com.amazonaws.services.simpleworkflow.flow.core

クラス Promise<V>

java.lang.Object

com.amazonaws.services.simpleworkflow.flow.core.Promise<V>

型パラメータ:

V - The result type returned by this Promise's get method. Use Void to represent Promise that indicates completion of operation that doesn't return a value.

直系の既知のサブクラス:

AndPromise, Functor, OrPromise, Settable

public abstract class Promise<V>
extends java.lang.Object

Promise is a future like object that is used as a placeholder for a result of an asynchronous API. Java Future is a synchronization construct that is used to block a thread that called get() method if result is not available yet. Promise differs from it as it cannot be used for blocking. A call to its get() method throws IllegalStateException if result is not available yet. The correct way to ensure that Promise is ready is to access it from a method that is annotated as @Asynchronous and have the given Promise as one its arguments or from Task.doExecute() method assuming that promise was passed to the Task as a constructor parameter.

Promise is not linked to error handling like Future is. In case of exceptions they are propagated to the TryCatchFinally.doCatch(Throwable) method of the TryCatchFinally that owns the asynchronous task that failed. See TryCatchFinally for more info on the error handling.

For promises that don't need a value and just used to ensure correct ordering of asynchronous operations the common pattern to use Void as a generic type.

コンストラクタの概要

コンストラクタ

コンストラクタと説明
Promise()

メソッドの概要

メソッド

修飾子とタイプ	メソッドと説明
protected abstract void	addCallback(java.lang.Runnable callback) Compliant implementation should notify callbacks after promise is set to ready state.
static <T> Promise<T>	asPromise(T value) Convenience method for creating a Promise object which is in ready state and returns the passed in value when get() is called.
abstract V	get()
java.lang.String	getDescription()
abstract boolean	isReady()
protected abstract void	removeCallback(java.lang.Runnable callback)
static Promise<java.lang.Void>	Void() This is a factory method to create a Promise object in ready state.

クラスから継承されたメソッド java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

コンストラクタの詳細

Promise

public Promise()

メソッドの詳細

get

public abstract V get()

戻り値:

result of your asynchronous computation

例外:

java.lang.IllegalStateException - if result of your asynchronous computation is not available yet

isReady

public abstract boolean isReady()

戻り値:

true if the result of your asynchronous computation is available

getDescription

public java.lang.String getDescription()

戻り値:

human friendly description on what this promise represents. Emitted for example as part of AsyncScope.getAsynchronousThreadDumpAsString()

addCallback

protected abstract void addCallback(java.lang.Runnable callback)

Compliant implementation should notify callbacks after promise is set to ready state.

パラメータ:

callback - callback to notify

removeCallback

protected abstract void removeCallback(java.lang.Runnable callback)

asPromise

public static <T> Promise<T> asPromise(T value)

Convenience method for creating a Promise object which is in ready state and returns the passed in value when get() is called.

The same as new Settable(value)

型パラメータ:

T - Type of value

パラメータ:

value - Object to return when get() is called

戻り値:

An instance of Promise wrapper object

Void

public static Promise<java.lang.Void> Void()

This is a factory method to create a Promise object in ready state.

戻り値:

An instance of Promise object with no value.