/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.lang3;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

 Helpers for java.lang.Thread and java.lang.ThreadGroup. 

#ThreadSafe#

See Also:
Thread
ThreadGroup
Since:
3.5/**
 * <p>
 * Helpers for {@code java.lang.Thread} and {@code java.lang.ThreadGroup}.
 * </p>
 * <p>
 * #ThreadSafe#
 * </p>
 *
 * @see java.lang.Thread
 * @see java.lang.ThreadGroup
 * @since 3.5
 */
public class ThreadUtils {

    
Finds the active thread with the specified id if it belongs to the specified thread group.
Params:
threadId – The thread id
threadGroup – The thread group
Throws:
IllegalArgumentException – if the specified id is zero or negative or the group is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
The thread which belongs to a specified thread group and the thread's id match the specified id. null is returned if no such thread exists/**
     * Finds the active thread with the specified id if it belongs to the specified thread group.
     *
     * @param threadId The thread id
     * @param threadGroup The thread group
     * @return The thread which belongs to a specified thread group and the thread's id match the specified id.
     * {@code null} is returned if no such thread exists
     * @throws IllegalArgumentException if the specified id is zero or negative or the group is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Thread findThreadById(final long threadId, final ThreadGroup threadGroup) {
        Validate.notNull(threadGroup, "The thread group must not be null");
        final Thread thread = findThreadById(threadId);
        if (thread != null && threadGroup.equals(thread.getThreadGroup())) {
            return thread;
        }
        return null;
    }

    
Finds the active thread with the specified id if it belongs to a thread group with the specified group name.
Params:
threadId – The thread id
threadGroupName – The thread group name
Throws:
IllegalArgumentException – if the specified id is zero or negative or the group name is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
The threads which belongs to a thread group with the specified group name and the thread's id match the specified id. null is returned if no such thread exists/**
     * Finds the active thread with the specified id if it belongs to a thread group with the specified group name.
     *
     * @param threadId The thread id
     * @param threadGroupName The thread group name
     * @return The threads which belongs to a thread group with the specified group name and the thread's id match the specified id.
     * {@code null} is returned if no such thread exists
     * @throws IllegalArgumentException if the specified id is zero or negative or the group name is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Thread findThreadById(final long threadId, final String threadGroupName) {
        Validate.notNull(threadGroupName, "The thread group name must not be null");
        final Thread thread = findThreadById(threadId);
        if (thread != null && thread.getThreadGroup() != null && thread.getThreadGroup().getName().equals(threadGroupName)) {
            return thread;
        }
        return null;
    }

    
Finds active threads with the specified name if they belong to a specified thread group.
Params:
threadName – The thread name
threadGroup – The thread group
Throws:
IllegalArgumentException – if the specified thread name or group is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
The threads which belongs to a thread group and the thread's name match the specified name,
An empty collection is returned if no such thread exists. The collection returned is always unmodifiable./**
     * Finds active threads with the specified name if they belong to a specified thread group.
     *
     * @param threadName The thread name
     * @param threadGroup The thread group
     * @return The threads which belongs to a thread group and the thread's name match the specified name,
     * An empty collection is returned if no such thread exists. The collection returned is always unmodifiable.
     * @throws IllegalArgumentException if the specified thread name or group is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<Thread> findThreadsByName(final String threadName, final ThreadGroup threadGroup) {
        return findThreads(threadGroup, false, new NamePredicate(threadName));
    }

    
Finds active threads with the specified name if they belong to a thread group with the specified group name.
Params:
threadName – The thread name
threadGroupName – The thread group name
Throws:
IllegalArgumentException – if the specified thread name or group name is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
The threads which belongs to a thread group with the specified group name and the thread's name match the specified name,
An empty collection is returned if no such thread exists. The collection returned is always unmodifiable./**
     * Finds active threads with the specified name if they belong to a thread group with the specified group name.
     *
     * @param threadName The thread name
     * @param threadGroupName The thread group name
     * @return The threads which belongs to a thread group with the specified group name and the thread's name match the specified name,
     * An empty collection is returned if no such thread exists. The collection returned is always unmodifiable.
     * @throws IllegalArgumentException if the specified thread name or group name is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<Thread> findThreadsByName(final String threadName, final String threadGroupName) {
        Validate.notNull(threadName, "The thread name must not be null");
        Validate.notNull(threadGroupName, "The thread group name must not be null");

        final Collection<ThreadGroup> threadGroups = findThreadGroups(new NamePredicate(threadGroupName));

        if (threadGroups.isEmpty()) {
            return Collections.emptyList();
        }

        final Collection<Thread> result = new ArrayList<>();
        final NamePredicate threadNamePredicate = new NamePredicate(threadName);
        for (final ThreadGroup group : threadGroups) {
            result.addAll(findThreads(group, false, threadNamePredicate));
        }
        return Collections.unmodifiableCollection(result);
    }

    
Finds active thread groups with the specified group name.
Params:
threadGroupName – The thread group name
Throws:
IllegalArgumentException – if group name is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
the thread groups with the specified group name or an empty collection if no such thread group exists. The collection returned is always unmodifiable./**
     * Finds active thread groups with the specified group name.
     *
     * @param threadGroupName The thread group name
     * @return the thread groups with the specified group name or an empty collection if no such thread group exists. The collection returned is always unmodifiable.
     * @throws IllegalArgumentException if group name is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<ThreadGroup> findThreadGroupsByName(final String threadGroupName) {
        return findThreadGroups(new NamePredicate(threadGroupName));
    }

    
Gets all active thread groups excluding the system thread group (A thread group is active if it has been not destroyed).
Throws:
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
all thread groups excluding the system thread group. The collection returned is always unmodifiable./**
     * Gets all active thread groups excluding the system thread group (A thread group is active if it has been not destroyed).
     *
     * @return all thread groups excluding the system thread group. The collection returned is always unmodifiable.
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<ThreadGroup> getAllThreadGroups() {
        return findThreadGroups(ALWAYS_TRUE_PREDICATE);
    }

    
Gets the system thread group (sometimes also referred as "root thread group").
Throws:
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
the system thread group/**
     * Gets the system thread group (sometimes also referred as "root thread group").
     *
     * @return the system thread group
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static ThreadGroup getSystemThreadGroup() {
        ThreadGroup threadGroup = Thread.currentThread().getThreadGroup();
        while (threadGroup.getParent() != null) {
            threadGroup = threadGroup.getParent();
        }
        return threadGroup;
    }

    
Gets all active threads (A thread is active if it has been started and has not yet died).
Throws:
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
all active threads. The collection returned is always unmodifiable./**
     * Gets all active threads (A thread is active if it has been started and has not yet died).
     *
     * @return all active threads. The collection returned is always unmodifiable.
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<Thread> getAllThreads() {
        return findThreads(ALWAYS_TRUE_PREDICATE);
    }

    
Finds active threads with the specified name.
Params:
threadName – The thread name
Throws:
IllegalArgumentException – if the specified name is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
The threads with the specified name or an empty collection if no such thread exists. The collection returned is always unmodifiable./**
     * Finds active threads with the specified name.
     *
     * @param threadName The thread name
     * @return The threads with the specified name or an empty collection if no such thread exists. The collection returned is always unmodifiable.
     * @throws IllegalArgumentException if the specified name is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<Thread> findThreadsByName(final String threadName) {
        return findThreads(new NamePredicate(threadName));
    }

    
Finds the active thread with the specified id.
Params:
threadId – The thread id
Throws:
IllegalArgumentException – if the specified id is zero or negative
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
The thread with the specified id or null if no such thread exists/**
     * Finds the active thread with the specified id.
     *
     * @param threadId The thread id
     * @return The thread with the specified id or {@code null} if no such thread exists
     * @throws IllegalArgumentException if the specified id is zero or negative
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     *
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Thread findThreadById(final long threadId) {
        final Collection<Thread> result = findThreads(new ThreadIdPredicate(threadId));
        return result.isEmpty() ? null : result.iterator().next();
    }

    
 ThreadUtils instances should NOT be constructed in standard programming. Instead, the class should be used as ThreadUtils.getAllThreads() 

This constructor is public to permit tools that require a JavaBean instance to operate.

/**
     * <p>
     * ThreadUtils instances should NOT be constructed in standard programming. Instead, the class should be used as
     * {@code ThreadUtils.getAllThreads()}
     * </p>
     * <p>
     * This constructor is public to permit tools that require a JavaBean instance to operate.
     * </p>
     */
    public ThreadUtils() {
        super();
    }

    
A predicate for selecting threads.
/**
     * A predicate for selecting threads.
     */
    // When breaking BC, replace this with Predicate<Thread>
    @FunctionalInterface
    public interface ThreadPredicate {

        
Evaluates this predicate on the given thread.
Params:
thread – the thread
Returns:
true if the thread matches the predicate, otherwise false/**
         * Evaluates this predicate on the given thread.
         * @param thread the thread
         * @return {@code true} if the thread matches the predicate, otherwise {@code false}
         */
        boolean test(Thread thread);
    }

    
A predicate for selecting threadgroups.
/**
     * A predicate for selecting threadgroups.
     */
    // When breaking BC, replace this with Predicate<ThreadGroup>
    @FunctionalInterface
    public interface ThreadGroupPredicate {

        
Evaluates this predicate on the given threadgroup.
Params:
threadGroup – the threadgroup
Returns:
true if the threadGroup matches the predicate, otherwise false/**
         * Evaluates this predicate on the given threadgroup.
         * @param threadGroup the threadgroup
         * @return {@code true} if the threadGroup matches the predicate, otherwise {@code false}
         */
        boolean test(ThreadGroup threadGroup);
    }

    
Predicate which always returns true.
/**
     * Predicate which always returns true.
     */
    public static final AlwaysTruePredicate ALWAYS_TRUE_PREDICATE = new AlwaysTruePredicate();

    
A predicate implementation which always returns true.
/**
     * A predicate implementation which always returns true.
     */
    private static final class AlwaysTruePredicate implements ThreadPredicate, ThreadGroupPredicate {

        private AlwaysTruePredicate() {
        }

        @Override
        public boolean test(final ThreadGroup threadGroup) {
            return true;
        }

        @Override
        public boolean test(final Thread thread) {
            return true;
        }
    }

    
A predicate implementation which matches a thread or threadgroup name.
/**
     * A predicate implementation which matches a thread or threadgroup name.
     */
    public static class NamePredicate implements ThreadPredicate, ThreadGroupPredicate {

        private final String name;

        
Predicate constructor
Params:
name – thread or threadgroup name
Throws:
IllegalArgumentException – if the name is null/**
         * Predicate constructor
         *
         * @param name thread or threadgroup name
         * @throws IllegalArgumentException if the name is {@code null}
         */
        public NamePredicate(final String name) {
            super();
            Validate.notNull(name, "The name must not be null");
            this.name = name;
        }

        @Override
        public boolean test(final ThreadGroup threadGroup) {
            return threadGroup != null && threadGroup.getName().equals(name);
        }

        @Override
        public boolean test(final Thread thread) {
            return thread != null && thread.getName().equals(name);
        }
    }

    
A predicate implementation which matches a thread id.
/**
     * A predicate implementation which matches a thread id.
     */
    public static class ThreadIdPredicate implements ThreadPredicate {

        private final long threadId;

        
Predicate constructor
Params:
threadId – the threadId to match
Throws:
IllegalArgumentException – if the threadId is zero or negative/**
         * Predicate constructor
         *
         * @param threadId the threadId to match
         * @throws IllegalArgumentException if the threadId is zero or negative
         */
        public ThreadIdPredicate(final long threadId) {
            super();
            if (threadId <= 0) {
                throw new IllegalArgumentException("The thread id must be greater than zero");
            }
            this.threadId = threadId;
        }

        @Override
        public boolean test(final Thread thread) {
            return thread != null && thread.getId() == threadId;
        }
    }

    
Select all active threads which match the given predicate.
Params:
predicate – the predicate
Throws:
IllegalArgumentException – if the predicate is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
An unmodifiable Collection of active threads matching the given predicate/**
     * Select all active threads which match the given predicate.
     *
     * @param predicate the predicate
     * @return An unmodifiable {@code Collection} of active threads matching the given predicate
     *
     * @throws IllegalArgumentException if the predicate is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<Thread> findThreads(final ThreadPredicate predicate) {
        return findThreads(getSystemThreadGroup(), true, predicate);
    }

    
Select all active threadgroups which match the given predicate.
Params:
predicate – the predicate
Throws:
IllegalArgumentException – if the predicate is null
SecurityException – 
         if the current thread cannot access the system thread group
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
An unmodifiable Collection of active threadgroups matching the given predicate/**
     * Select all active threadgroups which match the given predicate.
     *
     * @param predicate the predicate
     * @return An unmodifiable {@code Collection} of active threadgroups matching the given predicate
     * @throws IllegalArgumentException if the predicate is null
     * @throws  SecurityException
     *          if the current thread cannot access the system thread group
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<ThreadGroup> findThreadGroups(final ThreadGroupPredicate predicate) {
        return findThreadGroups(getSystemThreadGroup(), true, predicate);
    }

    
Select all active threads which match the given predicate and which belongs to the given thread group (or one of its subgroups).
Params:
group – the thread group
recurse – if true then evaluate the predicate recursively on all threads in all subgroups of the given group
predicate – the predicate
Throws:
IllegalArgumentException – if the given group or predicate is null
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
An unmodifiable Collection of active threads which match the given predicate and which belongs to the given thread group/**
     * Select all active threads which match the given predicate and which belongs to the given thread group (or one of its subgroups).
     *
     * @param group the thread group
     * @param recurse if {@code true} then evaluate the predicate recursively on all threads in all subgroups of the given group
     * @param predicate the predicate
     * @return An unmodifiable {@code Collection} of active threads which match the given predicate and which belongs to the given thread group
     * @throws IllegalArgumentException if the given group or predicate is null
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<Thread> findThreads(final ThreadGroup group, final boolean recurse, final ThreadPredicate predicate) {
        Validate.notNull(group, "The group must not be null");
        Validate.notNull(predicate, "The predicate must not be null");

        int count = group.activeCount();
        Thread[] threads;
        do {
            threads = new Thread[count + (count / 2) + 1]; //slightly grow the array size
            count = group.enumerate(threads, recurse);
            //return value of enumerate() must be strictly less than the array size according to javadoc
        } while (count >= threads.length);

        final List<Thread> result = new ArrayList<>(count);
        for (int i = 0; i < count; ++i) {
            if (predicate.test(threads[i])) {
                result.add(threads[i]);
            }
        }
        return Collections.unmodifiableCollection(result);
    }

    
Select all active threadgroups which match the given predicate and which is a subgroup of the given thread group (or one of its subgroups).
Params:
group – the thread group
recurse – if true then evaluate the predicate recursively on all threadgroups in all subgroups of the given group
predicate – the predicate
Throws:
IllegalArgumentException – if the given group or predicate is null
SecurityException –  if the current thread cannot modify
         thread groups from this thread's thread group up to the system thread group
Returns:
An unmodifiable Collection of active threadgroups which match the given predicate and which is a subgroup of the given thread group/**
     * Select all active threadgroups which match the given predicate and which is a subgroup of the given thread group (or one of its subgroups).
     *
     * @param group the thread group
     * @param recurse if {@code true} then evaluate the predicate recursively on all threadgroups in all subgroups of the given group
     * @param predicate the predicate
     * @return An unmodifiable {@code Collection} of active threadgroups which match the given predicate and which is a subgroup of the given thread group
     * @throws IllegalArgumentException if the given group or predicate is null
     * @throws  SecurityException  if the current thread cannot modify
     *          thread groups from this thread's thread group up to the system thread group
     */
    public static Collection<ThreadGroup> findThreadGroups(final ThreadGroup group, final boolean recurse, final ThreadGroupPredicate predicate) {
        Validate.notNull(group, "The group must not be null");
        Validate.notNull(predicate, "The predicate must not be null");

        int count = group.activeGroupCount();
        ThreadGroup[] threadGroups;
        do {
            threadGroups = new ThreadGroup[count + (count / 2) + 1]; //slightly grow the array size
            count = group.enumerate(threadGroups, recurse);
            //return value of enumerate() must be strictly less than the array size according to javadoc
        } while (count >= threadGroups.length);

        final List<ThreadGroup> result = new ArrayList<>(count);
        for (int i = 0; i < count; ++i) {
            if (predicate.test(threadGroups[i])) {
                result.add(threadGroups[i]);
            }
        }
        return Collections.unmodifiableCollection(result);
    }
}