Thread.UncaughtExceptionHandler
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 group has a name and maximum priority. The name is specified when creating the group and cannot be changed. The group's maximum priority is the maximum priority for threads created in the group. It is initially inherited from the parent thread group but may be changed using the setMaxPriority method.
A thread group is weakly reachable from its parent group so that it is eligible for garbage collection when there are no live threads in the group and the thread group is otherwise unreachable.
Unless otherwise specified, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
The Java runtime creates a special thread group for
virtual threads. This group is returned by the
Thread.getThreadGroup
method when invoked on a virtual thread. The thread group differs to other thread groups in that its maximum priority is fixed and cannot be changed with the
setMaxPriority
method. Virtual threads are not included in the estimated thread count returned by the
activeCount
method, are not enumerated by the
enumerate
method, and are not interrupted by the
interrupt
method.
Constructors
Constructs a new thread group.
Creates a new thread group.
int
Returns an estimate of the number of
liveplatform threads in this thread group and its subgroups.
int
Returns an estimate of the number of groups in this thread group and its subgroups.
boolean
final void
final void
int
Copies into the specified array every
liveplatform thread in this thread group and its subgroups.
int
Copies into the specified array every
liveplatform thread in this thread group.
int
Copies into the specified array references to every subgroup in this thread group and its subgroups.
int
Copies into the specified array references to every subgroup in this thread group.
final int
Returns the maximum priority of this thread group.
Returns the name of this thread group.
Returns the parent of this thread group.
final void
Interrupts all
liveplatform threads in this thread group and its subgroups.
final boolean
boolean
void
Prints information about this thread group to the standard output.
final boolean
Tests if this thread group is either the thread group argument or one of its ancestor thread groups.
final void
final void
final void
Sets the maximum priority of the group.
final void
final void
Returns a string representation of this Thread group.
void
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 checkAccess method of the parent thread group is called with no arguments; this may result in a security exception.
name - the name of the new thread group, can be null
SecurityException - if the current thread cannot create a thread in the specified thread group.
The checkAccess method of the parent thread group is called with no arguments; this may result in a security exception.
parent - the parent thread group.
name - the name of the new thread group, can be null
SecurityException - if the current thread cannot create a thread in the specified thread group.
()
Returns the name of this thread group.
null
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.
null.
SecurityException - if the current thread cannot modify this thread group.
public final int getMaxPriority()
Returns the maximum priority of this thread group. This is the maximum priority for new threads created in the thread group.
Returns the daemon status of this thread group. The daemon status is not used for anything.
Returns false.
First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.
daemon - the daemon status
SecurityException - if the current thread cannot modify this thread group.
public final void setMaxPriority(int pri)
Sets the maximum priority of the group. The maximum priority of the
ThreadGroup for virtual threadsis not changed by this method (the new priority is ignored). Threads in the thread group (or subgroups) that already have a higher priority are not affected by this method.
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, the maximum priority of the group remains unchanged.
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.
pri - the new priority of the thread group.
SecurityException - if the current thread cannot modify this thread group.
Tests if this thread group is either the thread group argument or one of its ancestor thread groups.
g - a thread group, can be null
true if this thread group is the thread group argument or one of its ancestor thread groups; false otherwise.
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.
SecurityException - if the current thread is not allowed to access this thread group.
public int activeCount()
Returns an estimate of the number of
liveplatform threads in this thread group and its subgroups. Virtual threads are not included in the estimate. This method 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.
Copies into the specified array every
liveplatform thread in this thread group and its subgroups. Virtual threads are not enumerated by this method.
An invocation of this method behaves in exactly the same way as the invocation
enumerate(list, true)
list - an array into which to put the list of threads
SecurityException - if checkAccess determines that the current thread cannot access this thread group
Copies into the specified array every
liveplatform thread in this thread group. Virtual threads are not enumerated by this method. If
recurse
is
true
, this method recursively enumerates all subgroups of this thread group and references to every live platform 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 live 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.
list - an array into which to put the list of threads
recurse - if true, recursively enumerate all subgroups of this thread group
SecurityException - if checkAccess determines that the current thread cannot access this thread group
public int activeGroupCount()
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.
Copies into the specified array references to every 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)
list - an array into which to put the list of thread groups
SecurityException - if checkAccess determines that the current thread cannot access this thread group
Copies into the specified array references to every subgroup in this thread group. If
recurse
is
true
, this method recursively enumerates all subgroups of this thread group and references to every 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 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.
list - an array into which to put the list of thread groups
recurse - if true, recursively enumerate all subgroups
SecurityException - if checkAccess determines that the current thread cannot access this thread group
Throws UnsupportedOperationException.
public final void interrupt()
Interrupts all
liveplatform threads in this thread group and its subgroups.
SecurityException - if the current thread is not allowed to access this thread group or any of the threads in the thread group.
Throws UnsupportedOperationException.
Throws UnsupportedOperationException.
Does nothing.
public void list()
Prints information about this thread group to the standard output. This method is useful only for debugging.
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:
uncaughtException method of that parent is called with the same two arguments.uncaughtException method is called with the same two arguments.Throwable argument is an instance of ThreadDeath. If so, nothing special is done. Otherwise, a message containing the thread's name, as returned from the thread's getName method, and a stack backtrace, using the Throwable's printStackTrace method, is printed to the standard error stream.Applications can override this method in subclasses of ThreadGroup to provide alternative handling of uncaught exceptions.
uncaughtException in interface Thread.UncaughtExceptionHandler
t - the thread that is about to exit.
e - the uncaught exception.
Does nothing.
b - ignored
Returns a string representation of this Thread group.
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