javax.realtime.enforce

Class ImmortalConstraint

java.lang.Object

javax.realtime.enforce.ResourceConstraint<ImmortalConstraint>

javax.realtime.enforce.ImmortalConstraint

public class ImmortalConstraint
extends ResourceConstraint<ImmortalConstraint>

A constraint to limit the amount of immortal memory available to a task.

Since:

RTSJ 2.0

Constructor Summary

Constructors

Constructor and Description
ImmortalConstraint(RealtimeThreadGroup group, long limit) Create a new contraint for the given RealtimeThreadGroup.

Method Summary

Modifier and Type	Method and Description
long	available() Determine how much of the resource are available for use.
static ImmortalConstraint	currentConstraint() Determine the processing constraint for the current execution context.
static ImmortalConstraint	currentConstraint(Thread thread) Determine the processing constraint for the give execution context.
static ImmortalConstraint	currentConstraint(ThreadGroup group) Determine the processing constraint for the give execution context.
protected void	finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
long	getBudget() Determine the total amount of a memory under the control of this resource constraint instance.
static ImmortalConstraint	getRootConstraint() Get the root instance for this constraint type.
boolean	isEnforcing() Determine whether or not enforcing is in effect.
void	start() Start applying this constraint to is tasks.
void	stop() Stop applying this constraint to is tasks.
long	used() Determine how much of the resource have been used of the amount available.

Methods inherited from class javax.realtime.enforce.ResourceConstraint

getNotificationHandler, getParent, getRealtimeThreadGroup, governs, governs, governs, setNotificationHandler, visitBorrowers, visitGoverned

Methods inherited from class java.lang.Object

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

Constructor Detail

ImmortalConstraint

public ImmortalConstraint(RealtimeThreadGroup group,
                          long limit)

Create a new contraint for the given RealtimeThreadGroup.

Parameters:

group - The RealtimeThreadGroup to govern.

limit - the amount of memory to take from its parent to manage.

Method Detail

getRootConstraint

public static ImmortalConstraint getRootConstraint()

Get the root instance for this constraint type.

Returns:

the root constraint.

currentConstraint

public static ImmortalConstraint currentConstraint()

Determine the processing constraint for the current execution context.

Returns:

the constraint for this context.

currentConstraint

public static ImmortalConstraint currentConstraint(Thread thread)

Determine the processing constraint for the give execution context.

Parameters:

thread - The given execution context.

Returns:

the constraint for this context.

currentConstraint

public static ImmortalConstraint currentConstraint(ThreadGroup group)

Determine the processing constraint for the give execution context.

Parameters:

thread - The given execution context.

Returns:

the constraint for this context.

isEnforcing

public boolean isEnforcing()

Determine whether or not enforcing is in effect.

Overrides:

isEnforcing in class ResourceConstraint<ImmortalConstraint>

Returns:

true when yes and false when not.

start

public void start()

Start applying this constraint to is tasks.

Specified by:

start in class ResourceConstraint<ImmortalConstraint>

stop

public void stop()

Stop applying this constraint to is tasks.

Specified by:

stop in class ResourceConstraint<ImmortalConstraint>

getBudget

public long getBudget()

Determine the total amount of a memory under the control of this resource constraint instance.

Returns:

the total amount under control of this instance in bytes.

used

public long used()

Determine how much of the resource have been used of the amount available.

Returns:

the amount used in number of bytes.

available

public long available()

Determine how much of the resource are available for use.

Returns:

the amount used in number of bytes.

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 ResourceConstraint<ImmortalConstraint>

Throws:

Throwable - the Exception raised by this method

See Also:

WeakReference, PhantomReference