在我们启动一个Java进程的时候，我们通常会想这个进程究竟会启动几个线程呢，其中显而易见的是肯定会启动一个主线程，也就是我们常说的Main方法。

要想弄明白到底有几个线程会被启动，最佳的方法是自己动手实践。

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadInfo;
import java.lang.management.ThreadMXBean;

/**
 * @author haohh.zhang
 * @date 2019-12-20
 */
public class ThreadNum {
    public static void main(String[] args) {
        //构建 ThreadMXBean
        ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();
        //获取所有存活的线程信息
        ThreadInfo[] threadInfos = threadMXBean.dumpAllThreads(false, false);
        for (ThreadInfo threadInfo : threadInfos) {
            //打印出线程id 以及 线程name
            System.out.println(threadInfo.getThreadId() + " - " + threadInfo.getThreadName());
        }
    }
}

执行完程序可以看到输出结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/...
4 - Signal Dispatcher
3 - Finalizer
2 - Reference Handler
1 - main

Process finished with exit code 0

从结果上可以看出 在JDK1.8.0_111版本下至少会启动四个线程。
这四个线程分别是：

• main : 主线程
• Reference Handler : 处理引用对象本身（软、弱、虚引用）的线程
• Finalizer : 调用对象的finalize方法的线程，也就是说垃圾回收的守护线程
• Signal Dispatcher : 接受处理各种信号的线程

其余还有一些前程分别是：

• Attach Listener : 监听各种请求的socket连接,把执行的操作扔给VM Thread的线程
• VM Thread : 线程母体,最原始的线程,单例,里面有个队列，存放上面的操作，它负责loop处理队列中的操作（包括对其他线程的创建，分配和对象的清理，cms-mark等工作）
• CompilerThread0 : JIT动态编译线程
• ConcurrentMark-SweepGCThread : CMS垃圾收集线程
• DestroyJavaVM : 负责卸载JVM的线程
• ContainerBackground Processor : JBoss守护线程
• Dispatcher-Thread-3 : Log4j异步日志守护线程
• Gang worker#0 : 新生代回收线程
• GC Daemon : RMI远程GC线程(调用system.gc())
• Low MemoryDetector : 发现可用内存低，则分配新的内存空间
• Process reaper : 执行os命令的线程
• SurrogateLockerThread: CMS垃圾回收
• VM Periodic Task Thread: 定期的内存监控、JVM运行状况监控

ThreadMXBean

* The management interface for the thread system of the Java virtual machine.
根据文档可以看出这个是 Java 虚拟机中线程系统的管理接口。

ThreadMXBean 主要方法

 /**
     * Returns the current number of live threads including both
     * daemon and non-daemon threads.
     *  返回当前存活的线程数
     * @return the current number of live threads.
     */
    public int getThreadCount();

    /**
     * Returns the peak live thread count since the Java virtual machine
     * started or peak was reset.
     *   返回峰值的线程总数
     * @return the peak live thread count.
     */
    public int getPeakThreadCount();

    /**
     * Returns the total number of threads created and also started
     * since the Java virtual machine started.
     *
     * @return the total number of threads started.
     */
    public long getTotalStartedThreadCount();

    /**
     * Returns the current number of live daemon threads.
     *
     * @return the current number of live daemon threads.
     */
    public int getDaemonThreadCount();

    /**
     * Returns all live thread IDs.
     * Some threads included in the returned array
     * may have been terminated when this method returns.
     *   返回所有线程ID
     * @return an array of <tt>long</tt>, each is a thread ID.
     *   
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     */
    public long[] getAllThreadIds();

    /**
     * Returns the thread info for a thread of the specified
     * <tt>id</tt> with no stack trace.
     * This method is equivalent to calling:
     * <blockquote>
     *   {@link #getThreadInfo(long, int) getThreadInfo(id, 0);}
     * </blockquote>
     *
     * <p>
     * This method returns a <tt>ThreadInfo</tt> object representing
     * the thread information for the thread of the specified ID.
     * The stack trace, locked monitors, and locked synchronizers
     * in the returned <tt>ThreadInfo</tt> object will
     * be empty.
     *
     * If a thread of the given ID is not alive or does not exist,
     * this method will return <tt>null</tt>.  A thread is alive if
     * it has been started and has not yet died.
     *
     * <p>
     * <b>MBeanServer access</b>:<br>
     * The mapped type of <tt>ThreadInfo</tt> is
     * <tt>CompositeData</tt> with attributes as specified in the
     * {@link ThreadInfo#from ThreadInfo.from} method.
     *
     * @param id the thread ID of the thread. Must be positive.
     *
     * @return a {@link ThreadInfo} object for the thread of the given ID
     * with no stack trace, no locked monitor and no synchronizer info;
     * <tt>null</tt> if the thread of the given ID is not alive or
     * it does not exist.
     *
     * @throws IllegalArgumentException if {@code id <= 0}.
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     */
    public ThreadInfo getThreadInfo(long id);

    /**
     * Returns the thread info for each thread
     * whose ID is in the input array <tt>ids</tt> with no stack trace.
     * This method is equivalent to calling:
     * <blockquote><pre>
     *   {@link #getThreadInfo(long[], int) getThreadInfo}(ids, 0);
     * </pre></blockquote>
     *
     * <p>
     * This method returns an array of the <tt>ThreadInfo</tt> objects.
     * The stack trace, locked monitors, and locked synchronizers
     * in each <tt>ThreadInfo</tt> object will be empty.
     *
     * If a thread of a given ID is not alive or does not exist,
     * the corresponding element in the returned array will
     * contain <tt>null</tt>.  A thread is alive if
     * it has been started and has not yet died.
     *
     * <p>
     * <b>MBeanServer access</b>:<br>
     * The mapped type of <tt>ThreadInfo</tt> is
     * <tt>CompositeData</tt> with attributes as specified in the
     * {@link ThreadInfo#from ThreadInfo.from} method.
     *
     * @param ids an array of thread IDs.
     * @return an array of the {@link ThreadInfo} objects, each containing
     * information about a thread whose ID is in the corresponding
     * element of the input array of IDs
     * with no stack trace, no locked monitor and no synchronizer info.
     *
     * @throws IllegalArgumentException if any element in the input array
     *         <tt>ids</tt> is {@code <= 0}.
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     */
    public ThreadInfo[] getThreadInfo(long[] ids);

    /**
     * Returns a thread info for a thread of the specified <tt>id</tt>,
     * with stack trace of a specified number of stack trace elements.
     * The <tt>maxDepth</tt> parameter indicates the maximum number of
     * {@link StackTraceElement} to be retrieved from the stack trace.
     * If <tt>maxDepth == Integer.MAX_VALUE</tt>, the entire stack trace of
     * the thread will be dumped.
     * If <tt>maxDepth == 0</tt>, no stack trace of the thread
     * will be dumped.
     * This method does not obtain the locked monitors and locked
     * synchronizers of the thread.
     * <p>
     * When the Java virtual machine has no stack trace information
     * about a thread or <tt>maxDepth == 0</tt>,
     * the stack trace in the
     * <tt>ThreadInfo</tt> object will be an empty array of
     * <tt>StackTraceElement</tt>.
     *
     * <p>
     * If a thread of the given ID is not alive or does not exist,
     * this method will return <tt>null</tt>.  A thread is alive if
     * it has been started and has not yet died.
     *
     * <p>
     * <b>MBeanServer access</b>:<br>
     * The mapped type of <tt>ThreadInfo</tt> is
     * <tt>CompositeData</tt> with attributes as specified in the
     * {@link ThreadInfo#from ThreadInfo.from} method.
     *
     * @param id the thread ID of the thread. Must be positive.
     * @param maxDepth the maximum number of entries in the stack trace
     * to be dumped. <tt>Integer.MAX_VALUE</tt> could be used to request
     * the entire stack to be dumped.
     *
     * @return a {@link ThreadInfo} of the thread of the given ID
     * with no locked monitor and synchronizer info.
     * <tt>null</tt> if the thread of the given ID is not alive or
     * it does not exist.
     *
     * @throws IllegalArgumentException if {@code id <= 0}.
     * @throws IllegalArgumentException if <tt>maxDepth is negative</tt>.
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     *
     */
    public ThreadInfo getThreadInfo(long id, int maxDepth);

    /**
     * Returns the thread info for each thread
     * whose ID is in the input array <tt>ids</tt>,
     * with stack trace of a specified number of stack trace elements.
     * The <tt>maxDepth</tt> parameter indicates the maximum number of
     * {@link StackTraceElement} to be retrieved from the stack trace.
     * If <tt>maxDepth == Integer.MAX_VALUE</tt>, the entire stack trace of
     * the thread will be dumped.
     * If <tt>maxDepth == 0</tt>, no stack trace of the thread
     * will be dumped.
     * This method does not obtain the locked monitors and locked
     * synchronizers of the threads.
     * <p>
     * When the Java virtual machine has no stack trace information
     * about a thread or <tt>maxDepth == 0</tt>,
     * the stack trace in the
     * <tt>ThreadInfo</tt> object will be an empty array of
     * <tt>StackTraceElement</tt>.
     * <p>
     * This method returns an array of the <tt>ThreadInfo</tt> objects,
     * each is the thread information about the thread with the same index
     * as in the <tt>ids</tt> array.
     * If a thread of the given ID is not alive or does not exist,
     * <tt>null</tt> will be set in the corresponding element
     * in the returned array.  A thread is alive if
     * it has been started and has not yet died.
     *
     * <p>
     * <b>MBeanServer access</b>:<br>
     * The mapped type of <tt>ThreadInfo</tt> is
     * <tt>CompositeData</tt> with attributes as specified in the
     * {@link ThreadInfo#from ThreadInfo.from} method.
     *
     * @param ids an array of thread IDs
     * @param maxDepth the maximum number of entries in the stack trace
     * to be dumped. <tt>Integer.MAX_VALUE</tt> could be used to request
     * the entire stack to be dumped.
     *
     * @return an array of the {@link ThreadInfo} objects, each containing
     * information about a thread whose ID is in the corresponding
     * element of the input array of IDs with no locked monitor and
     * synchronizer info.
     *
     * @throws IllegalArgumentException if <tt>maxDepth is negative</tt>.
     * @throws IllegalArgumentException if any element in the input array
     *      <tt>ids</tt> is {@code <= 0}.
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     *
     */
    public ThreadInfo[] getThreadInfo(long[] ids, int maxDepth);

    /**
     * Tests if the Java virtual machine supports thread contention monitoring.
     *
     * @return
     *   <tt>true</tt>
     *     if the Java virtual machine supports thread contention monitoring;
     *   <tt>false</tt> otherwise.
     */
    public boolean isThreadContentionMonitoringSupported();

    /**
     * Tests if thread contention monitoring is enabled.
     *
     * @return <tt>true</tt> if thread contention monitoring is enabled;
     *         <tt>false</tt> otherwise.
     *
     * @throws java.lang.UnsupportedOperationException if the Java virtual
     * machine does not support thread contention monitoring.
     *
     * @see #isThreadContentionMonitoringSupported
     */
    public boolean isThreadContentionMonitoringEnabled();

    /**
     * Enables or disables thread contention monitoring.
     * Thread contention monitoring is disabled by default.
     *
     * @param enable <tt>true</tt> to enable;
     *               <tt>false</tt> to disable.
     *
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support thread contention monitoring.
     *
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("control").
     *
     * @see #isThreadContentionMonitoringSupported
     */
    public void setThreadContentionMonitoringEnabled(boolean enable);

    /**
     * Returns the total CPU time for the current thread in nanoseconds.
     * The returned value is of nanoseconds precision but
     * not necessarily nanoseconds accuracy.
     * If the implementation distinguishes between user mode time and system
     * mode time, the returned CPU time is the amount of time that
     * the current thread has executed in user mode or system mode.
     *
     * <p>
     * This is a convenient method for local management use and is
     * equivalent to calling:
     * <blockquote><pre>
     *   {@link #getThreadCpuTime getThreadCpuTime}(Thread.currentThread().getId());
     * </pre></blockquote>
     *
     * @return the total CPU time for the current thread if CPU time
     * measurement is enabled; <tt>-1</tt> otherwise.
     *
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support CPU time measurement for
     * the current thread.
     *
     * @see #getCurrentThreadUserTime
     * @see #isCurrentThreadCpuTimeSupported
     * @see #isThreadCpuTimeEnabled
     * @see #setThreadCpuTimeEnabled
     */
    public long getCurrentThreadCpuTime();

    /**
     * Returns the CPU time that the current thread has executed
     * in user mode in nanoseconds.
     * The returned value is of nanoseconds precision but
     * not necessarily nanoseconds accuracy.
     *
     * <p>
     * This is a convenient method for local management use and is
     * equivalent to calling:
     * <blockquote><pre>
     *   {@link #getThreadUserTime getThreadUserTime}(Thread.currentThread().getId());
     * </pre></blockquote>
     *
     * @return the user-level CPU time for the current thread if CPU time
     * measurement is enabled; <tt>-1</tt> otherwise.
     *
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support CPU time measurement for
     * the current thread.
     *
     * @see #getCurrentThreadCpuTime
     * @see #isCurrentThreadCpuTimeSupported
     * @see #isThreadCpuTimeEnabled
     * @see #setThreadCpuTimeEnabled
     */
    public long getCurrentThreadUserTime();

    /**
     * Returns the total CPU time for a thread of the specified ID in nanoseconds.
     * The returned value is of nanoseconds precision but
     * not necessarily nanoseconds accuracy.
     * If the implementation distinguishes between user mode time and system
     * mode time, the returned CPU time is the amount of time that
     * the thread has executed in user mode or system mode.
     *
     * <p>
     * If the thread of the specified ID is not alive or does not exist,
     * this method returns <tt>-1</tt>. If CPU time measurement
     * is disabled, this method returns <tt>-1</tt>.
     * A thread is alive if it has been started and has not yet died.
     * <p>
     * If CPU time measurement is enabled after the thread has started,
     * the Java virtual machine implementation may choose any time up to
     * and including the time that the capability is enabled as the point
     * where CPU time measurement starts.
     *
     * @param id the thread ID of a thread
     * @return the total CPU time for a thread of the specified ID
     * if the thread of the specified ID exists, the thread is alive,
     * and CPU time measurement is enabled;
     * <tt>-1</tt> otherwise.
     *
     * @throws IllegalArgumentException if {@code id <= 0}.
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support CPU time measurement for
     * other threads.
     *
     * @see #getThreadUserTime
     * @see #isThreadCpuTimeSupported
     * @see #isThreadCpuTimeEnabled
     * @see #setThreadCpuTimeEnabled
     */
    public long getThreadCpuTime(long id);

    /**
     * Returns the CPU time that a thread of the specified ID
     * has executed in user mode in nanoseconds.
     * The returned value is of nanoseconds precision but
     * not necessarily nanoseconds accuracy.
     *
     * <p>
     * If the thread of the specified ID is not alive or does not exist,
     * this method returns <tt>-1</tt>. If CPU time measurement
     * is disabled, this method returns <tt>-1</tt>.
     * A thread is alive if it has been started and has not yet died.
     * <p>
     * If CPU time measurement is enabled after the thread has started,
     * the Java virtual machine implementation may choose any time up to
     * and including the time that the capability is enabled as the point
     * where CPU time measurement starts.
     *
     * @param id the thread ID of a thread
     * @return the user-level CPU time for a thread of the specified ID
     * if the thread of the specified ID exists, the thread is alive,
     * and CPU time measurement is enabled;
     * <tt>-1</tt> otherwise.
     *
     * @throws IllegalArgumentException if {@code id <= 0}.
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support CPU time measurement for
     * other threads.
     *
     * @see #getThreadCpuTime
     * @see #isThreadCpuTimeSupported
     * @see #isThreadCpuTimeEnabled
     * @see #setThreadCpuTimeEnabled
     */
    public long getThreadUserTime(long id);

    /**
     * Tests if the Java virtual machine implementation supports CPU time
     * measurement for any thread.
     * A Java virtual machine implementation that supports CPU time
     * measurement for any thread will also support CPU time
     * measurement for the current thread.
     *
     * @return
     *   <tt>true</tt>
     *     if the Java virtual machine supports CPU time
     *     measurement for any thread;
     *   <tt>false</tt> otherwise.
     */
    public boolean isThreadCpuTimeSupported();

    /**
     * Tests if the Java virtual machine supports CPU time
     * measurement for the current thread.
     * This method returns <tt>true</tt> if {@link #isThreadCpuTimeSupported}
     * returns <tt>true</tt>.
     *
     * @return
     *   <tt>true</tt>
     *     if the Java virtual machine supports CPU time
     *     measurement for current thread;
     *   <tt>false</tt> otherwise.
     */
    public boolean isCurrentThreadCpuTimeSupported();

    /**
     * Tests if thread CPU time measurement is enabled.
     *
     * @return <tt>true</tt> if thread CPU time measurement is enabled;
     *         <tt>false</tt> otherwise.
     *
     * @throws java.lang.UnsupportedOperationException if the Java virtual
     * machine does not support CPU time measurement for other threads
     * nor for the current thread.
     *
     * @see #isThreadCpuTimeSupported
     * @see #isCurrentThreadCpuTimeSupported
     */
    public boolean isThreadCpuTimeEnabled();

    /**
     * Enables or disables thread CPU time measurement.  The default
     * is platform dependent.
     *
     * @param enable <tt>true</tt> to enable;
     *               <tt>false</tt> to disable.
     *
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support CPU time measurement for
     * any threads nor for the current thread.
     *
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("control").
     *
     * @see #isThreadCpuTimeSupported
     * @see #isCurrentThreadCpuTimeSupported
     */
    public void setThreadCpuTimeEnabled(boolean enable);

    /**
     * Finds cycles of threads that are in deadlock waiting to acquire
     * object monitors. That is, threads that are blocked waiting to enter a
     * synchronization block or waiting to reenter a synchronization block
     * after an {@link Object#wait Object.wait} call,
     * where each thread owns one monitor while
     * trying to obtain another monitor already held by another thread
     * in a cycle.
     * <p>
     * More formally, a thread is <em>monitor deadlocked</em> if it is
     * part of a cycle in the relation "is waiting for an object monitor
     * owned by".  In the simplest case, thread A is blocked waiting
     * for a monitor owned by thread B, and thread B is blocked waiting
     * for a monitor owned by thread A.
     * <p>
     * This method is designed for troubleshooting use, but not for
     * synchronization control.  It might be an expensive operation.
     * <p>
     * This method finds deadlocks involving only object monitors.
     * To find deadlocks involving both object monitors and
     * <a href="LockInfo.html#OwnableSynchronizer">ownable synchronizers</a>,
     * the {@link #findDeadlockedThreads findDeadlockedThreads} method
     * should be used.
     *
     * @return an array of IDs of the threads that are monitor
     * deadlocked, if any; <tt>null</tt> otherwise.
     *
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     *
     * @see #findDeadlockedThreads
     */
    public long[] findMonitorDeadlockedThreads();

    /**
     * Resets the peak thread count to the current number of
     * live threads.
     *
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("control").
     *
     * @see #getPeakThreadCount
     * @see #getThreadCount
     */
    public void resetPeakThreadCount();

    /**
     * Finds cycles of threads that are in deadlock waiting to acquire
     * object monitors or
     * <a href="LockInfo.html#OwnableSynchronizer">ownable synchronizers</a>.
     *
     * Threads are <em>deadlocked</em> in a cycle waiting for a lock of
     * these two types if each thread owns one lock while
     * trying to acquire another lock already held
     * by another thread in the cycle.
     * <p>
     * This method is designed for troubleshooting use, but not for
     * synchronization control.  It might be an expensive operation.
     *
     * @return an array of IDs of the threads that are
     * deadlocked waiting for object monitors or ownable synchronizers, if any;
     * <tt>null</tt> otherwise.
     *
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     * @throws java.lang.UnsupportedOperationException if the Java virtual
     * machine does not support monitoring of ownable synchronizer usage.
     *
     * @see #isSynchronizerUsageSupported
     * @see #findMonitorDeadlockedThreads
     * @since 1.6
     */
    public long[] findDeadlockedThreads();

    /**
     * Tests if the Java virtual machine supports monitoring of
     * object monitor usage.
     *
     * @return
     *   <tt>true</tt>
     *     if the Java virtual machine supports monitoring of
     *     object monitor usage;
     *   <tt>false</tt> otherwise.
     *
     * @see #dumpAllThreads
     * @since 1.6
     */
    public boolean isObjectMonitorUsageSupported();

    /**
     * Tests if the Java virtual machine supports monitoring of
     * <a href="LockInfo.html#OwnableSynchronizer">
     * ownable synchronizer</a> usage.
     *
     * @return
     *   <tt>true</tt>
     *     if the Java virtual machine supports monitoring of ownable
     *     synchronizer usage;
     *   <tt>false</tt> otherwise.
     *
     * @see #dumpAllThreads
     * @since 1.6
     */
    public boolean isSynchronizerUsageSupported();

    /**
     * Returns the thread info for each thread
     * whose ID is in the input array <tt>ids</tt>, with stack trace
     * and synchronization information.
     *
     * <p>
     * This method obtains a snapshot of the thread information
     * for each thread including:
     * <ul>
     *    <li>the entire stack trace,</li>
     *    <li>the object monitors currently locked by the thread
     *        if <tt>lockedMonitors</tt> is <tt>true</tt>, and</li>
     *    <li>the <a href="LockInfo.html#OwnableSynchronizer">
     *        ownable synchronizers</a> currently locked by the thread
     *        if <tt>lockedSynchronizers</tt> is <tt>true</tt>.</li>
     * </ul>
     * <p>
     * This method returns an array of the <tt>ThreadInfo</tt> objects,
     * each is the thread information about the thread with the same index
     * as in the <tt>ids</tt> array.
     * If a thread of the given ID is not alive or does not exist,
     * <tt>null</tt> will be set in the corresponding element
     * in the returned array.  A thread is alive if
     * it has been started and has not yet died.
     * <p>
     * If a thread does not lock any object monitor or <tt>lockedMonitors</tt>
     * is <tt>false</tt>, the returned <tt>ThreadInfo</tt> object will have an
     * empty <tt>MonitorInfo</tt> array.  Similarly, if a thread does not
     * lock any synchronizer or <tt>lockedSynchronizers</tt> is <tt>false</tt>,
     * the returned <tt>ThreadInfo</tt> object
     * will have an empty <tt>LockInfo</tt> array.
     *
     * <p>
     * When both <tt>lockedMonitors</tt> and <tt>lockedSynchronizers</tt>
     * parameters are <tt>false</tt>, it is equivalent to calling:
     * <blockquote><pre>
     *     {@link #getThreadInfo(long[], int)  getThreadInfo(ids, Integer.MAX_VALUE)}
     * </pre></blockquote>
     *
     * <p>
     * This method is designed for troubleshooting use, but not for
     * synchronization control.  It might be an expensive operation.
     *
     * <p>
     * <b>MBeanServer access</b>:<br>
     * The mapped type of <tt>ThreadInfo</tt> is
     * <tt>CompositeData</tt> with attributes as specified in the
     * {@link ThreadInfo#from ThreadInfo.from} method.
     *
     * @param  ids an array of thread IDs.
     * @param  lockedMonitors if <tt>true</tt>, retrieves all locked monitors.
     * @param  lockedSynchronizers if <tt>true</tt>, retrieves all locked
     *             ownable synchronizers.
     *
     * @return an array of the {@link ThreadInfo} objects, each containing
     * information about a thread whose ID is in the corresponding
     * element of the input array of IDs.
     *
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     * @throws java.lang.UnsupportedOperationException
     *         <ul>
     *           <li>if <tt>lockedMonitors</tt> is <tt>true</tt> but
     *               the Java virtual machine does not support monitoring
     *               of {@linkplain #isObjectMonitorUsageSupported
     *               object monitor usage}; or</li>
     *           <li>if <tt>lockedSynchronizers</tt> is <tt>true</tt> but
     *               the Java virtual machine does not support monitoring
     *               of {@linkplain #isSynchronizerUsageSupported
     *               ownable synchronizer usage}.</li>
     *         </ul>
     *
     * @see #isObjectMonitorUsageSupported
     * @see #isSynchronizerUsageSupported
     *
     * @since 1.6
     */
    public ThreadInfo[] getThreadInfo(long[] ids, boolean lockedMonitors, boolean lockedSynchronizers);

    /**
     * Returns the thread info for all live threads with stack trace
     * and synchronization information.
     * Some threads included in the returned array
     * may have been terminated when this method returns.
     *
     * <p>
     * This method returns an array of {@link ThreadInfo} objects
     * as specified in the {@link #getThreadInfo(long[], boolean, boolean)}
     * method.
     *
     * @param  lockedMonitors if <tt>true</tt>, dump all locked monitors.
     * @param  lockedSynchronizers if <tt>true</tt>, dump all locked
     *             ownable synchronizers.
     *  获取所有存活的线程信息
     * @return an array of {@link ThreadInfo} for all live threads.
     *
     * @throws java.lang.SecurityException if a security manager
     *         exists and the caller does not have
     *         ManagementPermission("monitor").
     * @throws java.lang.UnsupportedOperationException
     *         <ul>
     *           <li>if <tt>lockedMonitors</tt> is <tt>true</tt> but
     *               the Java virtual machine does not support monitoring
     *               of {@linkplain #isObjectMonitorUsageSupported
     *               object monitor usage}; or</li>
     *           <li>if <tt>lockedSynchronizers</tt> is <tt>true</tt> but
     *               the Java virtual machine does not support monitoring
     *               of {@linkplain #isSynchronizerUsageSupported
     *               ownable synchronizer usage}.</li>
     *         </ul>
     *
     * @see #isObjectMonitorUsageSupported
     * @see #isSynchronizerUsageSupported
     *
     * @since 1.6
     */
    public ThreadInfo[] dumpAllThreads(boolean lockedMonitors, boolean lockedSynchronizers);