。

當以blocking 引數設為True（預設值）來呼叫：

• 如果沒有執行緒擁有鎖，則獲得鎖並立即回傳。

• 如果另一個執行緒擁有鎖，則阻塞直到能夠取得鎖，或者達到timeout（如果設定為正浮點值）。

• 如果同一個執行緒擁有鎖，則再次取得鎖，並立即回傳。這就是Lock 和RLock 之間的差別；Lock 處理方式與上一種情況相同，會阻塞直到能夠取得鎖。

當以blocking 引數設為False 來呼叫：

• 如果沒有執行緒擁有鎖，則獲得鎖並立即回傳。

• 如果另一個執行緒擁有該鎖，則立即回傳。

• 如果同一個執行緒擁有鎖，則再次取得鎖並立即回傳。

在所有情況下，如果執行緒能夠取得鎖則回傳True。如果執行緒無法取得鎖（即沒有阻塞或已達超時限制）則回傳False。

如果多次呼叫，又未能呼叫相同次數的release()，則可能會導致死鎖。考慮將RLock 作為情境管理器使用，而不是直接呼叫 acquire/release。

在 3.2 版的變更:新的timeout 參數。

release()¶

釋放鎖並減少遞迴等級。如果被減至零，則將鎖重置為未鎖定（不屬於任何執行緒），並且如果任何其他執行緒被阻塞以等待鎖變成未鎖定狀態，則僅允許其中一個執行緒繼續進行。如果遞減後遞迴等級仍然非零，則鎖會保持鎖定並由呼叫它的執行緒所擁有。

僅當呼叫的執行緒擁有鎖時才能呼叫此方法。如果在未取得鎖時呼叫此方法則會引發RuntimeError。

沒有回傳值。

Condition objects¶

A condition variable is always associated with some kind of lock; this can bepassed in or one will be created by default. Passing one in is useful whenseveral condition variables must share the same lock. The lock is part ofthe condition object: you don't have to track it separately.

A condition variable obeys thecontext management protocol:using thewith statement acquires the associated lock for the duration ofthe enclosed block. Theacquire() andrelease() methods also call the corresponding methods ofthe associated lock.

Other methods must be called with the associated lock held. Thewait() method releases the lock, and then blocks untilanother thread awakens it by callingnotify() ornotify_all(). Once awakened,wait()re-acquires the lock and returns. It is also possible to specify a timeout.

Thenotify() method wakes up one of the threads waiting forthe condition variable, if any are waiting. Thenotify_all()method wakes up all threads waiting for the condition variable.

Note: thenotify() andnotify_all() methodsdon't release the lock; this means that the thread or threads awakened willnot return from theirwait() call immediately, but only whenthe thread that callednotify() ornotify_all()finally relinquishes ownership of the lock.

The typical programming style using condition variables uses the lock tosynchronize access to some shared state; threads that are interested in aparticular change of state callwait() repeatedly until theysee the desired state, while threads that modify the state callnotify() ornotify_all() when they changethe state in such a way that it could possibly be a desired state for oneof the waiters. For example, the following code is a genericproducer-consumer situation with unlimited buffer capacity:

# Consume one itemwithcv:whilenotan_item_is_available():cv.wait()get_an_available_item()# Produce one itemwithcv:make_an_item_available()cv.notify()

Thewhile loop checking for the application's condition is necessarybecausewait() can return after an arbitrary long time,and the condition which prompted thenotify() call mayno longer hold true. This is inherent to multi-threaded programming. Thewait_for() method can be used to automate the conditionchecking, and eases the computation of timeouts:

# Consume an itemwithcv:cv.wait_for(an_item_is_available)get_an_available_item()

To choose betweennotify() andnotify_all(),consider whether one state change can be interesting for only one or severalwaiting threads. E.g. in a typical producer-consumer situation, adding oneitem to the buffer only needs to wake up one consumer thread.

classthreading.Condition(lock=None)¶

This class implements condition variable objects. A condition variableallows one or more threads to wait until they are notified by another thread.

If thelock argument is given and notNone, it must be aLockorRLock object, and it is used as the underlying lock. Otherwise,a newRLock object is created and used as the underlying lock.

在 3.3 版的變更:changed from a factory function to a class.

acquire(*args)¶

Acquire the underlying lock. This method calls the corresponding method onthe underlying lock; the return value is whatever that method returns.

release()¶

Release the underlying lock. This method calls the corresponding method onthe underlying lock; there is no return value.

wait(timeout=None)¶

Wait until notified or until a timeout occurs. If the calling thread hasnot acquired the lock when this method is called, aRuntimeError israised.

This method releases the underlying lock, and then blocks until it isawakened by anotify() ornotify_all() call for the samecondition variable in another thread, or until the optional timeoutoccurs. Once awakened or timed out, it re-acquires the lock and returns.

When thetimeout argument is present and notNone, it should be afloating-point number specifying a timeout for the operation in seconds(or fractions thereof).

When the underlying lock is anRLock, it is not released usingitsrelease() method, since this may not actually unlock the lockwhen it was acquired multiple times recursively. Instead, an internalinterface of theRLock class is used, which really unlocks iteven when it has been recursively acquired several times. Another internalinterface is then used to restore the recursion level when the lock isreacquired.

The return value isTrue unless a giventimeout expired, in whichcase it isFalse.

在 3.2 版的變更:Previously, the method always returnedNone.

wait_for(predicate,timeout=None)¶

Wait until a condition evaluates to true.predicate should be acallable which result will be interpreted as a boolean value.Atimeout may be provided giving the maximum time to wait.

This utility method may callwait() repeatedly until the predicateis satisfied, or until a timeout occurs. The return value isthe 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 towriting:

whilenotpredicate():cv.wait()

Therefore, the same rules apply as withwait(): The lock must beheld when called and is re-acquired on return. The predicate is evaluatedwith the lock held.

在 3.2 版被加入.

notify(n=1)¶

By default, wake up one thread waiting on this condition, if any. If thecalling thread has not acquired the lock when this method is called, aRuntimeError is raised.

This method wakes up at mostn of the threads waiting for the conditionvariable; it is a no-op if no threads are waiting.

The current implementation wakes up exactlyn threads, if at leastnthreads are waiting. However, it's not safe to rely on this behavior.A future, optimized implementation may occasionally wake up more thann threads.

Note: an awakened thread does not actually return from itswait()call until it can reacquire the lock. Sincenotify() does notrelease the lock, its caller should.

notify_all()¶

Wake up all threads waiting on this condition. This method acts likenotify(), but wakes up all waiting threads instead of one. If thecalling thread has not acquired the lock when this method is called, aRuntimeError is raised.

The methodnotifyAll is a deprecated alias for this method.

Semaphore objects¶

This is one of the oldest synchronization primitives in the history of computerscience, invented by the early Dutch computer scientist Edsger W. Dijkstra (heused the namesP() andV() instead ofacquire() andrelease()).

A semaphore manages an internal counter which is decremented by eachacquire() call and incremented by eachrelease()call. The counter can never go below zero; whenacquire()finds that it is zero, it blocks, waiting until some other thread callsrelease().

Semaphores also support thecontext management protocol.

classthreading.Semaphore(value=1)¶

This class implements semaphore objects. A semaphore manages an atomiccounter representing the number ofrelease() calls minus the number ofacquire() calls, plus an initial value. Theacquire() methodblocks if necessary until it can return without making the counter negative.If not given,value defaults to 1.

The optional argument gives the initialvalue for the internal counter; itdefaults to1. If thevalue given is less than 0,ValueError israised.

在 3.3 版的變更: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 byone and returnTrue immediately.

• If the internal counter is zero on entry, block until awoken by a call torelease(). Once awoken (and the counter is greaterthan 0), decrement the counter by 1 and returnTrue. Exactly onethread will be awoken by each call torelease(). Theorder in which threads are awoken should not be relied on.

When invoked withblocking set toFalse, do not block. If a callwithout an argument would block, returnFalse immediately; otherwise, dothe same thing as when called without arguments, and returnTrue.

When invoked with atimeout other thanNone, it will block for atmosttimeout seconds. If acquire does not complete successfully inthat interval, returnFalse. ReturnTrue otherwise.

在 3.2 版的變更:新的timeout 參數。

release(n=1)¶

Release a semaphore, incrementing the internal counter byn. When itwas zero on entry and other threads are waiting for it to become largerthan zero again, wake upn of those threads.

在 3.9 版的變更:Added then parameter to release multiple waiting threads at once.

classthreading.BoundedSemaphore(value=1)¶

Class implementing bounded semaphore objects. A bounded semaphore checks tomake sure its current value doesn't exceed its initial value. If it does,ValueError is raised. In most situations semaphores are used to guardresources with limited capacity. If the semaphore is released too many timesit's a sign of a bug. If not given,value defaults to 1.

在 3.3 版的變更: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, yourmain thread would initialize the semaphore:

maxconnections=5# ...pool_sema=BoundedSemaphore(value=maxconnections)

Once spawned, worker threads call the semaphore's acquire and release methodswhen they need to connect to the server:

withpool_sema:conn=connectdb()try:# ... 使用該連線 ...finally:conn.close()

The use of a bounded semaphore reduces the chance that a programming error whichcauses 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: onethread signals an event and other threads wait for it.

An event object manages an internal flag that can be set to true with theset() method and reset to false with theclear()method. Thewait() method blocks until the flag is true.

classthreading.Event¶

Class implementing event objects. An event manages a flag that can be set totrue with theset() method and reset to false with theclear() method. Thewait() method blocks until the flag is true.The flag is initially false.

在 3.3 版的變更:changed from a factory function to a class.

is_set()¶

ReturnTrue if and only if the internal flag is true.

The methodisSet is a deprecated alias for this method.

set()¶

Set the internal flag to true. All threads waiting for it to become trueare awakened. Threads that callwait() once the flag is true willnot block at all.

clear()¶

Reset the internal flag to false. Subsequently, threads callingwait() will block untilset() is called to set the internalflag 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 thereason that this blocking method returned;True if returning becausethe internal flag is set to true, orFalse if a timeout is given andthe internal flag did not become true within the given wait time.

When the timeout argument is present and notNone, it should be afloating-point number specifying a timeout for the operation in seconds,or fractions thereof.

在 3.1 版的變更:Previously, the method always returnedNone.

Timer objects¶

This class represents an action that should be run only after a certain amountof time has passed --- a timer.Timer is a subclass ofThreadand as such also functions as an example of creating custom threads.

Timers are started, as with threads, by calling theirTimer.startmethod. The timer can be stopped (before its action has begun) by calling thecancel() method. The interval the timer will wait beforeexecuting its action may not be exactly the same as the interval specified bythe user.

舉例來說：

defhello():print("hello, world")t=Timer(30.0,hello)t.start()# 30 秒後會印出 "hello, world"

classthreading.Timer(interval,function,args=None,kwargs=None)¶

Create a timer that will runfunction with argumentsargs and keywordargumentskwargs, afterinterval seconds have passed.Ifargs isNone (the default) then an empty list will be used.Ifkwargs isNone (the default) then an empty dict will be used.

在 3.3 版的變更:changed from a factory function to a class.

cancel()¶

Stop the timer, and cancel the execution of the timer's action. This willonly work if the timer is still in its waiting stage.

Barrier objects¶

This class provides a simple synchronization primitive for use by a fixed numberof threads that need to wait for each other. Each of the threads tries to passthe barrier by calling thewait() method and will block untilall of the threads have made theirwait() 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)defserver():start_server()b.wait()whileTrue:connection=accept_connection()process_server_connection(connection)defclient():b.wait()whileTrue:connection=make_connection()process_client_connection(connection)

classthreading.Barrier(parties,action=None,timeout=None)¶

Create a barrier object forparties number of threads. Anaction, whenprovided, is a callable to be called by one of the threads when they arereleased.timeout is the default timeout value if none is specified forthewait() method.

wait(timeout=None)¶

Pass the barrier. When all the threads party to the barrier have calledthis function, they are all released simultaneously. If atimeout isprovided, it is used in preference to any that was supplied to the classconstructor.

The return value is an integer in the range 0 toparties -- 1, differentfor each thread. This can be used to select a thread to do some specialhousekeeping, e.g.:

i=barrier.wait()ifi==0:# 只會有一個執行緒會印出這個print("passed the barrier")

If anaction was provided to the constructor, one of the threads willhave 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 aBrokenBarrierError exception if thebarrier is broken or reset while a thread is waiting.

reset()¶

Return the barrier to the default, empty state. Any threads waiting on itwill receive theBrokenBarrierError exception.

Note that using this function may require some externalsynchronization if there are other threads whose state is unknown. If abarrier 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 futurecalls towait() to fail with theBrokenBarrierError. Usethis for example if one of the threads needs to abort, to avoid deadlocking theapplication.

It may be preferable to simply create the barrier with a sensibletimeout value to automatically guard against one of the threads goingawry.

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 isTrue if the barrier is in the broken state.

exceptionthreading.BrokenBarrierError¶

This exception, a subclass ofRuntimeError, is raised when theBarrier object is reset or broken.