ThreadGroup
public
class
ThreadGroup
extends Object
implements
Thread.UncaughtExceptionHandler
java.lang.Object | |
↳ | java.lang.ThreadGroup |
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.
Summary
Public constructors | |
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ThreadGroup(String name)
Constructs a new thread group. |
|
ThreadGroup(ThreadGroup parent, String name)
Creates a new thread group. |
Public methods | |
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int
|
activeCount()
Returns an estimate of the number of active threads in this thread group and its subgroups. |
int
|
activeGroupCount()
Returns an estimate of the number of active groups in this thread group and its subgroups. |
boolean
|
allowThreadSuspension(boolean b)
This method was deprecated
in API level 15.
The definition of this call depends on |
final
void
|
checkAccess()
Determines if the currently running thread has permission to modify this thread group. |
final
void
|
destroy()
Destroys this thread group and all of its subgroups. |
int
|
enumerate(ThreadGroup[] list)
Copies into the specified array references to every active subgroup in this thread group and its subgroups. |
int
|
enumerate(ThreadGroup[] list, boolean recurse)
Copies into the specified array references to every active subgroup in this thread group. |
int
|
enumerate(Thread[] list)
Copies into the specified array every active thread in this thread group and its subgroups. |
int
|
enumerate(Thread[] list, boolean recurse)
Copies into the specified array every active thread in this thread group. |
final
int
|
getMaxPriority()
Returns the maximum priority of this thread group. |
final
String
|
getName()
Returns the name of this thread group. |
final
ThreadGroup
|
getParent()
Returns the parent of this thread group. |
final
void
|
interrupt()
Interrupts all threads in this thread group. |
final
boolean
|
isDaemon()
Tests if this thread group is a daemon thread group. |
boolean
|
isDestroyed()
Tests if this thread group has been destroyed. |
void
|
list()
Prints information about this thread group to the standard output. |
final
boolean
|
parentOf(ThreadGroup g)
Tests if this thread group is either the thread group argument or one of its ancestor thread groups. |
final
void
|
resume()
This method was deprecated
in API level 15.
This method is used solely in conjunction with
|
final
void
|
setDaemon(boolean daemon)
Changes the daemon status of this thread group. |
final
void
|
setMaxPriority(int pri)
Sets the maximum priority of the group. |
final
void
|
stop()
This method was deprecated
in API level 15.
This method is inherently unsafe. See
|
final
void
|
suspend()
This method was deprecated
in API level 15.
This method is inherently deadlock-prone. See
|
String
|
toString()
Returns a string representation of this Thread group. |
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, and the thread
does not have a specific |
Inherited methods | |
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Public constructors
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.
The checkAccess
method of the parent thread group is
called with no arguments; this may result in a security exception.
Parameters | |
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name |
String : the name of the new thread group. |
Throws | |
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SecurityException |
if the current thread cannot create a thread in the specified thread group. |
See also:
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 |
ThreadGroup : the parent thread group. |
name |
String : the name of the new thread group. |
Throws | |
---|---|
NullPointerException |
if the thread group argument is
null . |
SecurityException |
if the current thread cannot create a thread in the specified thread group. |
See also:
Public methods
activeCount
public int activeCount ()
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.
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.
Returns | |
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int |
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 |
activeGroupCount
public int activeGroupCount ()
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.
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.
Returns | |
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int |
the number of active thread groups with this thread group as an ancestor |
allowThreadSuspension
public boolean allowThreadSuspension (boolean b)
This method was deprecated
in API level 15.
The definition of this call depends on suspend()
,
which is deprecated. Further, the behavior of this call
was never specified.
Used by VM to control lowmem implicit suspension.
Parameters | |
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b |
boolean : boolean to allow or disallow suspension |
Returns | |
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boolean |
true on success |
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. |
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.
First, the checkAccess
method of this thread group is
called with no arguments; this may result in a security exception.
Throws | |
---|---|
IllegalThreadStateException |
if the thread group is not empty or if the thread group has already been destroyed. |
SecurityException |
if the current thread cannot modify this thread group. |
See also:
enumerate
public int enumerate (ThreadGroup[] list)
Copies into the specified array references to every active subgroup in this thread group and its subgroups.
An invocation of this method behaves in exactly the same way as the invocation
enumerate(list, true)
Parameters | |
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list |
ThreadGroup : an array into which to put the list of thread groups |
Returns | |
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int |
the number of thread groups put into the array |
Throws | |
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SecurityException |
if checkAccess determines that the current thread cannot access this thread group |
enumerate
public int enumerate (ThreadGroup[] list, boolean recurse)
Copies into the specified array references to every active
subgroup in this thread group. If recurse
is
true
, this method recursively enumerates all subgroups of this
thread group and references to every active thread group in these
subgroups are also included.
An application might use the
activeGroupCount method to
get an estimate of how big the array should be, however if the
array is too short to hold all the thread groups, the extra thread
groups are silently ignored. 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
list
.
Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.
Parameters | |
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list |
ThreadGroup : an array into which to put the list of thread groups |
recurse |
boolean : if true , recursively enumerate all subgroups |
Returns | |
---|---|
int |
the number of thread groups put into the array |
Throws | |
---|---|
SecurityException |
if checkAccess determines that the current thread cannot access this thread group |
enumerate
public int enumerate (Thread[] list)
Copies into the specified array every active thread in this thread group and its subgroups.
An invocation of this method behaves in exactly the same way as the invocation
enumerate(list, true)
Parameters | |
---|---|
list |
Thread : an array into which to put the list of threads |
Returns | |
---|---|
int |
the number of threads put into the array |
Throws | |
---|---|
SecurityException |
if checkAccess determines that the current thread cannot access this thread group |
enumerate
public int enumerate (Thread[] list, boolean recurse)
Copies into the specified array every active thread in this
thread group. If recurse
is 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.
An application might use the activeCount
method to get an estimate of how big the array should be, however
if the array is too short to hold all the threads, the extra threads
are silently ignored. 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 list
.
Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.
Parameters | |
---|---|
list |
Thread : an array into which to put the list of threads |
recurse |
boolean : if true , recursively enumerate all subgroups of this
thread group |
Returns | |
---|---|
int |
the number of threads put into the array |
Throws | |
---|---|
SecurityException |
if checkAccess determines that the current thread cannot access this thread group |
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 | |
---|---|
int |
the maximum priority that a thread in this thread group can have. |
See also:
getName
public final String getName ()
Returns the name of this thread group.
Returns | |
---|---|
String |
the name of this thread group. |
getParent
public final ThreadGroup getParent ()
Returns the parent of this thread group.
First, if the parent is not null
, the
checkAccess
method of the parent thread group is
called with no arguments; this may result in a security exception.
Returns | |
---|---|
ThreadGroup |
the parent of this thread group. The top-level thread group
is the only thread group whose parent is null . |
Throws | |
---|---|
SecurityException |
if the current thread cannot modify this thread group. |
interrupt
public final void interrupt ()
Interrupts all threads 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 interrupt
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. |
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 | |
---|---|
boolean |
true if this thread group is a daemon thread group;
false otherwise. |
isDestroyed
public boolean isDestroyed ()
Tests if this thread group has been destroyed.
Returns | |
---|---|
boolean |
true if this object is destroyed |
list
public void list ()
Prints information about this thread group to the standard output. This method is useful only for debugging.
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 |
ThreadGroup : a thread group. |
Returns | |
---|---|
boolean |
true if this thread group is the thread group
argument or one of its ancestor thread groups;
false otherwise. |
resume
public final void resume ()
This method was deprecated
in API level 15.
This method is used solely in conjunction with
Thread.suspend
and ThreadGroup.suspend
,
both of which have been deprecated, as they are inherently
deadlock-prone. See Thread#suspend
for details.
Resumes all threads 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. |
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 |
boolean : 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 group. |
See also:
setMaxPriority
public final void setMaxPriority (int pri)
Sets the maximum priority of the group. Threads in the thread group that already have a higher priority are not affected.
First, the checkAccess
method of this thread group is
called with no arguments; this may result in a security exception.
If the pri
argument is less than
Thread#MIN_PRIORITY
or greater than
Thread#MAX_PRIORITY
, it is clamped to those values.
Otherwise, the priority of this ThreadGroup object is set to the
smaller of the specified 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 pri
.) Then this method is
called recursively, with pri
as its argument, for
every thread group that belongs to this thread group.
Parameters | |
---|---|
pri |
int : the new priority of the thread group. |
Throws | |
---|---|
SecurityException |
if the current thread cannot modify this thread group. |
stop
public final void stop ()
This method was deprecated
in API level 15.
This method is inherently unsafe. See
Thread#stop
for details.
Stops all threads 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. |
suspend
public final void suspend ()
This method was deprecated
in API level 15.
This method is inherently deadlock-prone. See
Thread#suspend
for details.
Suspends all threads 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. |
toString
public String toString ()
Returns a string representation of this Thread group.
Returns | |
---|---|
String |
a string representation of this thread group. |
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, and the thread
does not have a specific Thread.UncaughtExceptionHandler
installed.
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 checks to see if there is a
uncaught exception handler installed, and if so, its
uncaughtException
method is called with the same two arguments. - Otherwise, this method determines if the
Throwable
argument is an instance ofThreadDeath
. If so, nothing special is done. Otherwise, a message containing the thread's name, as returned from the thread'sgetName
method, and a stack backtrace, using theThrowable
'sprintStackTrace
method, is printed to the standard error stream.
Applications can override this method in subclasses of
ThreadGroup
to provide alternative handling of
uncaught exceptions.
Parameters | |
---|---|
t |
Thread : the thread that is about to exit. |
e |
Throwable : the uncaught exception. |