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/*
* Copyright 2016 Davide Maestroni
*
* 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 com.github.dm.jrt.object.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Through this annotation it is possible to indicate that the result returned by the target object
* method must be dispatched in an asynchronous way.
*
* If, on the contrary, this annotation is missing, be aware that the proxy method will block until
* the target one completes, even if no result is expected (that is, the method returns a void
* result).
*
* The only use case in which this annotation is useful, is when an interface is used as a proxy
* of another class methods. The interface can return the output in an asynchronous way. In such
* case, the value specified in the annotation will indicate the mode in which the output is
* transferred outside the routine.
*
* For example, a method returning an integer:
*
*
*
* public int sum(int i1, int i2);
*
*
*
* can be proxied by a method defined as:
*
*
*
* @AsyncOutput
* public Channel<?, Integer> sum(int i1, int i2);
*
*
* Note that the transfer mode is specifically chosen through the annotation {@code mode} attribute
* (it's {@link AsyncOutput.OutputMode#VALUE VALUE} by default).
*
* This annotation is used to decorate methods that are to be invoked in an asynchronous way.
*
* Note that the piece of code inside such methods will be automatically protected so to avoid
* concurrency issues. Though, other parts of the code inside the same class will be not.
*
* In order to prevent unexpected behaviors, it is advisable to avoid using the same class fields
* (unless immutable) in protected and non-protected code, or to call synchronous methods through
* routines as well.
*
* Finally, be aware that a method might need to be made accessible in order to be called. That
* means that, in case a {@link java.lang.SecurityManager} is installed, a security exception might
* be raised based on the specific policy implemented.
*
* Remember also that, in order for the annotation to properly work at run time, the following rules
* must be added to the project Proguard file (if employed for shrinking or obfuscation):
*
*
*
* -keepattributes RuntimeVisibleAnnotations
* -keepclassmembers class ** {
* @com.github.dm.jrt.object.annotation.AsyncOutput *;
* }
*
*
*
* Created by davide-maestroni on 05/24/2015.
*/
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface AsyncOutput {
/**
* The output transfer mode.
*
* @return the mode.
*/
OutputMode value() default OutputMode.VALUE;
/**
* Output transfer mode type.
*
* The mode indicates in which way the result is passed outside.
*/
enum OutputMode {
/**
* Value mode.
*
* The variable is just passed to the channel.
*
* The annotated method must return a superclass of
* {@link com.github.dm.jrt.core.channel.Channel Channel}.
*/
VALUE,
/**
* Element mode.
*
* The elements of the result array or iterable are passed one by one to the channel.
*
* The annotated method must return a superclass of
* {@link com.github.dm.jrt.core.channel.Channel Channel}.
*/
ELEMENT
}
}