/*
 * Copyright 2017-2020 original authors
 *
 * 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
 *
 * https://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 io.micronaut.context.annotation;

import io.micronaut.core.annotation.Experimental;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.RetentionPolicy.RUNTIME;

A hint annotation that can be added to Bean definitions or Executable methods to indicate that they can be initialized in parallel with the application context.
This allows optimized startup time by allowing beans that have slow initialization paths to startup and without impacting the overall startup time of the application.
Note that beans and methods that are processed in parallel (unlike Context scoped beans) will not initially fail the startup of the ApplicationContext as they may be initialized after the ApplicationContext has started and cannot participate in StartupEvent processing. If a parallel bean fails to startup it will by default stop the ApplicationContext with an error unless shutdownOnError() set to to false.
Adding Parallel to methods is most useful when used in conjunction with a ExecutableMethodProcessor. Be aware however, that the processor in this case should be thread safe as could be executed in parallel for different methods.
NOTE: The use of Parallel generally only makes sense when combined with non Prototype scopes such as Singleton and Context
Author:
graemerocher
See Also:
Context
Executable
ExecutableMethodProcessor
Since:
1.0/**
 * <p>A hint annotation that can be added to {@link Bean} definitions or {@link Executable} methods to indicate that they can be initialized in
 * parallel with the application context.</p>
 *
 * <p>This allows optimized startup time by allowing beans that have slow initialization paths to startup and without impacting the overall startup time of the application.</p>
 *
 * <p>Note that beans and methods that are processed in parallel (unlike {@link Context} scoped beans) will not initially fail the startup of the {@link io.micronaut.context.ApplicationContext}
 * as they may be initialized after the {@link io.micronaut.context.ApplicationContext} has started and cannot participate in {@link io.micronaut.context.event.StartupEvent} processing. If a parallel bean fails to startup it will by default stop the {@link io.micronaut.context.ApplicationContext} with an error unless {@link #shutdownOnError()} set to to {@code false}.</p>
 *
 * <p>Adding {@link Parallel} to methods is most useful when used in conjunction with a {@link io.micronaut.context.processor.ExecutableMethodProcessor}. Be aware however, that the processor in this case should be thread safe as could be executed in parallel for different methods.</p>
 *
 * <p>NOTE: The use of {@link Parallel} generally only makes sense when combined with non {@link Prototype} scopes such as {@link javax.inject.Singleton} and {@link Context}</p>
 *
 * @author graemerocher
 * @since 1.0
 * @see Context
 * @see Executable
 * @see io.micronaut.context.processor.ExecutableMethodProcessor
 */
@Documented
@Retention(RUNTIME)
@Target({ElementType.METHOD, ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Experimental
public @interface Parallel {
    
The default behaviour is to shutdown the context if an error occurs on initialization. Can be set false if shutdown is not required.
Returns:
Whether to shutdown the application if an error occurs./**
     * The default behaviour is to shutdown the context if an error occurs on initialization. Can be set false if shutdown is not required.
     *
     * @return Whether to shutdown the application if an error occurs.
     */
    boolean shutdownOnError() default true;
}