cs.threads 20210306

threading and communication/synchronisation conveniences

Thread related convenience classes and functions.

Latest release 20210306: bg: include the current Pfx prefix in the thread name and thread body Pfx, obsoletes cs.pfx.PfxThread.

Class AdjustableSemaphore

A semaphore whose value may be tuned after instantiation.

Method AdjustableSemaphore.acquire(self, blocking=True)

The acquire() method calls the base acquire() method if not blocking. If blocking is true, the base acquire() is called inside a lock to avoid competing with a reducing adjust().

Method AdjustableSemaphore.adjust(self, newvalue)

Set capacity to newvalue by calling release() or acquire() an appropriate number of times.

If newvalue lowers the semaphore capacity then adjust() may block until the overcapacity is released.

Method AdjustableSemaphore.adjust_delta(self, delta)

Adjust capacity by delta by calling release() or acquire() an appropriate number of times.

If delta lowers the semaphore capacity then adjust() may block until the overcapacity is released.

Method AdjustableSemaphore.release(self)

Release the semaphore.

Function bg(func, daemon=None, name=None, no_start=False, no_logexc=False, args=None, kwargs=None)

Dispatch the callable func in its own Thread; return the Thread.

Parameters:

• func: a callable for the Thread target.
• daemon: optional argument specifying the .daemon attribute.
• name: optional argument specifying the Thread name, default: the name of func.
• no_logexc: if false (default False), wrap func in @logexc.
• no_start: optional argument, default False. If true, do not start the Thread.
• args, kwargs: passed to the Thread constructor

Class LockableMixin

Trite mixin to control access to an object via its ._lock attribute. Exposes the ._lock as the property .lock. Presents a context manager interface for obtaining an object's lock.

Property LockableMixin.lock

Return the lock.

Function locked(*da, **dkw)

A decorator for instance methods that must run within a lock.

Decorator keyword arguments:

• initial_timeout: the initial lock attempt timeout; if this is >0 and exceeded a warning is issued and then an indefinite attempt is made. Default: 2.0s
• lockattr: the name of the attribute of self which references the lock object. Default '_lock'

Function locked_property(*da, **dkw)

A thread safe property whose value is cached. The lock is taken if the value needs to computed.

The default lock attribute is ._lock. The default attribute for the cached value is ._funcname where funcname is func.__name__. The default "unset" value for the cache is None.

Function monitor(*da, **dkw)

Turn a class into a monitor, all of whose public methods are @locked.

This is a simple approach requires class instances to have a ._lock which is an RLock or compatible because methods may naively call each other.

Parameters:

• attrs: optional iterable of attribute names to wrap in @locked. If omitted, all names commencing with a letter are chosen.
• initial_timeout: optional initial lock timeout, default 10.0s.
• lockattr: optional lock attribute name, default '_lock'.

Only attributes satifying inspect.ismethod are wrapped because @locked requires access to the instance ._lock attribute.

Class PriorityLock

A priority based mutex which is acquired by and released to waiters in priority order.

The initialiser sets a default priority, itself defaulting to 0.

The acquire() method accepts an optional priority value which specifies the priority of the acquire request; lower values have higher priorities. acquire returns a new PriorityLockSubLock.

Note that internally this allocates a threading.Lock per acquirer.

When acquire is called, if the PriorityLock is taken then the acquirer blocks on their personal Lock.

When release() is called the highest priority Lock is released.

Within a priority level acquires are served in FIFO order.

Used as a context manager, the mutex is obtained at the default priority. The priority() method offers a context manager with a specified priority. Both context managers return the PriorityLockSubLock allocated by the acquire.

Method PriorityLock.__init__(self, default_priority=0, name=None)

Initialise the PriorityLock.

Parameters:

• default_priority: the default acquire priority, default 0.
• name: optional identifying name

Method PriorityLock.__enter__(self)

Enter the mutex as a context manager at the default priority. Returns the new Lock.

Method PriorityLock.__exit__(self, *_)

Exit the context manager.

Method PriorityLock.acquire(self, priority=None)

Acquire the mutex with priority (default from default_priority). Return the new PriorityLockSubLock.

This blocks behind any higher priority acquires or any earlier acquires of the same priority.

Method PriorityLock.priority(self, this_priority)

A context manager with the specified this_priority. Returns the new Lock.

Method PriorityLock.release(self)

Release the mutex.

Internally, this releases the highest priority Lock, allowing that acquirer to go forward.

Class PriorityLockSubLock(PriorityLockSubLock,builtins.tuple)

The record for the per-acquirer Lock held by PriorityLock.acquire.

Class State(_thread._local)

A Thread local object with attributes which can be used as a context manager to stack attribute values.

Example:

from cs.threads import State

S = State(verbose=False)

with S(verbose=True) as prev_attrs:
    if S.verbose:
        print("verbose! (formerly verbose=%s)" % prev_attrs['verbose'])

Method State.__init__(self, **kw)

Initiale the State, providing the per-Thread initial values.

Method State.__call__(self, **kw)

Calling a State returns a context manager which stacks some state. The context manager yields the previous values for the attributes which were stacked.

Function via(cmanager, func, *a, **kw)

Return a callable that calls the supplied func inside a with statement using the context manager cmanager. This intended use case is aimed at deferred function calls.

Class WorkerThreadPool(cs.resources.MultiOpenMixin)

A pool of worker threads to run functions.

Method WorkerThreadPool.__init__(self, name=None, max_spare=4)

Initialise the WorkerThreadPool.

Parameters:

• name: optional name for the pool
• max_spare: maximum size of each idle pool (daemon and non-daemon)

Method WorkerThreadPool.dispatch(self, *a, **kw)

Wrapper function to check that this instance is not closed.

Method WorkerThreadPool.join(self)

Wait for all outstanding Threads to complete.

Method WorkerThreadPool.shutdown(self)

Shut down the pool.

Close all the request queues.

Note: does not wait for all Threads to complete; call .join after close.

Method WorkerThreadPool.startup(self)

Start the pool.

Class WTPoolEntry(builtins.tuple)

WTPoolEntry(thread, queue)

Property WTPoolEntry.queue

Alias for field number 1

Property WTPoolEntry.thread

Alias for field number 0

Release Log

Release 20210306: bg: include the current Pfx prefix in the thread name and thread body Pfx, obsoletes cs.pfx.PfxThread.

Release 20210123: New @monitor class decorator for simple RLock based reentrance protection.

Release 20201025:

• @locked: bump the default warning timeout to 10s, was firing too often.
• New State class for thread local state objects with default attribute values and a stacking call context manager.

Release 20200718: @locked: apply the interior doc to the wrapper.

Release 20200521: @locked_property: decorate with @cs.deco.decorator to support keyword arguments.

Release 20191102: @locked: report slow-to-acquire locks, add initial_timeout and lockattr decorator keyword parameters.

Release 20190923.2: Fix annoying docstring typo.

Release 20190923.1: Docstring updates.

Release 20190923: Remove dependence on cs.obj.

Release 20190921: New PriorityLock class for a mutex which releases in (priority,fifo) order.

Release 20190812: bg: compute default name before wrapping func in @logexc.

Release 20190729: bg: provide default name, run callable inside Pfx, add optional no_logexc=False param preventing @logec wrapper if true.

Release 20190422: bg(): new optional no_start=False keyword argument, preventing Thread.start if true

Release 20190102:

• Drop some unused classes.
• New LockableMixin, presenting a context manager and a .lock property.

Release 20160828: Use "install_requires" instead of "requires" in DISTINFO.

Release 20160827:

• Replace bare "excepts" with "except BaseException".
• Doc updates. Other minor improvements.

Release 20150115: First PyPI release.