深入学习java源码之Thread.sleep()与 Thread.setPriority()
通过并发编程的形式可以将多核CPU的计算能力发挥到极致，性能得到提升。
在特殊的业务场景下先天的就适合于并发编程。比如在图像处理领域，一张1024X768像素的图片，包含达到78万6千多个像素。即时将所有的像素遍历一边都需要很长的时间，面对如此复杂的计算量就需要充分利用多核的计算的能力。又比如当我们在网上购物时，为了提升响应速度，需要拆分，减库存，生成订单等等这些操作，就可以进行拆分利用多线程的技术完成。面对复杂业务模型，并行程序会比串行程序更适应业务需求，而并发编程更能吻合这种业务拆分
时间片是CPU分配给各个线程的时间，因为时间非常短，所以CPU不断通过切换线程，让我们觉得多个线程是同时执行的，时间片一般是几十毫秒。而每次切换时，需要保存当前的状态起来，以便能够进行恢复先前状态，而这个切换时非常损耗性能，过于频繁反而无法发挥出多线程编程的优势。通常减少上下文切换可以采用无锁并发编程，CAS算法，使用了乐观锁，可以有效的减少一部分不必要的锁竞争带来的上下文切换，使用最少的线程和使用协程。
同步VS异步
同步和异步通常用来形容一次方法调用。同步方法调用一开始，调用者必须等待被调用的方法结束后，调用者后面的代码才能执行。而异步调用，指的是，调用者不用管被调用方法是否完成，都会继续执行后面的代码，当被调用的方法完成后会通知调用者。
并发与并行
并发和并行是十分容易混淆的概念。并发指的是多个任务交替进行，而并行则是指真正意义上的“同时进行”。实际上，如果系统内只有一个CPU，而使用多线程时，那么真实系统环境下不能并行，只能通过切换时间片的方式交替进行，而成为并发执行任务。真正的并行也只能出现在拥有多个CPU的系统中。
阻塞和非阻塞
阻塞和非阻塞通常用来形容多线程间的相互影响，比如一个线程占有了临界区资源，那么其他线程需要这个资源就必须进行等待该资源的释放，会导致等待的线程挂起，这种情况就是阻塞，而非阻塞就恰好相反，它强调没有一个线程可以阻塞其他线程，所有的线程都会尝试地往前运行。
临界区
临界区用来表示一种公共资源或者说是共享数据，可以被多个线程使用。但是每个线程使用时，一旦临界区资源被一个线程占有，那么其他线程必须等待。
实际上java程序天生就是一个多线程程序，包含了：（1）分发处理发送给给JVM信号的线程；（2）调用对象的finalize方法的线程；（3）清除Reference的线程；（4）main线程，用户程序的入口。那么，如何在用户程序中新建一个线程了，只要有三种方式：
-
通过继承Thread类，重写run方法；
-
通过实现runable接口；
-
通过实现callable接口这三种方式，下面看具体demo。
public class CreateThreadDemo {
public static void main(String[] args) {
//1.继承Thread
Thread thread = new Thread() {
@Override
public void run() {
System.out.println("继承Thread");
super.run();
}
};
thread.start();
//2.实现runable接口
Thread thread1 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("实现runable接口");
}
});
thread1.start();
//3.实现callable接口
ExecutorService service = Executors.newSingleThreadExecutor();
Future<String> future = service.submit(new Callable() {
@Override
public String call() throws Exception {
return "通过实现Callable接口";
}
});
try {
String result = future.get();
System.out.println(result);
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
}三种新建线程的方式具体看以上注释，需要主要的是：
- 由于java不能多继承可以实现多个接口，因此，在创建线程的时候尽量多考虑采用实现接口的形式；
- 实现callable接口，提交给ExecutorService返回的是异步执行的结果，另外，通常也可以利用FutureTask(Callable<V> callable)将callable进行包装然后FeatureTask提交给ExecutorsService。如图
另外由于FeatureTask也实现了Runable接口也可以利用上面第二种方式（实现Runable接口）来新建线程；
- 可以通过Executors将Runable转换成Callable，具体方法是：Callable<T> callable(Runnable task, T result)， Callable<Object> callable(Runnable task)。
线程状态转换
线程是会在不同的状态间进行转换的，java线程线程转换图如上图所示。线程创建之后调用start()方法开始运行，当调用wait(),join(),LockSupport.lock()方法线程会进入到WAITING状态，而同样的wait(long timeout)，sleep(long),join(long),LockSupport.parkNanos(),LockSupport.parkUtil()增加了超时等待的功能，也就是调用这些方法后线程会进入TIMED_WAITING状态，当超时等待时间到达后，线程会切换到Runable的状态，另外当WAITING和TIMED _WAITING状态时可以通过Object.notify(),Object.notifyAll()方法使线程转换到Runable状态。当线程出现资源竞争时，即等待获取锁的时候，线程会进入到BLOCKED阻塞状态，当线程获取锁时，线程进入到Runable状态。线程运行结束后，线程进入到TERMINATED状态，状态转换可以说是线程的生命周期。
线程状态的基本操作
除了新建一个线程外，线程在生命周期内还有需要基本操作，而这些操作会成为线程间一种通信方式，比如使用中断（interrupted）方式通知实现线程间的交互等等
interrupted
中断可以理解为线程的一个标志位，它表示了一个运行中的线程是否被其他线程进行了中断操作。中断好比其他线程对该线程打了一个招呼。其他线程可以调用该线程的interrupt()方法对其进行中断操作，同时该线程可以调用
isInterrupted（）来感知其他线程对其自身的中断操作，从而做出响应。另外，同样可以调用Thread的静态方法
interrupted（）对当前线程进行中断操作，该方法会清除中断标志位。需要注意的是，当抛出InterruptedException时候，会清除中断标志位，也就是说在调用isInterrupted会返回false。
public class InterruptDemo {
public static void main(String[] args) throws InterruptedException {
//sleepThread睡眠1000ms
final Thread sleepThread = new Thread() {
@Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
super.run();
}
};
//busyThread一直执行死循环
Thread busyThread = new Thread() {
@Override
public void run() {
while (true) ;
}
};
sleepThread.start();
busyThread.start();
sleepThread.interrupt();
busyThread.interrupt();
while (sleepThread.isInterrupted()) ;
System.out.println("sleepThread isInterrupted: " + sleepThread.isInterrupted());
System.out.println("busyThread isInterrupted: " + busyThread.isInterrupted());
}
}
sleepThread isInterrupted: false
busyThread isInterrupted: true开启了两个线程分别为sleepThread和BusyThread, sleepThread睡眠1s，BusyThread执行死循环。然后分别对着两个线程进行中断操作，可以看出sleepThread抛出InterruptedException后清除标志位，而busyThread就不会清除标志位。
另外，同样可以通过中断的方式实现线程间的简单交互， while (sleepThread.isInterrupted()) 表示在Main中会持续监测sleepThread，一旦sleepThread的中断标志位清零，即sleepThread.isInterrupted()返回为false时才会继续Main线程才会继续往下执行。因此，中断操作可以看做线程间一种简便的交互方式。一般在结束线程时通过中断标志位或者标志位的方式可以有机会去清理资源，相对于武断而直接的结束线程，这种方式要优雅和安全。
join
join方法可以看做是线程间协作的一种方式，很多时候，一个线程的输入可能非常依赖于另一个线程的输出，这就像两个好基友，一个基友先走在前面突然看见另一个基友落在后面了，这个时候他就会在原处等一等这个基友，等基友赶上来后，就两人携手并进。其实线程间的这种协作方式也符合现实生活。在软件开发的过程中，从客户那里获取需求后，需要经过需求分析师进行需求分解后，这个时候产品，开发才会继续跟进。如果一个线程实例A执行了threadB.join(),其含义是：当前线程A会等待threadB线程终止后threadA才会继续执行。关于join方法一共提供如下这些方法:
public final synchronized void join(long millis)
public final synchronized void join(long millis, int nanos)
public final void join() throws InterruptedExceptionThread类除了提供join()方法外，另外还提供了超时等待的方法，如果线程threadB在等待的时间内还没有结束的话，threadA会在超时之后继续执行。join方法源码关键是：
while (isAlive()) {
wait(0);
}可以看出来当前等待对象threadA会一直阻塞，直到被等待对象threadB结束后即isAlive()返回false的时候才会结束while循环，当threadB退出时会调用notifyAll()方法通知所有的等待线程。下面用一个具体的例子来说说join方法的使用：
public class JoinDemo {
public static void main(String[] args) {
Thread previousThread = Thread.currentThread();
for (int i = 1; i <= 10; i++) {
Thread curThread = new JoinThread(previousThread);
curThread.start();
previousThread = curThread;
}
}
static class JoinThread extends Thread {
private Thread thread;
public JoinThread(Thread thread) {
this.thread = thread;
}
@Override
public void run() {
try {
thread.join();
System.out.println(thread.getName() + " terminated.");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}在上面的例子中一个创建了10个线程，每个线程都会等待前一个线程结束才会继续运行。可以通俗的理解成接力，前一个线程将接力棒传给下一个线程，然后又传给下一个线程......
main terminated.
Thread-0 terminated.
Thread-1 terminated.
Thread-2 terminated.
Thread-3 terminated.
Thread-4 terminated.
Thread-5 terminated.
Thread-6 terminated.
Thread-7 terminated.
Thread-8 terminated.sleep
public static native void sleep(long millis)方法显然是Thread的静态方法，很显然它是让当前线程按照指定的时间休眠，其休眠时间的精度取决于处理器的计时器和调度器。需要注意的是如果当前线程获得了锁，sleep方法并不会失去锁。sleep方法经常拿来与Object.wait()方法进行比价，这也是面试经常被问的地方。
sleep() VS wait()
两者主要的区别：
- sleep()方法是Thread的静态方法，而wait是Object实例方法
- wait()方法必须要在同步方法或者同步块中调用，也就是必须已经获得对象锁。而sleep()方法没有这个限制可以在任何地方种使用。另外，wait()方法会释放占有的对象锁，使得该线程进入等待池中，等待下一次获取资源。而sleep()方法只是会让出CPU并不会释放掉对象锁；
- sleep()方法在休眠时间达到后如果再次获得CPU时间片就会继续执行，而wait()方法必须等待Object.notift/Object.notifyAll通知后，才会离开等待池，并且再次获得CPU时间片才会继续执行。
yield
public static native void yield();这是一个静态方法，一旦执行，它会是当前线程让出CPU，但是，需要注意的是，让出的CPU并不是代表当前线程不再运行了，如果在下一次竞争中，又获得了CPU时间片当前线程依然会继续运行。另外，让出的时间片只会分配给当前线程相同优先级的线程。什么是线程优先级了？下面就来具体聊一聊。
现代操作系统基本采用时分的形式调度运行的线程，操作系统会分出一个个时间片，线程会分配到若干时间片，当前时间片用完后就会发生线程调度，并等待这下次分配。线程分配到的时间多少也就决定了线程使用处理器资源的多少，而线程优先级就是决定线程需要或多或少分配一些处理器资源的线程属性。
在Java程序中，通过一个整型成员变量Priority来控制优先级，优先级的范围从1~10.在构建线程的时候可以通过setPriority(int)方法进行设置，默认优先级为5，优先级高的线程相较于优先级低的线程优先获得处理器时间片。需要注意的是在不同JVM以及操作系统上，线程规划存在差异，有些操作系统甚至会忽略线程优先级的设定。
另外需要注意的是，sleep()和yield()方法，同样都是当前线程会交出处理器资源，而它们不同的是，sleep()交出来的时间片其他线程都可以去竞争，也就是说都有机会获得当前线程让出的时间片。而yield()方法只允许与当前线程具有相同优先级的线程能够获得释放出来的CPU时间片。
守护线程Daemon
守护线程是一种特殊的线程，就和它的名字一样，它是系统的守护者，在后台默默地守护一些系统服务，比如垃圾回收线程，JIT线程就可以理解守护线程。与之对应的就是用户线程，用户线程就可以认为是系统的工作线程，它会完成整个系统的业务操作。用户线程完全结束后就意味着整个系统的业务任务全部结束了，因此系统就没有对象需要守护的了，守护线程自然而然就会退。当一个Java应用，只有守护线程的时候，虚拟机就会自然退出。下面以一个简单的例子来表述Daemon线程的使用。
public class DaemonDemo {
public static void main(String[] args) {
Thread daemonThread = new Thread(new Runnable() {
@Override
public void run() {
while (true) {
try {
System.out.println("i am alive");
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println("finally block");
}
}
}
});
daemonThread.setDaemon(true);
daemonThread.start();
//确保main线程结束前能给daemonThread能够分到时间片
try {
Thread.sleep(800);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}输出结果为：
i am alive
finally block
i am alive上面的例子中daemodThread run方法中是一个while死循环，会一直打印,但是当main线程结束后daemonThread就会退出所以不会出现死循环的情况。main线程先睡眠800ms保证daemonThread能够拥有一次时间片的机会，也就是说可以正常执行一次打印“i am alive”操作和一次finally块中"finally block"操作。紧接着main 线程结束后，daemonThread退出，这个时候只打印了"i am alive"并没有打印finnal块中的。因此，这里需要注意的是守护线程在退出的时候并不会执行finnaly块中的代码，所以将释放资源等操作不要放在finnaly块中执行，这种操作是不安全的。
线程可以通过setDaemon(true)的方法将线程设置为守护线程。并且需要注意的是设置守护线程要先于start()方法，否则会报
Exception in thread "main" java.lang.IllegalThreadStateException
at java.lang.Thread.setDaemon(Thread.java:1365)
at learn.DaemonDemo.main(DaemonDemo.java:19)这样的异常，但是该线程还是会执行，只不过会当做正常的用户线程执行。
java源码
| Modifier and Type | Method and Description |
|---|---|
static int |
activeCount() 返回当前线程的thread group及其子组中活动线程数的估计。 |
void |
checkAccess() 确定当前正在运行的线程是否有权限修改此线程。 |
protected Object |
clone() 将CloneNotSupportedException作为线程抛出无法有意义地克隆。 |
int |
countStackFrames()已弃用 此呼叫的定义取决于 |
static Thread |
currentThread() 返回对当前正在执行的线程对象的引用。 |
void |
destroy()已弃用 这种方法最初是为了销毁这个线程而没有任何清理。 它所持有的任何监视器都将保持锁定。 但是，该方法从未实现。 如果要实施，那么它将是 |
static void |
dumpStack() 将当前线程的堆栈跟踪打印到标准错误流。 |
static int |
enumerate(Thread[] tarray) 将当前线程的线程组及其子组中的每个活动线程复制到指定的数组中。 |
static Map<Thread,StackTraceElement[]> |
getAllStackTraces() 返回所有活动线程的堆栈跟踪图。 |
ClassLoader |
getContextClassLoader() 返回此Thread的上下文ClassLoader。 |
static Thread.UncaughtExceptionHandler |
getDefaultUncaughtExceptionHandler() 返回当线程由于未捕获异常突然终止而调用的默认处理程序。 |
long |
getId() 返回此线程的标识符。 |
String |
getName() 返回此线程的名称。 |
int |
getPriority() 返回此线程的优先级。 |
StackTraceElement[] |
getStackTrace() 返回表示此线程的堆栈转储的堆栈跟踪元素数组。 |
Thread.State |
getState() 返回此线程的状态。 |
ThreadGroup |
getThreadGroup() 返回此线程所属的线程组。 |
Thread.UncaughtExceptionHandler |
getUncaughtExceptionHandler() 返回由于未捕获的异常，此线程突然终止时调用的处理程序。 |
static boolean |
holdsLock(Object obj) 返回 true当且仅当当前线程在指定的对象上保持监视器锁。 |
void |
interrupt() 中断这个线程。 |
static boolean |
interrupted() 测试当前线程是否中断。 |
boolean |
isAlive() 测试这个线程是否活着。 |
boolean |
isDaemon() 测试这个线程是否是守护线程。 |
boolean |
isInterrupted() 测试这个线程是否被中断。 |
void |
join() 等待这个线程死亡。 |
void |
join(long millis) 等待这个线程死亡最多 |
void |
join(long millis, int nanos) 等待最多 |
void |
resume()已弃用 该方法仅用于与 |
void |
run() 如果这个线程使用单独的 |
void |
setContextClassLoader(ClassLoader cl) 设置此线程的上下文ClassLoader。 |
void |
setDaemon(boolean on) 将此线程标记为 daemon线程或用户线程。 |
static void |
setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh) 设置当线程由于未捕获的异常突然终止而调用的默认处理程序，并且没有为该线程定义其他处理程序。 |
void |
setName(String name) 将此线程的名称更改为等于参数 |
void |
setPriority(int newPriority) 更改此线程的优先级。 |
void |
setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh) 设置当该线程由于未捕获的异常而突然终止时调用的处理程序。 |
static void |
sleep(long millis) 使当前正在执行的线程以指定的毫秒数暂停（暂时停止执行），具体取决于系统定时器和调度程序的精度和准确性。 |
static void |
sleep(long millis, int nanos) 导致正在执行的线程以指定的毫秒数加上指定的纳秒数来暂停（临时停止执行），这取决于系统定时器和调度器的精度和准确性。 |
void |
start() 导致此线程开始执行; Java虚拟机调用此线程的 |
void |
stop()已弃用 这种方法本质上是不安全的。 使用Thread.stop停止线程可以解锁所有已锁定的监视器（由于未 |
void |
stop(Throwable obj)已弃用 该方法最初设计为强制线程停止并抛出一个给定的 |
void |
suspend()已弃用 这种方法已被弃用，因为它本身就是死锁的。 如果目标线程在挂起时保护关键系统资源的监视器上的锁定，则在目标线程恢复之前，线程不能访问该资源。 如果要恢复目标线程的线程在调用 |
String |
toString() 返回此线程的字符串表示，包括线程的名称，优先级和线程组。 |
static void |
yield() 对调度程序的一个暗示，即当前线程愿意产生当前使用的处理器。 |
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 sun.nio.ch.Interruptible;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.security.util.SecurityConstants;
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;
private Thread threadQ;
private long eetop;
private boolean single_step;
private boolean daemon = false;
private boolean stillborn = false;
private Runnable target;
private ThreadGroup group;
private ClassLoader contextClassLoader;
private AccessControlContext inheritedAccessControlContext;
private static int threadInitNumber;
private static synchronized int nextThreadNum() {
return threadInitNumber++;
}
ThreadLocal.ThreadLocalMap threadLocals = null;
ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
private long stackSize;
private long nativeParkEventPointer;
private long tid;
private static long threadSeqNumber;
private volatile int threadStatus = 0;
private static synchronized long nextThreadID() {
return ++threadSeqNumber;
}
volatile Object parkBlocker;
private volatile Interruptible blocker;
private final Object blockerLock = new Object();
void blockedOn(Interruptible b) {
synchronized (blockerLock) {
blocker = b;
}
}
public final static int MIN_PRIORITY = 1;
public final static int NORM_PRIORITY = 5;
public final static int MAX_PRIORITY = 10;
public static native Thread currentThread();
public static native void yield();
public static native void sleep(long millis) throws InterruptedException;
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);
}
private void init(ThreadGroup g, Runnable target, String name,
long stackSize) {
init(g, target, name, stackSize, null, true);
}
private void init(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 doesn't have a strong opinion of 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(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 */
tid = nextThreadID();
}
@Override
protected Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
public Thread() {
init(null, null, "Thread-" + nextThreadNum(), 0);
}
public Thread(Runnable target) {
init(null, target, "Thread-" + nextThreadNum(), 0);
}
Thread(Runnable target, AccessControlContext acc) {
init(null, target, "Thread-" + nextThreadNum(), 0, acc, false);
}
public Thread(ThreadGroup group, Runnable target) {
init(group, target, "Thread-" + nextThreadNum(), 0);
}
public Thread(String name) {
init(null, null, name, 0);
}
public Thread(ThreadGroup group, String name) {
init(group, null, name, 0);
}
public Thread(Runnable target, String name) {
init(null, target, name, 0);
}
public Thread(ThreadGroup group, Runnable target, String name) {
init(group, target, name, 0);
}
public Thread(ThreadGroup group, Runnable target, String name,
long stackSize) {
init(group, target, name, stackSize);
}
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();
@Override
public void run() {
if (target != null) {
target.run();
}
}
private void exit() {
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;
}
@Deprecated
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());
}
@Deprecated
public final synchronized void stop(Throwable obj) {
throw new UnsupportedOperationException();
}
public void interrupt() {
if (this != Thread.currentThread())
checkAccess();
synchronized (blockerLock) {
Interruptible b = blocker;
if (b != null) {
interrupt0(); // Just to set the interrupt flag
b.interrupt(this);
return;
}
}
interrupt0();
}
public static boolean interrupted() {
return currentThread().isInterrupted(true);
}
public boolean isInterrupted() {
return isInterrupted(false);
}
private native boolean isInterrupted(boolean ClearInterrupted);
@Deprecated
public void destroy() {
throw new NoSuchMethodError();
}
public final native boolean isAlive();
@Deprecated
public final void suspend() {
checkAccess();
suspend0();
}
@Deprecated
public final void resume() {
checkAccess();
resume0();
}
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);
}
}
public final int getPriority() {
return priority;
}
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);
}
}
public final String getName() {
return name;
}
public final ThreadGroup getThreadGroup() {
return group;
}
public static int activeCount() {
return currentThread().getThreadGroup().activeCount();
}
public static int enumerate(Thread tarray[]) {
return currentThread().getThreadGroup().enumerate(tarray);
}
@Deprecated
public native int countStackFrames();
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;
}
}
}
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);
}
public final void join() throws InterruptedException {
join(0);
}
public static void dumpStack() {
new Exception("Stack trace").printStackTrace();
}
public final void setDaemon(boolean on) {
checkAccess();
if (isAlive()) {
throw new IllegalThreadStateException();
}
daemon = on;
}
public final boolean isDaemon() {
return daemon;
}
public final void checkAccess() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkAccess(this);
}
}
public String toString() {
ThreadGroup group = getThreadGroup();
if (group != null) {
return "Thread[" + getName() + "," + getPriority() + "," +
group.getName() + "]";
} else {
return "Thread[" + getName() + "," + getPriority() + "," +
"" + "]";
}
}
@CallerSensitive
public ClassLoader getContextClassLoader() {
if (contextClassLoader == null)
return null;
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
ClassLoader.checkClassLoaderPermission(contextClassLoader,
Reflection.getCallerClass());
}
return contextClassLoader;
}
public void setContextClassLoader(ClassLoader cl) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("setContextClassLoader"));
}
contextClassLoader = cl;
}
public static native boolean holdsLock(Object obj);
private static final StackTraceElement[] EMPTY_STACK_TRACE
= new StackTraceElement[0];
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 {
// Don't need JVM help for current thread
return (new Exception()).getStackTrace();
}
}
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;
}
private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
new RuntimePermission("enableContextClassLoaderOverride");
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<>();
}
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();
}
private static boolean auditSubclass(final Class<?> subcl) {
Boolean result = AccessController.doPrivileged(
new PrivilegedAction<Boolean>() {
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 native static StackTraceElement[][] dumpThreads(Thread[] threads);
private native static Thread[] getThreads();
public long getId() {
return tid;
}
public enum State {
NEW,
RUNNABLE,
BLOCKED,
WAITING,
TIMED_WAITING,
TERMINATED;
}
public State getState() {
// get current thread state
return sun.misc.VM.toThreadState(threadStatus);
}
@FunctionalInterface
public interface UncaughtExceptionHandler {
void uncaughtException(Thread t, Throwable e);
}
private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(
new RuntimePermission("setDefaultUncaughtExceptionHandler")
);
}
defaultUncaughtExceptionHandler = eh;
}
public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
return defaultUncaughtExceptionHandler;
}
public UncaughtExceptionHandler getUncaughtExceptionHandler() {
return uncaughtExceptionHandler != null ?
uncaughtExceptionHandler : group;
}
public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
checkAccess();
uncaughtExceptionHandler = eh;
}
private void dispatchUncaughtException(Throwable e) {
getUncaughtExceptionHandler().uncaughtException(this, e);
}
static void processQueue(ReferenceQueue<Class<?>> queue,
ConcurrentMap<? extends
WeakReference<Class<?>>, ?> map)
{
Reference<? extends Class<?>> ref;
while((ref = queue.poll()) != null) {
map.remove(ref);
}
}
static class WeakClassKey extends WeakReference<Class<?>> {
private final int hash;
WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
super(cl, refQueue);
hash = System.identityHashCode(cl);
}
@Override
public int hashCode() {
return hash;
}
@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;
}
}
}
@sun.misc.Contended("tlr")
long threadLocalRandomSeed;
@sun.misc.Contended("tlr")
int threadLocalRandomProbe;
@sun.misc.Contended("tlr")
int threadLocalRandomSecondarySeed;
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);
}
package java.lang;
@FunctionalInterface
public interface Runnable {
public abstract void run();
}| Modifier and Type | Method and Description |
|---|---|
int |
activeCount() 返回此线程组及其子组中活动线程数的估计。 |
int |
activeGroupCount() 返回此线程组及其子组中活动组数的估计。 |
boolean |
allowThreadSuspension(boolean b)已弃用 此呼叫的定义取决于 |
void |
checkAccess() 确定当前运行的线程是否有权限修改此线程组。 |
void |
destroy() 销毁此线程组及其所有子组。 |
int |
enumerate(Thread[] list) 将此线程组及其子组中的每个活动线程复制到指定的数组中。 |
int |
enumerate(Thread[] list, boolean recurse) 将此线程组中的每个活动线程复制到指定的数组中。 |
int |
enumerate(ThreadGroup[] list) 复制到该线程组及其子组中每个活动子组的指定数组引用。 |
int |
enumerate(ThreadGroup[] list, boolean recurse) 复制到该线程组中每个活动子组的指定数组引用。 |
int |
getMaxPriority() 返回此线程组的最大优先级。 |
String |
getName() 返回此线程组的名称。 |
ThreadGroup |
getParent() 返回此线程组的父级。 |
void |
interrupt() 中断此线程组中的所有线程。 |
boolean |
isDaemon() 测试此线程组是否是守护线程组。 |
boolean |
isDestroyed() 测试此线程组是否已被破坏。 |
void |
list() 将有关此线程组的信息打印到标准输出。 |
boolean |
parentOf(ThreadGroup g) 测试此线程组是线程组参数还是其祖先线程组之一。 |
void |
resume()已弃用 这种方法仅与Thread.suspend和ThreadGroup.suspend一起使用 ，这两种方法都已经被弃用，因为它们本身就是死锁的。 详见 |
void |
setDaemon(boolean daemon) 更改此线程组的守护程序状态。 |
void |
setMaxPriority(int pri) 设置组的最大优先级。 |
void |
stop()已弃用 这种方法本质上是不安全的。 详见 |
void |
suspend()已弃用 这种方法本质上是死锁的。 详见 |
String |
toString() 返回此Thread组的字符串表示形式。 |
void |
uncaughtException(Thread t, Throwable e) 当此线程组中的线程因为一个未捕获的异常由Java Virtual Machine调用，而线程不具有特定 |
package java.lang;
import java.io.PrintStream;
import java.util.Arrays;
import sun.misc.VM;
public
class ThreadGroup implements Thread.UncaughtExceptionHandler {
private final ThreadGroup parent;
String name;
int maxPriority;
boolean destroyed;
boolean daemon;
boolean vmAllowSuspension;
int nUnstartedThreads = 0;
int nthreads;
Thread threads[];
int ngroups;
ThreadGroup groups[];
private ThreadGroup() { // called from C code
this.name = "system";
this.maxPriority = Thread.MAX_PRIORITY;
this.parent = null;
}
public ThreadGroup(String name) {
this(Thread.currentThread().getThreadGroup(), name);
}
public ThreadGroup(ThreadGroup parent, String name) {
this(checkParentAccess(parent), parent, name);
}
private ThreadGroup(Void unused, ThreadGroup parent, String name) {
this.name = name;
this.maxPriority = parent.maxPriority;
this.daemon = parent.daemon;
this.vmAllowSuspension = parent.vmAllowSuspension;
this.parent = parent;
parent.add(this);
}
private static Void checkParentAccess(ThreadGroup parent) {
parent.checkAccess();
return null;
}
public final String getName() {
return name;
}
public final ThreadGroup getParent() {
if (parent != null)
parent.checkAccess();
return parent;
}
public final int getMaxPriority() {
return maxPriority;
}
public final boolean isDaemon() {
return daemon;
}
public synchronized boolean isDestroyed() {
return destroyed;
}
public final void setDaemon(boolean daemon) {
checkAccess();
this.daemon = daemon;
}
public final void setMaxPriority(int pri) {
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
checkAccess();
if (pri < Thread.MIN_PRIORITY || pri > Thread.MAX_PRIORITY) {
return;
}
maxPriority = (parent != null) ? Math.min(pri, parent.maxPriority) : pri;
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
groupsSnapshot[i].setMaxPriority(pri);
}
}
public final boolean parentOf(ThreadGroup g) {
for (; g != null ; g = g.parent) {
if (g == this) {
return true;
}
}
return false;
}
public final void checkAccess() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkAccess(this);
}
}
public int activeCount() {
int result;
// Snapshot sub-group data so we don't hold this lock
// while our children are computing.
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
if (destroyed) {
return 0;
}
result = nthreads;
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
result += groupsSnapshot[i].activeCount();
}
return result;
}
public int enumerate(Thread list[]) {
checkAccess();
return enumerate(list, 0, true);
}
public int enumerate(Thread list[], boolean recurse) {
checkAccess();
return enumerate(list, 0, recurse);
}
private int enumerate(Thread list[], int n, boolean recurse) {
int ngroupsSnapshot = 0;
ThreadGroup[] groupsSnapshot = null;
synchronized (this) {
if (destroyed) {
return 0;
}
int nt = nthreads;
if (nt > list.length - n) {
nt = list.length - n;
}
for (int i = 0; i < nt; i++) {
if (threads[i].isAlive()) {
list[n++] = threads[i];
}
}
if (recurse) {
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
}
if (recurse) {
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
n = groupsSnapshot[i].enumerate(list, n, true);
}
}
return n;
}
public int activeGroupCount() {
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
if (destroyed) {
return 0;
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
int n = ngroupsSnapshot;
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
n += groupsSnapshot[i].activeGroupCount();
}
return n;
}
public int enumerate(ThreadGroup list[]) {
checkAccess();
return enumerate(list, 0, true);
}
public int enumerate(ThreadGroup list[], boolean recurse) {
checkAccess();
return enumerate(list, 0, recurse);
}
private int enumerate(ThreadGroup list[], int n, boolean recurse) {
int ngroupsSnapshot = 0;
ThreadGroup[] groupsSnapshot = null;
synchronized (this) {
if (destroyed) {
return 0;
}
int ng = ngroups;
if (ng > list.length - n) {
ng = list.length - n;
}
if (ng > 0) {
System.arraycopy(groups, 0, list, n, ng);
n += ng;
}
if (recurse) {
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
}
if (recurse) {
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
n = groupsSnapshot[i].enumerate(list, n, true);
}
}
return n;
}
@Deprecated
public final void stop() {
if (stopOrSuspend(false))
Thread.currentThread().stop();
}
public final void interrupt() {
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
checkAccess();
for (int i = 0 ; i < nthreads ; i++) {
threads[i].interrupt();
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
groupsSnapshot[i].interrupt();
}
}
@Deprecated
@SuppressWarnings("deprecation")
public final void suspend() {
if (stopOrSuspend(true))
Thread.currentThread().suspend();
}
@SuppressWarnings("deprecation")
private boolean stopOrSuspend(boolean suspend) {
boolean suicide = false;
Thread us = Thread.currentThread();
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot = null;
synchronized (this) {
checkAccess();
for (int i = 0 ; i < nthreads ; i++) {
if (threads[i]==us)
suicide = true;
else if (suspend)
threads[i].suspend();
else
threads[i].stop();
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i++)
suicide = groupsSnapshot[i].stopOrSuspend(suspend) || suicide;
return suicide;
}
@Deprecated
@SuppressWarnings("deprecation")
public final void resume() {
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
checkAccess();
for (int i = 0 ; i < nthreads ; i++) {
threads[i].resume();
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
groupsSnapshot[i].resume();
}
}
public final void destroy() {
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
checkAccess();
if (destroyed || (nthreads > 0)) {
throw new IllegalThreadStateException();
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
if (parent != null) {
destroyed = true;
ngroups = 0;
groups = null;
nthreads = 0;
threads = null;
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i += 1) {
groupsSnapshot[i].destroy();
}
if (parent != null) {
parent.remove(this);
}
}
private final void add(ThreadGroup g){
synchronized (this) {
if (destroyed) {
throw new IllegalThreadStateException();
}
if (groups == null) {
groups = new ThreadGroup[4];
} else if (ngroups == groups.length) {
groups = Arrays.copyOf(groups, ngroups * 2);
}
groups[ngroups] = g;
// This is done last so it doesn't matter in case the
// thread is killed
ngroups++;
}
}
private void remove(ThreadGroup g) {
synchronized (this) {
if (destroyed) {
return;
}
for (int i = 0 ; i < ngroups ; i++) {
if (groups[i] == g) {
ngroups -= 1;
System.arraycopy(groups, i + 1, groups, i, ngroups - i);
// Zap dangling reference to the dead group so that
// the garbage collector will collect it.
groups[ngroups] = null;
break;
}
}
if (nthreads == 0) {
notifyAll();
}
if (daemon && (nthreads == 0) &&
(nUnstartedThreads == 0) && (ngroups == 0))
{
destroy();
}
}
}
void addUnstarted() {
synchronized(this) {
if (destroyed) {
throw new IllegalThreadStateException();
}
nUnstartedThreads++;
}
}
void add(Thread t) {
synchronized (this) {
if (destroyed) {
throw new IllegalThreadStateException();
}
if (threads == null) {
threads = new Thread[4];
} else if (nthreads == threads.length) {
threads = Arrays.copyOf(threads, nthreads * 2);
}
threads[nthreads] = t;
// This is done last so it doesn't matter in case the
// thread is killed
nthreads++;
// The thread is now a fully fledged member of the group, even
// though it may, or may not, have been started yet. It will prevent
// the group from being destroyed so the unstarted Threads count is
// decremented.
nUnstartedThreads--;
}
}
void threadStartFailed(Thread t) {
synchronized(this) {
remove(t);
nUnstartedThreads++;
}
}
void threadTerminated(Thread t) {
synchronized (this) {
remove(t);
if (nthreads == 0) {
notifyAll();
}
if (daemon && (nthreads == 0) &&
(nUnstartedThreads == 0) && (ngroups == 0))
{
destroy();
}
}
}
private void remove(Thread t) {
synchronized (this) {
if (destroyed) {
return;
}
for (int i = 0 ; i < nthreads ; i++) {
if (threads[i] == t) {
System.arraycopy(threads, i + 1, threads, i, --nthreads - i);
// Zap dangling reference to the dead thread so that
// the garbage collector will collect it.
threads[nthreads] = null;
break;
}
}
}
}
public void list() {
list(System.out, 0);
}
void list(PrintStream out, int indent) {
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
for (int j = 0 ; j < indent ; j++) {
out.print(" ");
}
out.println(this);
indent += 4;
for (int i = 0 ; i < nthreads ; i++) {
for (int j = 0 ; j < indent ; j++) {
out.print(" ");
}
out.println(threads[i]);
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
} else {
groupsSnapshot = null;
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i++) {
groupsSnapshot[i].list(out, indent);
}
}
public void uncaughtException(Thread t, Throwable e) {
if (parent != null) {
parent.uncaughtException(t, e);
} else {
Thread.UncaughtExceptionHandler ueh =
Thread.getDefaultUncaughtExceptionHandler();
if (ueh != null) {
ueh.uncaughtException(t, e);
} else if (!(e instanceof ThreadDeath)) {
System.err.print("Exception in thread \""
+ t.getName() + "\" ");
e.printStackTrace(System.err);
}
}
}
@Deprecated
public boolean allowThreadSuspension(boolean b) {
this.vmAllowSuspension = b;
if (!b) {
VM.unsuspendSomeThreads();
}
return true;
}
public String toString() {
return getClass().getName() + "[name=" + getName() + ",maxpri=" + maxPriority + "]";
}
}