/*

 * Copyright (c) 2005, 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 sun.rmi.runtime;

import java.security.AccessController;

import java.security.Permission;

import java.security.PrivilegedAction;

import java.util.concurrent.ScheduledThreadPoolExecutor;

import java.util.concurrent.ThreadFactory;

import java.util.concurrent.TimeUnit;

import java.util.concurrent.atomic.AtomicInteger;

import java.util.logging.Level;

/**

 * RMI runtime implementation utilities.

 *

 * There is a single instance of this class, which can be obtained

 * with a GetInstanceAction.  Getting the instance requires

 * RuntimePermission("sun.rmi.runtime.RuntimeUtil.getInstance")

 * because the public methods of this class expose security-sensitive

 * capabilities.

 *

 * @author      Peter Jones

 **/

public final class RuntimeUtil {

    /** runtime package log */

    private static final Log runtimeLog =

        Log.getLog("sun.rmi.runtime", null, false);

    /** number of scheduler threads */

    private static final int schedulerThreads =         // default 1

        AccessController.doPrivileged((PrivilegedAction<Integer>) () ->

            Integer.getInteger("sun.rmi.runtime.schedulerThreads", 1));

    /** permission required to get instance */

    private static final Permission GET_INSTANCE_PERMISSION =

        new RuntimePermission("sun.rmi.runtime.RuntimeUtil.getInstance");

    /** the singleton instance of this class */

    private static final RuntimeUtil instance = new RuntimeUtil();

    /** thread pool for scheduling delayed tasks */

    private final ScheduledThreadPoolExecutor scheduler;

    private RuntimeUtil() {

        scheduler = new ScheduledThreadPoolExecutor(

            schedulerThreads,

            new ThreadFactory() {

                private final AtomicInteger count = new AtomicInteger(0);

                public Thread newThread(Runnable runnable) {

                    try {

                        return AccessController.doPrivileged(

                            new NewThreadAction(runnable,

                                "Scheduler(" + count.getAndIncrement() + ")",

                                true));

                    } catch (Throwable t) {

                        runtimeLog.log(Level.WARNING,

                                       "scheduler thread factory throws", t);

                        return null;

                    }

                }

            });

        /*

         * We would like to allow the scheduler's threads to terminate

         * if possible, but a bug in DelayQueue.poll can cause code

         * like this to result in a busy loop:

         */

        // stpe.setKeepAliveTime(10, TimeUnit.MINUTES);

        // stpe.allowCoreThreadTimeOut(true);

    }

    /**

     * A PrivilegedAction for getting the RuntimeUtil instance.

     **/

    public static class GetInstanceAction

        implements PrivilegedAction<RuntimeUtil>

    {

        /**

         * Creates an action that returns the RuntimeUtil instance.

         **/

        public GetInstanceAction() {

        }

        public RuntimeUtil run() {

            return getInstance();

        }

    }

    private static RuntimeUtil getInstance() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(GET_INSTANCE_PERMISSION);

        }

        return instance;

    }

    /**

     * Returns the shared thread pool for scheduling delayed tasks.

     *

     * Note that the returned pool has limited concurrency, so

     * submitted tasks should be short-lived and should not block.

     **/

    public ScheduledThreadPoolExecutor getScheduler() {

        return scheduler;

    }

}