commonMain.Dispatchers.common.kt Maven / Gradle / Ivy
package kotlinx.coroutines
import kotlin.coroutines.*
/**
* Groups various implementations of [CoroutineDispatcher].
*/
public expect object Dispatchers {
/**
* The default [CoroutineDispatcher] that is used by all standard builders like
* [launch][CoroutineScope.launch], [async][CoroutineScope.async], etc.
* if neither a dispatcher nor any other [ContinuationInterceptor] is specified in their context.
*
* It is backed by a shared pool of threads on JVM and Native. By default, the maximum number of threads used
* by this dispatcher is equal to the number of CPU cores, but is at least two.
*/
public val Default: CoroutineDispatcher
/**
* A coroutine dispatcher that is confined to the Main thread operating with UI objects.
* Usually such dispatchers are single-threaded.
*
* Access to this property may throw an [IllegalStateException] if no main dispatchers are present in the classpath.
*
* Depending on platform and classpath, it can be mapped to different dispatchers:
* - On JVM it is either the Android main thread dispatcher, JavaFx, or Swing EDT dispatcher. It is chosen by the
* [`ServiceLoader`](https://docs.oracle.com/javase/8/docs/api/java/util/ServiceLoader.html).
* - On JS it is equivalent to the [Default] dispatcher with [immediate][MainCoroutineDispatcher.immediate] support.
* - On Native Darwin-based targets, it is a dispatcher backed by Darwin's main queue.
* - On other Native targets, it is not available.
* - `Dispatchers.setMain` from the `kotlinx-coroutines-test` artifact can replace the main dispatcher with a mock one for testing.
*
* In order to work with the `Main` dispatcher on the JVM, the following artifact should be added to the project runtime dependencies:
* - `kotlinx-coroutines-android` — for Android Main thread dispatcher
* - `kotlinx-coroutines-javafx` — for JavaFx Application thread dispatcher
* - `kotlinx-coroutines-swing` — for Swing EDT dispatcher
*/
public val Main: MainCoroutineDispatcher
/**
* A coroutine dispatcher that is not confined to any specific thread.
* It executes the initial continuation of a coroutine in the current call-frame
* and lets the coroutine resume in whatever thread that is used by the corresponding suspending function, without
* mandating any specific threading policy. Nested coroutines launched in this dispatcher form an event-loop to avoid
* stack overflows.
*
* ### Event loop
* Event loop semantics is a purely internal concept and has no guarantees on the order of execution
* except that all queued coroutines will be executed on the current thread in the lexical scope of the outermost
* unconfined coroutine.
*
* For example, the following code:
* ```
* withContext(Dispatchers.Unconfined) {
* println(1)
* launch(Dispatchers.Unconfined) { // Nested unconfined
* println(2)
* }
* println(3)
* }
* println("Done")
* ```
* Can print both "1 2 3" and "1 3 2". This is an implementation detail that can be changed.
* However, it is guaranteed that "Done" will only be printed once the code in both `withContext` and `launch` completes.
*
* 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, you can use
* an optional [CoroutineStart] parameter in coroutine builders like
* [launch][CoroutineScope.launch] and [async][CoroutineScope.async] setting it to
* the value of [CoroutineStart.UNDISPATCHED].
*/
public val Unconfined: CoroutineDispatcher
}