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Coroutines support libraries for Kotlin
/*
* Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
*/
package kotlinx.coroutines.flow.internal
import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
import kotlinx.coroutines.flow.*
import kotlinx.coroutines.internal.*
import kotlin.coroutines.*
import kotlin.coroutines.intrinsics.*
import kotlin.jvm.*
internal fun Flow.asChannelFlow(): ChannelFlow =
this as? ChannelFlow ?: ChannelFlowOperatorImpl(this)
/**
* Operators that use channels extend this ChannelFlow and are always fused with each other.
*
* @suppress **This an internal API and should not be used from general code.**
*/
@InternalCoroutinesApi
public abstract class ChannelFlow(
// upstream context
@JvmField val context: CoroutineContext,
// buffer capacity between upstream and downstream context
@JvmField val capacity: Int
) : Flow {
public fun update(
context: CoroutineContext = EmptyCoroutineContext,
capacity: Int = Channel.OPTIONAL_CHANNEL
): ChannelFlow {
// note: previous upstream context (specified before) takes precedence
val newContext = context + this.context
val newCapacity = when {
this.capacity == Channel.OPTIONAL_CHANNEL -> capacity
capacity == Channel.OPTIONAL_CHANNEL -> this.capacity
this.capacity == Channel.BUFFERED -> capacity
capacity == Channel.BUFFERED -> this.capacity
this.capacity == Channel.CONFLATED -> Channel.CONFLATED
capacity == Channel.CONFLATED -> Channel.CONFLATED
else -> {
// sanity checks
assert { this.capacity >= 0 }
assert { capacity >= 0 }
// combine capacities clamping to UNLIMITED on overflow
val sum = this.capacity + capacity
if (sum >= 0) sum else Channel.UNLIMITED // unlimited on int overflow
}
}
if (newContext == this.context && newCapacity == this.capacity) return this
return create(newContext, newCapacity)
}
protected abstract fun create(context: CoroutineContext, capacity: Int): ChannelFlow
protected abstract suspend fun collectTo(scope: ProducerScope)
// shared code to create a suspend lambda from collectTo function in one place
internal val collectToFun: suspend (ProducerScope) -> Unit
get() = { collectTo(it) }
private val produceCapacity: Int
get() = if (capacity == Channel.OPTIONAL_CHANNEL) Channel.BUFFERED else capacity
open fun broadcastImpl(scope: CoroutineScope, start: CoroutineStart): BroadcastChannel =
scope.broadcast(context, produceCapacity, start, block = collectToFun)
open fun produceImpl(scope: CoroutineScope): ReceiveChannel =
scope.produce(context, produceCapacity, block = collectToFun)
override suspend fun collect(collector: FlowCollector) =
coroutineScope {
collector.emitAll(produceImpl(this))
}
// debug toString
override fun toString(): String =
"$classSimpleName[${additionalToStringProps()}context=$context, capacity=$capacity]"
open fun additionalToStringProps() = ""
}
// ChannelFlow implementation that operates on another flow before it
internal abstract class ChannelFlowOperator(
@JvmField val flow: Flow,
context: CoroutineContext,
capacity: Int
) : ChannelFlow(context, capacity) {
protected abstract suspend fun flowCollect(collector: FlowCollector)
// Changes collecting context upstream to the specified newContext, while collecting in the original context
private suspend fun collectWithContextUndispatched(collector: FlowCollector, newContext: CoroutineContext) {
val originalContextCollector = collector.withUndispatchedContextCollector(coroutineContext)
// invoke flowCollect(originalContextCollector) in the newContext
return withContextUndispatched(newContext, block = { flowCollect(it) }, value = originalContextCollector)
}
// Slow path when output channel is required
protected override suspend fun collectTo(scope: ProducerScope) =
flowCollect(SendingCollector(scope))
// Optimizations for fast-path when channel creation is optional
override suspend fun collect(collector: FlowCollector) {
// Fast-path: When channel creation is optional (flowOn/flowWith operators without buffer)
if (capacity == Channel.OPTIONAL_CHANNEL) {
val collectContext = coroutineContext
val newContext = collectContext + context // compute resulting collect context
// #1: If the resulting context happens to be the same as it was -- fallback to plain collect
if (newContext == collectContext)
return flowCollect(collector)
// #2: If we don't need to change the dispatcher we can go without channels
if (newContext[ContinuationInterceptor] == collectContext[ContinuationInterceptor])
return collectWithContextUndispatched(collector, newContext)
}
// Slow-path: create the actual channel
super.collect(collector)
}
// debug toString
override fun toString(): String = "$flow -> ${super.toString()}"
}
// Simple channel flow operator: flowOn, buffer, or their fused combination
internal class ChannelFlowOperatorImpl(
flow: Flow,
context: CoroutineContext = EmptyCoroutineContext,
capacity: Int = Channel.OPTIONAL_CHANNEL
) : ChannelFlowOperator(flow, context, capacity) {
override fun create(context: CoroutineContext, capacity: Int): ChannelFlow =
ChannelFlowOperatorImpl(flow, context, capacity)
override suspend fun flowCollect(collector: FlowCollector) =
flow.collect(collector)
}
// Now if the underlying collector was accepting concurrent emits, then this one is too
// todo: we might need to generalize this pattern for "thread-safe" operators that can fuse with channels
private fun FlowCollector.withUndispatchedContextCollector(emitContext: CoroutineContext): FlowCollector = when (this) {
// SendingCollector & NopCollector do not care about the context at all and can be used as is
is SendingCollector, is NopCollector -> this
// Otherwise just wrap into UndispatchedContextCollector interface implementation
else -> UndispatchedContextCollector(this, emitContext)
}
private class UndispatchedContextCollector(
downstream: FlowCollector,
private val emitContext: CoroutineContext
) : FlowCollector {
private val countOrElement = threadContextElements(emitContext) // precompute for fast withContextUndispatched
private val emitRef: suspend (T) -> Unit = { downstream.emit(it) } // allocate suspend function ref once on creation
override suspend fun emit(value: T): Unit =
withContextUndispatched(emitContext, countOrElement, emitRef, value)
}
// Efficiently computes block(value) in the newContext
private suspend fun withContextUndispatched(
newContext: CoroutineContext,
countOrElement: Any = threadContextElements(newContext), // can be precomputed for speed
block: suspend (V) -> T, value: V
): T =
suspendCoroutineUninterceptedOrReturn sc@{ uCont ->
withCoroutineContext(newContext, countOrElement) {
block.startCoroutineUninterceptedOrReturn(value, Continuation(newContext) {
uCont.resumeWith(it)
})
}
}