| /* |
| * Copyright 2016-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license. |
| */ |
| |
| @file:Suppress("FunctionName") |
| |
| package kotlinx.coroutines.channels |
| |
| import kotlinx.coroutines.* |
| import kotlinx.coroutines.channels.Channel.Factory.BUFFERED |
| import kotlinx.coroutines.channels.Channel.Factory.CHANNEL_DEFAULT_CAPACITY |
| import kotlinx.coroutines.channels.Channel.Factory.CONFLATED |
| import kotlinx.coroutines.channels.Channel.Factory.RENDEZVOUS |
| import kotlinx.coroutines.channels.Channel.Factory.UNLIMITED |
| import kotlinx.coroutines.internal.* |
| import kotlinx.coroutines.selects.* |
| import kotlin.internal.* |
| import kotlin.jvm.* |
| |
| /** |
| * Sender's interface to [Channel]. |
| */ |
| public interface SendChannel<in E> { |
| /** |
| * Returns `true` if this channel was closed by an invocation of [close]. This means that |
| * calling [send] or [offer] will result in an exception. |
| * |
| * **Note: This is an experimental api.** This property may change its semantics and/or name in the future. |
| */ |
| @ExperimentalCoroutinesApi |
| public val isClosedForSend: Boolean |
| |
| /** |
| * Returns `true` if the channel is full (out of capacity), which means that an attempt to [send] will suspend. |
| * This function returns `false` if the channel [is closed for `send`][isClosedForSend]. |
| * |
| * @suppress **Will be removed in next releases, no replacement.** |
| */ |
| @ExperimentalCoroutinesApi |
| @Deprecated(level = DeprecationLevel.ERROR, message = "Will be removed in next releases without replacement") |
| public val isFull: Boolean |
| |
| /** |
| * Sends the specified [element] to this channel, suspending the caller while the buffer of this channel is full |
| * or if it does not exist, or throws an exception if the channel [is closed for `send`][isClosedForSend] (see [close] for details). |
| * |
| * [Closing][close] a channel _after_ this function has 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 sent over the channel are delivered in first-in first-out order. The sent element |
| * will be delivered to receivers before the 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 a [CancellationException]. |
| * There is a **prompt cancellation guarantee**. If the job was cancelled while this function was |
| * suspended, it will not resume successfully. The `send` call can send the element to the channel, |
| * but then throw [CancellationException], thus an exception should not be treated as a failure to deliver the element. |
| * See "Undelivered elements" section in [Channel] documentation for details on handling undelivered elements. |
| * |
| * 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] invocations with the [onSend] clause. |
| * Use [offer] to try sending to this channel without waiting. |
| */ |
| public suspend fun send(element: E) |
| |
| /** |
| * Clause for the [select] expression of the [send] suspending function that selects when the element that is specified |
| * as the 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 an exception if the channel [is closed for `send`][isClosedForSend] (see [close] for details). |
| */ |
| public val onSend: SelectClause2<E, SendChannel<E>> |
| |
| /** |
| * Immediately adds the specified [element] to this channel, if this doesn't violate its capacity restrictions, |
| * and returns `true`. Otherwise, just returns `false`. This is a synchronous variant of [send] which backs off |
| * in situations when `send` suspends. |
| * |
| * Throws an exception if the channel [is closed for `send`][isClosedForSend] (see [close] for details). |
| * |
| * When `offer` call returns `false` it guarantees that the element was not delivered to the consumer and it |
| * it does not call `onUndeliveredElement` that was installed for this channel. If the channel was closed, |
| * then it calls `onUndeliveredElement` before throwing an exception. |
| * See "Undelivered elements" section in [Channel] documentation for details on handling undelivered elements. |
| */ |
| public fun offer(element: E): Boolean |
| |
| /** |
| * Closes this channel. |
| * This is an idempotent operation — subsequent 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 a [ClosedSendChannelException] on attempts to [send] or [offer] |
| * and [ClosedReceiveChannelException] on attempts to [receive][ReceiveChannel.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 a [handler] which is synchronously invoked once the channel is [closed][close] |
| * or the receiving side of this channel is [cancelled][ReceiveChannel.cancel]. |
| * Only one handler can be attached to a channel during its lifetime. |
| * The `handler` is invoked when [isClosedForSend] starts to return `true`. |
| * If the channel is closed already, the handler is invoked immediately. |
| * |
| * The meaning of `cause` that is passed to the handler: |
| * * `null` if the channel was closed or cancelled without the corresponding argument |
| * * the cause of `close` or `cancel` otherwise. |
| * |
| * Example of usage (exception handling is omitted): |
| * ``` |
| * val events = Channel(UNLIMITED) |
| * callbackBasedApi.registerCallback { event -> |
| * events.offer(event) |
| * } |
| * |
| * val uiUpdater = launch(Dispatchers.Main, parent = UILifecycle) { |
| * events.consume {} |
| * events.cancel() |
| * } |
| * |
| * events.invokeOnClose { callbackBasedApi.stop() } |
| * |
| * ``` |
| * |
| * **Note: This is an experimental api.** This function may change its semantics, parameters or return type in the future. |
| * |
| * @throws UnsupportedOperationException if the 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 |
| */ |
| @ExperimentalCoroutinesApi |
| public fun invokeOnClose(handler: (cause: Throwable?) -> Unit) |
| } |
| |
| /** |
| * Receiver's interface to [Channel]. |
| */ |
| public interface ReceiveChannel<out E> { |
| /** |
| * 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. This means that calling [receive] |
| * will result in a [ClosedReceiveChannelException]. If the channel was closed because of an exception, it |
| * is considered closed, too, but is called a _failed_ channel. All suspending attempts to receive |
| * an element from a failed channel throw the original [close][SendChannel.close] cause exception. |
| * |
| * **Note: This is an experimental api.** This property may change its semantics and/or name in the future. |
| */ |
| @ExperimentalCoroutinesApi |
| public val isClosedForReceive: Boolean |
| |
| /** |
| * Returns `true` if the channel is empty (contains no elements), which means that an attempt to [receive] will suspend. |
| * This function returns `false` if the channel [is closed for `receive`][isClosedForReceive]. |
| */ |
| @ExperimentalCoroutinesApi |
| public val isEmpty: Boolean |
| |
| /** |
| * Retrieves and removes an element from this channel if it's not empty, or suspends the caller while the channel is empty, |
| * or throws a [ClosedReceiveChannelException] if the channel [is closed for `receive`][isClosedForReceive]. |
| * If the channel was closed because of an exception, it is called a _failed_ channel and this function |
| * will throw 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 a [CancellationException]. |
| * There is a **prompt cancellation guarantee**. If the job was cancelled while this function was |
| * suspended, it will not resume successfully. The `receive` call can retrieve the element from the channel, |
| * but then throw [CancellationException], thus failing to deliver the element. |
| * See "Undelivered elements" section in [Channel] documentation for details on handling undelivered elements. |
| * |
| * 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] invocations with the [onReceive] clause. |
| * Use [poll] to try receiving from this channel without waiting. |
| */ |
| public suspend fun receive(): E |
| |
| /** |
| * Clause for the [select] expression of the [receive] suspending function that selects with the element |
| * received from the channel. |
| * The [select] invocation fails with an exception if the channel |
| * [is closed for `receive`][isClosedForReceive] (see [close][SendChannel.close] for details). |
| */ |
| public val onReceive: SelectClause1<E> |
| |
| /** |
| * Retrieves and removes an element from this channel if it's not empty, or suspends the caller while the channel is empty, |
| * or returns `null` if the channel is [closed for `receive`][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 a [CancellationException]. |
| * There is a **prompt cancellation guarantee**. If the job was cancelled while this function was |
| * suspended, it will not resume successfully. The `receiveOrNull` call can retrieve the element from the channel, |
| * but then throw [CancellationException], thus failing to deliver the element. |
| * See "Undelivered elements" section in [Channel] documentation for details on handling undelivered elements. |
| * |
| * 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] invocations with the [onReceiveOrNull] clause. |
| * Use [poll] to try receiving from this channel without waiting. |
| * |
| * @suppress **Deprecated**: in favor of receiveOrClosed and receiveOrNull extension. |
| */ |
| @ObsoleteCoroutinesApi |
| @Suppress("INVISIBLE_REFERENCE", "INVISIBLE_MEMBER") |
| @LowPriorityInOverloadResolution |
| @Deprecated( |
| message = "Deprecated in favor of receiveOrClosed and receiveOrNull extension", |
| level = DeprecationLevel.WARNING, |
| replaceWith = ReplaceWith("receiveOrNull", "kotlinx.coroutines.channels.receiveOrNull") |
| ) |
| public suspend fun receiveOrNull(): E? |
| |
| /** |
| * Clause for the [select] expression of the [receiveOrNull] suspending function that selects with the element |
| * received from the channel or `null` if the channel is |
| * [closed for `receive`][isClosedForReceive] without a cause. The [select] invocation fails with |
| * the original [close][SendChannel.close] cause exception if the channel has _failed_. |
| * |
| * @suppress **Deprecated**: in favor of onReceiveOrClosed and onReceiveOrNull extension. |
| */ |
| @ObsoleteCoroutinesApi |
| @Suppress("INVISIBLE_REFERENCE", "INVISIBLE_MEMBER") |
| @LowPriorityInOverloadResolution |
| @Deprecated( |
| message = "Deprecated in favor of onReceiveOrClosed and onReceiveOrNull extension", |
| level = DeprecationLevel.WARNING, |
| replaceWith = ReplaceWith("onReceiveOrNull", "kotlinx.coroutines.channels.onReceiveOrNull") |
| ) |
| public val onReceiveOrNull: SelectClause1<E?> |
| |
| /** |
| * Retrieves and removes an element from this channel if it's not empty, or suspends the caller while this channel is empty. |
| * This method returns [ValueOrClosed] with the value of an element successfully retrieved from the channel |
| * or the close cause if the channel was closed. |
| * |
| * 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 a [CancellationException]. |
| * There is a **prompt cancellation guarantee**. If the job was cancelled while this function was |
| * suspended, it will not resume successfully. The `receiveOrClosed` call can retrieve the element from the channel, |
| * but then throw [CancellationException], thus failing to deliver the element. |
| * See "Undelivered elements" section in [Channel] documentation for details on handling undelivered elements. |
| * |
| * 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] invocations with the [onReceiveOrClosed] clause. |
| * Use [poll] to try receiving from this channel without waiting. |
| * |
| * @suppress *This is an internal API, do not use*: Inline classes ABI is not stable yet and |
| * [KT-27524](https://youtrack.jetbrains.com/issue/KT-27524) needs to be fixed. |
| */ |
| @InternalCoroutinesApi // until https://youtrack.jetbrains.com/issue/KT-27524 is fixed |
| public suspend fun receiveOrClosed(): ValueOrClosed<E> |
| |
| /** |
| * Clause for the [select] expression of the [receiveOrClosed] suspending function that selects with the [ValueOrClosed] with a value |
| * that is received from the channel or with a close cause if the channel |
| * [is closed for `receive`][isClosedForReceive]. |
| * |
| * @suppress *This is an internal API, do not use*: Inline classes ABI is not stable yet and |
| * [KT-27524](https://youtrack.jetbrains.com/issue/KT-27524) needs to be fixed. |
| */ |
| @InternalCoroutinesApi // until https://youtrack.jetbrains.com/issue/KT-27524 is fixed |
| public val onReceiveOrClosed: SelectClause1<ValueOrClosed<E>> |
| |
| /** |
| * Retrieves and removes an element from this channel if its not empty, or returns `null` if the channel is empty |
| * or is [is closed for `receive`][isClosedForReceive] without a cause. |
| * It throws the original [close][SendChannel.close] cause exception if the channel has _failed_. |
| */ |
| public fun poll(): E? |
| |
| /** |
| * Returns a new iterator to receive elements from this channel using a `for` loop. |
| * Iteration completes normally when the channel [is closed for `receive`][isClosedForReceive] without a cause and |
| * throws the original [close][SendChannel.close] cause exception if the channel has _failed_. |
| */ |
| public operator fun iterator(): ChannelIterator<E> |
| |
| /** |
| * Cancels reception of remaining elements from this channel with an optional [cause]. |
| * This function closes the channel and removes all buffered sent elements from it. |
| * |
| * A cause can be used to specify an error message or to provide other details on |
| * the cancellation reason for debugging purposes. |
| * If the cause is not specified, then an instance of [CancellationException] with a |
| * default message is created to [close][SendChannel.close] the channel. |
| * |
| * Immediately after invocation of this function [isClosedForReceive] and |
| * [isClosedForSend][SendChannel.isClosedForSend] |
| * on the side of [SendChannel] start returning `true`. Any attempt to send to or receive from this channel |
| * will lead to a [CancellationException]. |
| */ |
| public fun cancel(cause: CancellationException? = null) |
| |
| /** |
| * @suppress This method implements old version of JVM ABI. Use [cancel]. |
| */ |
| @Deprecated(level = DeprecationLevel.HIDDEN, message = "Since 1.2.0, binary compatibility with versions <= 1.1.x") |
| public fun cancel(): Unit = cancel(null) |
| |
| /** |
| * @suppress This method has bad semantics when cause is not a [CancellationException]. Use [cancel]. |
| */ |
| @Deprecated(level = DeprecationLevel.HIDDEN, message = "Since 1.2.0, binary compatibility with versions <= 1.1.x") |
| public fun cancel(cause: Throwable? = null): Boolean |
| } |
| |
| /** |
| * A discriminated union of [ReceiveChannel.receiveOrClosed] result |
| * that encapsulates either an element of type [T] successfully received from the channel or a close cause. |
| * |
| * :todo: Do not make it public before resolving todos in the code of this class. |
| * |
| * @suppress *This is an internal API, do not use*: Inline classes ABI is not stable yet and |
| * [KT-27524](https://youtrack.jetbrains.com/issue/KT-27524) needs to be fixed. |
| */ |
| @Suppress("NON_PUBLIC_PRIMARY_CONSTRUCTOR_OF_INLINE_CLASS", "EXPERIMENTAL_FEATURE_WARNING") |
| @InternalCoroutinesApi // until https://youtrack.jetbrains.com/issue/KT-27524 is fixed |
| public inline class ValueOrClosed<out T> |
| internal constructor(private val holder: Any?) { |
| /** |
| * Returns `true` if this instance represents a received element. |
| * In this case [isClosed] returns `false`. |
| * todo: it is commented for now, because it is not used |
| */ |
| //public val isValue: Boolean get() = holder !is Closed |
| |
| /** |
| * Returns `true` if this instance represents a close cause. |
| * In this case [isValue] returns `false`. |
| */ |
| public val isClosed: Boolean get() = holder is Closed |
| |
| /** |
| * Returns the received value if this instance represents a received value, or throws an [IllegalStateException] otherwise. |
| * |
| * :todo: Decide, if it is needed, how it shall be named with relation to [valueOrThrow]: |
| * |
| * So we have the following methods on `ValueOrClosed`: `value`, `valueOrNull`, `valueOrThrow`. |
| * On the other hand, the channel has the following `receive` variants: |
| * * `receive` which corresponds to `receiveOrClosed().valueOrThrow`... huh? |
| * * `receiveOrNull` which corresponds to `receiveOrClosed().valueOrNull` |
| * * `receiveOrClosed` |
| * For the sake of simplicity consider dropping this version of `value` and rename [valueOrThrow] to simply `value`. |
| */ |
| @Suppress("UNCHECKED_CAST") |
| public val value: T |
| get() = if (holder is Closed) error(DEFAULT_CLOSE_MESSAGE) else holder as T |
| |
| /** |
| * Returns the received value if this element represents a received value, or `null` otherwise. |
| * :todo: Decide if it shall be made into extension that is available only for non-null T. |
| * Note: it might become inconsistent with kotlin.Result |
| */ |
| @Suppress("UNCHECKED_CAST") |
| public val valueOrNull: T? |
| get() = if (holder is Closed) null else holder as T |
| |
| /** |
| * :todo: Decide, if it is needed, how it shall be named with relation to [value]. |
| * Note that `valueOrThrow` rethrows the cause adding no meaningful information about the call site, |
| * so if one is sure that `ValueOrClosed` always holds a value, this very property should be used. |
| * Otherwise, it could be very hard to locate the source of the exception. |
| * todo: it is commented for now, because it is not used |
| */ |
| //@Suppress("UNCHECKED_CAST") |
| //public val valueOrThrow: T |
| // get() = if (holder is Closed) throw holder.exception else holder as T |
| |
| /** |
| * Returns the close cause of the channel if this instance represents a close cause, or throws |
| * an [IllegalStateException] otherwise. |
| */ |
| @Suppress("UNCHECKED_CAST") |
| public val closeCause: Throwable? get() = |
| if (holder is Closed) holder.cause else error("Channel was not closed") |
| |
| /** |
| * @suppress |
| */ |
| public override fun toString(): String = |
| when (holder) { |
| is Closed -> holder.toString() |
| else -> "Value($holder)" |
| } |
| |
| internal class Closed(@JvmField val cause: Throwable?) { |
| // todo: it is commented for now, because it is not used |
| //val exception: Throwable get() = cause ?: ClosedReceiveChannelException(DEFAULT_CLOSE_MESSAGE) |
| override fun equals(other: Any?): Boolean = other is Closed && cause == other.cause |
| override fun hashCode(): Int = cause.hashCode() |
| override fun toString(): String = "Closed($cause)" |
| } |
| |
| /** |
| * todo: consider making value/closed constructors public in the future. |
| */ |
| internal companion object { |
| @Suppress("NOTHING_TO_INLINE") |
| internal inline fun <E> value(value: E): ValueOrClosed<E> = |
| ValueOrClosed(value) |
| |
| @Suppress("NOTHING_TO_INLINE") |
| internal inline fun <E> closed(cause: Throwable?): ValueOrClosed<E> = |
| ValueOrClosed(Closed(cause)) |
| } |
| } |
| |
| /** |
| * Iterator for [ReceiveChannel]. Instances of this interface are *not thread-safe* and shall not be used |
| * from concurrent coroutines. |
| */ |
| public interface ChannelIterator<out E> { |
| /** |
| * Returns `true` if the channel has more elements, suspending the caller while this channel is empty, |
| * or returns `false` if the channel [is closed for `receive`][ReceiveChannel.isClosedForReceive] without a cause. |
| * It throws the original [close][SendChannel.close] cause exception if the channel has _failed_. |
| * |
| * This function retrieves and removes an 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 a [CancellationException]. |
| * There is a **prompt cancellation guarantee**. If the job was cancelled while this function was |
| * suspended, it will not resume successfully. The `hasNext` call can retrieve the element from the channel, |
| * but then throw [CancellationException], thus failing to deliver the element. |
| * See "Undelivered elements" section in [Channel] documentation for details on handling undelivered elements. |
| * |
| * 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 |
| |
| @Deprecated(message = "Since 1.3.0, binary compatibility with versions <= 1.2.x", level = DeprecationLevel.HIDDEN) |
| @Suppress("INAPPLICABLE_JVM_NAME") |
| @JvmName("next") |
| public suspend fun next0(): E { |
| /* |
| * Before 1.3.0 the "next()" could have been used without invoking "hasNext" first and there were code samples |
| * demonstrating this behavior, so we preserve this logic for full binary backwards compatibility with previously |
| * compiled code. |
| */ |
| if (!hasNext()) throw ClosedReceiveChannelException(DEFAULT_CLOSE_MESSAGE) |
| return next() |
| } |
| |
| /** |
| * Retrieves the element removed from the channel by a preceding call to [hasNext], or |
| * throws an [IllegalStateException] if [hasNext] was not invoked. |
| * This method should only be used in pair with [hasNext]: |
| * ``` |
| * while (iterator.hasNext()) { |
| * val element = iterator.next() |
| * // ... handle element ... |
| * } |
| * ``` |
| * |
| * This method throws a [ClosedReceiveChannelException] if the channel [is closed for `receive`][ReceiveChannel.isClosedForReceive] without a cause. |
| * It throws the original [close][SendChannel.close] cause exception if the channel has _failed_. |
| */ |
| public operator fun next(): E |
| } |
| |
| /** |
| * Channel is a non-blocking primitive for communication between a sender (via [SendChannel]) and a receiver (via [ReceiveChannel]). |
| * Conceptually, a channel is similar to Java's [BlockingQueue][java.util.concurrent.BlockingQueue], |
| * but it has suspending operations instead of blocking ones and can be [closed][SendChannel.close]. |
| * |
| * ### Creating channels |
| * |
| * The `Channel(capacity)` factory function is used to create channels of different kinds depending on |
| * the value of the `capacity` integer: |
| * |
| * * When `capacity` is 0 — it creates a _rendezvous_ channel. |
| * This channel does not have any buffer at all. An element is transferred from the sender |
| * to the receiver only when [send] and [receive] invocations meet in time (rendezvous), so [send] suspends |
| * until another coroutine invokes [receive], and [receive] suspends until another coroutine invokes [send]. |
| * |
| * * When `capacity` is [Channel.UNLIMITED] — it creates a channel with effectively unlimited buffer. |
| * This channel has a linked-list buffer of unlimited capacity (limited only by available memory). |
| * [Sending][send] to this channel never suspends, and [offer] always returns `true`. |
| * |
| * * When `capacity` is [Channel.CONFLATED] — it creates a _conflated_ channel |
| * This channel buffers at most one element and conflates all subsequent `send` and `offer` invocations, |
| * so that the receiver always gets the last element sent. |
| * Back-to-send sent elements are conflated — only the last sent element is received, |
| * while previously sent elements **are lost**. |
| * [Sending][send] to this channel never suspends, and [offer] always returns `true`. |
| * |
| * * When `capacity` is positive but less than [UNLIMITED] — it creates an array-based channel with the specified capacity. |
| * This channel has an array buffer of a fixed `capacity`. |
| * [Sending][send] suspends only when the buffer is full, and [receiving][receive] suspends only when the buffer is empty. |
| * |
| * Buffered channels can be configured with an additional [`onBufferOverflow`][BufferOverflow] parameter. It controls the behaviour |
| * of the channel's [send][Channel.send] function on buffer overflow: |
| * |
| * * [SUSPEND][BufferOverflow.SUSPEND] — the default, suspend `send` on buffer overflow until there is |
| * free space in the buffer. |
| * * [DROP_OLDEST][BufferOverflow.DROP_OLDEST] — do not suspend the `send`, add the latest value to the buffer, |
| * drop the oldest one from the buffer. |
| * A channel with `capacity = 1` and `onBufferOverflow = DROP_OLDEST` is a _conflated_ channel. |
| * * [DROP_LATEST][BufferOverflow.DROP_LATEST] — do not suspend the `send`, drop the value that is being sent, |
| * keep the buffer contents intact. |
| * |
| * A non-default `onBufferOverflow` implicitly creates a channel with at least one buffered element and |
| * is ignored for a channel with unlimited buffer. It cannot be specified for `capacity = CONFLATED`, which |
| * is a shortcut by itself. |
| * |
| * ### Prompt cancellation guarantee |
| * |
| * All suspending functions with channels provide **prompt cancellation guarantee**. |
| * If the job was cancelled while send or receive function was suspended, it will not resume successfully, |
| * but throws a [CancellationException]. |
| * With a single-threaded [dispatcher][CoroutineDispatcher] like [Dispatchers.Main] this gives a |
| * guarantee that if a piece code running in this thread cancels a [Job], then a coroutine running this job cannot |
| * resume successfully and continue to run, ensuring a prompt response to its cancellation. |
| * |
| * > **Prompt cancellation guarantee** for channel operations was added since `kotlinx.coroutines` version `1.4.0` |
| * > and had replaced a channel-specific atomic-cancellation that was not consistent with other suspending functions. |
| * > The low-level mechanics of prompt cancellation are explained in [suspendCancellableCoroutine] function. |
| * |
| * ### Undelivered elements |
| * |
| * As a result of a prompt cancellation guarantee, when a closeable resource |
| * (like open file or a handle to another native resource) is transferred via channel from one coroutine to another |
| * it can fail to be delivered and will be lost if either send or receive operations are cancelled in transit. |
| * |
| * A `Channel()` constructor function has an `onUndeliveredElement` optional parameter. |
| * When `onUndeliveredElement` parameter is set, the corresponding function is called once for each element |
| * that was sent to the channel with the call to the [send][SendChannel.send] function but failed to be delivered, |
| * which can happen in the following cases: |
| * |
| * * When [send][SendChannel.send] operation throws an exception because it was cancelled before it had a chance to actually |
| * send the element or because the channel was [closed][SendChannel.close] or [cancelled][ReceiveChannel.cancel]. |
| * * When [offer][SendChannel.offer] operation throws an exception when |
| * the channel was [closed][SendChannel.close] or [cancelled][ReceiveChannel.cancel]. |
| * * When [receive][ReceiveChannel.receive], [receiveOrNull][ReceiveChannel.receiveOrNull], or [hasNext][ChannelIterator.hasNext] |
| * operation throws an exception when it had retrieved the element from the |
| * channel but was cancelled before the code following the receive call resumed. |
| * * The channel was [cancelled][ReceiveChannel.cancel], in which case `onUndeliveredElement` is called on every |
| * remaining element in the channel's buffer. |
| * |
| * Note, that `onUndeliveredElement` function is called synchronously in an arbitrary context. It should be fast, non-blocking, |
| * and should not throw exceptions. Any exception thrown by `onUndeliveredElement` is wrapped into an internal runtime |
| * exception which is either rethrown from the caller method or handed off to the exception handler in the current context |
| * (see [CoroutineExceptionHandler]) when one is available. |
| * |
| * A typical usage for `onDeliveredElement` is to close a resource that is being transferred via the channel. The |
| * following code pattern guarantees that opened resources are closed even if producer, consumer, and/or channel |
| * are cancelled. Resources are never lost. |
| * |
| * ``` |
| * // Create the channel with onUndeliveredElement block that closes a resource |
| * val channel = Channel<Resource>(capacity) { resource -> resource.close() } |
| * |
| * // Producer code |
| * val resourceToSend = openResource() |
| * channel.send(resourceToSend) |
| * |
| * // Consumer code |
| * val resourceReceived = channel.receive() |
| * try { |
| * // work with received resource |
| * } finally { |
| * resourceReceived.close() |
| * } |
| * ``` |
| * |
| * > Note, that if you do any kind of work in between `openResource()` and `channel.send(...)`, then you should |
| * > ensure that resource gets closed in case this additional code fails. |
| */ |
| public interface Channel<E> : SendChannel<E>, ReceiveChannel<E> { |
| /** |
| * Constants for the channel factory function `Channel()`. |
| */ |
| public companion object Factory { |
| /** |
| * Requests a channel with an unlimited capacity buffer in the `Channel(...)` factory function. |
| */ |
| public const val UNLIMITED: Int = Int.MAX_VALUE |
| |
| /** |
| * Requests a rendezvous channel in the `Channel(...)` factory function — a channel that does not have a buffer. |
| */ |
| public const val RENDEZVOUS: Int = 0 |
| |
| /** |
| * Requests a conflated channel in the `Channel(...)` factory function. This is a shortcut to creating |
| * a channel with [`onBufferOverflow = DROP_OLDEST`][BufferOverflow.DROP_OLDEST]. |
| */ |
| public const val CONFLATED: Int = -1 |
| |
| /** |
| * Requests a buffered channel with the default buffer capacity in the `Channel(...)` factory function. |
| * The default capacity for a channel that [suspends][BufferOverflow.SUSPEND] on overflow |
| * is 64 and can be overridden by setting [DEFAULT_BUFFER_PROPERTY_NAME] on JVM. |
| * For non-suspending channels, a buffer of capacity 1 is used. |
| */ |
| public const val BUFFERED: Int = -2 |
| |
| // only for internal use, cannot be used with Channel(...) |
| internal const val OPTIONAL_CHANNEL = -3 |
| |
| /** |
| * Name of the property that defines the default channel capacity when |
| * [BUFFERED] is used as parameter in `Channel(...)` factory function. |
| */ |
| public const val DEFAULT_BUFFER_PROPERTY_NAME: String = "kotlinx.coroutines.channels.defaultBuffer" |
| |
| internal val CHANNEL_DEFAULT_CAPACITY = systemProp(DEFAULT_BUFFER_PROPERTY_NAME, |
| 64, 1, UNLIMITED - 1 |
| ) |
| } |
| } |
| |
| /** |
| * Creates a channel with the specified buffer capacity (or without a buffer by default). |
| * See [Channel] interface documentation for details. |
| * |
| * @param capacity either a positive channel capacity or one of the constants defined in [Channel.Factory]. |
| * @param onBufferOverflow configures an action on buffer overflow (optional, defaults to |
| * a [suspending][BufferOverflow.SUSPEND] attempt to [send][Channel.send] a value, |
| * supported only when `capacity >= 0` or `capacity == Channel.BUFFERED`, |
| * implicitly creates a channel with at least one buffered element). |
| * @param onUndeliveredElement an optional function that is called when element was sent but was not delivered to the consumer. |
| * See "Undelivered elements" section in [Channel] documentation. |
| * @throws IllegalArgumentException when [capacity] < -2 |
| */ |
| public fun <E> Channel( |
| capacity: Int = RENDEZVOUS, |
| onBufferOverflow: BufferOverflow = BufferOverflow.SUSPEND, |
| onUndeliveredElement: ((E) -> Unit)? = null |
| ): Channel<E> = |
| when (capacity) { |
| RENDEZVOUS -> { |
| if (onBufferOverflow == BufferOverflow.SUSPEND) |
| RendezvousChannel(onUndeliveredElement) // an efficient implementation of rendezvous channel |
| else |
| ArrayChannel(1, onBufferOverflow, onUndeliveredElement) // support buffer overflow with buffered channel |
| } |
| CONFLATED -> { |
| require(onBufferOverflow == BufferOverflow.SUSPEND) { |
| "CONFLATED capacity cannot be used with non-default onBufferOverflow" |
| } |
| ConflatedChannel(onUndeliveredElement) |
| } |
| UNLIMITED -> LinkedListChannel(onUndeliveredElement) // ignores onBufferOverflow: it has buffer, but it never overflows |
| BUFFERED -> ArrayChannel( // uses default capacity with SUSPEND |
| if (onBufferOverflow == BufferOverflow.SUSPEND) CHANNEL_DEFAULT_CAPACITY else 1, |
| onBufferOverflow, onUndeliveredElement |
| ) |
| else -> { |
| if (capacity == 1 && onBufferOverflow == BufferOverflow.DROP_OLDEST) |
| ConflatedChannel(onUndeliveredElement) // conflated implementation is more efficient but appears to work in the same way |
| else |
| ArrayChannel(capacity, onBufferOverflow, onUndeliveredElement) |
| } |
| } |
| |
| @Deprecated(level = DeprecationLevel.HIDDEN, message = "Since 1.4.0, binary compatibility with earlier versions") |
| public fun <E> Channel(capacity: Int = RENDEZVOUS): Channel<E> = Channel(capacity) |
| |
| /** |
| * Indicates an attempt to [send][SendChannel.send] to a [isClosedForSend][SendChannel.isClosedForSend] channel |
| * that was closed without a cause. A _failed_ channel rethrows the original [close][SendChannel.close] cause |
| * exception on send attempts. |
| * |
| * This exception is a subclass of [IllegalStateException], because, conceptually, it is the sender's responsibility |
| * to close the channel and not try to send anything thereafter. Attempts to |
| * send to a closed channel indicate a logical error in the sender's code. |
| */ |
| public class ClosedSendChannelException(message: String?) : IllegalStateException(message) |
| |
| /** |
| * Indicates an attempt to [receive][ReceiveChannel.receive] from a [isClosedForReceive][ReceiveChannel.isClosedForReceive] |
| * channel that was closed without a cause. A _failed_ channel rethrows the original [close][SendChannel.close] cause |
| * exception on receive attempts. |
| * |
| * This exception is a subclass of [NoSuchElementException] to be consistent with plain collections. |
| */ |
| public class ClosedReceiveChannelException(message: String?) : NoSuchElementException(message) |