/*
 * Copyright (c) 1994, 2018, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

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
 * &nbsp;.&nbsp;.&nbsp;.
 * }
 * }
 * </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
 * &nbsp;.&nbsp;.&nbsp;.
 * }
 * }
 * </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 &quot;default&quot; 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);
}