Core primitives to work with coroutines.
Coroutine builder functions:
| Name | Result | Scope | Description |
|---|---|---|---|
| launch | Job | CoroutineScope | Launches coroutine that does not have any result |
| async | Deferred | CoroutineScope | Returns a single value with the future result |
| produce | ReceiveChannel | ProducerScope | Produces a stream of elements |
| runBlocking | T | CoroutineScope | Blocks the thread while the coroutine runs |
Coroutine dispatchers implementing CoroutineDispatcher:
| Name | Description |
|---|---|
| Dispatchers.Main | Confines coroutine execution to the UI thread |
| Dispatchers.Default | Confines coroutine execution to a shared pool of background threads |
| Dispatchers.Unconfined | Does not confine coroutine execution in any way |
| CoroutineDispatcher.limitedParallelism | Creates a view of the given dispatcher, limiting the number of tasks executing in parallel |
More context elements:
| Name | Description |
|---|---|
| NonCancellable | A non-cancelable job that is always active |
| CoroutineExceptionHandler | Handler for uncaught exception |
Synchronization primitives for coroutines:
| Name | Suspending functions | Description |
|---|---|---|
| Mutex | lock | Mutual exclusion |
| Semaphore | acquire | Limiting the maximum concurrency |
| Channel | send, receive | Communication channel (aka queue or exchanger) |
| Flow | collect | Asynchronous stream of values |
Top-level suspending functions:
| Name | Description |
|---|---|
| delay | Non-blocking sleep |
| yield | Yields thread in single-threaded dispatchers |
| withContext | Switches to a different context |
| withTimeout | Set execution time-limit with exception on timeout |
| withTimeoutOrNull | Set execution time-limit will null result on timeout |
| awaitAll | Awaits for successful completion of all given jobs or exceptional completion of any |
| joinAll | Joins on all given jobs |
Cancellation support for user-defined suspending functions is available with suspendCancellableCoroutine helper function. The NonCancellable job object is provided to suppress cancellation inside the withContext(NonCancellable) {...} block of code.
Ways to construct asynchronous streams of values:
| Name | Type | Description |
|---|---|---|
| flow | cold | Runs a generator-style block of code that emits values |
| flowOf | cold | Emits the values passed as arguments |
| channelFlow | cold | Runs the given code, providing a channel sending to which means emitting from the flow |
| callbackFlow | cold | Allows transforming a callback-based API into a flow |
| ReceiveChannel.consumeAsFlow | hot | Transforms a channel into a flow, emitting all of the received values to a single subscriber |
| ReceiveChannel.receiveAsFlow | hot | Transforms a channel into a flow, distributing the received values among its subscribers |
| MutableSharedFlow | hot | Allows emitting each value to arbitrarily many subscribers at once |
| MutableStateFlow | hot | Represents mutable state as a flow |
A cold stream is some process of generating values, and this process is performed separately for each subscriber. A hot stream uses the same source of values independently of whether there are subscribers.
A select expression waits for the result of multiple suspending functions simultaneously:
| Receiver | Suspending function | Select clause | Non-suspending version |
|---|---|---|---|
| Job | join | onJoin | isCompleted |
| Deferred | await | onAwait | isCompleted |
| SendChannel | send | onSend | trySend |
| ReceiveChannel | receive | onReceive | tryReceive |
| ReceiveChannel | receiveCatching | onReceiveCatching | tryReceive |
| none | delay | onTimeout | none |
General-purpose coroutine builders, contexts, and helper functions.
Synchronization primitives (mutex and semaphore).
Channels — non-blocking primitives for communicating a stream of elements between coroutines.
Flow — asynchronous cold and hot streams of elements.
Select — expressions that perform multiple suspending operations simultaneously until one of them succeeds.
Low-level primitives for finer-grained control of coroutines.
JDK 8's CompletableFuture support.
JDK 8's Stream support.
JDK 8's Duration support via additional overloads for existing time-based operators.