cs-threads 20250528
threading and communication/synchronisation conveniences
Keywords: python2, python3

Thread related convenience classes and functions.

*Latest release 20250528*:
Small doc update.

Short summary:
* `AdjustableSemaphore`: A semaphore whose value may be tuned after instantiation.
* `bg`: Dispatch the callable `func` in its own `Thread`; return the `Thread`.
* `DeadlockError`: Raised by `NRLock` when a lock is attempted from the `Thread` currently holding the lock.
* `HasThreadState`: A mixin for classes with a `cs.threads.ThreadState` instance as `.state` providing a context manager which pushes `current=self` onto that state and a `default()` class method returning `cls.perthread_state.current` as the default instance of that class.
* `joinif`: Call `T.join()` if `T` is not the current `Thread`.
* `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.
* `locked`: A decorator for instance methods that must run within a lock.
* `locked_property`: A thread safe property whose value is cached. The lock is taken if the value needs to computed.
* `monitor`: Turn a class into a monitor, all of whose public methods are `@locked`.
* `NRLock`: A nonrecursive lock. Attempting to take this lock when it is already held by the current `Thread` will raise `DeadlockError`. Otherwise this behaves like `threading.Lock`.
* `PriorityLock`: A priority based mutex which is acquired by and released to waiters in priority order.
* `PriorityLockSubLock`: The record for the per-`acquire`r `Lock` held by `PriorityLock.acquire`.
* `State`: A `Thread` local object with attributes which can be used as a context manager to stack attribute values.
* `ThreadState`: A `Thread` local object with attributes which can be used as a context manager to stack attribute values.
* `via`: 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.

Module contents:
- <a name="AdjustableSemaphore"></a>`Class `AdjustableSemaphore``: A semaphore whose value may be tuned after instantiation.

*`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().

*`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.

*`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.

*`AdjustableSemaphore.release(self)`*:
Release the semaphore.
- <a name="bg"></a>`bg(func, *, daemon=None, name=None, no_start=False, no_logexc=False, args=None, kwargs=None, thread_factory=None, pre_enter_objects=None, **thread_factory_kw)`: Dispatch the callable `func` in its own `Thread`;
  return the `Thread`.

  Parameters:
  * `func`: a callable for the `Thread` target.
  * `args`, `kwargs`: passed to the `Thread` constructor
  * `kwargs`, `kwargs`: passed to the `Thread` constructor
  * `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`.
  * `pre_enter_objects`: an optional iterable of objects which
    should be entered using `with`

  If `pre_enter_objects` is supplied, these context manager
  objects will be entered using `with` via the `closeall()`
  function before the `Thread` is started and exited when the
  `Thread` target function ends.
  If the `Thread` is _not_ started (`no_start=True`, very
  unusual) then the objects will still be entered and it will
  be the caller's responsibility to manage the entered objects.
- <a name="DeadlockError"></a>`Class `DeadlockError(builtins.RuntimeError)``: Raised by `NRLock` when a lock is attempted from the `Thread` currently holding the lock.
- <a name="HasThreadState"></a>`Class `HasThreadState(cs.context.ContextManagerMixin)``: A mixin for classes with a `cs.threads.ThreadState` instance as `.state`
  providing a context manager which pushes `current=self` onto that state
  and a `default()` class method returning `cls.perthread_state.current`
  as the default instance of that class.

  *NOTE*: the documentation here refers to `cls.perthread_state`, but in
  fact we honour the `cls.THREAD_STATE_ATTR` attribute to name
  the state attribute which allows perclass state attributes,
  and also use with classes which already use `.perthread_state` for
  another purpose.

  *NOTE*: `HasThreadState.Thread` is a _class_ method whose default
  is to push state for all active `HasThreadState` subclasses.
  Contrast with `HasThreadState.bg` which is an _instance_method
  whose default is to push state for just that instance.
  The top level `cs.threads.bg` function calls `HasThreadState.Thread`
  to obtain its `Thread`.

*`HasThreadState.Thread(*, name=None, target, enter_objects=None, **Thread_kw)`*:
Factory for a `Thread` to push the `.current` state for the
currently active classes.

The optional parameter `enter_objects` may be used to pass
an iterable of objects whose contexts should be entered
using `with obj:`.
If this is set to `True` that indicates that every "current"
`HasThreadStates` instance should be entered.
The default does not enter any object contexts.
The `HasThreadStates.bg` method defaults to passing
`enter_objects=(self,)` to enter the context for `self`.

*`HasThreadState.__enter_exit__(self)`*:
Push `self.perthread_state.current=self` as the `Thread` local current instance.

Include `self.__class__` in the set of currently active classes for the duration.

*`HasThreadState.bg(self, func, *, enter_objects=None, **bg_kw)`*:
Get a `Thread` using `type(self).Thread` and start it.
Return the `Thread`.

The `HasThreadState.Thread` factory duplicates the current `Thread`'s
`HasThreadState` current objects as current in the new `Thread`.
Additionally it enters the contexts of various objects using
`with obj` according to the `enter_objects` parameter.

The value of the optional parameter `enter_objects` governs
which objects have their context entered using `with obj`
in the child `Thread` while running `func` as follows:
- `None`: the default, meaning `(self,)`
- `False`: no object contexts are entered
- `True`: all current `HasThreadState` object contexts will be entered
- an iterable of objects whose contexts will be entered;
  pass `()` to enter no objects

*`HasThreadState.default(*, factory=None, raise_on_None=False)`*:
The default instance of this class from `cls.perthread_state.current`.

Parameters:
* `factory`: optional callable to create an instance of `cls`
  if `cls.perthread_state.current` is `None` or missing;
  if `factory` is `True` then `cls` is used as the factory
* `raise_on_None`: if `cls.perthread_state.current` is `None` or missing
  and `factory` is false and `raise_on_None` is true,
  raise a `RuntimeError`;
  this is primarily a debugging aid

*`HasThreadState.get_thread_states(all_classes=None)`*:
Return a mapping of `class`->*current_instance*`
for use with `HasThreadState.with_thread_states`
or `HasThreadState.Thread` or `HasThreadState.bg`.

The default behaviour returns just a mapping for this class,
expecting the default instance to be responsible for what
other resources it holds.

There is also a legacy mode for `all_classes=True`
where the mapping is for all active classes,
probably best used for `Thread`s spawned outside
a `HasThreadState` context.

Parameters:
* `all_classes`: optional flag, default `False`;
  if true, return a mapping of class to current instance
  for all `HasThreadState` subclasses with an open instance,
  otherwise just a mapping from this class to its current instance
- <a name="joinif"></a>`joinif(T: threading.Thread)`: Call `T.join()` if `T` is not the current `Thread`.

  Unlike `threading.Thread.join`, this function is a no-op if
  `T` is the current `Thread.

  The use case is situations such as the shutdown phase of the
  `MultiOpenMixin.startup_shutdown` context manager. Because
  the "initial open" startup phase is not necessarily run in
  the same thread as the "final close" shutdown phase, it is
  possible for example for a worker `Thread` to execute the
  shutdown phase and try to join itself. Using this function
  supports that scenario.
- <a name="LockableMixin"></a>`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.

*`LockableMixin.__exit__(self, exc_type, exc_value, traceback)`*:
pylint: disable=unused-argument

*`LockableMixin.lock`*:
The internal lock object.
- <a name="locked"></a>`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: `2.0`s
  * `lockattr`:
    the name of the attribute of `self`
    which references the lock object.
    Default `'_lock'`
- <a name="locked_property"></a>`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`.
- <a name="monitor"></a>`monitor(*da, **dkw)`: Turn a class into a monitor, all of whose public methods are `@locked`.

  This is a simple approach which 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 `10.0`s.
  * `lockattr`: optional lock attribute name, default `'_lock'`.

  Only attributes satifying `inspect.ismethod` are wrapped
  because `@locked` requires access to the instance `._lock` attribute.
- <a name="NRLock"></a>`Class `NRLock``: A nonrecursive lock.
  Attempting to take this lock when it is already held by the current `Thread`
  will raise `DeadlockError`.
  Otherwise this behaves like `threading.Lock`.

*`NRLock.acquire(self, *a, caller_frame=None, **kw)`*:
Acquire the lock as for `threading.Lock`.
Raises `DeadlockError` is the lock is already held by the current `Thread`.

*`NRLock.locked(self)`*:
Return the lock status.

*`NRLock.release(self)`*:
Release the lock as for `threading.Lock`.
- <a name="PriorityLock"></a>`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 `acquire`s 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`.

*`PriorityLock.__init__(self, default_priority=0, name=None)`*:
Initialise the `PriorityLock`.

Parameters:
* `default_priority`: the default `acquire` priority,
  default `0`.
* `name`: optional identifying name

*`PriorityLock.__enter__(self)`*:
Enter the mutex as a context manager at the default priority.
Returns the new `Lock`.

*`PriorityLock.__exit__(self, *_)`*:
Exit the context manager.

*`PriorityLock.acquire(self, priority=None)`*:
Acquire the mutex with `priority` (default from `default_priority`).
Return the new `PriorityLockSubLock`.

This blocks behind any higher priority `acquire`s
or any earlier `acquire`s of the same priority.

*`PriorityLock.priority(self, this_priority)`*:
A context manager with the specified `this_priority`.
Returns the new `Lock`.

*`PriorityLock.release(self)`*:
Release the mutex.

Internally, this releases the highest priority `Lock`,
allowing that `acquire`r to go forward.
- <a name="PriorityLockSubLock"></a>`Class `PriorityLockSubLock(PriorityLockSubLock)``: The record for the per-`acquire`r `Lock` held by `PriorityLock.acquire`.
- <a name="State"></a>`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 ThreadState

      S = ThreadState(verbose=False)

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

*`State.__init__(self, **kw)`*:
Initiate the `ThreadState`, providing the per-Thread initial values.

*`State.__call__(self, **kw)`*:
Calling a `ThreadState` returns a context manager which stacks some state.
The context manager yields the previous values
for the attributes which were stacked.
- <a name="ThreadState"></a>`Class `ThreadState(_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 ThreadState

      S = ThreadState(verbose=False)

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

*`ThreadState.__init__(self, **kw)`*:
Initiate the `ThreadState`, providing the per-Thread initial values.

*`ThreadState.__call__(self, **kw)`*:
Calling a `ThreadState` returns a context manager which stacks some state.
The context manager yields the previous values
for the attributes which were stacked.
- <a name="via"></a>`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.

# Release Log



*Release 20250528*:
Small doc update.

*Release 20250325*:
NRLock: include the lock name in DeadLock exceptions.

*Release 20250306*:
HasThreadState: various fixes.

*Release 20241005*:
Remove some debug noise.

*Release 20240630*:
* bg: use closeall instead of twostep/withall.
* HasThreadState.bg: drop pre_enter_objects (unused), gets plumbed by the **bg_kw.

*Release 20240422*:
HasThreadState.default: make factory and raise_on keyword only.

*Release 20240412*:
* New NRLock, an nonrecursive Lock and associated exception DeadlockError.
* bg: rename thread_class to thread_factory for clarity.
* HasThreadState: big refactor to separate the mapping of default instances from the previously automatic opening of a context for each.
* HasThreadState.bg: new optional pre_enter_objects to supply objects which should be opened before the Thread starts (before bg returns) and closed when the Thread exits.

*Release 20240316*:
Fixed release upload artifacts.

*Release 20240303*:
* HasThreadState: rename thread_states() to get_thread_states().
* HasThreadState.get_thread_states: some logic fixes.

*Release 20231129*:
* HasThreadState.thread_states: *policy change*: the default now makes a mapping only for this class, not for all HasThreadState subclasses, on the premise that this class can manage use of other classes if required.
* HasThreadState: new bg() class method like Thread() but also starting the Thread.

*Release 20230331*:
* HasThreadState: new thread_states() method to snapshot the current states.
* HasThreadState: new with_thread_states() context manager to apply a set of states.
* HasThreadState: rename the default state from .state to .perthread_state.
* HasThreadState.__enter_exit__: pass cls._HasThreadState_lock to stackset as the modification guard lock, prevents race in thread_states.
* Rename State to ThreadState, which how I always use it anyway, and leave a compatibility name behind.
* New joinif(Thread) method to join a Thread unless we are that Thread - this is because MultiOpenMixin.startup_shutdown stuff may run the shutdown in a differ Thread from that which ran the startup.
* @uses_runstate: use the prevailing RunState or create one.
* Drop Python 2 support.

*Release 20230212*:
* HasThreadState: maintain a set of the HasThreadState classes in use.
* New HasThreadState.Thread class factory method to create a new Thread with the current threads states at time of call instantiated in the new Thread.
* bg: new no_context=False parameter to suppress use of HasThreadState.Thread to create the new Thread.

*Release 20230125*:
New HasThreadState mixin for classes with a state=State() attribute to provide a cls.default() class method for the default instance and a context manager to push/pop self.state.current=self.

*Release 20221228*:
* Get error and warning from cs.gimmicks, breaks circular import with cs.logutils.
* Late import of cs.logutils.LogTime to avoid circular import.

*Release 20221207*:
Small bug fix.

*Release 20221118*:
REMOVE WorkerThreadPool, pulls in too many other things and was never used.

*Release 20211208*:
bg: do not pass the current Pfx prefix into the new Thread, seems to leak and grow.

*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.