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);
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