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Class java.lang.ThreadGroup
java.lang.Object
|
+----java.lang.ThreadGroup
- public class ThreadGroup
- extends Object
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.
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.
-
ThreadGroup(String)
- Constructs a new thread group.
-
ThreadGroup(ThreadGroup, String)
- Creates a new thread group.
-
activeCount()
- Returns an estimate of the number of active threads in this
thread group.
-
activeGroupCount()
- Returns an estimate of the number of active groups in this
thread group.
-
allowThreadSuspension(boolean)
- Used by VM to control lowmem implicit suspension.
-
checkAccess()
- Determines if the currently running thread has permission to
modify this thread group.
-
destroy()
- Destroys this thread group and all of its subgroups.
-
enumerate(Thread[])
- Copies into the specified array every active thread in this
thread group and its subgroups.
-
enumerate(Thread[], boolean)
- Copies into the specified array every active thread in this
thread group.
-
enumerate(ThreadGroup[])
- Copies into the specified array references to every active
subgroup in this thread group.
-
enumerate(ThreadGroup[], boolean)
- Copies into the specified array references to every active
subgroup in this thread group.
-
getMaxPriority()
- Returns the maximum priority of this thread group.
-
getName()
- Returns the name of this thread group.
-
getParent()
- Returns the parent of this thread group.
-
isDaemon()
- Tests if this thread group is a daemon thread group.
-
isDestroyed()
- Tests if this thread group has been destroyed.
-
list()
- Prints information about this thread group to the standard
output.
-
parentOf(ThreadGroup)
- Tests if this thread group is either the thread group
argument or one of its ancestor thread groups.
-
resume()
- Resumes all processes in this thread group.
-
setDaemon(boolean)
- Changes the daemon status of this thread group.
-
setMaxPriority(int)
- Sets the maximum priority of the group.
-
stop()
- Stops all processes in this thread group.
-
suspend()
- Suspends all processes in this thread group.
-
toString()
- Returns a string representation of this Thread group.
-
uncaughtException(Thread, Throwable)
- Called by the Java Virtual Machine when a thread in this
thread group stops because of an uncaught exception.
ThreadGroup
public ThreadGroup(String name)
- Constructs a new thread group. The parent of this new group is
the thread group of the currently running thread.
- Parameters:
- name - the name of the new thread group.
ThreadGroup
public ThreadGroup(ThreadGroup parent,
String name)
- Creates a new thread group. The parent of this new group is the
specified thread group.
The checkAccess
method of the parent thread group is
called with no arguments; this may result in a security exception.
- Parameters:
- parent - the parent thread group.
- name - the name of the new thread group.
- Throws: NullPointerException
- if the thread group argument is
null
.
- Throws: SecurityException
- if the current thread cannot create a
thread in the specified thread group.
- See Also:
- SecurityException, checkAccess
getName
public final String getName()
- Returns the name of this thread group.
- Returns:
- the name of this thread group.
getParent
public final ThreadGroup getParent()
- Returns the parent of this thread group.
- Returns:
- the parent of this thread group. The top-level thread group
is the only thread group whose parent is
null
.
getMaxPriority
public final int getMaxPriority()
- Returns the maximum priority of this thread group. Threads that are
part of this group cannot have a higher priority than the maximum
priority.
- Returns:
- the maximum priority that a thread in this thread group
can have.
isDaemon
public final boolean isDaemon()
- 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.
- Returns:
-
true
if this thread group is a daemon thread group;
false
otherwise.
isDestroyed
public synchronized boolean isDestroyed()
- Tests if this thread group has been destroyed.
setDaemon
public final void setDaemon(boolean daemon)
- Changes the daemon status of this thread group.
First, the checkAccess
method of this thread group is
called with no arguments; this may result in a security exception.
A daemon thread group is automatically destroyed when its last
thread is stopped or its last thread group is destroyed.
- Parameters:
- daemon - if
true
, marks this thread group as
a daemon thread group; otherwise, marks this
thread group as normal.
- Throws: SecurityException
- if the current thread cannot modify
this thread.
- See Also:
- SecurityException, checkAccess
setMaxPriority
public final void setMaxPriority(int pri)
- Sets the maximum priority of the group.
First, the checkAccess
method of this thread group is
called with no arguments; this may result in a security exception.
Threads in the thread group that already have a higher priority
are not affected.
- Parameters:
- pri - the new priority of the thread group.
- Throws: SecurityException
- if the current thread cannot modify
this thread group.
- See Also:
- SecurityException, checkAccess
parentOf
public final boolean parentOf(ThreadGroup g)
- Tests if this thread group is either the thread group
argument or one of its ancestor thread groups.
- Parameters:
- g - a thread group.
- Returns:
-
true
if this thread group is the thread group
argument or one of its ancestor thread groups;
false
otherwise.
checkAccess
public final void checkAccess()
- Determines if the currently running thread has permission to
modify this thread group.
If there is a security manager, its checkAccess
method
is called with this thread group as its argument. This may result
in throwing a SecurityException
.
- Throws: SecurityException
- if the current thread is not allowed to
access this thread group.
- See Also:
- checkAccess
activeCount
public int activeCount()
- Returns an estimate of the number of active threads in this
thread group.
- Returns:
- the number of active threads in this thread group and in any
other thread group that has this thread group as an ancestor.
enumerate
public int enumerate(Thread list[])
- Copies into the specified array every active thread in this
thread group and its subgroups.
An application should use the activeCount
method to
get an estimate of how big the array should be. If the array is
too short to hold all the threads, the extra threads are silently
ignored.
- Parameters:
- list - an array into which to place the list of threads.
- Returns:
- the number of threads put into the array.
- See Also:
- activeCount
enumerate
public int enumerate(Thread list[],
boolean recurse)
- Copies into the specified array every active thread in this
thread group. If the
recurse
flag is
true
, references to every active thread in this
thread's subgroups are also included. If the array is too short to
hold all the threads, the extra threads are silently ignored.
An application should use the activeCount
method to
get an estimate of how big the array should be.
- Parameters:
- list - an array into which to place the list of threads.
- recurse - a flag indicating whether also to include threads
in thread groups that are subgroups of this
thread group.
- Returns:
- the number of threads placed into the array.
- See Also:
- activeCount
activeGroupCount
public int activeGroupCount()
- Returns an estimate of the number of active groups in this
thread group.
- Returns:
- the number of active thread groups with this thread group as
an ancestor.
enumerate
public int enumerate(ThreadGroup list[])
- Copies into the specified array references to every active
subgroup in this thread group.
An application should use the activeGroupCount
method to get an estimate of how big the array should be. If the
array is too short to hold all the thread groups, the extra thread
groups are silently ignored.
- Parameters:
- list - an array into which to place the list of thread groups.
- Returns:
- the number of thread groups put into the array.
- See Also:
- activeGroupCount
enumerate
public int enumerate(ThreadGroup list[],
boolean recurse)
- Copies into the specified array references to every active
subgroup in this thread group. If the
recurse
flag is
true
, references to all active subgroups of the
subgroups and so forth are also included.
An application should use the activeGroupCount
method to get an estimate of how big the array should be.
- Parameters:
- list - an array into which to place the list of threads.
- recurse - a flag indicating whether to recursively enumerate
all included thread groups.
- Returns:
- the number of thread groups put into the array.
- See Also:
- activeGroupCount
stop
public final void stop()
- Stops all processes in this thread group.
First, the checkAccess
method of this thread group is
called with no arguments; this may result in a security exception.
This method then calls the stop
method on all the
threads in this thread group and in all of its subgroups.
- Throws: SecurityException
- if the current thread is not allowed
to access this thread group or any of the threads in
the thread group.
- See Also:
- SecurityException, stop, checkAccess
suspend
public final void suspend()
- Suspends all processes in this thread group.
First, the checkAccess
method of this thread group is
called with no arguments; this may result in a security exception.
This method then calls the suspend
method on all the
threads in this thread group and in all of its subgroups.
- Throws: SecurityException
- if the current thread is not allowed
to access this thread group or any of the threads in
the thread group.
- See Also:
- SecurityException, suspend, checkAccess
resume
public final void resume()
- Resumes all processes in this thread group.
First, the checkAccess
method of this thread group is
called with no arguments; this may result in a security exception.
This method then calls the resume
method on all the
threads in this thread group and in all of its sub groups.
- Throws: SecurityException
- if the current thread is not allowed to
access this thread group or any of the threads in the
thread group.
- See Also:
- SecurityException, resume, checkAccess
destroy
public final void destroy()
- 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.
- Throws: IllegalThreadStateException
- if the thread group is not
empty or if the thread group has already been destroyed.
- Throws: SecurityException
- if the current thread cannot modify this
thread group.
list
public void list()
- Prints information about this thread group to the standard
output. This method is useful only for debugging.
uncaughtException
public void uncaughtException(Thread t,
Throwable e)
- Called by the Java Virtual Machine when a thread in this
thread group stops because of an uncaught exception.
The uncaughtException
method of
ThreadGroup
does the following:
- If this thread group has a parent thread group, the
uncaughtException
method of that parent is called
with the same two arguments.
- Otherwise, this method determines if the
Throwable
argument is an instance of ThreadDeath
. If so, nothing
special is done. Otherwise, the Throwable
's
printStackTrace
method is called to print a stack
backtrace to the standard error stream.
Applications can override this method in subclasses of
ThreadGroup
to provide alternative handling of
uncaught exceptions.
- Parameters:
- t - the thread that is about to exit.
- e - the uncaught exception.
- See Also:
- err, ThreadDeath, printStackTrace
allowThreadSuspension
public boolean allowThreadSuspension(boolean b)
- Used by VM to control lowmem implicit suspension.
toString
public String toString()
- Returns a string representation of this Thread group.
- Returns:
- a string representation of this thread group.
- Overrides:
- toString in class Object
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