javax.realtime

Class RealtimeThreadGroup

java.lang.Object

java.lang.ThreadGroup

javax.realtime.RealtimeThreadGroup

All Implemented Interfaces:

Thread.UncaughtExceptionHandler

Direct Known Subclasses:

AsynchronousControlGroup

public class RealtimeThreadGroup
extends ThreadGroup

An enhanced ThreadGroup in which a RealtimeThread instance may be started, as well as a convention Thread. Limits for what realtime scheduler and scheduling parameters can be enforced on all tasks in this group. A normal ThreadGroup may not contain an instance of Schedulable or instances of RealtimeThreadGroup. Every thread is in some instance of ThreadGroup and every instance of RealtimeThread is in some instance of RealtimeThreadGroup. This means that the main thread of a realtime Java implementation must be in an instance of this class, not a normal ThreadGroup. Please note that some of the method of this class are not thread safe, as they use methods from ThreadGroup that are not thread safe.

Since:

RTSJ 2.0

Constructor Summary

Constructors

Constructor and Description
RealtimeThreadGroup(RealtimeThreadGroup parent, String name) Creates a new realtime thread group with its scheduler type inherited from parent.
RealtimeThreadGroup(RealtimeThreadGroup parent, String name, Class<? extends Scheduler> scheduler) Creates a new realtime thread group with its scheduler type inherited from parent.
RealtimeThreadGroup(String name) Creates a new group with the current ThreadGroup instance as its parent and that parent's scheduler type for its scheduler type.

Method Summary

Modifier and Type	Method and Description
int	activeCount() Returns an estimate of the number of active threads in this thread group and its subgroups.
protected void	finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
SchedulingParameters	getMaxEligibility() Finds the upper bound on scheduling eligibility that tasks in this group may have.
Class<? extends Scheduler>	getScheduler() Finds the type of scheduler tasks in this group may use.
RealtimeThreadGroup	setMaxEligibility(SchedulingParameters parameters) Sets the upper bound on scheduling eligibility that tasks in this group may have.
void	visitThreadGroups(Consumer<ThreadGroup> visitor) Performs some operation on all the groups in the current group.
void	visitThreadGroups(Consumer<ThreadGroup> visitor, boolean recurse) Performs some operation on all the groups in the current group.
void	visitThreads(Consumer<Thread> visitor) Visit all java.lang.Thread instances contained by this group.
void	visitThreads(Consumer<Thread> visitor, boolean recurse) Visit all java.lang.Thread instances contained by this group and optionally all ThreadGroup instances contained within recursively.

Methods inherited from class java.lang.ThreadGroup

activeGroupCount, allowThreadSuspension, checkAccess, destroy, enumerate, enumerate, enumerate, enumerate, getMaxPriority, getName, getParent, interrupt, isDaemon, isDestroyed, list, parentOf, resume, setDaemon, setMaxPriority, stop, suspend, toString, uncaughtException

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

RealtimeThreadGroup

public RealtimeThreadGroup(RealtimeThreadGroup parent,
                           String name,
                           Class<? extends Scheduler> scheduler)

Creates a new realtime thread group with its scheduler type inherited from parent.

Throws:

StaticIllegalStateException - when the scheduler of parent does not subsume scheduler.

IllegalAssignmentError - when the parent ThreadGroup instance is not assignable to this.

Parameters:

parent - The parent group of the new group

name - The name of the new group

scheduler - a scheduler class limiting the schedulers allowed for scheduling group members. When null inherits from parent. Instances of java.lang.ThreadGroup do not have a scheduler and may not contain instances of RealtimeSchedulerGroup.

RealtimeThreadGroup

public RealtimeThreadGroup(RealtimeThreadGroup parent,
                           String name)
                    throws StaticIllegalStateException,
                           IllegalAssignmentError

Creates a new realtime thread group with its scheduler type inherited from parent.

Throws:

StaticIllegalStateException - when the parent ThreadGroup instance is not an instance of RealtimeThreadGroup.

IllegalAssignmentError - when the parent ThreadGroup instance is not assignable to this.

Parameters:

parent - The parent group of the new group

name - The name of the new group

RealtimeThreadGroup

public RealtimeThreadGroup(String name)
                    throws StaticIllegalStateException,
                           IllegalAssignmentError

Creates a new group with the current ThreadGroup instance as its parent and that parent's scheduler type for its scheduler type. That parent must be an instance of RealtimeThreadGroup. The primordial realtime thread group has Scheduler.class as its scheduler type.

Throws:

StaticIllegalStateException - when the parent ThreadGroup instance is not an instance of RealtimeThreadGroup.

IllegalAssignmentError - when the parent ThreadGroup instance is not assignable to this.

Parameters:

name - The name of the new group

Method Detail

activeCount

public int activeCount()

Description copied from class: ThreadGroup

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.

Overrides:

activeCount in class ThreadGroup

Returns:

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

getScheduler

public Class<? extends Scheduler> getScheduler()

Finds the type of scheduler tasks in this group may use. The scheduler of each thread must be an instance of the type returned. The default is class<Scheduler>, but it may be set to any subtype.

Returns:

the scheduler type

getMaxEligibility

public SchedulingParameters getMaxEligibility()

Finds the upper bound on scheduling eligibility that tasks in this group may have. For example, when it is an instance of PriorityParameters, it gives the maximum base priority any task in this group.

Returns:

the scheduling parameter instance denoting the upper bound on the scheduling eligibility of threads in this group, null when no such bound has been specified.

setMaxEligibility

public RealtimeThreadGroup setMaxEligibility(SchedulingParameters parameters)
                                      throws StaticIllegalStateException

Sets the upper bound on scheduling eligibility that tasks in this group may have. For example, when it is an instance of PriorityParameters, it sets the maximum base priority any task in this group may have. When a task in the group has a higher eligibility than specified in parameters, the task's eligibility is silently set to the max specified in parameters.

When the new eligibility is higher than that of any parent's eligibility, then eligibility is set to the minimum of those priorities. When a child of this RealtimeThreadGroup has a higher max eligibility than specified in parameters, its max eligibility is silently set to the max specified in parameters as if setMaxEligibility were invoked on it recursively.

When a task in this RealtimeThreadGroup or a child of this RealtimeThreadGroup has previously had its maximum eligibility reduced by a call to this method, setting a higher maximum eligibility via this method will not automatically reraise its eligibility. Please note that this method is not thread safe, as it uses methods from ThreadGroup that are not thread safe.

Throws:

StaticIllegalArgumentException - when parameters are not consistent with the scheduler type. The scheduler specified must be specific enough that only mutually compatible SchedulingParameters could be set. For example, Scheduler is not sufficient to restrict the scheduling parameters to compatible types, but PriorityScheduler does since all PriorityScheduler instances require PriorityParameters.

StaticIllegalStateException - when parameters is a higher eligibility than the max eligibility enforced by a SchedulingParameters above this in the hierarchy.

Parameters:

parameters - The SchedulingParameter instance denoting the new upper bound on the scheduling eligibility of threads in this group.

Returns:

this

visitThreads

public void visitThreads(Consumer<Thread> visitor,
                         boolean recurse)
                  throws ForEachTerminationException

Visit all java.lang.Thread instances contained by this group and optionally all ThreadGroup instances contained within recursively.

Throws:

ForEachTerminationException - when the visitor is prematurely ended.

Parameters:

visitor - A consumer of each schedulable instance.

recurse - A boolean to indicated that the visit should be recursive.

visitThreads

public void visitThreads(Consumer<Thread> visitor)
                  throws ForEachTerminationException

Visit all java.lang.Thread instances contained by this group. It is equivalent to calling visitThreads(Consumer, boolean) with recurse set to false.

Throws:

ForEachTerminationException - when the visitor is prematurely ended.

Parameters:

visitor - A consumer of each thread instance

visitThreadGroups

public void visitThreadGroups(Consumer<ThreadGroup> visitor,
                              boolean recurse)
                       throws ForEachTerminationException

Performs some operation on all the groups in the current group. The traversal of these children continues as long as visitor does not throw a ForEachTerminationException. Thus the traversal can be prematurely ended by visitor throwing this exception, e.g., when a particular element is found.

Throws:

ForEachTerminationException - when the traversal ends prematurely.

Parameters:

visitor - The function to be called on each child thread group.

recurse - A boolean to determine whether or not all subgroups are included, where true means yes and false means no.

visitThreadGroups

public void visitThreadGroups(Consumer<ThreadGroup> visitor)
                       throws ForEachTerminationException

Performs some operation on all the groups in the current group. The traversal of these children continues as long as visitor does not throw a ForEachTerminationException. Thus the traversal can be prematurely ended by visitor throwing this exception, e.g., when a particular element is found. It is equivalent to a call to visitThreadGroups(Consumer, boolean) with recurse set to false.

Throws:

ForEachTerminationException - when the traversal ends prematurely.

Parameters:

visitor - The function to be called on each child thread group.

finalize

protected void finalize()
                 throws Throwable

Description copied from class: Object

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

JamaicaVM: Realtime code requires special care when using finalize:

NOTE: The use of finalize() is strongly discouraged for realtime or safety-critical code. This method should only be used for debugging purposes. If used as a last resort to reclaim non-memory resources, finalize() should indicate the resource leak with a loud error message.

There is no guarantee that finalize() will be called, the memory management may decide not to reclaim this object's memory or to delay the call to finalize() to an unspecified point in time. It is therefore recommended never to use the finalize method to release any resources (files, network connections, non-Java memory, etc.) since releasing of these resource may be delayed perpetually.

The order of finalization is not specified, i.e., the finalize method of any two objects that become unreachable may be called in an arbitrary order. It therefore has to be assumed that when finalize() is called on an object, that the finalize() method of any object that is only reachable through this object() has been called as well or is called simultaneously by another thread.

The presence of a finalize-method in any sub-class of Object causes the reclamation of the memory of this object to be delayed until the finalize() method has been executed. The finalize() method is typically executed by the finalizer thread (that may run at a low priority) or by a call to Runtime.runFinalization().

Any code sequence that creates instances of a class that defines a finalize() method must therefore ensure that sufficient CPU time is allocated to the finalizer thread or that Runtime.runFinalization() is called regularly such that the finalize() methods can be executed and the object's memory can be reclaimed.

The finalize method itself should never block or run for long times since it would otherwise block the finalizer thread or the thread that called Runtime.runFinalization() and prevent the execution other finalize() method and consequently prevent the reclamation of these object's memory.

For objects that are allocated in a javax.realtime.memory.ScopedMemory, the finalize() methods will be called when this scoped memory is exited by the last thread. Unlike HeapMemory, which is controlled by the garbage collector, ScopedMemory provides a defined execution point for the finalize() mehods and it is therefore safer to use finalize() here.

Overrides:

finalize in class Object

Throws:

Throwable - the Exception raised by this method

See Also:

WeakReference, PhantomReference