| /* |
| * Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license. |
| */ |
| |
| package kotlinx.coroutines.experimental.channels |
| |
| import kotlinx.coroutines.experimental.selects.ALREADY_SELECTED |
| import kotlinx.coroutines.experimental.selects.SelectInstance |
| |
| /** |
| * Channel that buffers at most one element and conflates all subsequent `send` and `offer` invocations, |
| * so that the receiver always gets the most recently sent element. |
| * Back-to-send sent elements are _conflated_ -- only the the most recently sent element is received, |
| * while previously sent elements **are lost**. |
| * Sender to this channel never suspends and [offer] always returns `true`. |
| * |
| * This channel is created by `Channel(Channel.CONFLATED)` factory function invocation. |
| * |
| * This implementation is fully lock-free. |
| */ |
| public open class ConflatedChannel<E> : AbstractChannel<E>() { |
| protected final override val isBufferAlwaysEmpty: Boolean get() = true |
| protected final override val isBufferEmpty: Boolean get() = true |
| protected final override val isBufferAlwaysFull: Boolean get() = false |
| protected final override val isBufferFull: Boolean get() = false |
| |
| /** |
| * This implementation conflates last sent item when channel is closed. |
| * @suppress **This is unstable API and it is subject to change.** |
| */ |
| override fun onClosed(closed: Closed<E>) { |
| conflatePreviousSendBuffered(closed) |
| } |
| |
| // result is always `OFFER_SUCCESS | Closed` |
| protected override fun offerInternal(element: E): Any { |
| while (true) { |
| val result = super.offerInternal(element) |
| when { |
| result === OFFER_SUCCESS -> return OFFER_SUCCESS |
| result === OFFER_FAILED -> { // try to buffer |
| val sendResult = sendConflated(element) |
| when (sendResult) { |
| null -> return OFFER_SUCCESS |
| is Closed<*> -> return sendResult |
| } |
| // otherwise there was receiver in queue, retry super.offerInternal |
| } |
| result is Closed<*> -> return result |
| else -> error("Invalid offerInternal result $result") |
| } |
| } |
| } |
| |
| // result is always `ALREADY_SELECTED | OFFER_SUCCESS | Closed`. |
| protected override fun offerSelectInternal(element: E, select: SelectInstance<*>): Any { |
| while (true) { |
| val result = if (hasReceiveOrClosed) |
| super.offerSelectInternal(element, select) else |
| (select.performAtomicTrySelect(describeSendConflated(element)) ?: OFFER_SUCCESS) |
| when { |
| result === ALREADY_SELECTED -> return ALREADY_SELECTED |
| result === OFFER_SUCCESS -> return OFFER_SUCCESS |
| result === OFFER_FAILED -> {} // retry |
| result is Closed<*> -> return result |
| else -> error("Invalid result $result") |
| } |
| } |
| } |
| } |