/*

 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package com.sun.tools.sjavac.server;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.Semaphore;

import java.util.Stack;

import java.util.concurrent.Future;

/** The compiler pool maintains compiler threads.

 *

 * <p><b>This is NOT part of any supported API.

 * If you write code that depends on this, you do so at your own

 * risk.  This code and its internal interfaces are subject to change

 * or deletion without notice.</b></p>

 */

public class CompilerPool {

    // The javac server that created this pool.

    private JavacServer javacServer;

    // A semaphore protecting the poolsize number of threads.

    private Semaphore available;

    // The stack of compiler threads.

    private Stack<CompilerThread> compilers = new Stack<>();

    // And the executor server to spawn threads.

    private final ExecutorService executorPool;

    // How many requests are active right now?

    private int concurrentRequests = 0;

    // When was the last request finished?

    private long lastRequestFinished = 0;

    // The total number of requests to this pool.

    private int numRequests = 0;

    // Protect access to the three above values.

    private static final Object conc = new Object();

    /**

     * Return the javac server that this pool belongs to.

     */

    public JavacServer getJavacServer() {

        return javacServer;

    }

    /**

     * Return how many threads are running at this very moment.

     */

    public int numActiveRequests()

    {

        synchronized (conc) {

            return concurrentRequests;

        }

    }

    /**

     * Return when the last request was finished.

     * I.e. the pool has been idle since.

     */

    public long lastRequestFinished()

    {

        synchronized (conc) {

            return lastRequestFinished;

        }

    }

    /**

     * Up the number of active requests.

     */

    public int startRequest() {

        int n;

        synchronized (conc) {

            concurrentRequests++;

            numRequests++;

            n = numRequests;

        }

        return n;

    }

    /**

     * Down the number of active requests. Return the current time.

     */

    public long stopRequest() {

        synchronized (conc) {

            concurrentRequests--;

            lastRequestFinished = System.currentTimeMillis();

        }

        return lastRequestFinished;

    }

    /**

     * Create a new compiler pool.

     */

    CompilerPool(int poolsize, JavacServer server) {

        available = new Semaphore(poolsize, true);

        javacServer = server;

        executorPool = Executors.newFixedThreadPool(poolsize);

        lastRequestFinished = System.currentTimeMillis();

    }

    /**

     * Execute a compiler thread.

     */

    public void execute(CompilerThread ct) {

        executorPool.execute(ct);

    }

    /**

     * Execute a minor task, for example generating bytecodes and writing them to disk,

     * that belong to a major compiler thread task.

     */

    public Future<?> executeSubtask(CompilerThread t, Runnable r) {

        return executorPool.submit(r);

    }

    /**

     * Shutdown the pool.

     */

    public void shutdown() {

        executorPool.shutdown();

    }

    /**

     * Acquire a compiler thread from the pool, or block until a thread is available.

     * If the pools is empty, create a new thread, but never more than is "available".

     */

    public CompilerThread grabCompilerThread() throws InterruptedException {

        available.acquire();

        if (compilers.empty()) {

            return new CompilerThread(this);

        }

        return compilers.pop();

    }

    /**

     * Return the specified compiler thread to the pool.

     */

    public void returnCompilerThread(CompilerThread h) {

        compilers.push(h);

        available.release();

    }

}