Skip to content

pending

Classes:

PendingCancelled

Bases: ClosedResourceError

Used to indicate the Pending is cancelled.

Raised by:
Source code in src/async_kernel/pending.py 
35
36
class PendingCancelled(anyio.ClosedResourceError):
    """Used to indicate the [Pending][async_kernel.pending.Pending] is cancelled."""

PendingNotDone

Bases: RuntimeError

Used to indicate the Pending is not done.

Raised by:
Source code in src/async_kernel/pending.py 
39
40
class PendingNotDone(RuntimeError):
    """Used to indicate the [Pending][async_kernel.pending.Pending] is not done."""

PendingTracker

The base class for tracking Pending.

Notes
  • It must be subclassed to be used.
  • Each subclass is assigned one context variable.
    • This means that only one instance of the subclass can be active in a specific context at any time.
  • It is linearly proportionally expensive per subclass of PendingTracker so it is recommended to use aiologic.lowlevel.once or lazy imports to limit subclassing until the subclass is actually required.
Subclassed by: Used by:

Methods:

  • current –

    The instance of the active tracker in the current context.

  • active_id –

    The id of the active tracker in the current context.

  • add –

    Add pen to the pending set Pending.

Attributes:

Source code in src/async_kernel/pending.py 
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
class PendingTracker:
    """The base class for tracking [Pending][async_kernel.pending.Pending].

    Notes:
        - It must be subclassed to be used.
        - Each subclass is assigned one context variable.
            - This means that only one instance of the subclass can be active
                in a specific context at any time.
        - It is linearly proportionally expensive per subclass of PendingTracker
            so it is recommended to use [aiologic.lowlevel.once][] or lazy imports
            to limit subclassing until the subclass is actually required.
    """

    _subclasses: ClassVar[tuple[type[Self], ...]] = ()
    _instances: ClassVar[weakref.WeakValueDictionary[str, Self]] = weakref.WeakValueDictionary()
    _id_contextvar: ClassVar[contextvars.ContextVar[str | None]]
    _pending: Fixed[Self, set[Pending[Any]]] = Fixed(set)
    _subclass_lock = BinarySemaphore()

    id: Fixed[Self, str] = Fixed(lambda _: str(uuid.uuid4()))
    """The unique id of the pending tracker instance."""

    @property
    def pending(self) -> set[Pending[Any]]:
        """The pending currently associated with this instance."""
        return self._pending.copy()

    def __init_subclass__(cls) -> None:
        if cls.__name__ != "PendingManager":
            with cls._subclass_lock:
                PendingTracker._subclasses = (*cls._subclasses, cls)
            # Each subclass is assigned a new context variable.
            cls._id_contextvar = contextvars.ContextVar(f"{cls.__module__}.{cls.__name__}", default=None)
        return super().__init_subclass__()

    @classmethod
    def current(cls) -> Self | None:
        """The instance of the active tracker in the current context."""
        if (id_ := cls._id_contextvar.get()) and (current := cls._instances.get(id_)):
            return current
        return None

    @classmethod
    def active_id(cls) -> str | None:
        """The id of the active tracker in the current context."""
        return cls._id_contextvar.get()

    def __init__(self) -> None:
        self._instances[self.id] = self

    def _activate(self) -> Token[str | None]:
        return self._id_contextvar.set(self.id)

    def _deactivate(self, token: contextvars.Token[str | None]) -> None:
        self._id_contextvar.reset(token)

    def add(self, pen: Pending) -> None:
        """Add `pen` to the pending set [Pending][async_kernel.pending.Pending].

        `pen` is automatically removed from the set once it is done.
        """
        if not pen.done() and pen not in self._pending:
            self._pending.add(pen)
            pen.add_done_callback(self._on_pending_done)

    def _on_pending_done(self, pen: Pending) -> None:
        """A done_callback that is registered with pen when it is added (don't call directly)."""
        self._pending.discard(pen)

id class-attribute instance-attribute 

id: Fixed[Self, str] = Fixed(lambda _: str(uuid.uuid4()))

The unique id of the pending tracker instance.

pending property 

pending: set[Pending[Any]]

The pending currently associated with this instance.

current classmethod 

current() -> Self | None

The instance of the active tracker in the current context.

Source code in src/async_kernel/pending.py 
78
79
80
81
82
83
@classmethod
def current(cls) -> Self | None:
    """The instance of the active tracker in the current context."""
    if (id_ := cls._id_contextvar.get()) and (current := cls._instances.get(id_)):
        return current
    return None

active_id classmethod 

active_id() -> str | None

The id of the active tracker in the current context.

Source code in src/async_kernel/pending.py 
85
86
87
88
@classmethod
def active_id(cls) -> str | None:
    """The id of the active tracker in the current context."""
    return cls._id_contextvar.get()

add 

add(pen: Pending) -> None

Add pen to the pending set Pending.

pen is automatically removed from the set once it is done.

Source code in src/async_kernel/pending.py 
 99
100
101
102
103
104
105
106
def add(self, pen: Pending) -> None:
    """Add `pen` to the pending set [Pending][async_kernel.pending.Pending].

    `pen` is automatically removed from the set once it is done.
    """
    if not pen.done() and pen not in self._pending:
        self._pending.add(pen)
        pen.add_done_callback(self._on_pending_done)

PendingManager

Bases: PendingTracker

Tracks the creation of Pending in multiple contexts.

This class must be subclassed to be useful.

For each subclass there is zero or one active trackers at a time. Activating a manager will 'replace' a previously active pending manager.

Usage 
class MyPendingManager(PendingManager):
    "Manages the context of ..."


m = MyPendingManager()
m2 = MyPendingManager()

# In one or more contexts
token = m.activate()
try:
    ...
    try:
        token2 = m2.activate()
        pen = m2.caller.call_soon(lambda: 1 + 1)
        assert pen in m2.pending
        assert (
            pen not in m.pending
        ), "pen is associated should only be associated with m2"
        ...
    finally:
        m2.deactivate(token2)

finally:
    m.deactivate(token)
Referenced by:

Methods:

  • activate –

    Start tracking Pending in the current context.

  • deactivate –

    Stop tracking.

  • remove –

    Remove pen from the pending set.

  • context –

    A context manager where the pending manager is activated.

Source code in src/async_kernel/pending.py 
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
class PendingManager(PendingTracker):
    """Tracks the creation of [Pending][async_kernel.pending.Pending] in multiple contexts.

    This class must be subclassed to be useful.

    For each subclass there is zero or one active trackers at a time. Activating a manager will 'replace' a
    previously active pending manager.

    Usage:
        ```python
        class MyPendingManager(PendingManager):
            "Manages the context of ..."


        m = MyPendingManager()
        m2 = MyPendingManager()

        # In one or more contexts
        token = m.activate()
        try:
            ...
            try:
                token2 = m2.activate()
                pen = m2.caller.call_soon(lambda: 1 + 1)
                assert pen in m2.pending
                assert (
                    pen not in m.pending
                ), "pen is associated should only be associated with m2"
                ...
            finally:
                m2.deactivate(token2)

        finally:
            m.deactivate(token)
        ```
    """

    def activate(self) -> contextvars.Token[str | None]:
        """Start tracking [Pending][async_kernel.pending.Pending] in the current context."""
        return self._activate()

    def deactivate(self, token: contextvars.Token[str | None]) -> None:
        """Stop tracking.

        Args:
            token: The token returned from [activate][].
        """
        self._deactivate(token)

    def remove(self, pen: Pending) -> None:
        """Remove `pen` from the pending set."""
        self._pending.discard(pen)

    @contextlib.contextmanager
    def context(self) -> Generator[None, Any, None]:
        """A context manager where the pending manager is activated."""
        token = self.activate()
        try:
            yield
        finally:
            self.deactivate(token)

activate 

activate() -> Token[str | None]

Start tracking Pending in the current context.

Referenced by:
Source code in src/async_kernel/pending.py 
150
151
152
def activate(self) -> contextvars.Token[str | None]:
    """Start tracking [Pending][async_kernel.pending.Pending] in the current context."""
    return self._activate()

deactivate 

deactivate(token: Token[str | None]) -> None

Stop tracking.

Parameters:

Source code in src/async_kernel/pending.py 
154
155
156
157
158
159
160
def deactivate(self, token: contextvars.Token[str | None]) -> None:
    """Stop tracking.

    Args:
        token: The token returned from [activate][].
    """
    self._deactivate(token)

remove 

remove(pen: Pending) -> None

Remove pen from the pending set.

Source code in src/async_kernel/pending.py 
162
163
164
def remove(self, pen: Pending) -> None:
    """Remove `pen` from the pending set."""
    self._pending.discard(pen)

context 

context() -> Generator[None, Any, None]

A context manager where the pending manager is activated.

Source code in src/async_kernel/pending.py 
166
167
168
169
170
171
172
173
@contextlib.contextmanager
def context(self) -> Generator[None, Any, None]:
    """A context manager where the pending manager is activated."""
    token = self.activate()
    try:
        yield
    finally:
        self.deactivate(token)

PendingGroup

Bases: PendingTracker, AsyncContextManagerMixin

An asynchronous context manager for tracking Pending that are created in it's context.

Usage

Enter the async context and create new pending.

async with PendingGroup() as pg:
    assert pg.caller.to_thread(lambda: None) in pg.pending
Referenced by: Returned by:

Methods:

  • __init__ –

    An async context to capture all pending (that opt in) created in the context.

  • cancel –

    Cancel the pending group (internally synchronised).

  • cancelled –

    Returns: If the pending group is marked as cancelled.

Attributes:

Source code in src/async_kernel/pending.py 
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
@final
class PendingGroup(PendingTracker, anyio.AsyncContextManagerMixin):
    """An asynchronous context manager for tracking [Pending][async_kernel.pending.Pending] that are created in it's context.

    Usage:
        Enter the async context and create new pending.

        ```python
        async with PendingGroup() as pg:
            assert pg.caller.to_thread(lambda: None) in pg.pending
        ```
    """

    _parent_id: str | None = None
    _cancel_scope: anyio.CancelScope
    _cancelled: str | None = None
    _leaving_context: bool = False
    _failed: Fixed[Self, list[Pending]] = Fixed(list)

    cancellation_timeout = 10
    """The maximum time to wait for cancelled pending to be done."""

    caller: Fixed[Self, Caller] = Fixed(lambda _: async_kernel.Caller())
    """The caller where the pending group was instantiated."""

    def __init__(
        self,
        *,
        mode: Literal[0, 1, 2, 3] = 0,
        shield: bool = False,
        timeout: float | None = None,
    ) -> None:
        """An async context to capture all pending (that opt in) created in the context.

        The pending group will only exit once all pending in the group are done.

        Pending can be added to and removed from the group manually.

        Args:
            mode: The mode.
                - 0: Ignore cancellation of pending, if any pending is cancelled - exit quietly.
                - 1: Cancel if any pending is cancelled - raise PendingCancelled on exit.
                - 2: Cancel if any pending is cancelled - exit quietly.
                - 3: Ignore cancellation of pending, if any pending is cancelled - raise PendingCancelled on exit.
            shield: Passed to the cancel scope.
            timeout: The timeout for the pending group once it has been entered.
        """
        assert mode in [0, 1, 2, 3]
        self._mode = mode
        self._shield = shield
        self._timeout = timeout
        self.caller  # noqa: B018
        super().__init__()

    @override
    def __repr__(self) -> str:
        info = " ⛔ cancelled" if self._cancelled else ""
        return f"<PendingGroup at {id(self)}{info} | {len(self.pending)} pending | mode:{self._mode}>"

    @override
    def _activate(self) -> Token[str | None]:
        self._parent_id = None if (parent_id := self._id_contextvar.get()) == self.id else parent_id
        return super()._activate()

    @contextlib.asynccontextmanager
    async def __asynccontextmanager__(self) -> AsyncGenerator[Self]:
        if self._leaving_context:
            msg = f"Re-entry of {self.__class__} is not supported!"
            raise RuntimeError(msg)
        deadline = math.inf if self._timeout is None else anyio.current_time() + self._timeout
        self._cancel_scope = anyio.CancelScope(shield=self._shield, deadline=deadline)
        self._all_done = create_async_event()
        token = self._activate()
        try:
            with self._cancel_scope:
                try:
                    yield self
                    self._leaving_context = True
                    if self._pending:
                        await self._all_done
                except (anyio.get_cancelled_exc_class(), Exception) as e:
                    self.cancel(f"An error occurred: {e!r}")
                    raise
            if self._cancelled is not None:
                if exceptions := [e for pen in self._failed if isinstance(e := pen.exception(), Exception)]:
                    msg = f"One or more exceptions occurred in this context! {list(map(str, exceptions))}"
                    raise ExceptionGroup(msg, exceptions)
                if self._mode in [1, 3]:
                    raise PendingCancelled(self._cancelled)
        finally:
            self._leaving_context = True
            self._deactivate(token)
            self._instances.pop(self.id, None)
            if self._pending:
                if self._all_done or self._all_done.cancelled():
                    self._all_done = create_async_event()
                if self._pending and not self._all_done:
                    with anyio.CancelScope(shield=True), anyio.move_on_after(self.cancellation_timeout):
                        await self._all_done

    @override
    def add(self, pen: Pending) -> None:
        if pen not in self._pending:
            self._pending.add(pen)
            pen.add_done_callback(self._on_pending_done)
        if (id_ := self._parent_id) and (parent := self._instances.get(id_)):
            parent.add(pen)

    @override
    def _on_pending_done(self, pen: Pending) -> None:
        try:
            self._pending.remove(pen)
            if pen.cancelled():
                if self._mode in [1, 2]:
                    self.cancel(f"A monitored pending was cancelled {pen=}")
            elif pen.exception():
                self._failed.append(pen)
                self.cancel(f"Exception in member: {pen}")
        except KeyError:  # pragma: no cover
            pass
        if self._leaving_context and not self._pending:
            self._all_done.set()

    def cancel(self, msg: str | None = None) -> bool:
        """Cancel the pending group (internally synchronised)."""
        self._cancelled = "\n".join(((self._cancelled or ""), msg or ""))
        if not self._cancel_scope.cancel_called:
            self.caller.call_direct(self._cancel_scope.cancel, msg)
            for pen_ in self.pending:
                pen_.cancel(msg)
        return self.cancelled()

    def cancelled(self) -> bool:
        """Returns: If the pending group is marked as cancelled."""
        return self._cancelled is not None

cancellation_timeout class-attribute instance-attribute 

cancellation_timeout = 10

The maximum time to wait for cancelled pending to be done.

caller class-attribute instance-attribute 

caller: Fixed[Self, Caller] = Fixed(lambda _: async_kernel.Caller())

The caller where the pending group was instantiated.

__init__ 

__init__(
    *, mode: Literal[0, 1, 2, 3] = 0, shield: bool = False, timeout: float | None = None
) -> None

The pending group will only exit once all pending in the group are done.

Pending can be added to and removed from the group manually.

Parameters:

  • mode

    (Literal[0, 1, 2, 3], default: 0 ) –

    The mode. - 0: Ignore cancellation of pending, if any pending is cancelled - exit quietly. - 1: Cancel if any pending is cancelled - raise PendingCancelled on exit. - 2: Cancel if any pending is cancelled - exit quietly. - 3: Ignore cancellation of pending, if any pending is cancelled - raise PendingCancelled on exit.

  • shield

    (bool, default: False ) –

    Passed to the cancel scope.

  • timeout

    (float | None, default: None ) –

    The timeout for the pending group once it has been entered.

Source code in src/async_kernel/pending.py 
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
def __init__(
    self,
    *,
    mode: Literal[0, 1, 2, 3] = 0,
    shield: bool = False,
    timeout: float | None = None,
) -> None:
    """An async context to capture all pending (that opt in) created in the context.

    The pending group will only exit once all pending in the group are done.

    Pending can be added to and removed from the group manually.

    Args:
        mode: The mode.
            - 0: Ignore cancellation of pending, if any pending is cancelled - exit quietly.
            - 1: Cancel if any pending is cancelled - raise PendingCancelled on exit.
            - 2: Cancel if any pending is cancelled - exit quietly.
            - 3: Ignore cancellation of pending, if any pending is cancelled - raise PendingCancelled on exit.
        shield: Passed to the cancel scope.
        timeout: The timeout for the pending group once it has been entered.
    """
    assert mode in [0, 1, 2, 3]
    self._mode = mode
    self._shield = shield
    self._timeout = timeout
    self.caller  # noqa: B018
    super().__init__()

cancel 

cancel(msg: str | None = None) -> bool

Cancel the pending group (internally synchronised).

Source code in src/async_kernel/pending.py 
299
300
301
302
303
304
305
306
def cancel(self, msg: str | None = None) -> bool:
    """Cancel the pending group (internally synchronised)."""
    self._cancelled = "\n".join(((self._cancelled or ""), msg or ""))
    if not self._cancel_scope.cancel_called:
        self.caller.call_direct(self._cancel_scope.cancel, msg)
        for pen_ in self.pending:
            pen_.cancel(msg)
    return self.cancelled()

cancelled 

cancelled() -> bool

Returns: If the pending group is marked as cancelled.

Source code in src/async_kernel/pending.py 
308
309
310
def cancelled(self) -> bool:
    """Returns: If the pending group is marked as cancelled."""
    return self._cancelled is not None

Pending

Bases: Awaitable[T_co]

Pending is an internally synchronised, cancellable, waitable/awaitable representation of a pending result.

It can be thought of as a hybrid between of asyncio.Future and concurrent.futures.Future.

Features

  • It can be wait/awaited and cancelled from any thread (not considering deadlocks) and event loop.
  • Provides metadata storage.
  • Has built-in support for tracking pending created in a specific context (see: PendingManager and PendingGroup).

Properties

High level methods

Low level methods

Referenced by: Returned by: Used by:

Methods:

  • __init__ –

    Initializes a new pending object with optional creation options and metadata.

  • wait –

    Wait for the pending to be done (internally synchronised).

  • wait_sync –

    Wait synchronously for the pending to be done (internally synchronised) returning the result if specified.

  • set_result –

    Set the result (low-level internally synchronised).

  • set_exception –

    Set the exception (low-level internally synchronised).

  • cancel –

    Cancel the pending.

  • cancel_wait –

    Cancel the pending and wait for it to be done.

  • cancelled –

    Returns True if the pending is marked as cancelled.

  • set_canceller –

    Set a callback to handle cancellation (low-level).

  • done –

    Returns True if a result or exception has been set, or when cancelled without a defined canceller.

  • add_done_callback –

    Add a callback that is called when the pending is done (low-level).

  • remove_done_callback –

    Remove fn from the done callback list.

  • result –

    Return the result.

  • exception –

    Return the exception.

Attributes:

Source code in src/async_kernel/pending.py 
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
class Pending(Awaitable[T_co]):
    """Pending is an internally synchronised, cancellable, waitable/awaitable representation of a pending result.

    It can be thought of as a hybrid between of [asyncio.Future][] and [concurrent.futures.Future][].

    **Features**

    - It can be wait/awaited and cancelled from any thread (not considering deadlocks) and event loop.
    - Provides metadata storage.
    - Has built-in support for tracking pending created in a specific context (see: [PendingManager][] and [PendingGroup][]).

    **Properties**

    - [Pending.metadata][]: Metadata associated with the pending.
    - [Pending.context][]: The context associated with the pending.

    **High level methods**

    - [Pending.wait][]: Wait asynchronously for the pending to be complete.
    - [Pending.wait_sync][]: Wait synchronously for the pending to be complete.
    - [Pending.cancel][]: Cancel the pending.
    - [Pending.cancel_wait][]: Cancel the pending and wait for it to be done.
    - [Pending.result][]: Get the result of the pending.
    - [Pending.exception][]: Get the exception of the pending.

    **Low level methods**

    - [Pending.add_done_callback][]: Add a callback that is called once the pending is complete.
    - [Pending.remove_done_callback][]: Remove a previously added callback.
    - [Pending.set_canceller][]: Set a callback to handle cancellation.
    """

    __slots__ = [
        "__weakref__",
        "_cancelled",
        "_canceller",
        "_done",
        "_done_callbacks",
        "_exception",
        "_result",
        "_waiting",
        "context",
    ]

    _REPR_OMIT: ClassVar[list[str]] = ["func", "args", "kwargs", "caller"]
    """Keys of metadata to omit when creating a repr of the pending."""

    _metadata_mappings: ClassVar[dict[int, dict[str, Any]]] = {}
    """A mapping of pending ids to metadata."""

    _cancelled: str | None
    _canceller: Callable[[str | None], Any] | None
    _exception: Exception
    _done: bool
    _result: T_co
    context: contextvars.Context | None
    """The context associated with Pending."""

    @property
    def metadata(self) -> dict[str, Any]:
        """The metadata associated with the pending."""
        return self._metadata_mappings[id(self)]

    def __init__(
        self,
        context: contextvars.Context | None = None,
        trackers: type[PendingTracker] | tuple[type[PendingTracker], ...] = (),
        /,
        **metadata: Any,
    ) -> None:
        """Initializes a new pending object with optional creation options and metadata.

        Args:
            context: A context to associate with the pending, if provided it is copied.
            trackers: A subclass or tuple of `PendingTracker` subclasses to which the pending can be added in the current context.
            **metadata: Arbitrary keyword arguments containing metadata to associate with this Pending instance.

        Behavior:
            - Initializes internal state for tracking completion and cancellation.
            - Stores provided metadata in a class-level mapping.
        """
        self._done_callbacks: list[Callable[[Self], Any]] = []
        self._metadata_mappings[id(self)] = metadata
        self._done = False
        self._cancelled = None
        self._canceller = None

        if trackers or context:
            # A copy the context is required to avoid `PendingTracker.id` leakage.
            context = context.copy() if context else contextvars.copy_context()
        self.context = context

        # PendingTacker registration.
        if context:
            for cls in PendingTracker._subclasses:  # pyright: ignore[reportPrivateUsage]
                if id_ := context.get(cls._id_contextvar):  # pyright: ignore[reportPrivateUsage]
                    if trackers and issubclass(cls, trackers) and (tracker := PendingTracker._instances.get(id_)):  # pyright: ignore[reportPrivateUsage]
                        tracker.add(self)
                    else:
                        # Clear `PendingTracker.id`.
                        context.run(cls._id_contextvar.set, None)  # pyright: ignore[reportPrivateUsage]

    def __del__(self) -> None:
        self._metadata_mappings.pop(id(self), None)

    @override
    def __repr__(self) -> str:
        rep = (
            "<Pending"
            + ((" ⛔" + (f"message={self._cancelled!s}" if self._cancelled else "")) if self.cancelled() else "")
            + ((f" ❗ {e!r}" if (e := getattr(self, "_exception", None)) else " 🏁") if self._done else " 🏃")
        )
        rep = f"{rep} at {id(self)}"
        with contextlib.suppress(Exception):
            if md := self.metadata:
                rep = f"{rep} metadata:"
                if "func" in md:
                    items = [f"{k}={truncated_rep.repr(v)}" for k, v in md.items() if k not in self._REPR_OMIT]
                    rep += f" | {md['func']} {' | '.join(items) if items else ''}"
                else:
                    rep += f"{truncated_rep.repr(md)}"
        return rep + " >"

    @override
    def __await__(self) -> Generator[Any, None, T_co]:
        return self.wait().__await__()

    if TYPE_CHECKING:

        @overload
        async def wait(
            self,
            *,
            timeout: float | None = ...,
            protect: bool = False | ...,
            result: Literal[True] = True,
            shield: bool = ...,
        ) -> T_co: ...

        @overload
        async def wait(
            self,
            *,
            timeout: float | None = ...,
            protect: bool = ...,
            result: Literal[False],
            shield: bool = ...,
        ) -> None: ...

    async def wait(
        self,
        *,
        timeout: float | None = None,
        protect: bool = False,
        result: bool = True,
        shield: bool = False,
    ) -> T_co | None:
        """Wait for the pending to be done (internally synchronised).

        Args:
            timeout: Timeout in seconds.
            protect: Protect the pending from a [TimeoutError][] or external cancellation.
            result: If the result should be returned.
            shield: Shield from external cancellation.

        Returns:
            T_co: If `result` is `True`.
            None: If `result` is 'False`.

        Raises:
            TimeoutError: When the timeout expires and a result or exception has not been set.
            PendingCancelled: If `result` is `True` and the pending has been cancelled.
            Exception: If `result` is `True` and an exception was set on the pending.

        Tip:
            To wait for a cancelled pending to complete use `await pen.wait(result=False)`.
        """
        if not self._done:
            waiter = create_async_waiter(shield=shield)
            e = None
            wait_ = waiter.with_(timeout)

            def done(_) -> None:
                waiter.wake()

            try:
                try:
                    self._done_callbacks.append(done)
                    await wait_
                    if not self._done:
                        e = TimeoutError
                    del done, wait_, waiter
                except AttributeError:
                    # _done_callbacks was deleted meaning _done will be set soon.
                    wait_.close()
                    while not self._done:
                        await async_checkpoint(force=True)
            except anyio.get_cancelled_exc_class() as exc:
                e = exc
            if e:
                if not protect and not isinstance(self, ProtectedPending):
                    self.cancel(f"Cancelled due to cancellation or timeout: {e}.")
                raise e
        return self.result() if result else None

    if TYPE_CHECKING:

        @overload
        def wait_sync(
            self,
            *,
            timeout: float | None = ...,
            protect: bool = False | ...,
            result: Literal[True] = True,
            shield: bool = ...,
        ) -> T_co: ...

        @overload
        def wait_sync(
            self,
            *,
            timeout: float | None = ...,
            protect: bool = ...,
            result: Literal[False],
            shield: bool = ...,
        ) -> None: ...

    def wait_sync(
        self,
        *,
        timeout: float | None = None,
        protect: bool = False,
        result: bool = True,
        shield: bool = False,
    ) -> T_co | None:
        """Wait synchronously for the pending to be done (internally synchronised) returning the result if specified.

        Args:
            timeout: Timeout in seconds.
            protect: Protect the pending from cancellation from a `TimeoutError`.
            result: When `True` the result is returned.
            shield: Shield from external cancellation.

        Raises:
            TimeoutError: When the timeout expires and a result or exception has not been set.
            PendingCancelled: If `result=True` and the pending has been cancelled.
            Exception: If `result=True` and an exception was set on the pending.

        Warning:
            **Calling this method in the same thread where the result or exception is set
            will result in deadlock unless a greenlet based event library is in use.**
        """
        if not self._done:
            event = create_green_event(shield=shield)
            self.add_done_callback(lambda _: event.set())
            event.wait(timeout)
            if not self._done:
                msg = f"Timeout waiting for {self}"
                if not protect and not isinstance(self, ProtectedPending):
                    self.cancel(msg)
                raise TimeoutError(msg)
        return self.result() if result else None

    def _set_done(self, result: bool, value, /) -> None:
        if self._done:
            return
        try:
            callbacks = self._done_callbacks
            del self._done_callbacks
            if result:
                self._result = value
            else:
                self._exception = value
            self._done = True
            self._canceller = None
        except AttributeError:  # pragma: no cover
            return
        e = None
        # List reversal and BaseException handling inspiration: https://gist.github.com/x42005e1f/4f18c3c62da9135020bdea8c44c248a2
        callbacks.reverse()
        while callbacks:
            try:
                callbacks.pop()(self)
            except Exception:
                logging.getLogger().exception("An exception occurred in pending callback %r", self, exc_info=e)
            except BaseException as exc:
                e = exc
        if e:
            raise e from None

    def set_result(self, value: T_co) -> None:  # pyright: ignore[reportGeneralTypeIssues]
        """Set the result (low-level internally synchronised).

        This is noop if already done.

        Args:
            value: The result to set.
        """
        self._set_done(True, value)

    def set_exception(self, exception: BaseException) -> None:
        """Set the exception (low-level internally synchronised).

        This is noop if already done.

        Args:
            exception: The value to set as the exception.
        """
        self._set_done(False, exception)

    def cancel(self, msg: str | None = None) -> bool:
        """Cancel the pending.

        This is noop if already done.

        Args:
            msg: The cancellation message.

        Returns:
            bool: If the pending is marked as cancelled.

        Notes:
            - Cancellation cannot be undone.
            - Multiple calls append `msg` to the cancellation message with no other effect.
            - The done state is a function of the canceller, if no canceller is set, done
                will be set immediately.
        """
        if not self._done:
            if (cancelled := self._cancelled or "") and msg:
                msg = f"{cancelled}\n{msg}"
            self._cancelled = msg or cancelled
            if (canceller := self._canceller) is None:
                self._set_done(False, None)
            else:
                canceller(msg)
        return self._cancelled is not None

    async def cancel_wait(self, msg: str | None = None, *, timeout: float | None = None, shield: bool = False) -> None:
        """Cancel the pending and wait for it to be done.

        Args:
            msg: A reason for the cancellation.
            timeout: Timeout in seconds.
            shield: Shield from external cancellation.
        """
        if not self._done:
            self.cancel(msg)
            if not self._done:
                await self.wait(result=False, timeout=timeout, shield=shield)

    def cancelled(self) -> bool:
        """Returns `True` if the pending is marked as cancelled.

        Notes:
            - This can return `True` before a pending is done.
            - To wait for a pending to complete use `await pen.cancel_wait()`,
                `await pen.wait(result=False)` or `pen.wait_sync(result=False)`.
        """
        return self._cancelled is not None

    def set_canceller(self, canceller: Callable[[str | None], Any], /) -> None:
        """Set a callback to handle cancellation (low-level).

        Args:
            canceller: A callback that performs the cancellation of the pending.

                - It must accept the cancellation message as the first argument.
                - `canceller` must be externally synchronised.
                - [set_result][] or [set_exception][] *MUST* be called by the `canceller`,
                    or as a result of the call to `canceller` to mark the pending as done.
        """
        if not self._done:
            self._canceller = canceller

    def done(self) -> bool:
        """Returns `True` if a result or exception has been set, or when cancelled without a defined canceller."""
        return self._done

    def add_done_callback(self, fn: Callable[[Self], Any], /) -> None:
        """Add a callback that is called when the pending is done (low-level).

        Notes:
            - If the pending is:
                - *not* done: `fn` is added to the callback list.
                - done: `fn` is called immediately.
            - Callbacks are called FIFO in the thread where the pending is set done (potentially any thread).
            - The callback should be light weight and provide its own thread safety.
        """
        try:
            self._done_callbacks.append(fn)
        except AttributeError:
            fn(self)

    def remove_done_callback(self, fn: Callable[[Self], object], /) -> int:
        """Remove `fn` from the done callback list.

        Returns the number of items removed.
        """
        n = 0
        if not self._done and (callbacks := getattr(self, "_done_callbacks", None)):
            while True:
                try:
                    callbacks.remove(fn)
                    n += 1
                except ValueError:
                    break
        return n

    def result(self) -> T_co:
        """Return the result.

        Raises:
            PendingCancelled: If the pending has been cancelled.
            PendingNotDone: If the pending isn't done yet.
        """
        if self._cancelled is not None:
            raise PendingCancelled(self._cancelled)
        if not self._done:
            raise PendingNotDone
        if hasattr(self, "_result"):
            return self._result
        raise self._exception from None

    def exception(self) -> BaseException | None:
        """Return the exception.

        Raises:
            PendingCancelled: If the pending has been cancelled.
            PendingNotDone: If the pending isn't done yet.
        """
        if self._cancelled is not None:
            raise PendingCancelled(self._cancelled)
        if not self._done:
            raise PendingNotDone
        return getattr(self, "_exception", None)

metadata property 

metadata: dict[str, Any]

The metadata associated with the pending.

Referenced by:

context instance-attribute 

context: Context | None = context

The context associated with Pending.

Referenced by:

__init__ 

__init__(
    context: Context | None = None,
    trackers: type[PendingTracker] | tuple[type[PendingTracker], ...] = (),
    /,
    **metadata: Any,
) -> None

Parameters:

  • context

    (Context | None, default: None ) –

    A context to associate with the pending, if provided it is copied.

  • trackers

    (type[PendingTracker] | tuple[type[PendingTracker], ...], default: () ) –

    A subclass or tuple of PendingTracker subclasses to which the pending can be added in the current context.

  • **metadata

    (Any, default: {} ) –

    Arbitrary keyword arguments containing metadata to associate with this Pending instance.

Behavior
  • Initializes internal state for tracking completion and cancellation.
  • Stores provided metadata in a class-level mapping.
Source code in src/async_kernel/pending.py 
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
def __init__(
    self,
    context: contextvars.Context | None = None,
    trackers: type[PendingTracker] | tuple[type[PendingTracker], ...] = (),
    /,
    **metadata: Any,
) -> None:
    """Initializes a new pending object with optional creation options and metadata.

    Args:
        context: A context to associate with the pending, if provided it is copied.
        trackers: A subclass or tuple of `PendingTracker` subclasses to which the pending can be added in the current context.
        **metadata: Arbitrary keyword arguments containing metadata to associate with this Pending instance.

    Behavior:
        - Initializes internal state for tracking completion and cancellation.
        - Stores provided metadata in a class-level mapping.
    """
    self._done_callbacks: list[Callable[[Self], Any]] = []
    self._metadata_mappings[id(self)] = metadata
    self._done = False
    self._cancelled = None
    self._canceller = None

    if trackers or context:
        # A copy the context is required to avoid `PendingTracker.id` leakage.
        context = context.copy() if context else contextvars.copy_context()
    self.context = context

    # PendingTacker registration.
    if context:
        for cls in PendingTracker._subclasses:  # pyright: ignore[reportPrivateUsage]
            if id_ := context.get(cls._id_contextvar):  # pyright: ignore[reportPrivateUsage]
                if trackers and issubclass(cls, trackers) and (tracker := PendingTracker._instances.get(id_)):  # pyright: ignore[reportPrivateUsage]
                    tracker.add(self)
                else:
                    # Clear `PendingTracker.id`.
                    context.run(cls._id_contextvar.set, None)  # pyright: ignore[reportPrivateUsage]

wait async 

wait(
    *,
    timeout: float | None = ...,
    protect: bool = False | ...,
    result: Literal[True] = True,
    shield: bool = ...,
) -> T_co

wait(
    *,
    timeout: float | None = ...,
    protect: bool = ...,
    result: Literal[False],
    shield: bool = ...,
) -> None

wait(
    *,
    timeout: float | None = None,
    protect: bool = False,
    result: bool = True,
    shield: bool = False,
) -> T_co | None

Wait for the pending to be done (internally synchronised).

Parameters:

  • timeout

    (float | None, default: None ) –

    Timeout in seconds.

  • protect

    (bool, default: False ) –

    Protect the pending from a TimeoutError or external cancellation.

  • result

    (bool, default: True ) –

    If the result should be returned.

  • shield

    (bool, default: False ) –

    Shield from external cancellation.

Returns:

  • T_co ( T_co | None ) –

    If result is True.

  • None ( T_co | None ) –

    If result is 'False`.

Raises:

  • TimeoutError –

    When the timeout expires and a result or exception has not been set.

  • PendingCancelled –

    If result is True and the pending has been cancelled.

  • Exception –

    If result is True and an exception was set on the pending.

Tip

To wait for a cancelled pending to complete use await pen.wait(result=False).

Referenced by:
Source code in src/async_kernel/pending.py 
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
async def wait(
    self,
    *,
    timeout: float | None = None,
    protect: bool = False,
    result: bool = True,
    shield: bool = False,
) -> T_co | None:
    """Wait for the pending to be done (internally synchronised).

    Args:
        timeout: Timeout in seconds.
        protect: Protect the pending from a [TimeoutError][] or external cancellation.
        result: If the result should be returned.
        shield: Shield from external cancellation.

    Returns:
        T_co: If `result` is `True`.
        None: If `result` is 'False`.

    Raises:
        TimeoutError: When the timeout expires and a result or exception has not been set.
        PendingCancelled: If `result` is `True` and the pending has been cancelled.
        Exception: If `result` is `True` and an exception was set on the pending.

    Tip:
        To wait for a cancelled pending to complete use `await pen.wait(result=False)`.
    """
    if not self._done:
        waiter = create_async_waiter(shield=shield)
        e = None
        wait_ = waiter.with_(timeout)

        def done(_) -> None:
            waiter.wake()

        try:
            try:
                self._done_callbacks.append(done)
                await wait_
                if not self._done:
                    e = TimeoutError
                del done, wait_, waiter
            except AttributeError:
                # _done_callbacks was deleted meaning _done will be set soon.
                wait_.close()
                while not self._done:
                    await async_checkpoint(force=True)
        except anyio.get_cancelled_exc_class() as exc:
            e = exc
        if e:
            if not protect and not isinstance(self, ProtectedPending):
                self.cancel(f"Cancelled due to cancellation or timeout: {e}.")
            raise e
    return self.result() if result else None

wait_sync 

wait_sync(
    *,
    timeout: float | None = ...,
    protect: bool = False | ...,
    result: Literal[True] = True,
    shield: bool = ...,
) -> T_co

wait_sync(
    *,
    timeout: float | None = ...,
    protect: bool = ...,
    result: Literal[False],
    shield: bool = ...,
) -> None

wait_sync(
    *,
    timeout: float | None = None,
    protect: bool = False,
    result: bool = True,
    shield: bool = False,
) -> T_co | None

Wait synchronously for the pending to be done (internally synchronised) returning the result if specified.

Parameters:

  • timeout

    (float | None, default: None ) –

    Timeout in seconds.

  • protect

    (bool, default: False ) –

    Protect the pending from cancellation from a TimeoutError.

  • result

    (bool, default: True ) –

    When True the result is returned.

  • shield

    (bool, default: False ) –

    Shield from external cancellation.

Raises:

  • TimeoutError –

    When the timeout expires and a result or exception has not been set.

  • PendingCancelled –

    If result=True and the pending has been cancelled.

  • Exception –

    If result=True and an exception was set on the pending.

Warning

Calling this method in the same thread where the result or exception is set will result in deadlock unless a greenlet based event library is in use.

Referenced by:
Source code in src/async_kernel/pending.py 
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
def wait_sync(
    self,
    *,
    timeout: float | None = None,
    protect: bool = False,
    result: bool = True,
    shield: bool = False,
) -> T_co | None:
    """Wait synchronously for the pending to be done (internally synchronised) returning the result if specified.

    Args:
        timeout: Timeout in seconds.
        protect: Protect the pending from cancellation from a `TimeoutError`.
        result: When `True` the result is returned.
        shield: Shield from external cancellation.

    Raises:
        TimeoutError: When the timeout expires and a result or exception has not been set.
        PendingCancelled: If `result=True` and the pending has been cancelled.
        Exception: If `result=True` and an exception was set on the pending.

    Warning:
        **Calling this method in the same thread where the result or exception is set
        will result in deadlock unless a greenlet based event library is in use.**
    """
    if not self._done:
        event = create_green_event(shield=shield)
        self.add_done_callback(lambda _: event.set())
        event.wait(timeout)
        if not self._done:
            msg = f"Timeout waiting for {self}"
            if not protect and not isinstance(self, ProtectedPending):
                self.cancel(msg)
            raise TimeoutError(msg)
    return self.result() if result else None

set_result 

set_result(value: T_co) -> None

Set the result (low-level internally synchronised).

This is noop if already done.

Parameters:

  • value

    (T_co) –

    The result to set.

Referenced by:
Source code in src/async_kernel/pending.py 
603
604
605
606
607
608
609
610
611
def set_result(self, value: T_co) -> None:  # pyright: ignore[reportGeneralTypeIssues]
    """Set the result (low-level internally synchronised).

    This is noop if already done.

    Args:
        value: The result to set.
    """
    self._set_done(True, value)

set_exception 

set_exception(exception: BaseException) -> None

Set the exception (low-level internally synchronised).

This is noop if already done.

Parameters:

Referenced by:
Source code in src/async_kernel/pending.py 
613
614
615
616
617
618
619
620
621
def set_exception(self, exception: BaseException) -> None:
    """Set the exception (low-level internally synchronised).

    This is noop if already done.

    Args:
        exception: The value to set as the exception.
    """
    self._set_done(False, exception)

cancel 

cancel(msg: str | None = None) -> bool

Cancel the pending.

This is noop if already done.

Parameters:

  • msg

    (str | None, default: None ) –

    The cancellation message.

Returns:

  • bool ( bool ) –

    If the pending is marked as cancelled.

Notes
  • Cancellation cannot be undone.
  • Multiple calls append msg to the cancellation message with no other effect.
  • The done state is a function of the canceller, if no canceller is set, done will be set immediately.
Referenced by:
Source code in src/async_kernel/pending.py 
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
def cancel(self, msg: str | None = None) -> bool:
    """Cancel the pending.

    This is noop if already done.

    Args:
        msg: The cancellation message.

    Returns:
        bool: If the pending is marked as cancelled.

    Notes:
        - Cancellation cannot be undone.
        - Multiple calls append `msg` to the cancellation message with no other effect.
        - The done state is a function of the canceller, if no canceller is set, done
            will be set immediately.
    """
    if not self._done:
        if (cancelled := self._cancelled or "") and msg:
            msg = f"{cancelled}\n{msg}"
        self._cancelled = msg or cancelled
        if (canceller := self._canceller) is None:
            self._set_done(False, None)
        else:
            canceller(msg)
    return self._cancelled is not None

cancel_wait async 

cancel_wait(
    msg: str | None = None, *, timeout: float | None = None, shield: bool = False
) -> None

Cancel the pending and wait for it to be done.

Parameters:

  • msg

    (str | None, default: None ) –

    A reason for the cancellation.

  • timeout

    (float | None, default: None ) –

    Timeout in seconds.

  • shield

    (bool, default: False ) –

    Shield from external cancellation.

Referenced by:
Source code in src/async_kernel/pending.py 
650
651
652
653
654
655
656
657
658
659
660
661
async def cancel_wait(self, msg: str | None = None, *, timeout: float | None = None, shield: bool = False) -> None:
    """Cancel the pending and wait for it to be done.

    Args:
        msg: A reason for the cancellation.
        timeout: Timeout in seconds.
        shield: Shield from external cancellation.
    """
    if not self._done:
        self.cancel(msg)
        if not self._done:
            await self.wait(result=False, timeout=timeout, shield=shield)

cancelled 

cancelled() -> bool

Returns True if the pending is marked as cancelled.

Notes
  • This can return True before a pending is done.
  • To wait for a pending to complete use await pen.cancel_wait(), await pen.wait(result=False) or pen.wait_sync(result=False).
Source code in src/async_kernel/pending.py 
663
664
665
666
667
668
669
670
671
def cancelled(self) -> bool:
    """Returns `True` if the pending is marked as cancelled.

    Notes:
        - This can return `True` before a pending is done.
        - To wait for a pending to complete use `await pen.cancel_wait()`,
            `await pen.wait(result=False)` or `pen.wait_sync(result=False)`.
    """
    return self._cancelled is not None

set_canceller 

set_canceller(canceller: Callable[[str | None], Any]) -> None

Set a callback to handle cancellation (low-level).

Parameters:

  • canceller

    (Callable[[str | None], Any]) –

    A callback that performs the cancellation of the pending.

    • It must accept the cancellation message as the first argument.
    • canceller must be externally synchronised.
    • set_result or set_exception MUST be called by the canceller, or as a result of the call to canceller to mark the pending as done.
Referenced by:
Source code in src/async_kernel/pending.py 
673
674
675
676
677
678
679
680
681
682
683
684
685
def set_canceller(self, canceller: Callable[[str | None], Any], /) -> None:
    """Set a callback to handle cancellation (low-level).

    Args:
        canceller: A callback that performs the cancellation of the pending.

            - It must accept the cancellation message as the first argument.
            - `canceller` must be externally synchronised.
            - [set_result][] or [set_exception][] *MUST* be called by the `canceller`,
                or as a result of the call to `canceller` to mark the pending as done.
    """
    if not self._done:
        self._canceller = canceller

done 

done() -> bool

Returns True if a result or exception has been set, or when cancelled without a defined canceller.

Source code in src/async_kernel/pending.py 
687
688
689
def done(self) -> bool:
    """Returns `True` if a result or exception has been set, or when cancelled without a defined canceller."""
    return self._done

add_done_callback 

add_done_callback(fn: Callable[[Self], Any]) -> None

Add a callback that is called when the pending is done (low-level).

Notes
  • If the pending is:
    • not done: fn is added to the callback list.
    • done: fn is called immediately.
  • Callbacks are called FIFO in the thread where the pending is set done (potentially any thread).
  • The callback should be light weight and provide its own thread safety.
Referenced by:
Source code in src/async_kernel/pending.py 
691
692
693
694
695
696
697
698
699
700
701
702
703
704
def add_done_callback(self, fn: Callable[[Self], Any], /) -> None:
    """Add a callback that is called when the pending is done (low-level).

    Notes:
        - If the pending is:
            - *not* done: `fn` is added to the callback list.
            - done: `fn` is called immediately.
        - Callbacks are called FIFO in the thread where the pending is set done (potentially any thread).
        - The callback should be light weight and provide its own thread safety.
    """
    try:
        self._done_callbacks.append(fn)
    except AttributeError:
        fn(self)

remove_done_callback 

remove_done_callback(fn: Callable[[Self], object]) -> int

Remove fn from the done callback list.

Returns the number of items removed.

Referenced by:
Source code in src/async_kernel/pending.py 
706
707
708
709
710
711
712
713
714
715
716
717
718
719
def remove_done_callback(self, fn: Callable[[Self], object], /) -> int:
    """Remove `fn` from the done callback list.

    Returns the number of items removed.
    """
    n = 0
    if not self._done and (callbacks := getattr(self, "_done_callbacks", None)):
        while True:
            try:
                callbacks.remove(fn)
                n += 1
            except ValueError:
                break
    return n

result 

result() -> T_co

Return the result.

Raises:

Referenced by:
Source code in src/async_kernel/pending.py 
721
722
723
724
725
726
727
728
729
730
731
732
733
734
def result(self) -> T_co:
    """Return the result.

    Raises:
        PendingCancelled: If the pending has been cancelled.
        PendingNotDone: If the pending isn't done yet.
    """
    if self._cancelled is not None:
        raise PendingCancelled(self._cancelled)
    if not self._done:
        raise PendingNotDone
    if hasattr(self, "_result"):
        return self._result
    raise self._exception from None

exception 

exception() -> BaseException | None

Return the exception.

Raises:

Referenced by:
Source code in src/async_kernel/pending.py 
736
737
738
739
740
741
742
743
744
745
746
747
def exception(self) -> BaseException | None:
    """Return the exception.

    Raises:
        PendingCancelled: If the pending has been cancelled.
        PendingNotDone: If the pending isn't done yet.
    """
    if self._cancelled is not None:
        raise PendingCancelled(self._cancelled)
    if not self._done:
        raise PendingNotDone
    return getattr(self, "_exception", None)