js/kotlinx-coroutines-core-js/src/main/kotlin/kotlinx/coroutines/experimental/CoroutineContext.kt

/*
 * Copyright 2016-2017 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package kotlinx.coroutines.experimental

import kotlin.coroutines.experimental.*

/**
 * A coroutine dispatcher that is not confined to any specific thread.
 * It executes initial continuation of the coroutine _right here_ in the current call-frame
 * and let the coroutine resume in whatever thread that is used by the corresponding suspending function, without
 * mandating any specific threading policy.
 *
 * Note, that if you need your coroutine to be confined to a particular thread or a thread-pool after resumption,
 * but still want to execute it in the current call-frame until its first suspension, then you can use
 * an optional [CoroutineStart] parameter in coroutine builders like [launch] and [async] setting it to the
 * the value of [CoroutineStart.UNDISPATCHED].
 */
public actual object Unconfined : CoroutineDispatcher() {
    actual override fun isDispatchNeeded(context: CoroutineContext): Boolean = false
    actual override fun dispatch(context: CoroutineContext, block: Runnable) { throw UnsupportedOperationException() }
    override fun toString(): String = "Unconfined"
}

/**
 * This is the default [CoroutineDispatcher] that is used by all standard builders like
 * [launch], [async], etc if no dispatcher nor any other [ContinuationInterceptor] is specified in their context.
 */
@Suppress("PropertyName")
public actual val DefaultDispatcher: CoroutineDispatcher = JSDispatcher

/**
 * Creates context for the new coroutine. It installs [DefaultDispatcher] when no other dispatcher nor
 * [ContinuationInterceptor] is specified, and adds optional support for debugging facilities (when turned on).
 */
public fun newCoroutineContext(context: CoroutineContext, parent: Job? = null): CoroutineContext {
    val wp = if (parent == null) context else context + parent
    return if (context !== DefaultDispatcher && context[ContinuationInterceptor] == null)
        wp + DefaultDispatcher else wp
}

// No debugging facilities on JS
internal actual inline fun <T> withCoroutineContext(context: CoroutineContext, block: () -> T): T = block()
internal actual fun Continuation<*>.toDebugString(): String = toString()