com.axway.ats.agentapp.standalone.utils.ThreadUtils Maven / Gradle / Ivy

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/*
 * Copyright 2017 Axway Software
 * 
 * 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 com.axway.ats.agentapp.standalone.utils;

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * Singleton containing helper methods for browsing started threads in the JVM.
 */
public class ThreadUtils {

    /**
     * Reference to the root thread group so it wouldn't have to be
     * searched for every the the getRootThreadGroup method is invoked.
     */
    private ThreadGroup        rootThreadGroup;

    /**
     * The singleton instance.
     */
    private static ThreadUtils instance;

    private ThreadUtils() {

    }

    public static synchronized ThreadUtils getInstance() {

        if (instance == null) {
            instance = new ThreadUtils();
        }
        return instance;
    }

    public Thread getThread(
                             final long id ) {

        List threads = getAllThreads();
        for (Thread thread : threads) {
            if (thread.getId() == id) {
                return thread;
            }
        }

        return null;
    }

    /**
     * @return Set of the IDs of all threads that are started except the "main" thread.
     */
    public Set getAllThreadIDsExceptMain() {

        ThreadMXBean thbean = ManagementFactory.getThreadMXBean();
        // get the IDs of all live threads.
        long[] threadIDs = thbean.getAllThreadIds();
        Set res = new HashSet();

        // get the IDs of all threads except main
        for (long id : threadIDs) {
            Thread t = getThread(id);
            if (t != null && !"main".equals(t.getName())) {
                res.add(id);
            }
        }

        return res;
    }

    /**
     * @return a list of all threads started in the JVM.
     */
    public List getAllThreads() {

        final ThreadGroup root = getRootThreadGroup();
        final ThreadMXBean thbean = ManagementFactory.getThreadMXBean();
        // get the number of all live threads
        int nAlloc = thbean.getThreadCount();
        int n = 0;
        Thread[] threads;

        do {
            nAlloc *= 2; // increase the size since more threads may have been created
            threads = new Thread[nAlloc];
            n = root.enumerate(threads, true); // get all active threads from this thread group
        } while (n == nAlloc); // stop if all active threads are enumerated

        List res = new ArrayList();
        for (Thread th : threads) {
            res.add(th);
        }

        return res;
    }

    /**
     * @return the root thread group which has no parent thread group.
     */
    public ThreadGroup getRootThreadGroup() {

        if (rootThreadGroup != null) {
            return rootThreadGroup;
        }

        rootThreadGroup = Thread.currentThread().getThreadGroup();
        ThreadGroup ptg;

        while ( (ptg = rootThreadGroup.getParent()) != null) {
            rootThreadGroup = ptg;
        }

        return rootThreadGroup;
    }
}