1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
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
|
/*
* Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
*/
package kotlinx.coroutines
import kotlinx.coroutines.selects.*
/**
* Deferred value is a non-blocking cancellable future — it is a [Job] with a result.
*
* It is created with the [async][CoroutineScope.async] coroutine builder or via the constructor of [CompletableDeferred] class.
* It is in [active][isActive] state while the value is being computed.
*
* `Deferred` has the same state machine as the [Job] with additional convenience methods to retrieve
* the successful or failed result of the computation that was carried out. The result of the deferred is
* available when it is [completed][isCompleted] and can be retrieved by [await] method, which throws
* an exception if the deferred had failed.
* Note that a _cancelled_ deferred is also considered as completed.
* The corresponding exception can be retrieved via [getCompletionExceptionOrNull] from a completed instance of deferred.
*
* Usually, a deferred value is created in _active_ state (it is created and started).
* However, the [async][CoroutineScope.async] coroutine builder has an optional `start` parameter that creates a deferred value in _new_ state
* when this parameter is set to [CoroutineStart.LAZY].
* Such a deferred can be be made _active_ by invoking [start], [join], or [await].
*
* A deferred value is a [Job]. A job in the
* [coroutineContext](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.coroutines/coroutine-context.html)
* of [async][CoroutineScope.async] builder represents the coroutine itself.
*
* All functions on this interface and on all interfaces derived from it are **thread-safe** and can
* be safely invoked from concurrent coroutines without external synchronization.
*
* **`Deferred` interface and all its derived interfaces are not stable for inheritance in 3rd party libraries**,
* as new methods might be added to this interface in the future, but is stable for use.
*/
public interface Deferred<out T> : Job {
/**
* Awaits for completion of this value without blocking a thread and resumes when deferred computation is complete,
* returning the resulting value or throwing the corresponding exception if the deferred was cancelled.
*
* This suspending function is cancellable.
* If the [Job] of the current coroutine is cancelled or completed while this suspending function is waiting, this function
* immediately resumes with [CancellationException].
* There is a **prompt cancellation guarantee**. If the job was cancelled while this function was
* suspended, it will not resume successfully. See [suspendCancellableCoroutine] documentation for low-level details.
*
* This function can be used in [select] invocation with [onAwait] clause.
* Use [isCompleted] to check for completion of this deferred value without waiting.
*/
public suspend fun await(): T
/**
* Clause for [select] expression of [await] suspending function that selects with the deferred value when it is
* resolved. The [select] invocation fails if the deferred value completes exceptionally (either fails or
* it cancelled).
*/
public val onAwait: SelectClause1<T>
/**
* Returns *completed* result or throws [IllegalStateException] if this deferred value has not
* [completed][isCompleted] yet. It throws the corresponding exception if this deferred was [cancelled][isCancelled].
*
* This function is designed to be used from [invokeOnCompletion] handlers, when there is an absolute certainty that
* the value is already complete. See also [getCompletionExceptionOrNull].
*
* **Note: This is an experimental api.** This function may be removed or renamed in the future.
*/
@ExperimentalCoroutinesApi
public fun getCompleted(): T
/**
* Returns *completion exception* result if this deferred was [cancelled][isCancelled] and has [completed][isCompleted],
* `null` if it had completed normally, or throws [IllegalStateException] if this deferred value has not
* [completed][isCompleted] yet.
*
* This function is designed to be used from [invokeOnCompletion] handlers, when there is an absolute certainty that
* the value is already complete. See also [getCompleted].
*
* **Note: This is an experimental api.** This function may be removed or renamed in the future.
*/
@ExperimentalCoroutinesApi
public fun getCompletionExceptionOrNull(): Throwable?
}
|
