org.apache.samza.task

Interface AsyncStreamTask

public interface AsyncStreamTask

An AsyncStreamTask is the basic class to support multithreading execution in Samza container. It's provided for better parallelism and resource utilization. This class allows task to make asynchronous calls and fire callbacks upon completion. Similar to StreamTask, an AsyncStreamTask may be augmented by implementing other interfaces, such as InitableTask, WindowableTask, or ClosableTask. The following invariants hold with these mix-ins: InitableTask.init - always the first method invoked on an AsyncStreamTask. It happens-before every subsequent invocation on AsyncStreamTask (for happens-before semantics, see https://docs.oracle.com/javase/tutorial/essential/concurrency/memconsist.html). CloseableTask.close - always the last method invoked on an AsyncStreamTask and all other AsyncStreamTask are guaranteed to happen-before it. AsyncStreamTask.processAsync - can run in either a serialized or parallel mode. In the serialized mode (task.max.concurrency=1), each invocation of processAsync is guaranteed to happen-before the next. In a parallel execution mode (task.max.concurrency>1), there is no such happens-before constraint and the AsyncStreamTask is required to coordinate any shared state. WindowableTask.window - in either above mode, it is called when no invocations to processAsync are pending and no new processAsync invocations can be scheduled until it completes. Therefore, a guarantee that all previous processAsync invocations happen before an invocation of WindowableTask.window. An invocation to WindowableTask.window is guaranteed to happen-before any subsequent processAsync invocations. The Samza engine is responsible for ensuring that window is invoked in a timely manner. Similar to WindowableTask.window, commits are guaranteed to happen only when there are no pending processAsync or WindowableTask.window invocations. All preceding invocations happen-before commit and commit happens-before all subsequent invocations.

Method Summary

Modifier and Type	Method and Description
void	processAsync(IncomingMessageEnvelope envelope, MessageCollector collector, TaskCoordinator coordinator, TaskCallback callback) Called once for each message that this AsyncStreamTask receives.

Method Detail

processAsync

void processAsync(IncomingMessageEnvelope envelope,
                  MessageCollector collector,
                  TaskCoordinator coordinator,
                  TaskCallback callback)

Called once for each message that this AsyncStreamTask receives.

Parameters:

envelope - Contains the received deserialized message and key, and also information regarding the stream and partition of which the message was received from.

collector - Contains the means of sending message envelopes to the output stream. The collector must only be used during the current call to the process method; you should not reuse the collector between invocations of this method.

coordinator - Manages execution of tasks.

callback - Triggers the completion of the process.