Java example source code file (ThreadGroup.java)
The ThreadGroup.java Java example source code/*
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
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*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.lang;
import java.io.PrintStream;
import java.util.Arrays;
import sun.misc.VM;
/**
* A thread group represents a set of threads. In addition, a thread
* group can also include other thread groups. The thread groups form
* a tree in which every thread group except the initial thread group
* has a parent.
* <p>
* A thread is allowed to access information about its own thread
* group, but not to access information about its thread group's
* parent thread group or any other thread groups.
*
* @author unascribed
* @since JDK1.0
*/
/* The locking strategy for this code is to try to lock only one level of the
* tree wherever possible, but otherwise to lock from the bottom up.
* That is, from child thread groups to parents.
* This has the advantage of limiting the number of locks that need to be held
* and in particular avoids having to grab the lock for the root thread group,
* (or a global lock) which would be a source of contention on a
* multi-processor system with many thread groups.
* This policy often leads to taking a snapshot of the state of a thread group
* and working off of that snapshot, rather than holding the thread group locked
* while we work on the children.
*/
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[];
/**
* Creates an empty Thread group that is not in any Thread group.
* This method is used to create the system Thread group.
*/
private ThreadGroup() { // called from C code
this.name = "system";
this.maxPriority = Thread.MAX_PRIORITY;
this.parent = null;
}
/**
* Constructs a new thread group. The parent of this new group is
* the thread group of the currently running thread.
* <p>
* The <code>checkAccess method of the parent thread group is
* called with no arguments; this may result in a security exception.
*
* @param name the name of the new thread group.
* @exception SecurityException if the current thread cannot create a
* thread in the specified thread group.
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
public ThreadGroup(String name) {
this(Thread.currentThread().getThreadGroup(), name);
}
/**
* Creates a new thread group. The parent of this new group is the
* specified thread group.
* <p>
* The <code>checkAccess 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.
* @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) {
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);
}
/*
* @throws NullPointerException if the parent argument is {@code null}
* @throws SecurityException if the current thread cannot create a
* thread in the specified thread group.
*/
private static Void checkParentAccess(ThreadGroup parent) {
parent.checkAccess();
return null;
}
/**
* Returns the name of this thread group.
*
* @return the name of this thread group.
* @since JDK1.0
*/
public final String getName() {
return name;
}
/**
* Returns the parent of this thread group.
* <p>
* First, if the parent is not <code>null, the
* <code>checkAccess 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.
* @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;
}
/**
* Returns the maximum priority of this thread group. Threads that are
* part of this group cannot have a higher priority than the maximum
* priority.
*
* @return the maximum priority that a thread in this thread group
* can have.
* @see #setMaxPriority
* @since JDK1.0
*/
public final int getMaxPriority() {
return maxPriority;
}
/**
* Tests if this thread group is a daemon thread group. A
* daemon thread group is automatically destroyed when its last
* thread is stopped or its last thread group is destroyed.
*
* @return <code>true if this thread group is a daemon thread group;
* <code>false otherwise.
* @since JDK1.0
*/
public final boolean isDaemon() {
return daemon;
}
/**
* Tests if this thread group has been destroyed.
*
* @return true if this object is destroyed
* @since JDK1.1
*/
public synchronized boolean isDestroyed() {
return destroyed;
}
/**
* Changes the daemon status of this thread group.
* <p>
* First, the <code>checkAccess method of this thread group is
* called with no arguments; this may result in a security exception.
* <p>
* A daemon thread group is automatically destroyed when its last
* thread is stopped or its last thread group is destroyed.
*
* @param daemon if <code>true, marks this thread group as
* a daemon thread group; otherwise, marks this
* thread group as normal.
* @exception SecurityException if the current thread cannot modify
* this thread group.
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
public final void setDaemon(boolean daemon) {
checkAccess();
this.daemon = daemon;
}
/**
* Sets the maximum priority of the group. Threads in the thread
* group that already have a higher priority are not affected.
* <p>
* First, the <code>checkAccess method of this thread group is
* called with no arguments; this may result in a security exception.
* <p>
* If the <code>pri argument is less than
* {@link Thread#MIN_PRIORITY} or greater than
* {@link Thread#MAX_PRIORITY}, the maximum priority of the group
* remains unchanged.
* <p>
* Otherwise, the priority of this ThreadGroup object is set to the
* smaller of the specified <code>pri and the maximum permitted
* priority of the parent of this thread group. (If this thread group
* is the system thread group, which has no parent, then its maximum
* priority is simply set to <code>pri.) Then this method is
* called recursively, with <code>pri as its argument, for
* every thread group that belongs to this thread group.
*
* @param pri the new priority of the thread group.
* @exception SecurityException if the current thread cannot modify
* this thread group.
* @see #getMaxPriority
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
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);
}
}
/**
* Tests if this thread group is either the thread group
* argument or one of its ancestor thread groups.
*
* @param g a thread group.
* @return <code>true if this thread group is the thread group
* argument or one of its ancestor thread groups;
* <code>false otherwise.
* @since JDK1.0
*/
public final boolean parentOf(ThreadGroup g) {
for (; g != null ; g = g.parent) {
if (g == this) {
return true;
}
}
return false;
}
/**
* Determines if the currently running thread has permission to
* modify this thread group.
* <p>
* If there is a security manager, its <code>checkAccess method
* is called with this thread group as its argument. This may result
* in throwing a <code>SecurityException.
*
* @exception SecurityException if the current thread is not allowed to
* access this thread group.
* @see java.lang.SecurityManager#checkAccess(java.lang.ThreadGroup)
* @since JDK1.0
*/
public final void checkAccess() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkAccess(this);
}
}
/**
* Returns an estimate of the number of active threads in this thread
* group and its subgroups. Recursively iterates over all subgroups in
* this 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 this thread
* group and in any other thread group that has this thread
* group as an ancestor
*
* @since JDK1.0
*/
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;
}
/**
* Copies into the specified array every active thread in this
* thread group and its subgroups.
*
* <p> An invocation of this method behaves in exactly the same
* way as the invocation
*
* <blockquote>
* {@linkplain #enumerate(Thread[], boolean) enumerate}{@code (list, true)}
* </blockquote>
*
* @param list
* an array into which to put the list of threads
*
* @return the number of threads put into the array
*
* @throws SecurityException
* if {@linkplain #checkAccess checkAccess} determines that
* the current thread cannot access this thread group
*
* @since JDK1.0
*/
public int enumerate(Thread list[]) {
checkAccess();
return enumerate(list, 0, true);
}
/**
* Copies into the specified array every active thread in this
* thread group. If {@code recurse} is {@code true},
* this method recursively enumerates all subgroups of this
* thread group and references to every active thread in these
* subgroups are also included. If the array is too short to
* hold all the threads, the extra threads are silently ignored.
*
* <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 this thread group, the caller should verify that the returned
* int value is strictly less than the length of {@code list}.
*
* <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 list
* an array into which to put the list of threads
*
* @param recurse
* if {@code true}, recursively enumerate all subgroups of this
* thread group
*
* @return the number of threads put into the array
*
* @throws SecurityException
* if {@linkplain #checkAccess checkAccess} determines that
* the current thread cannot access this thread group
*
* @since JDK1.0
*/
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;
}
/**
* Returns an estimate of the number of active groups in this
* thread group and its subgroups. Recursively iterates over
* all subgroups in this thread group.
*
* <p> The value returned is only an estimate because the number of
* thread groups may change dynamically while this method traverses
* internal data structures. This method is intended primarily for
* debugging and monitoring purposes.
*
* @return the number of active thread groups with this thread group as
* an ancestor
*
* @since JDK1.0
*/
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;
}
/**
* Copies into the specified array references to every active
* subgroup in this thread group and its subgroups.
*
* <p> An invocation of this method behaves in exactly the same
* way as the invocation
*
* <blockquote>
* {@linkplain #enumerate(ThreadGroup[], boolean) enumerate}{@code (list, true)}
* </blockquote>
*
* @param list
* an array into which to put the list of thread groups
*
* @return the number of thread groups put into the array
*
* @throws SecurityException
* if {@linkplain #checkAccess checkAccess} determines that
* the current thread cannot access this thread group
*
* @since JDK1.0
*/
public int enumerate(ThreadGroup list[]) {
checkAccess();
return enumerate(list, 0, true);
}
/**
* Copies into the specified array references to every active
* subgroup in this thread group. If {@code recurse} is
* {@code true}, this method recursively enumerates all subgroups of this
* thread group and references to every active thread group in these
* subgroups are also included.
*
* <p> An application might use the
* {@linkplain #activeGroupCount activeGroupCount} method to
* get an estimate of how big the array should be, however <i>if the
* array is too short to hold all the thread groups, the extra thread
* groups are silently ignored.</i> If it is critical to obtain every
* active subgroup in this thread group, the caller should verify that
* the returned int value is strictly less than the length of
* {@code list}.
*
* <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 list
* an array into which to put the list of thread groups
*
* @param recurse
* if {@code true}, recursively enumerate all subgroups
*
* @return the number of thread groups put into the array
*
* @throws SecurityException
* if {@linkplain #checkAccess checkAccess} determines that
* the current thread cannot access this thread group
*
* @since JDK1.0
*/
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;
}
/**
* Stops all threads in this thread group.
* <p>
* First, the <code>checkAccess method of this thread group is
* called with no arguments; this may result in a security exception.
* <p>
* This method then calls the <code>stop method on all the
* threads in this thread group and in all of its subgroups.
*
* @exception SecurityException if the current thread is not allowed
* to access this thread group or any of the threads in
* the thread group.
* @see java.lang.SecurityException
* @see java.lang.Thread#stop()
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
* @deprecated This method is inherently unsafe. See
* {@link Thread#stop} for details.
*/
@Deprecated
public final void stop() {
if (stopOrSuspend(false))
Thread.currentThread().stop();
}
/**
* Interrupts all threads in this thread group.
* <p>
* First, the <code>checkAccess method of this thread group is
* called with no arguments; this may result in a security exception.
* <p>
* This method then calls the <code>interrupt method on all the
* threads in this thread group and in all of its subgroups.
*
* @exception SecurityException if the current thread is not allowed
* to access this thread group or any of the threads in
* the thread group.
* @see java.lang.Thread#interrupt()
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since 1.2
*/
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();
}
}
/**
* Suspends all threads in this thread group.
* <p>
* First, the <code>checkAccess method of this thread group is
* called with no arguments; this may result in a security exception.
* <p>
* This method then calls the <code>suspend method on all the
* threads in this thread group and in all of its subgroups.
*
* @exception SecurityException if the current thread is not allowed
* to access this thread group or any of the threads in
* the thread group.
* @see java.lang.Thread#suspend()
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
* @deprecated This method is inherently deadlock-prone. See
* {@link Thread#suspend} for details.
*/
@Deprecated
@SuppressWarnings("deprecation")
public final void suspend() {
if (stopOrSuspend(true))
Thread.currentThread().suspend();
}
/**
* Helper method: recursively stops or suspends (as directed by the
* boolean argument) all of the threads in this thread group and its
* subgroups, except the current thread. This method returns true
* if (and only if) the current thread is found to be in this thread
* group or one of its subgroups.
*/
@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;
}
/**
* Resumes all threads in this thread group.
* <p>
* First, the <code>checkAccess method of this thread group is
* called with no arguments; this may result in a security exception.
* <p>
* This method then calls the <code>resume method on all the
* threads in this thread group and in all of its sub groups.
*
* @exception SecurityException if the current thread is not allowed to
* access this thread group or any of the threads in the
* thread group.
* @see java.lang.SecurityException
* @see java.lang.Thread#resume()
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
* @deprecated This method is used solely in conjunction with
* <tt>Thread.suspend and ThreadGroup.suspend,
* both of which have been deprecated, as they are inherently
* deadlock-prone. See {@link Thread#suspend} for details.
*/
@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();
}
}
/**
* 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 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 = 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);
}
}
/**
* Adds the specified Thread group to this group.
* @param g the specified Thread group to be added
* @exception IllegalThreadStateException If the Thread group has been destroyed.
*/
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++;
}
}
/**
* Removes the specified Thread group from this group.
* @param g the Thread group to be removed
* @return if this Thread has already been destroyed.
*/
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();
}
}
}
/**
* Increments the count of unstarted threads in the thread group.
* Unstarted threads are not added to the thread group so that they
* can be collected if they are never started, but they must be
* counted so that daemon thread groups with unstarted threads in
* them are not destroyed.
*/
void addUnstarted() {
synchronized(this) {
if (destroyed) {
throw new IllegalThreadStateException();
}
nUnstartedThreads++;
}
}
/**
* Adds the specified thread to this thread group.
*
* <p> Note: This method is called from both library code
* and the Virtual Machine. It is called from VM to add
* certain system threads to the system thread group.
*
* @param t
* the Thread to be added
*
* @throws IllegalThreadStateException
* if the Thread group has been destroyed
*/
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--;
}
}
/**
* Notifies the group that the thread {@code t} has failed
* an attempt to start.
*
* <p> The state of this thread group is rolled back as if the
* attempt to start the thread has never occurred. The thread is again
* considered an unstarted member of the thread group, and a subsequent
* attempt to start the thread is permitted.
*
* @param t
* the Thread whose start method was invoked
*/
void threadStartFailed(Thread t) {
synchronized(this) {
remove(t);
nUnstartedThreads++;
}
}
/**
* Notifies the group that the thread {@code t} has terminated.
*
* <p> Destroy the group if all of the following conditions are
* true: this is a daemon thread group; there are no more alive
* or unstarted threads in the group; there are no subgroups in
* this thread group.
*
* @param t
* the Thread that has terminated
*/
void threadTerminated(Thread t) {
synchronized (this) {
remove(t);
if (nthreads == 0) {
notifyAll();
}
if (daemon && (nthreads == 0) &&
(nUnstartedThreads == 0) && (ngroups == 0))
{
destroy();
}
}
}
/**
* Removes the specified Thread from this group. Invoking this method
* on a thread group that has been destroyed has no effect.
*
* @param t
* the Thread to be removed
*/
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;
}
}
}
}
/**
* Prints information about this thread group to the standard
* output. This method is useful only for debugging.
*
* @since JDK1.0
*/
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);
}
}
/**
* Called by the Java Virtual Machine when a thread in this
* thread group stops because of an uncaught exception, and the thread
* does not have a specific {@link Thread.UncaughtExceptionHandler}
* installed.
* <p>
* The <code>uncaughtException method of
* <code>ThreadGroup does the following:
* <ul>
* <li>If this thread group has a parent thread group, the
* <code>uncaughtException method of that parent is called
* with the same two arguments.
* <li>Otherwise, this method checks to see if there is a
* {@linkplain Thread#getDefaultUncaughtExceptionHandler default
* uncaught exception handler} installed, and if so, its
* <code>uncaughtException method is called with the same
* two arguments.
* <li>Otherwise, this method determines if the
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