kotlinx-coroutines-core / kotlinx.coroutines.experimental.channels / Channel

Channel

interface Channel<E> : SendChannel<E>, ReceiveChannel<E> (source)

Platform and version requirements: JVM

Channel is a non-blocking primitive for communication between sender using SendChannel and receiver using ReceiveChannel. Conceptually, a channel is similar to 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.

Inherited Properties

isClosedForReceive	`abstract val isClosedForReceive: Boolean` Returns `true` if this channel was closed by invocation of 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 cause exception.
isClosedForSend	`abstract val isClosedForSend: Boolean` Returns `true` if this channel was closed by invocation of close and thus the send and offer attempts throws exception.
isEmpty	`abstract val isEmpty: Boolean` Returns `true` if the channel is empty (contains no elements) and the receive attempt will suspend. This function returns `false` for isClosedForReceive channel.
isFull	`abstract val isFull: Boolean` Returns `true` if the channel is full (out of capacity) and the send attempt will suspend. This function returns `false` for isClosedForSend channel.
onReceive	`abstract val onReceive: SelectClause1<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 for details).
onReceiveOrNull	`abstract val onReceiveOrNull: SelectClause1<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 cause exception if the channel has failed.
onSend	`abstract val onSend: SelectClause2<E, SendChannel<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.

Inherited Functions

cancel	`abstract fun cancel(cause: Throwable? = null): Boolean` 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.
close	`abstract fun close(cause: Throwable? = null): 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.
iterator	`abstract operator fun iterator(): ChannelIterator<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 cause exception if the channel has failed.
offer	`abstract fun offer(element: E): Boolean` 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).
poll	`abstract fun poll(): E?` 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 cause exception if the channel has failed.
receive	`abstract suspend fun receive(): E` 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 cause exception.
receiveOrNull	`abstract suspend fun receiveOrNull(): E?` Retrieves and removes the element from this channel suspending the caller while this channel isEmpty or returns `null` if the channel is closed without cause or throws the original close cause exception if the channel has failed.
send	`abstract suspend fun send(element: E): Unit` Adds element into to this channel, suspending the caller while this channel isFull, or throws exception if the channel isClosedForSend (see close for details).

Companion Object Properties

CONFLATED	`const val CONFLATED: Int` Requests conflated channel in `Channel(...)` factory function – the ConflatedChannel gets created.
UNLIMITED	`const val UNLIMITED: Int` Requests channel with unlimited capacity buffer in `Channel(...)` factory function – the LinkedListChannel gets created.

Extension Functions

all	`suspend fun <E> ReceiveChannel<E>.all( predicate: (E) -> Boolean ): Boolean` Returns `true` if all elements match the given predicate.
any	`suspend fun <E> ReceiveChannel<E>.any(): Boolean` Returns `true` if channel has at least one element. `suspend fun <E> ReceiveChannel<E>.any( predicate: (E) -> Boolean ): Boolean` Returns `true` if at least one element matches the given predicate.
associate	`suspend fun <E, K, V> ReceiveChannel<E>.associate( transform: (E) -> Pair<K, V> ): Map<K, V>` Returns a Map containing key-value pairs provided by transform function applied to elements of the given channel.
associateBy	`suspend fun <E, K> ReceiveChannel<E>.associateBy( keySelector: (E) -> K ): Map<K, E>` Returns a Map containing the elements from the given channel indexed by the key returned from keySelector function applied to each element. `suspend fun <E, K, V> ReceiveChannel<E>.associateBy( keySelector: (E) -> K, valueTransform: (E) -> V ): Map<K, V>` Returns a Map containing the values provided by valueTransform and indexed by keySelector functions applied to elements of the given channel.
associateByTo	`suspend fun <E, K, M : MutableMap<in K, in E>> ReceiveChannel<E>.associateByTo( destination: M, keySelector: (E) -> K ): M` Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function applied to each element of the given channel and value is the element itself. `suspend fun <E, K, V, M : MutableMap<in K, in V>> ReceiveChannel<E>.associateByTo( destination: M, keySelector: (E) -> K, valueTransform: (E) -> V ): M` Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function and and value is provided by the valueTransform function applied to elements of the given channel.
associateTo	`suspend fun <E, K, V, M : MutableMap<in K, in V>> ReceiveChannel<E>.associateTo( destination: M, transform: (E) -> Pair<K, V> ): M` Populates and returns the destination mutable map with key-value pairs provided by transform function applied to each element of the given channel.
consume	`fun <E, R> ReceiveChannel<E>.consume( block: ReceiveChannel<E>.() -> R ): R` Makes sure that the given block consumes all elements from the given channel by always invoking cancel after the execution of the block.
consumeEach	`suspend fun <E> ReceiveChannel<E>.consumeEach( action: (E) -> Unit ): Unit` Performs the given action for each received element.
consumeEachIndexed	`suspend fun <E> ReceiveChannel<E>.consumeEachIndexed( action: (IndexedValue<E>) -> Unit ): Unit` Performs the given action for each received element.
count	`suspend fun <E> ReceiveChannel<E>.count(): Int` Returns the number of elements in this channel. `suspend fun <E> ReceiveChannel<E>.count( predicate: (E) -> Boolean ): Int` Returns the number of elements matching the given predicate.
distinct	`fun <E> ReceiveChannel<E>.distinct(): ReceiveChannel<E>` Returns a channel containing only distinct elements from the given channel.
distinctBy	`fun <E, K> ReceiveChannel<E>.distinctBy( context: CoroutineContext = Unconfined, selector: suspend (E) -> K ): ReceiveChannel<E>` Returns a channel containing only elements from the given channel having distinct keys returned by the given selector function.
drop	`fun <E> ReceiveChannel<E>.drop( n: Int, context: CoroutineContext = Unconfined ): ReceiveChannel<E>` Returns a channel containing all elements except first n elements.
dropWhile	`fun <E> ReceiveChannel<E>.dropWhile( context: CoroutineContext = Unconfined, predicate: suspend (E) -> Boolean ): ReceiveChannel<E>` Returns a channel containing all elements except first elements that satisfy the given predicate.
elementAt	`suspend fun <E> ReceiveChannel<E>.elementAt(index: Int): E` Returns an element at the given index or throws an IndexOutOfBoundsException if the index is out of bounds of this channel.
elementAtOrElse	`suspend fun <E> ReceiveChannel<E>.elementAtOrElse( index: Int, defaultValue: (Int) -> E ): E` Returns an element at the given index or the result of calling the defaultValue function if the index is out of bounds of this channel.
elementAtOrNull	`suspend fun <E> ReceiveChannel<E>.elementAtOrNull( index: Int ): E?` Returns an element at the given index or `null` if the index is out of bounds of this channel.
filter	`fun <E> ReceiveChannel<E>.filter( context: CoroutineContext = Unconfined, predicate: suspend (E) -> Boolean ): ReceiveChannel<E>` Returns a channel containing only elements matching the given predicate.
filterIndexed	`fun <E> ReceiveChannel<E>.filterIndexed( context: CoroutineContext = Unconfined, predicate: suspend (index: Int, E) -> Boolean ): ReceiveChannel<E>` Returns a channel containing only elements matching the given predicate.
filterIndexedTo	`suspend fun <E, C : MutableCollection<in E>> ReceiveChannel<E>.filterIndexedTo( destination: C, predicate: (index: Int, E) -> Boolean ): C` Appends all elements matching the given predicate to the given destination.
filterNot	`fun <E> ReceiveChannel<E>.filterNot( context: CoroutineContext = Unconfined, predicate: suspend (E) -> Boolean ): ReceiveChannel<E>` Returns a channel containing all elements not matching the given predicate.
filterNotNull	`fun <E : Any> ReceiveChannel<E?>.filterNotNull(): ReceiveChannel<E>` Returns a channel containing all elements that are not `null`.
filterNotNullTo	`suspend fun <E : Any, C : MutableCollection<in E>> ReceiveChannel<E?>.filterNotNullTo( destination: C ): C` Appends all elements that are not `null` to the given destination.
filterNotTo	`suspend fun <E, C : MutableCollection<in E>> ReceiveChannel<E>.filterNotTo( destination: C, predicate: (E) -> Boolean ): C` Appends all elements not matching the given predicate to the given destination.
filterTo	`suspend fun <E, C : MutableCollection<in E>> ReceiveChannel<E>.filterTo( destination: C, predicate: (E) -> Boolean ): C` Appends all elements matching the given predicate to the given destination.
find	`suspend fun <E> ReceiveChannel<E>.find( predicate: (E) -> Boolean ): E?` Returns the first element matching the given predicate, or `null` if no such element was found.
findLast	`suspend fun <E> ReceiveChannel<E>.findLast( predicate: (E) -> Boolean ): E?` Returns the last element matching the given predicate, or `null` if no such element was found.
first	`suspend fun <E> ReceiveChannel<E>.first(): E` Returns first element. `suspend fun <E> ReceiveChannel<E>.first( predicate: (E) -> Boolean ): E` Returns the first element matching the given predicate.
firstOrNull	`suspend fun <E> ReceiveChannel<E>.firstOrNull(): E?` Returns the first element, or `null` if the channel is empty. `suspend fun <E> ReceiveChannel<E>.firstOrNull( predicate: (E) -> Boolean ): E?` Returns the first element matching the given predicate, or `null` if element was not found.
flatMap	`fun <E, R> ReceiveChannel<E>.flatMap( context: CoroutineContext = Unconfined, transform: suspend (E) -> ReceiveChannel<R> ): ReceiveChannel<R>` Returns a single channel of all elements from results of transform function being invoked on each element of original channel.
fold	`suspend fun <E, R> ReceiveChannel<E>.fold( initial: R, operation: (acc: R, E) -> R ): R` Accumulates value starting with initial value and applying operation from left to right to current accumulator value and each element.
foldIndexed	`suspend fun <E, R> ReceiveChannel<E>.foldIndexed( initial: R, operation: (index: Int, acc: R, E) -> R ): R` Accumulates value starting with initial value and applying operation from left to right to current accumulator value and each element with its index in the original channel.
groupBy	`suspend fun <E, K> ReceiveChannel<E>.groupBy( keySelector: (E) -> K ): Map<K, List<E>>` Groups elements of the original channel by the key returned by the given keySelector function applied to each element and returns a map where each group key is associated with a list of corresponding elements. `suspend fun <E, K, V> ReceiveChannel<E>.groupBy( keySelector: (E) -> K, valueTransform: (E) -> V ): Map<K, List<V>>` Groups values returned by the valueTransform function applied to each element of the original channel by the key returned by the given keySelector function applied to the element and returns a map where each group key is associated with a list of corresponding values.
groupByTo	`suspend fun <E, K, M : MutableMap<in K, MutableList<E>>> ReceiveChannel<E>.groupByTo( destination: M, keySelector: (E) -> K ): M` Groups elements of the original channel by the key returned by the given keySelector function applied to each element and puts to the destination map each group key associated with a list of corresponding elements. `suspend fun <E, K, V, M : MutableMap<in K, MutableList<V>>> ReceiveChannel<E>.groupByTo( destination: M, keySelector: (E) -> K, valueTransform: (E) -> V ): M` Groups values returned by the valueTransform function applied to each element of the original channel by the key returned by the given keySelector function applied to the element and puts to the destination map each group key associated with a list of corresponding values.
indexOf	`suspend fun <E> ReceiveChannel<E>.indexOf(element: E): Int` Returns first index of element, or -1 if the channel does not contain element.
indexOfFirst	`suspend fun <E> ReceiveChannel<E>.indexOfFirst( predicate: (E) -> Boolean ): Int` Returns index of the first element matching the given predicate, or -1 if the channel does not contain such element.
indexOfLast	`suspend fun <E> ReceiveChannel<E>.indexOfLast( predicate: (E) -> Boolean ): Int` Returns index of the last element matching the given predicate, or -1 if the channel does not contain such element.
last	`suspend fun <E> ReceiveChannel<E>.last(): E` Returns the last element. `suspend fun <E> ReceiveChannel<E>.last( predicate: (E) -> Boolean ): E` Returns the last element matching the given predicate.
lastIndexOf	`suspend fun <E> ReceiveChannel<E>.lastIndexOf( element: E ): Int` Returns last index of element, or -1 if the channel does not contain element.
lastOrNull	`suspend fun <E> ReceiveChannel<E>.lastOrNull(): E?` Returns the last element, or `null` if the channel is empty. `suspend fun <E> ReceiveChannel<E>.lastOrNull( predicate: (E) -> Boolean ): E?` Returns the last element matching the given predicate, or `null` if no such element was found.
map	`fun <E, R> ReceiveChannel<E>.map( context: CoroutineContext = Unconfined, transform: suspend (E) -> R ): ReceiveChannel<R>` Returns a channel containing the results of applying the given transform function to each element in the original channel.
mapIndexed	`fun <E, R> ReceiveChannel<E>.mapIndexed( context: CoroutineContext = Unconfined, transform: suspend (index: Int, E) -> R ): ReceiveChannel<R>` Returns a channel containing the results of applying the given transform function to each element and its index in the original channel.
mapIndexedNotNull	`fun <E, R : Any> ReceiveChannel<E>.mapIndexedNotNull( context: CoroutineContext = Unconfined, transform: suspend (index: Int, E) -> R? ): ReceiveChannel<R>` Returns a channel containing only the non-null results of applying the given transform function to each element and its index in the original channel.
mapIndexedNotNullTo	`suspend fun <E, R : Any, C : MutableCollection<in R>> ReceiveChannel<E>.mapIndexedNotNullTo( destination: C, transform: (index: Int, E) -> R? ): C` Applies the given transform function to each element and its index in the original channel and appends only the non-null results to the given destination.
mapIndexedTo	`suspend fun <E, R, C : MutableCollection<in R>> ReceiveChannel<E>.mapIndexedTo( destination: C, transform: (index: Int, E) -> R ): C` Applies the given transform function to each element and its index in the original channel and appends the results to the given destination.
mapNotNull	`fun <E, R : Any> ReceiveChannel<E>.mapNotNull( context: CoroutineContext = Unconfined, transform: suspend (E) -> R? ): ReceiveChannel<R>` Returns a channel containing only the non-null results of applying the given transform function to each element in the original channel.
mapNotNullTo	`suspend fun <E, R : Any, C : MutableCollection<in R>> ReceiveChannel<E>.mapNotNullTo( destination: C, transform: (E) -> R? ): C` Applies the given transform function to each element in the original channel and appends only the non-null results to the given destination.
mapTo	`suspend fun <E, R, C : MutableCollection<in R>> ReceiveChannel<E>.mapTo( destination: C, transform: (E) -> R ): C` Applies the given transform function to each element of the original channel and appends the results to the given destination.
maxBy	`suspend fun <E, R : Comparable<R>> ReceiveChannel<E>.maxBy( selector: (E) -> R ): E?` Returns the first element yielding the largest value of the given function or `null` if there are no elements.
maxWith	`suspend fun <E> ReceiveChannel<E>.maxWith( comparator: Comparator<in E> ): E?` Returns the first element having the largest value according to the provided comparator or `null` if there are no elements.
minBy	`suspend fun <E, R : Comparable<R>> ReceiveChannel<E>.minBy( selector: (E) -> R ): E?` Returns the first element yielding the smallest value of the given function or `null` if there are no elements.
minWith	`suspend fun <E> ReceiveChannel<E>.minWith( comparator: Comparator<in E> ): E?` Returns the first element having the smallest value according to the provided comparator or `null` if there are no elements.
none	`suspend fun <E> ReceiveChannel<E>.none(): Boolean` Returns `true` if the channel has no elements. `suspend fun <E> ReceiveChannel<E>.none( predicate: (E) -> Boolean ): Boolean` Returns `true` if no elements match the given predicate.
partition	`suspend fun <E> ReceiveChannel<E>.partition( predicate: (E) -> Boolean ): Pair<List<E>, List<E>>` Splits the original channel into pair of lists, where first list contains elements for which predicate yielded `true`, while second list contains elements for which predicate yielded `false`.
reduce	`suspend fun <S, E : S> ReceiveChannel<E>.reduce( operation: (acc: S, E) -> S ): S` Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element.
reduceIndexed	`suspend fun <S, E : S> ReceiveChannel<E>.reduceIndexed( operation: (index: Int, acc: S, E) -> S ): S` Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element with its index in the original channel.
requireNoNulls	`fun <E : Any> ReceiveChannel<E?>.requireNoNulls(): ReceiveChannel<E>` Returns an original collection containing all the non-`null` elements, throwing an IllegalArgumentException if there are any `null` elements.
sendBlocking	`fun <E> SendChannel<E>.sendBlocking(element: E): Unit` Adds element into to this channel, blocking the caller while this channel Channel.isFull, or throws exception if the channel Channel.isClosedForSend (see Channel.close for details).
single	`suspend fun <E> ReceiveChannel<E>.single(): E` Returns the single element, or throws an exception if the channel is empty or has more than one element. `suspend fun <E> ReceiveChannel<E>.single( predicate: (E) -> Boolean ): E` Returns the single element matching the given predicate, or throws exception if there is no or more than one matching element.
singleOrNull	`suspend fun <E> ReceiveChannel<E>.singleOrNull(): E?` Returns single element, or `null` if the channel is empty or has more than one element. `suspend fun <E> ReceiveChannel<E>.singleOrNull( predicate: (E) -> Boolean ): E?` Returns the single element matching the given predicate, or `null` if element was not found or more than one element was found.
sumBy	`suspend fun <E> ReceiveChannel<E>.sumBy( selector: (E) -> Int ): Int` Returns the sum of all values produced by selector function applied to each element in the channel.
sumByDouble	`suspend fun <E> ReceiveChannel<E>.sumByDouble( selector: (E) -> Double ): Double` Returns the sum of all values produced by selector function applied to each element in the channel.
take	`fun <E> ReceiveChannel<E>.take( n: Int, context: CoroutineContext = Unconfined ): ReceiveChannel<E>` Returns a channel containing first n elements.
takeWhile	`fun <E> ReceiveChannel<E>.takeWhile( context: CoroutineContext = Unconfined, predicate: suspend (E) -> Boolean ): ReceiveChannel<E>` Returns a channel containing first elements satisfying the given predicate.
toChannel	`suspend fun <E, C : SendChannel<E>> ReceiveChannel<E>.toChannel( destination: C ): C` Send each element of the original channel and appends the results to the given destination.
toCollection	`suspend fun <E, C : MutableCollection<in E>> ReceiveChannel<E>.toCollection( destination: C ): C` Appends all elements to the given destination collection.
toList	`suspend fun <E> ReceiveChannel<E>.toList(): List<E>` Returns a List containing all elements.
toMutableList	`suspend fun <E> ReceiveChannel<E>.toMutableList(): MutableList<E>` Returns a MutableList filled with all elements of this channel.
toMutableSet	`suspend fun <E> ReceiveChannel<E>.toMutableSet(): MutableSet<E>` Returns a mutable set containing all distinct elements from the given channel.
toSet	`suspend fun <E> ReceiveChannel<E>.toSet(): Set<E>` Returns a Set of all elements.
withIndex	`fun <E> ReceiveChannel<E>.withIndex( context: CoroutineContext = Unconfined ): ReceiveChannel<IndexedValue<E>>` Returns a channel of IndexedValue for each element of the original channel.
zip	`infix fun <E, R> ReceiveChannel<E>.zip( other: ReceiveChannel<R> ): ReceiveChannel<Pair<E, R>>` Returns a channel of pairs built from elements of both channels with same indexes. Resulting channel has length of shortest input channel. `fun <E, R, V> ReceiveChannel<E>.zip( other: ReceiveChannel<R>, context: CoroutineContext = Unconfined, transform: (a: E, b: R) -> V ): ReceiveChannel<V>` Returns a channel of values built from elements of both collections with same indexes using provided transform. Resulting channel has length of shortest input channels.

Inheritors

AbstractChannel

abstract class AbstractChannel<E> : 
    AbstractSendChannel<E>, 
    Channel<E>

Abstract send/receive channel. It is a base class for all channel implementations.