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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/*
 * Copyright (c) OSGi Alliance (2020). All Rights Reserved.
 * 
 * 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 org.osgi.service.condition;

import org.osgi.annotation.versioning.ConsumerType;

/**
 * Condition Service interface.
 * 
 * In dynamic systems, such as OSGi, one of the more challenging problems can be
 * to define when a system or part of it is ready to do work. The answer can
 * change depending on the individual perspective. The developer of a web server
 * might say, the system is ready when the server starts listening on port 80.
 * An application developer however would define the system as ready when the
 * database connection is up and all servlets are registered. Taking the
 * application developers view, the web server should start listening on port 80
 * when the application is ready and not beforehand.
 * 

 * The {@code Condition} service interface is a marker interface designed to
 * address this issue. Its role is to provide a dependency that can be tracked.
 * It acts as a defined signal to other services.
 * 

 * A {@code Condition} service must be registered with the
 * {@link Condition#CONDITION_ID} service property.
 * 
 * @ThreadSafe
 * @author $Id: 9736e5e1c38c45254f733d73ed7ae2c0e253f544 $
 */
@ConsumerType
public interface Condition {

	/**
	 * Service property identifying a condition's unique identifier.
	 * 

	 * Since a {@code Condition} service can potentially describe more then one
	 * condition, the type of this service property is {@code String+}.
	 */
	String		CONDITION_ID		= "osgi.condition.id";

	/**
	 * The unique identifier for the default True condition.
	 * 

	 * The default True condition is registered by the framework during
	 * framework initialization and therefore can always be relied upon.
	 * 
	 * @see Condition#CONDITION_ID
	 */
	String		CONDITION_ID_TRUE	= "true";

	/**
	 * A condition instance that can be used to register {@code Condition}
	 * services.
	 * 
	 * This can be helpful to avoid a bundle having to implement this interface
	 * to register a {@code Condition} service
	 */
	Condition	INSTANCE			= new ConditionImpl();
}

final class ConditionImpl implements Condition {
	ConditionImpl() {
	}
}