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Coroutines support libraries for Kotlin
/*
* Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
*/
package kotlinx.coroutines.channels
import kotlinx.coroutines.*
import kotlinx.coroutines.channels.Channel.Factory.CONFLATED
import kotlinx.coroutines.channels.Channel.Factory.UNLIMITED
import kotlinx.coroutines.selects.*
/**
* Sender's interface to [Channel].
*/
public interface SendChannel {
/**
* Returns `true` if this channel was closed by invocation of [close] and thus
* the [send] and [offer] attempts throws exception.
*/
public val isClosedForSend: Boolean
/**
* Returns `true` if the channel is full (out of capacity) and the [send] attempt will suspend.
* This function returns `false` for [isClosedForSend] channel.
*/
public val isFull: Boolean
/**
* Adds [element] into to this channel, suspending the caller while this channel [isFull],
* or throws exception if the channel [isClosedForSend] (see [close] for details).
*
* Note, that closing a channel _after_ this function had suspended does not cause this suspended send invocation
* to abort, because closing a channel is conceptually like sending a special "close token" over this channel.
* All elements that are sent over the channel are delivered in first-in first-out order. The element that
* is being sent will get delivered to receivers before a close token.
*
* This suspending function is cancellable. If the [Job] of the current coroutine is cancelled or completed while this
* function is suspended, this function immediately resumes with [CancellationException].
*
* *Cancellation of suspended send is atomic* -- when this function
* throws [CancellationException] it means that the [element] was not sent to this channel.
* As a side-effect of atomic cancellation, a thread-bound coroutine (to some UI thread, for example) may
* continue to execute even after it was cancelled from the same thread in the case when this send operation
* was already resumed and the continuation was posted for execution to the thread's queue.
*
* Note, that this function does not check for cancellation when it is not suspended.
* Use [yield] or [CoroutineScope.isActive] to periodically check for cancellation in tight loops if needed.
*
* This function can be used in [select] invocation with [onSend] clause.
* Use [offer] to try sending to this channel without waiting.
*/
public suspend fun send(element: E)
/**
* Clause for [select] expression of [send] suspending function that selects when the element that is specified
* as parameter is sent to the channel. When the clause is selected the reference to this channel
* is passed into the corresponding block.
*
* The [select] invocation fails with exception if the channel [isClosedForSend] (see [close] for details).
*/
public val onSend: SelectClause2>
/**
* Adds [element] into this queue if it is possible to do so immediately without violating capacity restrictions
* and returns `true`. Otherwise, it returns `false` immediately
* or throws exception if the channel [isClosedForSend] (see [close] for details).
*/
public fun offer(element: E): Boolean
/**
* Closes this channel with an optional exceptional [cause].
* This is an idempotent operation -- repeated invocations of this function have no effect and return `false`.
* Conceptually, its sends a special "close token" over this channel.
*
* Immediately after invocation of this function
* [isClosedForSend] starts returning `true`. However, [isClosedForReceive][ReceiveChannel.isClosedForReceive]
* on the side of [ReceiveChannel] starts returning `true` only after all previously sent elements
* are received.
*
* A channel that was closed without a [cause] throws [ClosedSendChannelException] on attempts to send or receive.
* A channel that was closed with non-null [cause] is called a _failed_ channel. Attempts to send or
* receive on a failed channel throw the specified [cause] exception.
*/
public fun close(cause: Throwable? = null): Boolean
/**
* Registers handler which is synchronously invoked once the channel is [closed][close]
* or receiving side of this channel is [cancelled][ReceiveChannel.cancel].
* Only one handler can be attached to the channel during channel's lifetime.
* Handler is invoked when [isClosedForSend] starts to return `true`.
* If channel is already closed, handler is invoked immediately.
*
* The meaning of `cause` that is passed to the handler:
* * `null` if channel was closed or cancelled without corresponding argument
* * close or cancel cause otherwise.
*
* Example of usage (exception handling is omitted):
* ```
* val events = Channel(UNLIMITED)
* callbackBasedApi.registerCallback { event ->
* events.offer(event)
* }
*
* val uiUpdater = launch(UI, parent = UILifecycle) {
* events.consume {}
* events.cancel()
* }
*
* events.invokeOnClose { callbackBasedApi.stop() }
*
* ```
*
* @throws UnsupportedOperationException if underlying channel doesn't support [invokeOnClose].
* Implementation note: currently, [invokeOnClose] is unsupported only by Rx-like integrations
*
* @throws IllegalStateException if another handler was already registered
*/
public fun invokeOnClose(handler: (cause: Throwable?) -> Unit)
}
/**
* Receiver's interface to [Channel].
*/
public interface ReceiveChannel {
/**
* Returns `true` if this channel was closed by invocation of [close][SendChannel.close] on the [SendChannel]
* side and all previously sent items were already received, so that the [receive] attempt
* throws [ClosedReceiveChannelException]. If the channel was closed because of the exception, it
* is considered closed, too, but it is called a _failed_ channel. All suspending attempts to receive
* an element from a failed channel throw the original [close][SendChannel.close] cause exception.
*/
public val isClosedForReceive: Boolean
/**
* Returns `true` if the channel is empty (contains no elements) and the [receive] attempt will suspend.
* This function returns `false` for [isClosedForReceive] channel.
*/
public val isEmpty: Boolean
/**
* Retrieves and removes the element from this channel suspending the caller while this channel [isEmpty]
* or throws [ClosedReceiveChannelException] if the channel [isClosedForReceive].
* If the channel was closed because of the exception, it is called a _failed_ channel and this function
* throws the original [close][SendChannel.close] cause exception.
*
* This suspending function is cancellable. If the [Job] of the current coroutine is cancelled or completed while this
* function is suspended, this function immediately resumes with [CancellationException].
*
* *Cancellation of suspended receive is atomic* -- when this function
* throws [CancellationException] it means that the element was not retrieved from this channel.
* As a side-effect of atomic cancellation, a thread-bound coroutine (to some UI thread, for example) may
* continue to execute even after it was cancelled from the same thread in the case when this receive operation
* was already resumed and the continuation was posted for execution to the thread's queue.
*
* Note, that this function does not check for cancellation when it is not suspended.
* Use [yield] or [CoroutineScope.isActive] to periodically check for cancellation in tight loops if needed.
*
* This function can be used in [select] invocation with [onReceive] clause.
* Use [poll] to try receiving from this channel without waiting.
*/
public suspend fun receive(): E
/**
* Clause for [select] expression of [receive] suspending function that selects with the element that
* is received from the channel.
* The [select] invocation fails with exception if the channel
* [isClosedForReceive] (see [close][SendChannel.close] for details).
*/
public val onReceive: SelectClause1
/**
* Retrieves and removes the element from this channel suspending the caller while this channel [isEmpty]
* or returns `null` if the channel is [closed][isClosedForReceive] without cause
* or throws the original [close][SendChannel.close] cause exception if the channel has _failed_.
*
* This suspending function is cancellable. If the [Job] of the current coroutine is cancelled or completed while this
* function is suspended, this function immediately resumes with [CancellationException].
*
* *Cancellation of suspended receive is atomic* -- when this function
* throws [CancellationException] it means that the element was not retrieved from this channel.
* As a side-effect of atomic cancellation, a thread-bound coroutine (to some UI thread, for example) may
* continue to execute even after it was cancelled from the same thread in the case when this receive operation
* was already resumed and the continuation was posted for execution to the thread's queue.
*
* Note, that this function does not check for cancellation when it is not suspended.
* Use [yield] or [CoroutineScope.isActive] to periodically check for cancellation in tight loops if needed.
*
* This function can be used in [select] invocation with [onReceiveOrNull] clause.
* Use [poll] to try receiving from this channel without waiting.
*/
public suspend fun receiveOrNull(): E?
/**
* Clause for [select] expression of [receiveOrNull] suspending function that selects with the element that
* is received from the channel or selects with `null` if if the channel
* [isClosedForReceive] without cause. The [select] invocation fails with
* the original [close][SendChannel.close] cause exception if the channel has _failed_.
*/
public val onReceiveOrNull: SelectClause1
/**
* Retrieves and removes the element from this channel, or returns `null` if this channel [isEmpty]
* or is [isClosedForReceive] without cause.
* It throws the original [close][SendChannel.close] cause exception if the channel has _failed_.
*/
public fun poll(): E?
/**
* Returns new iterator to receive elements from this channels using `for` loop.
* Iteration completes normally when the channel is [isClosedForReceive] without cause and
* throws the original [close][SendChannel.close] cause exception if the channel has _failed_.
*/
public operator fun iterator(): ChannelIterator
/**
* Cancels reception of remaining elements from this channel. This function closes the channel with
* the specified cause (unless it was already closed) and removes all buffered sent elements from it.
* This function returns `true` if the channel was not closed previously, or `false` otherwise.
*
* Immediately after invocation of this function [isClosedForReceive] and
* [isClosedForSend][SendChannel.isClosedForSend]
* on the side of [SendChannel] start returning `true`, so all attempts to send to this channel
* afterwards will throw [ClosedSendChannelException], while attempts to receive will throw
* [ClosedReceiveChannelException] if it was cancelled without a cause.
* A channel that was cancelled with non-null [cause] is called a _failed_ channel. Attempts to send or
* receive on a failed channel throw the specified [cause] exception.
*/
public fun cancel(cause: Throwable? = null): Boolean
}
/**
* Iterator for [ReceiveChannel]. Instances of this interface are *not thread-safe* and shall not be used
* from concurrent coroutines.
*/
public interface ChannelIterator {
/**
* Returns `true` if the channel has more elements suspending the caller while this channel
* [isEmpty][ReceiveChannel.isEmpty] or returns `false` if the channel
* [isClosedForReceive][ReceiveChannel.isClosedForReceive] without cause.
* It throws the original [close][SendChannel.close] cause exception if the channel has _failed_.
*
* This function retrieves and removes the element from this channel for the subsequent invocation
* of [next].
*
* This suspending function is cancellable. If the [Job] of the current coroutine is cancelled or completed while this
* function is suspended, this function immediately resumes with [CancellationException].
*
* *Cancellation of suspended receive is atomic* -- when this function
* throws [CancellationException] it means that the element was not retrieved from this channel.
* As a side-effect of atomic cancellation, a thread-bound coroutine (to some UI thread, for example) may
* continue to execute even after it was cancelled from the same thread in the case when this receive operation
* was already resumed and the continuation was posted for execution to the thread's queue.
*
* Note, that this function does not check for cancellation when it is not suspended.
* Use [yield] or [CoroutineScope.isActive] to periodically check for cancellation in tight loops if needed.
*/
public suspend operator fun hasNext(): Boolean
/**
* Retrieves and removes the element from this channel suspending the caller while this channel
* [isEmpty][ReceiveChannel.isEmpty] or throws [ClosedReceiveChannelException] if the channel
* [isClosedForReceive][ReceiveChannel.isClosedForReceive] without cause.
* It throws the original [close][SendChannel.close] cause exception if the channel has _failed_.
*
* This suspending function is cancellable. If the [Job] of the current coroutine is cancelled or completed while this
* function is suspended, this function immediately resumes with [CancellationException].
*
* *Cancellation of suspended receive is atomic* -- when this function
* throws [CancellationException] it means that the element was not retrieved from this channel.
* As a side-effect of atomic cancellation, a thread-bound coroutine (to some UI thread, for example) may
* continue to execute even after it was cancelled from the same thread in the case when this receive operation
* was already resumed and the continuation was posted for execution to the thread's queue.
*
* Note, that this function does not check for cancellation when it is not suspended.
* Use [yield] or [CoroutineScope.isActive] to periodically check for cancellation in tight loops if needed.
*/
public suspend operator fun next(): E
}
/**
* Channel is a non-blocking primitive for communication between sender using [SendChannel] and receiver using [ReceiveChannel].
* Conceptually, a channel is similar to [BlockingQueue][java.util.concurrent.BlockingQueue],
* but it has suspending operations instead of blocking ones and it can be closed.
*
* See `Channel(capacity)` factory function for the description of available channel implementations.
*/
public interface Channel : SendChannel, ReceiveChannel {
/**
* Constants for channel factory function `Channel()`.
*/
public companion object Factory {
/**
* Requests channel with unlimited capacity buffer in `Channel(...)` factory function --
* the [LinkedListChannel] gets created.
*/
public const val UNLIMITED = Int.MAX_VALUE
/**
* Requests conflated channel in `Channel(...)` factory function --
* the [ConflatedChannel] gets created.
*/
public const val CONFLATED = -1
/**
* Creates a channel with the specified buffer capacity (or without a buffer by default).
* @suppress **Deprecated**
*/
@Deprecated("Replaced with top-level function", level = DeprecationLevel.HIDDEN)
public operator fun invoke(capacity: Int = 0): Channel = Channel(capacity)
}
}
/**
* Creates a channel without a buffer -- [RendezvousChannel].
*/
public fun Channel(): Channel = RendezvousChannel()
/**
* Creates a channel with the specified buffer capacity (or without a buffer by default).
*
* The resulting channel type depends on the specified [capacity] parameter:
* * when `capacity` is 0 -- creates [RendezvousChannel] without a buffer;
* * when `capacity` is [Channel.UNLIMITED] -- creates [LinkedListChannel] with buffer of unlimited size;
* * when `capacity` is [Channel.CONFLATED] -- creates [ConflatedChannel] that conflates back-to-back sends;
* * when `capacity` is positive, but less than [UNLIMITED] -- creates [ArrayChannel] with a buffer of the specified `capacity`;
* * otherwise -- throws [IllegalArgumentException].
*/
public fun Channel(capacity: Int): Channel =
when (capacity) {
0 -> RendezvousChannel()
UNLIMITED -> LinkedListChannel()
CONFLATED -> ConflatedChannel()
else -> ArrayChannel(capacity)
}
/**
* Indicates attempt to [send][SendChannel.send] on [isClosedForSend][SendChannel.isClosedForSend] channel
* that was closed without a cause. A _failed_ channel rethrows the original [close][SendChannel.close] cause
* exception on send attempts.
*/
public class ClosedSendChannelException(message: String?) : CancellationException(message)
/**
* Indicates attempt to [receive][ReceiveChannel.receive] on [isClosedForReceive][ReceiveChannel.isClosedForReceive]
* channel that was closed without a cause. A _failed_ channel rethrows the original [close][SendChannel.close] cause
* exception on receive attempts.
*/
public class ClosedReceiveChannelException(message: String?) : NoSuchElementException(message)
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