Java suspend all threads

Class 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 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.

Thread groups and virtual threads

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.

Constructor Summary

Method Summary

This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release.

This method originally indicated if the thread group is a daemon thread group that is automatically destroyed when its last thread terminates.

This method originally configured whether the thread group is a daemon thread group that is automatically destroyed when its last thread terminates.

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.

Methods declared in class java.lang.Object

Constructor Details

ThreadGroup

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.

ThreadGroup

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.

Method Details

getName

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.

getMaxPriority

Returns the maximum priority of this thread group. This is the maximum priority for new threads created in the thread group.

isDaemon

This method originally indicated if the thread group is a daemon thread group that is automatically destroyed when its last thread terminates. The concept of daemon thread group no longer exists. A thread group is eligible to be GC’ed when there are no live threads in the group and it is otherwise unreachable.

isDestroyed

This method originally indicated if the thread group is destroyed. The ability to destroy a thread group and the concept of a destroyed thread group no longer exists. A thread group is eligible to be GC’ed when there are no live threads in the group and it is otherwise unreachable.

setDaemon

This method originally configured whether the thread group is a daemon thread group that is automatically destroyed when its last thread terminates. The concept of daemon thread group no longer exists. A thread group is eligible to be GC’ed when there are no live threads in the group and it is otherwise unreachable.

Sets the daemon status of this thread group. The daemon status is not used for anything. First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

setMaxPriority

Sets the maximum priority of the group. The maximum priority of the ThreadGroup for virtual threads is 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.

parentOf

checkAccess

This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. Consequently, this method is also deprecated and subject to removal. There is no replacement for the Security Manager or this method.

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 .

activeCount

Returns an estimate of the number of live platform 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.

enumerate

Copies into the specified array every live platform 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

Copies into the specified array every live platform 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.

activeGroupCount

Returns an estimate of the number of 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.

enumerate

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

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.

stop

This method was originally specified to stop all threads in the thread group. It was inherently unsafe.

interrupt

suspend

resume

destroy

This method was originally specified to destroy an empty thread group. The ability to explicitly destroy a thread group no longer exists. A thread group is eligible to be GC’ed when there are no live threads in the group and it is otherwise unreachable.

list

Prints information about this thread group to the standard output. This method is useful only for debugging.

uncaughtException

• 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 default uncaught exception handler installed, and if so, its uncaughtException method is called with the same two arguments.
• 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.

allowThreadSuspension

This method was originally intended for controlling suspension in low memory conditions. It was never specified.

toString

Report a bug or suggest an enhancement
For further API reference and developer documentation see the Java SE Documentation, which contains more detailed, developer-targeted descriptions with conceptual overviews, definitions of terms, workarounds, and working code examples. Other versions.
Java is a trademark or registered trademark of Oracle and/or its affiliates in the US and other countries.
Copyright © 1993, 2023, Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.
All rights reserved. Use is subject to license terms and the documentation redistribution policy.

Источник