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.

Now if we create alocal object:

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

we have a default number:

>>>mydata.number2

an initial color:

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

And a method that operates on the data:

>>>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.

Changed in version 3.3:Added thedaemon parameter.

Changed in version 3.10: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.

Example:

>>>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.

Deprecated since version 3.10.

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).

Note

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

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

Added in version 3.8.

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.

Deprecated since version 3.10.

Lock objects¶

A primitive lock is a synchronization primitive that is not owned by aparticular thread when locked. In Python, it is currently the lowest levelsynchronization primitive available, implemented directly by the_threadextension module.

A primitive lock is in one of two states, “locked” or “unlocked”. It is createdin the unlocked state. It has two basic methods,acquire() andrelease(). When the state is unlocked,acquire()changes the state to locked and returns immediately. When the state is locked,acquire() blocks until a call torelease() in anotherthread changes it to unlocked, then theacquire() call resets itto locked and returns. Therelease() method should only becalled in the locked state; it changes the state to unlocked and returnsimmediately. If an attempt is made to release an unlocked lock, aRuntimeError will be raised.

Locks also support thecontext management protocol.

When more than one thread is blocked inacquire() waiting for thestate to turn to unlocked, only one thread proceeds when arelease()call resets the state to unlocked; which one of the waiting threads proceedsis not defined, and may vary across implementations.

All methods are executed atomically.

classthreading.Lock¶

The class implementing primitive lock objects. Once a thread has acquired alock, subsequent attempts to acquire it block, until it is released; anythread may release it.

Changed in version 3.13:Lock is now a class. In earlier Pythons,Lock was a factoryfunction which returned an instance of the underlying private locktype.

acquire(blocking=True,timeout=-1)¶

Acquire a lock, blocking or non-blocking.

When invoked with theblocking argument set toTrue (the default),block until the lock is unlocked, then set it to locked and returnTrue.

When invoked with theblocking argument set toFalse, do not block.If a call withblocking set toTrue would block, returnFalseimmediately; otherwise, set the lock to locked and returnTrue.

When invoked with the floating-pointtimeout argument set to a positivevalue, block for at most the number of seconds specified bytimeoutand as long as the lock cannot be acquired. Atimeout argument of-1specifies an unbounded wait. It is forbidden to specify atimeoutwhenblocking isFalse.

The return value isTrue if the lock is acquired successfully,False if not (for example if thetimeout expired).

Changed in version 3.2:Thetimeout parameter is new.

Changed in version 3.2:Lock acquisition can now be interrupted by signals on POSIX if theunderlying threading implementation supports it.

release()¶

Release a lock. This can be called from any thread, not only the threadwhich has acquired the lock.

When the lock is locked, reset it to unlocked, and return. If any other threadsare blocked waiting for the lock to become unlocked, allow exactly one of themto proceed.

When invoked on an unlocked lock, aRuntimeError is raised.

There is no return value.

locked()¶

ReturnTrue if the lock is acquired.

RLock objects¶

A reentrant lock is a synchronization primitive that may be acquired multipletimes by the same thread. Internally, it uses the concepts of “owning thread”and “recursion level” in addition to the locked/unlocked state used by primitivelocks. In the locked state, some thread owns the lock; in the unlocked state,no thread owns it.

Threads call a lock’sacquire() method to lock it,and itsrelease() method to unlock it.

RLock’sacquire()/release() call pairs may be nested,unlike Lock’sacquire()/release(). Only the finalrelease() (therelease() of the outermost pair) resetsthe lock to an unlocked state and allows another thread blocked inacquire() to proceed.

acquire()/release() must be used in pairs: each acquiremust have a release in the thread that has acquired the lock. Failing tocall release as many times the lock has been acquired can lead to deadlock.

classthreading.RLock¶

This class implements reentrant lock objects. A reentrant lock must bereleased by the thread that acquired it. Once a thread has acquired areentrant lock, the same thread may acquire it again without blocking; thethread must release it once for each time it has acquired it.

Note thatRLock is actually a factory function which returns an instanceof the most efficient version of the concrete RLock class that is supportedby the platform.

acquire(blocking=True,timeout=-1)¶

Acquire a lock, blocking or non-blocking.

See also

Using RLock as a context manager

Recommended over manualacquire() andrelease() callswhenever practical.

When invoked with theblocking argument set toTrue (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 acquirelock, ortimeout, if set to a positive float value.

• If the same thread owns the lock, acquire the lock again, andreturn immediately. This is the difference betweenLock andRLock;Lock handles this case the same as the previous,blocking until the lock can be acquired.

When invoked with theblocking argument set toFalse:

• 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 returnimmediately.

In all cases, if the thread was able to acquire the lock, returnTrue.If the thread was unable to acquire the lock (i.e. if not blocking orthe timeout was reached) returnFalse.

If called multiple times, failing to callrelease() as many timesmay lead to deadlock. Consider usingRLock as a context manager rather thancalling acquire/release directly.

Changed in version 3.2:Thetimeout parameter is new.

release()¶

Release a lock, decrementing the recursion level. If after the decrement it iszero, reset the lock to unlocked (not owned by any thread), and if any otherthreads are blocked waiting for the lock to become unlocked, allow exactly oneof them to proceed. If after the decrement the recursion level is stillnonzero, the lock remains locked and owned by the calling thread.

Only call this method when the calling thread owns the lock. ARuntimeError is raised if this method is called when the lock isnot acquired.

There is no return value.

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.

Changed in version 3.3: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.

Changed in version 3.2: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.

Added in version 3.2.

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.

Changed in 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 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.

Changed in version 3.2:Thetimeout parameter is new.

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.

Changed in version 3.9: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.

Changed in 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, 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:# ... use connection ...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.

Changed in version 3.3: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.

Changed in version 3.1: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.

For example:

defhello():print("hello, world")t=Timer(30.0,hello)t.start()# after 30 seconds, "hello, world" will be printed

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.

Changed in 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 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:# Only one thread needs to print thisprint("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.