org.ldp4j.application.ApplicationContext.java Source code

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Here is the source code for org.ldp4j.application.ApplicationContext.java

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/**
 * #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
 *   This file is part of the LDP4j Project:
 *     http://www.ldp4j.org/
 *
 *   Center for Open Middleware
 *     http://www.centeropenmiddleware.com/
 * #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
 *   Copyright (C) 2014-2016 Center for Open Middleware.
 * #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
 *   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.
 * #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
 *   Artifact    : org.ldp4j.framework:ldp4j-application-api:0.2.1
 *   Bundle      : ldp4j-application-api-0.2.1.jar
 * #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
 */
package org.ldp4j.application;

import java.lang.ref.ReferenceQueue;
import java.util.Map;

import org.ldp4j.application.session.WriteSession;
import org.ldp4j.application.spi.RuntimeDelegate;
import org.ldp4j.application.spi.ShutdownListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.MoreObjects;
import com.google.common.collect.Maps;

/**
 * A proxy class that acts as a facade for interacting with the Application
 * Engine proactively.
 */
public final class ApplicationContext {

    private final class CleanerContextWriteSessionStateListener implements ContextWriteSessionStateListener {
        @Override
        public void onDispose(ContextWriteSessionState state) {
            untrackSession(state);
        }
    }

    private static final class ApplicationEngineSingleton {

        private static final ApplicationContext SINGLETON = new ApplicationContext();

        private ApplicationEngineSingleton() {
        }

    }

    private static final Logger LOGGER = LoggerFactory.getLogger(ApplicationContext.class);

    private final RuntimeDelegate delegate;
    private final Map<Long, ContextWriteSessionReference> references;
    private final Map<Long, Long> sessionOwner;
    private final Map<Long, Long> threadSession;
    private final ReferenceQueue<ContextWriteSession> referenceQueue;

    private ApplicationContext() {
        this.delegate = RuntimeDelegate.getInstance();
        this.references = Maps.newLinkedHashMap();
        this.sessionOwner = Maps.newLinkedHashMap();
        this.threadSession = Maps.newLinkedHashMap();
        this.referenceQueue = new ReferenceQueue<ContextWriteSession>();
        LOGGER.info("Initialized Application Context");
    }

    private ApplicationContextException failure(String fmt, Object... args) {
        String message = String.format(fmt, args);
        LOGGER.error(message);
        return new ApplicationContextException(message);
    }

    private void setUpWriteSessionCleaner() {
        if (WriteSessionCleaner.isActive()) {
            return;
        }
        WriteSessionCleaner.launch(this.referenceQueue);
        this.delegate.registerShutdownListener(new ShutdownListener() {
            @Override
            public void engineShutdown() {
                WriteSessionCleaner.terminate();
            }
        });
    }

    private ContextWriteSession trackSession(ContextWriteSessionState state) {
        ContextWriteSession leakedSession = new ContextWriteSession(state);
        ContextWriteSessionReference reference = new ContextWriteSessionReference(leakedSession, state,
                this.referenceQueue);
        this.references.put(state.id(), reference);
        this.sessionOwner.put(state.id(), Thread.currentThread().getId());
        this.threadSession.put(Thread.currentThread().getId(), state.id());
        return leakedSession;
    }

    private synchronized void untrackSession(ContextWriteSessionState session) {
        long sessionId = session.id();
        long ownerId = this.sessionOwner.get(sessionId);
        this.references.remove(sessionId);
        this.sessionOwner.remove(sessionId);
        this.threadSession.remove(ownerId);
    }

    /**
     * Create a {@code WriteSession}. Only one write session can be active per
     * thread. Sessions should not be shared among threads.
     *
     * @return the write session
     * @throws ApplicationContextException
     *             if no write session can be created for whichever reason,
     *             e.g., the Application Engine is off-line or is not available.
     */
    public synchronized WriteSession createSession() throws ApplicationContextException {
        if (this.threadSession.containsKey(Thread.currentThread().getId())) {
            throw failure("Thread already has an active session");
        }

        if (this.delegate.isOffline()) {
            throw failure("The Application Engine is off-line");
        }

        WriteSession nativeSession = this.delegate.createSession();
        if (nativeSession == null) {
            throw failure("Could not create native write session");
        }

        setUpWriteSessionCleaner();

        return trackSession(
                new ContextWriteSessionState(nativeSession, new CleanerContextWriteSessionStateListener()));
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public synchronized String toString() {
        return MoreObjects.toStringHelper(getClass()).omitNullValues().add("delegate", this.delegate)
                .add("references", this.references).add("sessionOwner", this.sessionOwner)
                .add("threadSession", this.threadSession).toString();
    }

    /**
     * Get the Application context.
     *
     * @return the application context.
     */
    public static ApplicationContext getInstance() {
        return ApplicationEngineSingleton.SINGLETON;
    }

}