Class ObservableSync
- java.lang.Object
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- EDU.oswego.cs.dl.util.concurrent.ObservableSync
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- All Implemented Interfaces:
Sync
public class ObservableSync extends Object implements Sync
The ObservableSync class performs no synchronization itself, but invokes event-style messages to other observer objects upon invocation of Sync methods. These observers typically perform monitoring, logging, or other bookkeeping operations surrounding the object being managed by this Sync object.Because ObservableSync does not itself perform any synchronization control, the attempt operation always succeeds. This class is typically used (via LayeredSync) as a wrapper around those that do perform synchronization control.
This class is based around a standard Observer design pattern. It is not hard to convert this to instead use a Listener design (as seen in AWT and JavaBeans), by defining associated EventObjects and forwarding them.
- See Also:
LayeredSync
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Nested Class Summary
Nested Classes Modifier and Type Class Description static interface
ObservableSync.SyncObserver
Interface for objects that observe ObservableSyncs.
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Field Summary
Fields Modifier and Type Field Description protected Object
arg_
protected CopyOnWriteArraySet
observers_
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Fields inherited from interface EDU.oswego.cs.dl.util.concurrent.Sync
ONE_CENTURY, ONE_DAY, ONE_HOUR, ONE_MINUTE, ONE_SECOND, ONE_WEEK, ONE_YEAR
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Constructor Summary
Constructors Constructor Description ObservableSync(Object notificationArgument)
Create an ObservableSync that uses the supplied argument for all notifications.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
acquire()
Wait (possibly forever) until successful passage.void
attach(ObservableSync.SyncObserver obs)
Add obs to the set of observersboolean
attempt(long msecs)
Wait at most msecs to pass; report whether passed.void
detach(ObservableSync.SyncObserver obs)
Remove obs from the set of observers.Object
getNotificationArgument()
Return the argument used for notificationsIterator
observers()
Return an iterator that can be used to traverse through current set of observersvoid
release()
Potentially enable others to pass.Object
setNotificationArgument(Object notificationArg)
Set the argument used for notifications.
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Field Detail
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observers_
protected final CopyOnWriteArraySet observers_
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arg_
protected Object arg_
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Constructor Detail
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ObservableSync
public ObservableSync(Object notificationArgument)
Create an ObservableSync that uses the supplied argument for all notifications. The argument is typically an object that is being managed by this Sync object.
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Method Detail
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getNotificationArgument
public Object getNotificationArgument()
Return the argument used for notifications
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setNotificationArgument
public Object setNotificationArgument(Object notificationArg)
Set the argument used for notifications.- Returns:
- the previous value of this argument
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acquire
public void acquire()
Description copied from interface:Sync
Wait (possibly forever) until successful passage. Fail only upon interuption. Interruptions always result in `clean' failures. On failure, you can be sure that it has not been acquired, and that no corresponding release should be performed. Conversely, a normal return guarantees that the acquire was successful.
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attempt
public boolean attempt(long msecs)
Description copied from interface:Sync
Wait at most msecs to pass; report whether passed.The method has best-effort semantics: The msecs bound cannot be guaranteed to be a precise upper bound on wait time in Java. Implementations generally can only attempt to return as soon as possible after the specified bound. Also, timers in Java do not stop during garbage collection, so timeouts can occur just because a GC intervened. So, msecs arguments should be used in a coarse-grained manner. Further, implementations cannot always guarantee that this method will return at all without blocking indefinitely when used in unintended ways. For example, deadlocks may be encountered when called in an unintended context.
- Specified by:
attempt
in interfaceSync
- Parameters:
msecs
- the number of milleseconds to wait. An argument less than or equal to zero means not to wait at all. However, this may still require access to a synchronization lock, which can impose unbounded delay if there is a lot of contention among threads.- Returns:
- true if acquired
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release
public void release()
Description copied from interface:Sync
Potentially enable others to pass.Because release does not raise exceptions, it can be used in `finally' clauses without requiring extra embedded try/catch blocks. But keep in mind that as with any java method, implementations may still throw unchecked exceptions such as Error or NullPointerException when faced with uncontinuable errors. However, these should normally only be caught by higher-level error handlers.
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attach
public void attach(ObservableSync.SyncObserver obs)
Add obs to the set of observers
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detach
public void detach(ObservableSync.SyncObserver obs)
Remove obs from the set of observers. No effect if not in set
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observers
public Iterator observers()
Return an iterator that can be used to traverse through current set of observers
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