Back to index...

	/*
	* Copyright (c) 1994, 2018, 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 java.lang;

	import java.lang.ref.Reference;
	import java.lang.ref.ReferenceQueue;
	import java.lang.ref.WeakReference;
	import java.security.AccessController;
	import java.security.AccessControlContext;
	import java.security.PrivilegedAction;
	import java.util.Map;
	import java.util.HashMap;
	import java.util.concurrent.ConcurrentHashMap;
	import java.util.concurrent.ConcurrentMap;
	import java.util.concurrent.locks.LockSupport;

	import jdk.internal.misc.TerminatingThreadLocal;
	import sun.nio.ch.Interruptible;
	import jdk.internal.reflect.CallerSensitive;
	import jdk.internal.reflect.Reflection;
	import sun.security.util.SecurityConstants;
	import jdk.internal.HotSpotIntrinsicCandidate;

	/**
	* A <i>thread</i> is a thread of execution in a program. The Java
	* Virtual Machine allows an application to have multiple threads of
	* execution running concurrently.
	* <p>
	* Every thread has a priority. Threads with higher priority are
	* executed in preference to threads with lower priority. Each thread
	* may or may not also be marked as a daemon. When code running in
	* some thread creates a new {@code Thread} object, the new
	* thread has its priority initially set equal to the priority of the
	* creating thread, and is a daemon thread if and only if the
	* creating thread is a daemon.
	* <p>
	* When a Java Virtual Machine starts up, there is usually a single
	* non-daemon thread (which typically calls the method named
	* {@code main} of some designated class). The Java Virtual
	* Machine continues to execute threads until either of the following
	* occurs:
	* <ul>
	* <li>The {@code exit} method of class {@code Runtime} has been
	* called and the security manager has permitted the exit operation
	* to take place.
	* <li>All threads that are not daemon threads have died, either by
	* returning from the call to the {@code run} method or by
	* throwing an exception that propagates beyond the {@code run}
	* method.
	* </ul>
	* <p>
	* There are two ways to create a new thread of execution. One is to
	* declare a class to be a subclass of {@code Thread}. This
	* subclass should override the {@code run} method of class
	* {@code Thread}. An instance of the subclass can then be
	* allocated and started. For example, a thread that computes primes
	* larger than a stated value could be written as follows:
	* <hr><blockquote><pre>
	* class PrimeThread extends Thread {
	* long minPrime;
	* PrimeThread(long minPrime) {
	* this.minPrime = minPrime;
	* }
	*
	* public void run() {
	* // compute primes larger than minPrime
	*  . . .
	* }
	* }
	* </pre></blockquote><hr>
	* <p>
	* The following code would then create a thread and start it running:
	* <blockquote><pre>
	* PrimeThread p = new PrimeThread(143);
	* p.start();
	* </pre></blockquote>
	* <p>
	* The other way to create a thread is to declare a class that
	* implements the {@code Runnable} interface. That class then
	* implements the {@code run} method. An instance of the class can
	* then be allocated, passed as an argument when creating
	* {@code Thread}, and started. The same example in this other
	* style looks like the following:
	* <hr><blockquote><pre>
	* class PrimeRun implements Runnable {
	* long minPrime;
	* PrimeRun(long minPrime) {
	* this.minPrime = minPrime;
	* }
	*
	* public void run() {
	* // compute primes larger than minPrime
	*  . . .
	* }
	* }
	* </pre></blockquote><hr>
	* <p>
	* The following code would then create a thread and start it running:
	* <blockquote><pre>
	* PrimeRun p = new PrimeRun(143);
	* new Thread(p).start();
	* </pre></blockquote>
	* <p>
	* Every thread has a name for identification purposes. More than
	* one thread may have the same name. If a name is not specified when
	* a thread is created, a new name is generated for it.
	* <p>
	* Unless otherwise noted, passing a {@code null} argument to a constructor
	* or method in this class will cause a {@link NullPointerException} to be
	* thrown.
	*
	* @author unascribed
	* @see Runnable
	* @see Runtime#exit(int)
	* @see #run()
	* @see #stop()
	* @since 1.0
	*/
	public
	class Thread implements Runnable {
	/* Make sure registerNatives is the first thing <clinit> does. */
	private static native void registerNatives();
	static {
	registerNatives();
	}

	private volatile String name;
	private int priority;

	/* Whether or not the thread is a daemon thread. */
	private boolean daemon = false;

	/* Fields reserved for exclusive use by the JVM */
	private boolean stillborn = false;
	private long eetop;

	/* What will be run. */
	private Runnable target;

	/* The group of this thread */
	private ThreadGroup group;

	/* The context ClassLoader for this thread */
	private ClassLoader contextClassLoader;

	/* The inherited AccessControlContext of this thread */
	private AccessControlContext inheritedAccessControlContext;

	/* For autonumbering anonymous threads. */
	private static int threadInitNumber;
	private static synchronized int nextThreadNum() {
	return threadInitNumber++;
	}

	/* ThreadLocal values pertaining to this thread. This map is maintained
	* by the ThreadLocal class. */
	ThreadLocal.ThreadLocalMap threadLocals = null;

	/*
	* InheritableThreadLocal values pertaining to this thread. This map is
	* maintained by the InheritableThreadLocal class.
	*/
	ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;

	/*
	* The requested stack size for this thread, or 0 if the creator did
	* not specify a stack size. It is up to the VM to do whatever it
	* likes with this number; some VMs will ignore it.
	*/
	private final long stackSize;

	/*
	* JVM-private state that persists after native thread termination.
	*/
	private long nativeParkEventPointer;

	/*
	* Thread ID
	*/
	private final long tid;

	/* For generating thread ID */
	private static long threadSeqNumber;

	private static synchronized long nextThreadID() {
	return ++threadSeqNumber;
	}

	/*
	* Java thread status for tools, default indicates thread 'not yet started'
	*/
	private volatile int threadStatus;

	/**
	* The argument supplied to the current call to
	* java.util.concurrent.locks.LockSupport.park.
	* Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
	* Accessed using java.util.concurrent.locks.LockSupport.getBlocker
	*/
	volatile Object parkBlocker;

	/* The object in which this thread is blocked in an interruptible I/O
	* operation, if any. The blocker's interrupt method should be invoked
	* after setting this thread's interrupt status.
	*/
	private volatile Interruptible blocker;
	private final Object blockerLock = new Object();

	/* Set the blocker field; invoked via jdk.internal.misc.SharedSecrets
	* from java.nio code
	*/
	static void blockedOn(Interruptible b) {
	Thread me = Thread.currentThread();
	synchronized (me.blockerLock) {
	me.blocker = b;
	}
	}

	/**
	* The minimum priority that a thread can have.
	*/
	public static final int MIN_PRIORITY = 1;

	/**
	* The default priority that is assigned to a thread.
	*/
	public static final int NORM_PRIORITY = 5;

	/**
	* The maximum priority that a thread can have.
	*/
	public static final int MAX_PRIORITY = 10;

	/**
	* Returns a reference to the currently executing thread object.
	*
	* @return the currently executing thread.
	*/
	@HotSpotIntrinsicCandidate
	public static native Thread currentThread();

	/**
	* A hint to the scheduler that the current thread is willing to yield
	* its current use of a processor. The scheduler is free to ignore this
	* hint.
	*
	* <p> Yield is a heuristic attempt to improve relative progression
	* between threads that would otherwise over-utilise a CPU. Its use
	* should be combined with detailed profiling and benchmarking to
	* ensure that it actually has the desired effect.
	*
	* <p> It is rarely appropriate to use this method. It may be useful
	* for debugging or testing purposes, where it may help to reproduce
	* bugs due to race conditions. It may also be useful when designing
	* concurrency control constructs such as the ones in the
	* {@link java.util.concurrent.locks} package.
	*/
	public static native void yield();

	/**
	* Causes the currently executing thread to sleep (temporarily cease
	* execution) for the specified number of milliseconds, subject to
	* the precision and accuracy of system timers and schedulers. The thread
	* does not lose ownership of any monitors.
	*
	* @param millis
	* the length of time to sleep in milliseconds
	*
	* @throws IllegalArgumentException
	* if the value of {@code millis} is negative
	*
	* @throws InterruptedException
	* if any thread has interrupted the current thread. The
	* <i>interrupted status</i> of the current thread is
	* cleared when this exception is thrown.
	*/
	public static native void sleep(long millis) throws InterruptedException;

	/**
	* Causes the currently executing thread to sleep (temporarily cease
	* execution) for the specified number of milliseconds plus the specified
	* number of nanoseconds, subject to the precision and accuracy of system
	* timers and schedulers. The thread does not lose ownership of any
	* monitors.
	*
	* @param millis
	* the length of time to sleep in milliseconds
	*
	* @param nanos
	* {@code 0-999999} additional nanoseconds to sleep
	*
	* @throws IllegalArgumentException
	* if the value of {@code millis} is negative, or the value of
	* {@code nanos} is not in the range {@code 0-999999}
	*
	* @throws InterruptedException
	* if any thread has interrupted the current thread. The
	* <i>interrupted status</i> of the current thread is
	* cleared when this exception is thrown.
	*/
	public static void sleep(long millis, int nanos)
	throws InterruptedException {
	if (millis < 0) {
	throw new IllegalArgumentException("timeout value is negative");
	}

	if (nanos < 0 \|\| nanos > 999999) {
	throw new IllegalArgumentException(
	"nanosecond timeout value out of range");
	}

	if (nanos >= 500000 \|\| (nanos != 0 && millis == 0)) {
	millis++;
	}

	sleep(millis);
	}

	/**
	* Indicates that the caller is momentarily unable to progress, until the
	* occurrence of one or more actions on the part of other activities. By
	* invoking this method within each iteration of a spin-wait loop construct,
	* the calling thread indicates to the runtime that it is busy-waiting.
	* The runtime may take action to improve the performance of invoking
	* spin-wait loop constructions.
	*
	* @apiNote
	* As an example consider a method in a class that spins in a loop until
	* some flag is set outside of that method. A call to the {@code onSpinWait}
	* method should be placed inside the spin loop.
	* <pre>{@code
	* class EventHandler {
	* volatile boolean eventNotificationNotReceived;
	* void waitForEventAndHandleIt() {
	* while ( eventNotificationNotReceived ) {
	* java.lang.Thread.onSpinWait();
	* }
	* readAndProcessEvent();
	* }
	*
	* void readAndProcessEvent() {
	* // Read event from some source and process it
	* . . .
	* }
	* }
	* }</pre>
	* <p>
	* The code above would remain correct even if the {@code onSpinWait}
	* method was not called at all. However on some architectures the Java
	* Virtual Machine may issue the processor instructions to address such
	* code patterns in a more beneficial way.
	*
	* @since 9
	*/
	@HotSpotIntrinsicCandidate
	public static void onSpinWait() {}

	/**
	* Initializes a Thread.
	*
	* @param g the Thread group
	* @param target the object whose run() method gets called
	* @param name the name of the new Thread
	* @param stackSize the desired stack size for the new thread, or
	* zero to indicate that this parameter is to be ignored.
	* @param acc the AccessControlContext to inherit, or
	* AccessController.getContext() if null
	* @param inheritThreadLocals if {@code true}, inherit initial values for
	* inheritable thread-locals from the constructing thread
	*/
	private Thread(ThreadGroup g, Runnable target, String name,
	long stackSize, AccessControlContext acc,
	boolean inheritThreadLocals) {
	if (name == null) {
	throw new NullPointerException("name cannot be null");
	}

	this.name = name;

	Thread parent = currentThread();
	SecurityManager security = System.getSecurityManager();
	if (g == null) {
	/* Determine if it's an applet or not */

	/* If there is a security manager, ask the security manager
	what to do. */
	if (security != null) {
	g = security.getThreadGroup();
	}

	/* If the security manager doesn't have a strong opinion
	on the matter, use the parent thread group. */
	if (g == null) {
	g = parent.getThreadGroup();
	}
	}

	/* checkAccess regardless of whether or not threadgroup is
	explicitly passed in. */
	g.checkAccess();

	/*
	* Do we have the required permissions?
	*/
	if (security != null) {
	if (isCCLOverridden(getClass())) {
	security.checkPermission(
	SecurityConstants.SUBCLASS_IMPLEMENTATION_PERMISSION);
	}
	}

	g.addUnstarted();

	this.group = g;
	this.daemon = parent.isDaemon();
	this.priority = parent.getPriority();
	if (security == null \|\| isCCLOverridden(parent.getClass()))
	this.contextClassLoader = parent.getContextClassLoader();
	else
	this.contextClassLoader = parent.contextClassLoader;
	this.inheritedAccessControlContext =
	acc != null ? acc : AccessController.getContext();
	this.target = target;
	setPriority(priority);
	if (inheritThreadLocals && parent.inheritableThreadLocals != null)
	this.inheritableThreadLocals =
	ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
	/* Stash the specified stack size in case the VM cares */
	this.stackSize = stackSize;

	/* Set thread ID */
	this.tid = nextThreadID();
	}

	/**
	* Throws CloneNotSupportedException as a Thread can not be meaningfully
	* cloned. Construct a new Thread instead.
	*
	* @throws CloneNotSupportedException
	* always
	*/
	@Override
	protected Object clone() throws CloneNotSupportedException {
	throw new CloneNotSupportedException();
	}

	/**
	* Allocates a new {@code Thread} object. This constructor has the same
	* effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
	* {@code (null, null, gname)}, where {@code gname} is a newly generated
	* name. Automatically generated names are of the form
	* {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
	*/
	public Thread() {
	this(null, null, "Thread-" + nextThreadNum(), 0);
	}

	/**
	* Allocates a new {@code Thread} object. This constructor has the same
	* effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
	* {@code (null, target, gname)}, where {@code gname} is a newly generated
	* name. Automatically generated names are of the form
	* {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
	*
	* @param target
	* the object whose {@code run} method is invoked when this thread
	* is started. If {@code null}, this classes {@code run} method does
	* nothing.
	*/
	public Thread(Runnable target) {
	this(null, target, "Thread-" + nextThreadNum(), 0);
	}

	/**
	* Creates a new Thread that inherits the given AccessControlContext
	* but thread-local variables are not inherited.
	* This is not a public constructor.
	*/
	Thread(Runnable target, AccessControlContext acc) {
	this(null, target, "Thread-" + nextThreadNum(), 0, acc, false);
	}

	/**
	* Allocates a new {@code Thread} object. This constructor has the same
	* effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
	* {@code (group, target, gname)} ,where {@code gname} is a newly generated
	* name. Automatically generated names are of the form
	* {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
	*
	* @param group
	* the thread group. If {@code null} and there is a security
	* manager, the group is determined by {@linkplain
	* SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
	* If there is not a security manager or {@code
	* SecurityManager.getThreadGroup()} returns {@code null}, the group
	* is set to the current thread's thread group.
	*
	* @param target
	* the object whose {@code run} method is invoked when this thread
	* is started. If {@code null}, this thread's run method is invoked.
	*
	* @throws SecurityException
	* if the current thread cannot create a thread in the specified
	* thread group
	*/
	public Thread(ThreadGroup group, Runnable target) {
	this(group, target, "Thread-" + nextThreadNum(), 0);
	}

	/**
	* Allocates a new {@code Thread} object. This constructor has the same
	* effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
	* {@code (null, null, name)}.
	*
	* @param name
	* the name of the new thread
	*/
	public Thread(String name) {
	this(null, null, name, 0);
	}

	/**
	* Allocates a new {@code Thread} object. This constructor has the same
	* effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
	* {@code (group, null, name)}.
	*
	* @param group
	* the thread group. If {@code null} and there is a security
	* manager, the group is determined by {@linkplain
	* SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
	* If there is not a security manager or {@code
	* SecurityManager.getThreadGroup()} returns {@code null}, the group
	* is set to the current thread's thread group.
	*
	* @param name
	* the name of the new thread
	*
	* @throws SecurityException
	* if the current thread cannot create a thread in the specified
	* thread group
	*/
	public Thread(ThreadGroup group, String name) {
	this(group, null, name, 0);
	}

	/**
	* Allocates a new {@code Thread} object. This constructor has the same
	* effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
	* {@code (null, target, name)}.
	*
	* @param target
	* the object whose {@code run} method is invoked when this thread
	* is started. If {@code null}, this thread's run method is invoked.
	*
	* @param name
	* the name of the new thread
	*/
	public Thread(Runnable target, String name) {
	this(null, target, name, 0);
	}

	/**
	* Allocates a new {@code Thread} object so that it has {@code target}
	* as its run object, has the specified {@code name} as its name,
	* and belongs to the thread group referred to by {@code group}.
	*
	* <p>If there is a security manager, its
	* {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
	* method is invoked with the ThreadGroup as its argument.
	*
	* <p>In addition, its {@code checkPermission} method is invoked with
	* the {@code RuntimePermission("enableContextClassLoaderOverride")}
	* permission when invoked directly or indirectly by the constructor
	* of a subclass which overrides the {@code getContextClassLoader}
	* or {@code setContextClassLoader} methods.
	*
	* <p>The priority of the newly created thread is set equal to the
	* priority of the thread creating it, that is, the currently running
	* thread. The method {@linkplain #setPriority setPriority} may be
	* used to change the priority to a new value.
	*
	* <p>The newly created thread is initially marked as being a daemon
	* thread if and only if the thread creating it is currently marked
	* as a daemon thread. The method {@linkplain #setDaemon setDaemon}
	* may be used to change whether or not a thread is a daemon.
	*
	* @param group
	* the thread group. If {@code null} and there is a security
	* manager, the group is determined by {@linkplain
	* SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
	* If there is not a security manager or {@code
	* SecurityManager.getThreadGroup()} returns {@code null}, the group
	* is set to the current thread's thread group.
	*
	* @param target
	* the object whose {@code run} method is invoked when this thread
	* is started. If {@code null}, this thread's run method is invoked.
	*
	* @param name
	* the name of the new thread
	*
	* @throws SecurityException
	* if the current thread cannot create a thread in the specified
	* thread group or cannot override the context class loader methods.
	*/
	public Thread(ThreadGroup group, Runnable target, String name) {
	this(group, target, name, 0);
	}

	/**
	* Allocates a new {@code Thread} object so that it has {@code target}
	* as its run object, has the specified {@code name} as its name,
	* and belongs to the thread group referred to by {@code group}, and has
	* the specified <i>stack size</i>.
	*
	* <p>This constructor is identical to {@link
	* #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
	* that it allows the thread stack size to be specified. The stack size
	* is the approximate number of bytes of address space that the virtual
	* machine is to allocate for this thread's stack. <b>The effect of the
	* {@code stackSize} parameter, if any, is highly platform dependent.</b>
	*
	* <p>On some platforms, specifying a higher value for the
	* {@code stackSize} parameter may allow a thread to achieve greater
	* recursion depth before throwing a {@link StackOverflowError}.
	* Similarly, specifying a lower value may allow a greater number of
	* threads to exist concurrently without throwing an {@link
	* OutOfMemoryError} (or other internal error). The details of
	* the relationship between the value of the {@code stackSize} parameter
	* and the maximum recursion depth and concurrency level are
	* platform-dependent. <b>On some platforms, the value of the
	* {@code stackSize} parameter may have no effect whatsoever.</b>
	*
	* <p>The virtual machine is free to treat the {@code stackSize}
	* parameter as a suggestion. If the specified value is unreasonably low
	* for the platform, the virtual machine may instead use some
	* platform-specific minimum value; if the specified value is unreasonably
	* high, the virtual machine may instead use some platform-specific
	* maximum. Likewise, the virtual machine is free to round the specified
	* value up or down as it sees fit (or to ignore it completely).
	*
	* <p>Specifying a value of zero for the {@code stackSize} parameter will
	* cause this constructor to behave exactly like the
	* {@code Thread(ThreadGroup, Runnable, String)} constructor.
	*
	* <p><i>Due to the platform-dependent nature of the behavior of this
	* constructor, extreme care should be exercised in its use.
	* The thread stack size necessary to perform a given computation will
	* likely vary from one JRE implementation to another. In light of this
	* variation, careful tuning of the stack size parameter may be required,
	* and the tuning may need to be repeated for each JRE implementation on
	* which an application is to run.</i>
	*
	* <p>Implementation note: Java platform implementers are encouraged to
	* document their implementation's behavior with respect to the
	* {@code stackSize} parameter.
	*
	*
	* @param group
	* the thread group. If {@code null} and there is a security
	* manager, the group is determined by {@linkplain
	* SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
	* If there is not a security manager or {@code
	* SecurityManager.getThreadGroup()} returns {@code null}, the group
	* is set to the current thread's thread group.
	*
	* @param target
	* the object whose {@code run} method is invoked when this thread
	* is started. If {@code null}, this thread's run method is invoked.
	*
	* @param name
	* the name of the new thread
	*
	* @param stackSize
	* the desired stack size for the new thread, or zero to indicate
	* that this parameter is to be ignored.
	*
	* @throws SecurityException
	* if the current thread cannot create a thread in the specified
	* thread group
	*
	* @since 1.4
	*/
	public Thread(ThreadGroup group, Runnable target, String name,
	long stackSize) {
	this(group, target, name, stackSize, null, true);
	}

	/**
	* Allocates a new {@code Thread} object so that it has {@code target}
	* as its run object, has the specified {@code name} as its name,
	* belongs to the thread group referred to by {@code group}, has
	* the specified {@code stackSize}, and inherits initial values for
	* {@linkplain InheritableThreadLocal inheritable thread-local} variables
	* if {@code inheritThreadLocals} is {@code true}.
	*
	* <p> This constructor is identical to {@link
	* #Thread(ThreadGroup,Runnable,String,long)} with the added ability to
	* suppress, or not, the inheriting of initial values for inheritable
	* thread-local variables from the constructing thread. This allows for
	* finer grain control over inheritable thread-locals. Care must be taken
	* when passing a value of {@code false} for {@code inheritThreadLocals},
	* as it may lead to unexpected behavior if the new thread executes code
	* that expects a specific thread-local value to be inherited.
	*
	* <p> Specifying a value of {@code true} for the {@code inheritThreadLocals}
	* parameter will cause this constructor to behave exactly like the
	* {@code Thread(ThreadGroup, Runnable, String, long)} constructor.
	*
	* @param group
	* the thread group. If {@code null} and there is a security
	* manager, the group is determined by {@linkplain
	* SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
	* If there is not a security manager or {@code
	* SecurityManager.getThreadGroup()} returns {@code null}, the group
	* is set to the current thread's thread group.
	*
	* @param target
	* the object whose {@code run} method is invoked when this thread
	* is started. If {@code null}, this thread's run method is invoked.
	*
	* @param name
	* the name of the new thread
	*
	* @param stackSize
	* the desired stack size for the new thread, or zero to indicate
	* that this parameter is to be ignored
	*
	* @param inheritThreadLocals
	* if {@code true}, inherit initial values for inheritable
	* thread-locals from the constructing thread, otherwise no initial
	* values are inherited
	*
	* @throws SecurityException
	* if the current thread cannot create a thread in the specified
	* thread group
	*
	* @since 9
	*/
	public Thread(ThreadGroup group, Runnable target, String name,
	long stackSize, boolean inheritThreadLocals) {
	this(group, target, name, stackSize, null, inheritThreadLocals);
	}

	/**
	* Causes this thread to begin execution; the Java Virtual Machine
	* calls the {@code run} method of this thread.
	* <p>
	* The result is that two threads are running concurrently: the
	* current thread (which returns from the call to the
	* {@code start} method) and the other thread (which executes its
	* {@code run} method).
	* <p>
	* It is never legal to start a thread more than once.
	* In particular, a thread may not be restarted once it has completed
	* execution.
	*
	* @throws IllegalThreadStateException if the thread was already started.
	* @see #run()
	* @see #stop()
	*/
	public synchronized void start() {
	/**
	* This method is not invoked for the main method thread or "system"
	* group threads created/set up by the VM. Any new functionality added
	* to this method in the future may have to also be added to the VM.
	*
	* A zero status value corresponds to state "NEW".
	*/
	if (threadStatus != 0)
	throw new IllegalThreadStateException();

	/* Notify the group that this thread is about to be started
	* so that it can be added to the group's list of threads
	* and the group's unstarted count can be decremented. */
	group.add(this);

	boolean started = false;
	try {
	start0();
	started = true;
	} finally {
	try {
	if (!started) {
	group.threadStartFailed(this);
	}
	} catch (Throwable ignore) {
	/* do nothing. If start0 threw a Throwable then
	it will be passed up the call stack */
	}
	}
	}

	private native void start0();

	/**
	* If this thread was constructed using a separate
	* {@code Runnable} run object, then that
	* {@code Runnable} object's {@code run} method is called;
	* otherwise, this method does nothing and returns.
	* <p>
	* Subclasses of {@code Thread} should override this method.
	*
	* @see #start()
	* @see #stop()
	* @see #Thread(ThreadGroup, Runnable, String)
	*/
	@Override
	public void run() {
	if (target != null) {
	target.run();
	}
	}

	/**
	* This method is called by the system to give a Thread
	* a chance to clean up before it actually exits.
	*/
	private void exit() {
	if (threadLocals != null && TerminatingThreadLocal.REGISTRY.isPresent()) {
	TerminatingThreadLocal.threadTerminated();
	}
	if (group != null) {
	group.threadTerminated(this);
	group = null;
	}
	/* Aggressively null out all reference fields: see bug 4006245 */
	target = null;
	/* Speed the release of some of these resources */
	threadLocals = null;
	inheritableThreadLocals = null;
	inheritedAccessControlContext = null;
	blocker = null;
	uncaughtExceptionHandler = null;
	}

	/**
	* Forces the thread to stop executing.
	* <p>
	* If there is a security manager installed, its {@code checkAccess}
	* method is called with {@code this}
	* as its argument. This may result in a
	* {@code SecurityException} being raised (in the current thread).
	* <p>
	* If this thread is different from the current thread (that is, the current
	* thread is trying to stop a thread other than itself), the
	* security manager's {@code checkPermission} method (with a
	* {@code RuntimePermission("stopThread")} argument) is called in
	* addition.
	* Again, this may result in throwing a
	* {@code SecurityException} (in the current thread).
	* <p>
	* The thread represented by this thread is forced to stop whatever
	* it is doing abnormally and to throw a newly created
	* {@code ThreadDeath} object as an exception.
	* <p>
	* It is permitted to stop a thread that has not yet been started.
	* If the thread is eventually started, it immediately terminates.
	* <p>
	* An application should not normally try to catch
	* {@code ThreadDeath} unless it must do some extraordinary
	* cleanup operation (note that the throwing of
	* {@code ThreadDeath} causes {@code finally} clauses of
	* {@code try} statements to be executed before the thread
	* officially dies). If a {@code catch} clause catches a
	* {@code ThreadDeath} object, it is important to rethrow the
	* object so that the thread actually dies.
	* <p>
	* The top-level error handler that reacts to otherwise uncaught
	* exceptions does not print out a message or otherwise notify the
	* application if the uncaught exception is an instance of
	* {@code ThreadDeath}.
	*
	* @throws SecurityException if the current thread cannot
	* modify this thread.
	* @see #interrupt()
	* @see #checkAccess()
	* @see #run()
	* @see #start()
	* @see ThreadDeath
	* @see ThreadGroup#uncaughtException(Thread,Throwable)
	* @see SecurityManager#checkAccess(Thread)
	* @see SecurityManager#checkPermission
	* @deprecated This method is inherently unsafe. Stopping a thread with
	* Thread.stop causes it to unlock all of the monitors that it
	* has locked (as a natural consequence of the unchecked
	* {@code ThreadDeath} exception propagating up the stack). If
	* any of the objects previously protected by these monitors were in
	* an inconsistent state, the damaged objects become visible to
	* other threads, potentially resulting in arbitrary behavior. Many
	* uses of {@code stop} should be replaced by code that simply
	* modifies some variable to indicate that the target thread should
	* stop running. The target thread should check this variable
	* regularly, and return from its run method in an orderly fashion
	* if the variable indicates that it is to stop running. If the
	* target thread waits for long periods (on a condition variable,
	* for example), the {@code interrupt} method should be used to
	* interrupt the wait.
	* For more information, see
	* <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
	* are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
	*/
	@Deprecated(since="1.2")
	public final void stop() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	checkAccess();
	if (this != Thread.currentThread()) {
	security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
	}
	}
	// A zero status value corresponds to "NEW", it can't change to
	// not-NEW because we hold the lock.
	if (threadStatus != 0) {
	resume(); // Wake up thread if it was suspended; no-op otherwise
	}

	// The VM can handle all thread states
	stop0(new ThreadDeath());
	}

	/**
	* Interrupts this thread.
	*
	* <p> Unless the current thread is interrupting itself, which is
	* always permitted, the {@link #checkAccess() checkAccess} method
	* of this thread is invoked, which may cause a {@link
	* SecurityException} to be thrown.
	*
	* <p> If this thread is blocked in an invocation of the {@link
	* Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
	* Object#wait(long, int) wait(long, int)} methods of the {@link Object}
	* class, or of the {@link #join()}, {@link #join(long)}, {@link
	* #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
	* methods of this class, then its interrupt status will be cleared and it
	* will receive an {@link InterruptedException}.
	*
	* <p> If this thread is blocked in an I/O operation upon an {@link
	* java.nio.channels.InterruptibleChannel InterruptibleChannel}
	* then the channel will be closed, the thread's interrupt
	* status will be set, and the thread will receive a {@link
	* java.nio.channels.ClosedByInterruptException}.
	*
	* <p> If this thread is blocked in a {@link java.nio.channels.Selector}
	* then the thread's interrupt status will be set and it will return
	* immediately from the selection operation, possibly with a non-zero
	* value, just as if the selector's {@link
	* java.nio.channels.Selector#wakeup wakeup} method were invoked.
	*
	* <p> If none of the previous conditions hold then this thread's interrupt
	* status will be set. </p>
	*
	* <p> Interrupting a thread that is not alive need not have any effect.
	*
	* @throws SecurityException
	* if the current thread cannot modify this thread
	*
	* @revised 6.0
	* @spec JSR-51
	*/
	public void interrupt() {
	if (this != Thread.currentThread()) {
	checkAccess();

	// thread may be blocked in an I/O operation
	synchronized (blockerLock) {
	Interruptible b = blocker;
	if (b != null) {
	interrupt0(); // set interrupt status
	b.interrupt(this);
	return;
	}
	}
	}

	// set interrupt status
	interrupt0();
	}

	/**
	* Tests whether the current thread has been interrupted. The
	* <i>interrupted status</i> of the thread is cleared by this method. In
	* other words, if this method were to be called twice in succession, the
	* second call would return false (unless the current thread were
	* interrupted again, after the first call had cleared its interrupted
	* status and before the second call had examined it).
	*
	* <p>A thread interruption ignored because a thread was not alive
	* at the time of the interrupt will be reflected by this method
	* returning false.
	*
	* @return {@code true} if the current thread has been interrupted;
	* {@code false} otherwise.
	* @see #isInterrupted()
	* @revised 6.0
	*/
	public static boolean interrupted() {
	return currentThread().isInterrupted(true);
	}

	/**
	* Tests whether this thread has been interrupted. The <i>interrupted
	* status</i> of the thread is unaffected by this method.
	*
	* <p>A thread interruption ignored because a thread was not alive
	* at the time of the interrupt will be reflected by this method
	* returning false.
	*
	* @return {@code true} if this thread has been interrupted;
	* {@code false} otherwise.
	* @see #interrupted()
	* @revised 6.0
	*/
	public boolean isInterrupted() {
	return isInterrupted(false);
	}

	/**
	* Tests if some Thread has been interrupted. The interrupted state
	* is reset or not based on the value of ClearInterrupted that is
	* passed.
	*/
	@HotSpotIntrinsicCandidate
	private native boolean isInterrupted(boolean ClearInterrupted);

	/**
	* Tests if this thread is alive. A thread is alive if it has
	* been started and has not yet died.
	*
	* @return {@code true} if this thread is alive;
	* {@code false} otherwise.
	*/
	public final native boolean isAlive();

	/**
	* Suspends this thread.
	* <p>
	* First, the {@code checkAccess} method of this thread is called
	* with no arguments. This may result in throwing a
	* {@code SecurityException }(in the current thread).
	* <p>
	* If the thread is alive, it is suspended and makes no further
	* progress unless and until it is resumed.
	*
	* @throws SecurityException if the current thread cannot modify
	* this thread.
	* @see #checkAccess
	* @deprecated This method has been deprecated, as it is
	* inherently deadlock-prone. If the target thread holds a lock on the
	* monitor protecting a critical system resource when it is suspended, no
	* thread can access this resource until the target thread is resumed. If
	* the thread that would resume the target thread attempts to lock this
	* monitor prior to calling {@code resume}, deadlock results. Such
	* deadlocks typically manifest themselves as "frozen" processes.
	* For more information, see
	* <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
	* are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
	*/
	@Deprecated(since="1.2")
	public final void suspend() {
	checkAccess();
	suspend0();
	}

	/**
	* Resumes a suspended thread.
	* <p>
	* First, the {@code checkAccess} method of this thread is called
	* with no arguments. This may result in throwing a
	* {@code SecurityException} (in the current thread).
	* <p>
	* If the thread is alive but suspended, it is resumed and is
	* permitted to make progress in its execution.
	*
	* @throws SecurityException if the current thread cannot modify this
	* thread.
	* @see #checkAccess
	* @see #suspend()
	* @deprecated This method exists solely for use with {@link #suspend},
	* which has been deprecated because it is deadlock-prone.
	* For more information, see
	* <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
	* are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
	*/
	@Deprecated(since="1.2")
	public final void resume() {
	checkAccess();
	resume0();
	}

	/**
	* Changes the priority of this thread.
	* <p>
	* First the {@code checkAccess} method of this thread is called
	* with no arguments. This may result in throwing a {@code SecurityException}.
	* <p>
	* Otherwise, the priority of this thread is set to the smaller of
	* the specified {@code newPriority} and the maximum permitted
	* priority of the thread's thread group.
	*
	* @param newPriority priority to set this thread to
	* @throws IllegalArgumentException If the priority is not in the
	* range {@code MIN_PRIORITY} to
	* {@code MAX_PRIORITY}.
	* @throws SecurityException if the current thread cannot modify
	* this thread.
	* @see #getPriority
	* @see #checkAccess()
	* @see #getThreadGroup()
	* @see #MAX_PRIORITY
	* @see #MIN_PRIORITY
	* @see ThreadGroup#getMaxPriority()
	*/
	public final void setPriority(int newPriority) {
	ThreadGroup g;
	checkAccess();
	if (newPriority > MAX_PRIORITY \|\| newPriority < MIN_PRIORITY) {
	throw new IllegalArgumentException();
	}
	if((g = getThreadGroup()) != null) {
	if (newPriority > g.getMaxPriority()) {
	newPriority = g.getMaxPriority();
	}
	setPriority0(priority = newPriority);
	}
	}

	/**
	* Returns this thread's priority.
	*
	* @return this thread's priority.
	* @see #setPriority
	*/
	public final int getPriority() {
	return priority;
	}

	/**
	* Changes the name of this thread to be equal to the argument {@code name}.
	* <p>
	* First the {@code checkAccess} method of this thread is called
	* with no arguments. This may result in throwing a
	* {@code SecurityException}.
	*
	* @param name the new name for this thread.
	* @throws SecurityException if the current thread cannot modify this
	* thread.
	* @see #getName
	* @see #checkAccess()
	*/
	public final synchronized void setName(String name) {
	checkAccess();
	if (name == null) {
	throw new NullPointerException("name cannot be null");
	}

	this.name = name;
	if (threadStatus != 0) {
	setNativeName(name);
	}
	}

	/**
	* Returns this thread's name.
	*
	* @return this thread's name.
	* @see #setName(String)
	*/
	public final String getName() {
	return name;
	}

	/**
	* Returns the thread group to which this thread belongs.
	* This method returns null if this thread has died
	* (been stopped).
	*
	* @return this thread's thread group.
	*/
	public final ThreadGroup getThreadGroup() {
	return group;
	}

	/**
	* Returns an estimate of the number of active threads in the current
	* thread's {@linkplain java.lang.ThreadGroup thread group} and its
	* subgroups. Recursively iterates over all subgroups in the current
	* thread's thread group.
	*
	* <p> The value returned is only an estimate because the number of
	* threads may change dynamically while this method traverses internal
	* data structures, and might be affected by the presence of certain
	* system threads. This method is intended primarily for debugging
	* and monitoring purposes.
	*
	* @return an estimate of the number of active threads in the current
	* thread's thread group and in any other thread group that
	* has the current thread's thread group as an ancestor
	*/
	public static int activeCount() {
	return currentThread().getThreadGroup().activeCount();
	}

	/**
	* Copies into the specified array every active thread in the current
	* thread's thread group and its subgroups. This method simply
	* invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
	* method of the current thread's thread group.
	*
	* <p> An application might use the {@linkplain #activeCount activeCount}
	* method to get an estimate of how big the array should be, however
	* <i>if the array is too short to hold all the threads, the extra threads
	* are silently ignored.</i> If it is critical to obtain every active
	* thread in the current thread's thread group and its subgroups, the
	* invoker should verify that the returned int value is strictly less
	* than the length of {@code tarray}.
	*
	* <p> Due to the inherent race condition in this method, it is recommended
	* that the method only be used for debugging and monitoring purposes.
	*
	* @param tarray
	* an array into which to put the list of threads
	*
	* @return the number of threads put into the array
	*
	* @throws SecurityException
	* if {@link java.lang.ThreadGroup#checkAccess} determines that
	* the current thread cannot access its thread group
	*/
	public static int enumerate(Thread tarray[]) {
	return currentThread().getThreadGroup().enumerate(tarray);
	}

	/**
	* Counts the number of stack frames in this thread. The thread must
	* be suspended.
	*
	* @return the number of stack frames in this thread.
	* @throws IllegalThreadStateException if this thread is not
	* suspended.
	* @deprecated The definition of this call depends on {@link #suspend},
	* which is deprecated. Further, the results of this call
	* were never well-defined.
	* This method is subject to removal in a future version of Java SE.
	* @see StackWalker
	*/
	@Deprecated(since="1.2", forRemoval=true)
	public native int countStackFrames();

	/**
	* Waits at most {@code millis} milliseconds for this thread to
	* die. A timeout of {@code 0} means to wait forever.
	*
	* <p> This implementation uses a loop of {@code this.wait} calls
	* conditioned on {@code this.isAlive}. As a thread terminates the
	* {@code this.notifyAll} method is invoked. It is recommended that
	* applications not use {@code wait}, {@code notify}, or
	* {@code notifyAll} on {@code Thread} instances.
	*
	* @param millis
	* the time to wait in milliseconds
	*
	* @throws IllegalArgumentException
	* if the value of {@code millis} is negative
	*
	* @throws InterruptedException
	* if any thread has interrupted the current thread. The
	* <i>interrupted status</i> of the current thread is
	* cleared when this exception is thrown.
	*/
	public final synchronized void join(long millis)
	throws InterruptedException {
	long base = System.currentTimeMillis();
	long now = 0;

	if (millis < 0) {
	throw new IllegalArgumentException("timeout value is negative");
	}

	if (millis == 0) {
	while (isAlive()) {
	wait(0);
	}
	} else {
	while (isAlive()) {
	long delay = millis - now;
	if (delay <= 0) {
	break;
	}
	wait(delay);
	now = System.currentTimeMillis() - base;
	}
	}
	}

	/**
	* Waits at most {@code millis} milliseconds plus
	* {@code nanos} nanoseconds for this thread to die.
	*
	* <p> This implementation uses a loop of {@code this.wait} calls
	* conditioned on {@code this.isAlive}. As a thread terminates the
	* {@code this.notifyAll} method is invoked. It is recommended that
	* applications not use {@code wait}, {@code notify}, or
	* {@code notifyAll} on {@code Thread} instances.
	*
	* @param millis
	* the time to wait in milliseconds
	*
	* @param nanos
	* {@code 0-999999} additional nanoseconds to wait
	*
	* @throws IllegalArgumentException
	* if the value of {@code millis} is negative, or the value
	* of {@code nanos} is not in the range {@code 0-999999}
	*
	* @throws InterruptedException
	* if any thread has interrupted the current thread. The
	* <i>interrupted status</i> of the current thread is
	* cleared when this exception is thrown.
	*/
	public final synchronized void join(long millis, int nanos)
	throws InterruptedException {

	if (millis < 0) {
	throw new IllegalArgumentException("timeout value is negative");
	}

	if (nanos < 0 \|\| nanos > 999999) {
	throw new IllegalArgumentException(
	"nanosecond timeout value out of range");
	}

	if (nanos >= 500000 \|\| (nanos != 0 && millis == 0)) {
	millis++;
	}

	join(millis);
	}

	/**
	* Waits for this thread to die.
	*
	* <p> An invocation of this method behaves in exactly the same
	* way as the invocation
	*
	* <blockquote>
	* {@linkplain #join(long) join}{@code (0)}
	* </blockquote>
	*
	* @throws InterruptedException
	* if any thread has interrupted the current thread. The
	* <i>interrupted status</i> of the current thread is
	* cleared when this exception is thrown.
	*/
	public final void join() throws InterruptedException {
	join(0);
	}

	/**
	* Prints a stack trace of the current thread to the standard error stream.
	* This method is used only for debugging.
	*/
	public static void dumpStack() {
	new Exception("Stack trace").printStackTrace();
	}

	/**
	* Marks this thread as either a {@linkplain #isDaemon daemon} thread
	* or a user thread. The Java Virtual Machine exits when the only
	* threads running are all daemon threads.
	*
	* <p> This method must be invoked before the thread is started.
	*
	* @param on
	* if {@code true}, marks this thread as a daemon thread
	*
	* @throws IllegalThreadStateException
	* if this thread is {@linkplain #isAlive alive}
	*
	* @throws SecurityException
	* if {@link #checkAccess} determines that the current
	* thread cannot modify this thread
	*/
	public final void setDaemon(boolean on) {
	checkAccess();
	if (isAlive()) {
	throw new IllegalThreadStateException();
	}
	daemon = on;
	}

	/**
	* Tests if this thread is a daemon thread.
	*
	* @return {@code true} if this thread is a daemon thread;
	* {@code false} otherwise.
	* @see #setDaemon(boolean)
	*/
	public final boolean isDaemon() {
	return daemon;
	}

	/**
	* Determines if the currently running thread has permission to
	* modify this thread.
	* <p>
	* If there is a security manager, its {@code checkAccess} method
	* is called with this thread as its argument. This may result in
	* throwing a {@code SecurityException}.
	*
	* @throws SecurityException if the current thread is not allowed to
	* access this thread.
	* @see SecurityManager#checkAccess(Thread)
	*/
	public final void checkAccess() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	security.checkAccess(this);
	}
	}

	/**
	* Returns a string representation of this thread, including the
	* thread's name, priority, and thread group.
	*
	* @return a string representation of this thread.
	*/
	public String toString() {
	ThreadGroup group = getThreadGroup();
	if (group != null) {
	return "Thread[" + getName() + "," + getPriority() + "," +
	group.getName() + "]";
	} else {
	return "Thread[" + getName() + "," + getPriority() + "," +
	"" + "]";
	}
	}

	/**
	* Returns the context {@code ClassLoader} for this thread. The context
	* {@code ClassLoader} is provided by the creator of the thread for use
	* by code running in this thread when loading classes and resources.
	* If not {@linkplain #setContextClassLoader set}, the default is the
	* {@code ClassLoader} context of the parent thread. The context
	* {@code ClassLoader} of the
	* primordial thread is typically set to the class loader used to load the
	* application.
	*
	*
	* @return the context {@code ClassLoader} for this thread, or {@code null}
	* indicating the system class loader (or, failing that, the
	* bootstrap class loader)
	*
	* @throws SecurityException
	* if a security manager is present, and the caller's class loader
	* is not {@code null} and is not the same as or an ancestor of the
	* context class loader, and the caller does not have the
	* {@link RuntimePermission}{@code ("getClassLoader")}
	*
	* @since 1.2
	*/
	@CallerSensitive
	public ClassLoader getContextClassLoader() {
	if (contextClassLoader == null)
	return null;
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	ClassLoader.checkClassLoaderPermission(contextClassLoader,
	Reflection.getCallerClass());
	}
	return contextClassLoader;
	}

	/**
	* Sets the context ClassLoader for this Thread. The context
	* ClassLoader can be set when a thread is created, and allows
	* the creator of the thread to provide the appropriate class loader,
	* through {@code getContextClassLoader}, to code running in the thread
	* when loading classes and resources.
	*
	* <p>If a security manager is present, its {@link
	* SecurityManager#checkPermission(java.security.Permission) checkPermission}
	* method is invoked with a {@link RuntimePermission RuntimePermission}{@code
	* ("setContextClassLoader")} permission to see if setting the context
	* ClassLoader is permitted.
	*
	* @param cl
	* the context ClassLoader for this Thread, or null indicating the
	* system class loader (or, failing that, the bootstrap class loader)
	*
	* @throws SecurityException
	* if the current thread cannot set the context ClassLoader
	*
	* @since 1.2
	*/
	public void setContextClassLoader(ClassLoader cl) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	sm.checkPermission(new RuntimePermission("setContextClassLoader"));
	}
	contextClassLoader = cl;
	}

	/**
	* Returns {@code true} if and only if the current thread holds the
	* monitor lock on the specified object.
	*
	* <p>This method is designed to allow a program to assert that
	* the current thread already holds a specified lock:
	* <pre>
	* assert Thread.holdsLock(obj);
	* </pre>
	*
	* @param obj the object on which to test lock ownership
	* @throws NullPointerException if obj is {@code null}
	* @return {@code true} if the current thread holds the monitor lock on
	* the specified object.
	* @since 1.4
	*/
	public static native boolean holdsLock(Object obj);

	private static final StackTraceElement[] EMPTY_STACK_TRACE
	= new StackTraceElement[0];

	/**
	* Returns an array of stack trace elements representing the stack dump
	* of this thread. This method will return a zero-length array if
	* this thread has not started, has started but has not yet been
	* scheduled to run by the system, or has terminated.
	* If the returned array is of non-zero length then the first element of
	* the array represents the top of the stack, which is the most recent
	* method invocation in the sequence. The last element of the array
	* represents the bottom of the stack, which is the least recent method
	* invocation in the sequence.
	*
	* <p>If there is a security manager, and this thread is not
	* the current thread, then the security manager's
	* {@code checkPermission} method is called with a
	* {@code RuntimePermission("getStackTrace")} permission
	* to see if it's ok to get the stack trace.
	*
	* <p>Some virtual machines may, under some circumstances, omit one
	* or more stack frames from the stack trace. In the extreme case,
	* a virtual machine that has no stack trace information concerning
	* this thread is permitted to return a zero-length array from this
	* method.
	*
	* @return an array of {@code StackTraceElement},
	* each represents one stack frame.
	*
	* @throws SecurityException
	* if a security manager exists and its
	* {@code checkPermission} method doesn't allow
	* getting the stack trace of thread.
	* @see SecurityManager#checkPermission
	* @see RuntimePermission
	* @see Throwable#getStackTrace
	*
	* @since 1.5
	*/
	public StackTraceElement[] getStackTrace() {
	if (this != Thread.currentThread()) {
	// check for getStackTrace permission
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	security.checkPermission(
	SecurityConstants.GET_STACK_TRACE_PERMISSION);
	}
	// optimization so we do not call into the vm for threads that
	// have not yet started or have terminated
	if (!isAlive()) {
	return EMPTY_STACK_TRACE;
	}
	StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
	StackTraceElement[] stackTrace = stackTraceArray[0];
	// a thread that was alive during the previous isAlive call may have
	// since terminated, therefore not having a stacktrace.
	if (stackTrace == null) {
	stackTrace = EMPTY_STACK_TRACE;
	}
	return stackTrace;
	} else {
	return (new Exception()).getStackTrace();
	}
	}

	/**
	* Returns a map of stack traces for all live threads.
	* The map keys are threads and each map value is an array of
	* {@code StackTraceElement} that represents the stack dump
	* of the corresponding {@code Thread}.
	* The returned stack traces are in the format specified for
	* the {@link #getStackTrace getStackTrace} method.
	*
	* <p>The threads may be executing while this method is called.
	* The stack trace of each thread only represents a snapshot and
	* each stack trace may be obtained at different time. A zero-length
	* array will be returned in the map value if the virtual machine has
	* no stack trace information about a thread.
	*
	* <p>If there is a security manager, then the security manager's
	* {@code checkPermission} method is called with a
	* {@code RuntimePermission("getStackTrace")} permission as well as
	* {@code RuntimePermission("modifyThreadGroup")} permission
	* to see if it is ok to get the stack trace of all threads.
	*
	* @return a {@code Map} from {@code Thread} to an array of
	* {@code StackTraceElement} that represents the stack trace of
	* the corresponding thread.
	*
	* @throws SecurityException
	* if a security manager exists and its
	* {@code checkPermission} method doesn't allow
	* getting the stack trace of thread.
	* @see #getStackTrace
	* @see SecurityManager#checkPermission
	* @see RuntimePermission
	* @see Throwable#getStackTrace
	*
	* @since 1.5
	*/
	public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
	// check for getStackTrace permission
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	security.checkPermission(
	SecurityConstants.GET_STACK_TRACE_PERMISSION);
	security.checkPermission(
	SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
	}

	// Get a snapshot of the list of all threads
	Thread[] threads = getThreads();
	StackTraceElement[][] traces = dumpThreads(threads);
	Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
	for (int i = 0; i < threads.length; i++) {
	StackTraceElement[] stackTrace = traces[i];
	if (stackTrace != null) {
	m.put(threads[i], stackTrace);
	}
	// else terminated so we don't put it in the map
	}
	return m;
	}

	/** cache of subclass security audit results */
	/* Replace with ConcurrentReferenceHashMap when/if it appears in a future
	* release */
	private static class Caches {
	/** cache of subclass security audit results */
	static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
	new ConcurrentHashMap<>();

	/** queue for WeakReferences to audited subclasses */
	static final ReferenceQueue<Class<?>> subclassAuditsQueue =
	new ReferenceQueue<>();
	}

	/**
	* Verifies that this (possibly subclass) instance can be constructed
	* without violating security constraints: the subclass must not override
	* security-sensitive non-final methods, or else the
	* "enableContextClassLoaderOverride" RuntimePermission is checked.
	*/
	private static boolean isCCLOverridden(Class<?> cl) {
	if (cl == Thread.class)
	return false;

	processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
	WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
	Boolean result = Caches.subclassAudits.get(key);
	if (result == null) {
	result = Boolean.valueOf(auditSubclass(cl));
	Caches.subclassAudits.putIfAbsent(key, result);
	}

	return result.booleanValue();
	}

	/**
	* Performs reflective checks on given subclass to verify that it doesn't
	* override security-sensitive non-final methods. Returns true if the
	* subclass overrides any of the methods, false otherwise.
	*/
	private static boolean auditSubclass(final Class<?> subcl) {
	Boolean result = AccessController.doPrivileged(
	new PrivilegedAction<>() {
	public Boolean run() {
	for (Class<?> cl = subcl;
	cl != Thread.class;
	cl = cl.getSuperclass())
	{
	try {
	cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
	return Boolean.TRUE;
	} catch (NoSuchMethodException ex) {
	}
	try {
	Class<?>[] params = {ClassLoader.class};
	cl.getDeclaredMethod("setContextClassLoader", params);
	return Boolean.TRUE;
	} catch (NoSuchMethodException ex) {
	}
	}
	return Boolean.FALSE;
	}
	}
	);
	return result.booleanValue();
	}

	private static native StackTraceElement[][] dumpThreads(Thread[] threads);
	private static native Thread[] getThreads();

	/**
	* Returns the identifier of this Thread. The thread ID is a positive
	* {@code long} number generated when this thread was created.
	* The thread ID is unique and remains unchanged during its lifetime.
	* When a thread is terminated, this thread ID may be reused.
	*
	* @return this thread's ID.
	* @since 1.5
	*/
	public long getId() {
	return tid;
	}

	/**
	* A thread state. A thread can be in one of the following states:
	* <ul>
	* <li>{@link #NEW}<br>
	* A thread that has not yet started is in this state.
	* </li>
	* <li>{@link #RUNNABLE}<br>
	* A thread executing in the Java virtual machine is in this state.
	* </li>
	* <li>{@link #BLOCKED}<br>
	* A thread that is blocked waiting for a monitor lock
	* is in this state.
	* </li>
	* <li>{@link #WAITING}<br>
	* A thread that is waiting indefinitely for another thread to
	* perform a particular action is in this state.
	* </li>
	* <li>{@link #TIMED_WAITING}<br>
	* A thread that is waiting for another thread to perform an action
	* for up to a specified waiting time is in this state.
	* </li>
	* <li>{@link #TERMINATED}<br>
	* A thread that has exited is in this state.
	* </li>
	* </ul>
	*
	* <p>
	* A thread can be in only one state at a given point in time.
	* These states are virtual machine states which do not reflect
	* any operating system thread states.
	*
	* @since 1.5
	* @see #getState
	*/
	public enum State {
	/**
	* Thread state for a thread which has not yet started.
	*/
	NEW,

	/**
	* Thread state for a runnable thread. A thread in the runnable
	* state is executing in the Java virtual machine but it may
	* be waiting for other resources from the operating system
	* such as processor.
	*/
	RUNNABLE,

	/**
	* Thread state for a thread blocked waiting for a monitor lock.
	* A thread in the blocked state is waiting for a monitor lock
	* to enter a synchronized block/method or
	* reenter a synchronized block/method after calling
	* {@link Object#wait() Object.wait}.
	*/
	BLOCKED,

	/**
	* Thread state for a waiting thread.
	* A thread is in the waiting state due to calling one of the
	* following methods:
	* <ul>
	* <li>{@link Object#wait() Object.wait} with no timeout</li>
	* <li>{@link #join() Thread.join} with no timeout</li>
	* <li>{@link LockSupport#park() LockSupport.park}</li>
	* </ul>
	*
	* <p>A thread in the waiting state is waiting for another thread to
	* perform a particular action.
	*
	* For example, a thread that has called {@code Object.wait()}
	* on an object is waiting for another thread to call
	* {@code Object.notify()} or {@code Object.notifyAll()} on
	* that object. A thread that has called {@code Thread.join()}
	* is waiting for a specified thread to terminate.
	*/
	WAITING,

	/**
	* Thread state for a waiting thread with a specified waiting time.
	* A thread is in the timed waiting state due to calling one of
	* the following methods with a specified positive waiting time:
	* <ul>
	* <li>{@link #sleep Thread.sleep}</li>
	* <li>{@link Object#wait(long) Object.wait} with timeout</li>
	* <li>{@link #join(long) Thread.join} with timeout</li>
	* <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
	* <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
	* </ul>
	*/
	TIMED_WAITING,

	/**
	* Thread state for a terminated thread.
	* The thread has completed execution.
	*/
	TERMINATED;
	}

	/**
	* Returns the state of this thread.
	* This method is designed for use in monitoring of the system state,
	* not for synchronization control.
	*
	* @return this thread's state.
	* @since 1.5
	*/
	public State getState() {
	// get current thread state
	return jdk.internal.misc.VM.toThreadState(threadStatus);
	}

	// Added in JSR-166

	/**
	* Interface for handlers invoked when a {@code Thread} abruptly
	* terminates due to an uncaught exception.
	* <p>When a thread is about to terminate due to an uncaught exception
	* the Java Virtual Machine will query the thread for its
	* {@code UncaughtExceptionHandler} using
	* {@link #getUncaughtExceptionHandler} and will invoke the handler's
	* {@code uncaughtException} method, passing the thread and the
	* exception as arguments.
	* If a thread has not had its {@code UncaughtExceptionHandler}
	* explicitly set, then its {@code ThreadGroup} object acts as its
	* {@code UncaughtExceptionHandler}. If the {@code ThreadGroup} object
	* has no
	* special requirements for dealing with the exception, it can forward
	* the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
	* default uncaught exception handler}.
	*
	* @see #setDefaultUncaughtExceptionHandler
	* @see #setUncaughtExceptionHandler
	* @see ThreadGroup#uncaughtException
	* @since 1.5
	*/
	@FunctionalInterface
	public interface UncaughtExceptionHandler {
	/**
	* Method invoked when the given thread terminates due to the
	* given uncaught exception.
	* <p>Any exception thrown by this method will be ignored by the
	* Java Virtual Machine.
	* @param t the thread
	* @param e the exception
	*/
	void uncaughtException(Thread t, Throwable e);
	}

	// null unless explicitly set
	private volatile UncaughtExceptionHandler uncaughtExceptionHandler;

	// null unless explicitly set
	private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;

	/**
	* Set the default handler invoked when a thread abruptly terminates
	* due to an uncaught exception, and no other handler has been defined
	* for that thread.
	*
	* <p>Uncaught exception handling is controlled first by the thread, then
	* by the thread's {@link ThreadGroup} object and finally by the default
	* uncaught exception handler. If the thread does not have an explicit
	* uncaught exception handler set, and the thread's thread group
	* (including parent thread groups) does not specialize its
	* {@code uncaughtException} method, then the default handler's
	* {@code uncaughtException} method will be invoked.
	* <p>By setting the default uncaught exception handler, an application
	* can change the way in which uncaught exceptions are handled (such as
	* logging to a specific device, or file) for those threads that would
	* already accept whatever "default" behavior the system
	* provided.
	*
	* <p>Note that the default uncaught exception handler should not usually
	* defer to the thread's {@code ThreadGroup} object, as that could cause
	* infinite recursion.
	*
	* @param eh the object to use as the default uncaught exception handler.
	* If {@code null} then there is no default handler.
	*
	* @throws SecurityException if a security manager is present and it denies
	* {@link RuntimePermission}{@code ("setDefaultUncaughtExceptionHandler")}
	*
	* @see #setUncaughtExceptionHandler
	* @see #getUncaughtExceptionHandler
	* @see ThreadGroup#uncaughtException
	* @since 1.5
	*/
	public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	sm.checkPermission(
	new RuntimePermission("setDefaultUncaughtExceptionHandler")
	);
	}

	defaultUncaughtExceptionHandler = eh;
	}

	/**
	* Returns the default handler invoked when a thread abruptly terminates
	* due to an uncaught exception. If the returned value is {@code null},
	* there is no default.
	* @since 1.5
	* @see #setDefaultUncaughtExceptionHandler
	* @return the default uncaught exception handler for all threads
	*/
	public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
	return defaultUncaughtExceptionHandler;
	}

	/**
	* Returns the handler invoked when this thread abruptly terminates
	* due to an uncaught exception. If this thread has not had an
	* uncaught exception handler explicitly set then this thread's
	* {@code ThreadGroup} object is returned, unless this thread
	* has terminated, in which case {@code null} is returned.
	* @since 1.5
	* @return the uncaught exception handler for this thread
	*/
	public UncaughtExceptionHandler getUncaughtExceptionHandler() {
	return uncaughtExceptionHandler != null ?
	uncaughtExceptionHandler : group;
	}

	/**
	* Set the handler invoked when this thread abruptly terminates
	* due to an uncaught exception.
	* <p>A thread can take full control of how it responds to uncaught
	* exceptions by having its uncaught exception handler explicitly set.
	* If no such handler is set then the thread's {@code ThreadGroup}
	* object acts as its handler.
	* @param eh the object to use as this thread's uncaught exception
	* handler. If {@code null} then this thread has no explicit handler.
	* @throws SecurityException if the current thread is not allowed to
	* modify this thread.
	* @see #setDefaultUncaughtExceptionHandler
	* @see ThreadGroup#uncaughtException
	* @since 1.5
	*/
	public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
	checkAccess();
	uncaughtExceptionHandler = eh;
	}

	/**
	* Dispatch an uncaught exception to the handler. This method is
	* intended to be called only by the JVM.
	*/
	private void dispatchUncaughtException(Throwable e) {
	getUncaughtExceptionHandler().uncaughtException(this, e);
	}

	/**
	* Removes from the specified map any keys that have been enqueued
	* on the specified reference queue.
	*/
	static void processQueue(ReferenceQueue<Class<?>> queue,
	ConcurrentMap<? extends
	WeakReference<Class<?>>, ?> map)
	{
	Reference<? extends Class<?>> ref;
	while((ref = queue.poll()) != null) {
	map.remove(ref);
	}
	}

	/**
	* Weak key for Class objects.
	**/
	static class WeakClassKey extends WeakReference<Class<?>> {
	/**
	* saved value of the referent's identity hash code, to maintain
	* a consistent hash code after the referent has been cleared
	*/
	private final int hash;

	/**
	* Create a new WeakClassKey to the given object, registered
	* with a queue.
	*/
	WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
	super(cl, refQueue);
	hash = System.identityHashCode(cl);
	}

	/**
	* Returns the identity hash code of the original referent.
	*/
	@Override
	public int hashCode() {
	return hash;
	}

	/**
	* Returns true if the given object is this identical
	* WeakClassKey instance, or, if this object's referent has not
	* been cleared, if the given object is another WeakClassKey
	* instance with the identical non-null referent as this one.
	*/
	@Override
	public boolean equals(Object obj) {
	if (obj == this)
	return true;

	if (obj instanceof WeakClassKey) {
	Object referent = get();
	return (referent != null) &&
	(referent == ((WeakClassKey) obj).get());
	} else {
	return false;
	}
	}
	}


	// The following three initially uninitialized fields are exclusively
	// managed by class java.util.concurrent.ThreadLocalRandom. These
	// fields are used to build the high-performance PRNGs in the
	// concurrent code, and we can not risk accidental false sharing.
	// Hence, the fields are isolated with @Contended.

	/** The current seed for a ThreadLocalRandom */
	@jdk.internal.vm.annotation.Contended("tlr")
	long threadLocalRandomSeed;

	/** Probe hash value; nonzero if threadLocalRandomSeed initialized */
	@jdk.internal.vm.annotation.Contended("tlr")
	int threadLocalRandomProbe;

	/** Secondary seed isolated from public ThreadLocalRandom sequence */
	@jdk.internal.vm.annotation.Contended("tlr")
	int threadLocalRandomSecondarySeed;

	/* Some private helper methods */
	private native void setPriority0(int newPriority);
	private native void stop0(Object o);
	private native void suspend0();
	private native void resume0();
	private native void interrupt0();
	private native void setNativeName(String name);
	}

Back to index...