/**
* Creates a new thread group. The parent of this new group is the specified thread group.
*
* <p>The <code>checkAccess</code> method of the parent thread group is called with no arguments;
* this may result in a security exception.
*
* @param parent the parent thread group.
* @param name the name of the new thread group.
* @exception NullPointerException if the thread group argument is <code>null</code>.
* @exception SecurityException if the current thread cannot create a thread in the specified
* thread group.
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
public ThreadGroup(ThreadGroup parent, String name) {
if (parent == null) {
throw new NullPointerException();
}
parent.checkAccess();
this.name = name;
this.maxPriority = parent.maxPriority;
this.daemon = parent.daemon;
this.vmAllowSuspension = parent.vmAllowSuspension;
this.parent = parent;
parent.add(this);
saveThreadStarterClassFlag = parent.saveThreadStarterClassFlag;
}
/**
* Sets the priority of this thread. If the requested priority is greater than the parent thread
* group's {@link java.lang.ThreadGroup#getMaxPriority}, the group's maximum priority will be used
* instead.
*
* @throws IllegalArgumentException - if the new priority is greater than {@link #MAX_PRIORITY} or
* less than {@link #MIN_PRIORITY}
*/
public final void setPriority(int priority) {
if (priority < Thread.MIN_PRIORITY || priority > Thread.MAX_PRIORITY) {
throw new IllegalArgumentException("Priority out of range: " + priority);
}
if (priority > group.getMaxPriority()) {
priority = group.getMaxPriority();
}
this.priority = priority;
VMThread vmt = this.vmThread;
if (vmt != null) {
vmt.setPriority(priority);
}
}
/**
* Destroys this thread group and all of its subgroups. This thread group must be empty,
* indicating that all threads that had been in this thread group have since stopped.
*
* <p>First, the <code>checkAccess</code> method of this thread group is called with no arguments;
* this may result in a security exception.
*
* @exception IllegalThreadStateException if the thread group is not empty or if the thread group
* has already been destroyed.
* @exception SecurityException if the current thread cannot modify this thread group.
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
public final void destroy() {
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot;
synchronized (this) {
checkAccess();
if (destroyed || (nthreads > 0)) {
throw new IllegalThreadStateException();
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = new ThreadGroup[ngroupsSnapshot];
System.arraycopy(groups, 0, groupsSnapshot, 0, 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);
}
}
/**
* Called by the Java Virtual Machine when a thread in this thread group stops because of an
* uncaught exception.
*
* <p>The <code>uncaughtException</code> method of <code>ThreadGroup</code> does the following:
*
* <ul>
* <li>If this thread group has a parent thread group, the <code>uncaughtException</code> method
* of that parent is called with the same two arguments.
* <li>Otherwise, this method determines if the <code>Throwable</code> argument is an instance
* of <code>ThreadDeath</code>. If so, nothing special is done. Otherwise, the <code>
* Throwable</code>'s <code>printStackTrace</code> method is called to print a stack
* backtrace to the standard error stream.
* </ul>
*
* <p>Applications can override this method in subclasses of <code>ThreadGroup</code> to provide
* alternative handling of uncaught exceptions.
*
* @param t the thread that is about to exit.
* @param e the uncaught exception.
* @see java.lang.System#err
* @see java.lang.ThreadDeath
* @see java.lang.Throwable#printStackTrace(java.io.PrintStream)
* @since JDK1.0
*/
public void uncaughtException(Thread t, Throwable e) {
if (parent != null) {
parent.uncaughtException(t, e);
} else if (!(e instanceof ThreadDeath)) {
if (System.err != null) {
/* can be null at startup */
e.printStackTrace(System.err);
}
}
}
/**
* Initializes a new, existing Thread object with a runnable object, the given name and belonging
* to the ThreadGroup passed as parameter. This is the method that the several public constructors
* delegate their work to.
*
* @param group ThreadGroup to which the new Thread will belong
* @param runnable a java.lang.Runnable whose method <code>run</code> will be executed by the new
* Thread
* @param threadName Name for the Thread being created
* @param stackSize Platform dependent stack size
* @throws IllegalThreadStateException if <code>group.destroy()</code> has already been done
* @see java.lang.ThreadGroup
* @see java.lang.Runnable
*/
private void create(ThreadGroup group, Runnable runnable, String threadName, long stackSize) {
Thread currentThread = Thread.currentThread();
if (group == null) {
group = currentThread.getThreadGroup();
}
if (group.isDestroyed()) {
throw new IllegalThreadStateException("Group already destroyed");
}
this.group = group;
synchronized (Thread.class) {
id = ++Thread.count;
}
if (threadName == null) {
this.name = "Thread-" + id;
} else {
this.name = threadName;
}
this.target = runnable;
this.stackSize = stackSize;
this.priority = currentThread.getPriority();
this.contextClassLoader = currentThread.contextClassLoader;
// Transfer over InheritableThreadLocals.
if (currentThread.inheritableValues != null) {
inheritableValues = new ThreadLocal.Values(currentThread.inheritableValues);
}
// add ourselves to our ThreadGroup of choice
this.group.addThread(this);
}
public static void main(String[] args) {
ThreadGroup group = new ThreadGroup("demo");
for (int i = 0; i < 3; i++) {
new Thread(
group,
new Runnable() {
public void run() {
System.out.print("");
}
})
.start();
}
group.list();
int count = group.activeCount(); // 获得线程组中活动的线程
System.out.println(count);
Thread threads[] = new Thread[group.activeCount()];
group.enumerate(threads); // 将当前线程组中活动的线程复制到一个线程数组中去。
for (Thread thread : threads) {
System.out.println(thread.getName());
}
ThreadGroup parent = group.getParent();
parent.list();
ThreadGroup parent2 = parent.getParent();
parent2.list();
}
/**
* Returns a string containing a concise, human-readable description of the Thread. It includes
* the Thread's name, priority, and group name.
*
* @return a printable representation for the receiver.
*/
@Override
public String toString() {
return "Thread[" + name + "," + priority + "," + group.getName() + "]";
}
/**
* Returns the parent of this thread group.
*
* <p>First, if the parent is not <code>null</code>, the <code>checkAccess</code> method of the
* parent thread group is called with no arguments; this may result in a security exception.
*
* @return the parent of this thread group. The top-level thread group is the only thread group
* whose parent is <code>null</code>.
* @exception SecurityException if the current thread cannot modify this thread group.
* @see java.lang.ThreadGroup#checkAccess()
* @see java.lang.SecurityException
* @see java.lang.RuntimePermission
* @since JDK1.0
*/
public final ThreadGroup getParent() {
if (parent != null) parent.checkAccess();
return parent;
}
