An interface for events that know how to dispatch themselves.
By implementing this interface an event can be placed upon the event
queue and its dispatch() method will be called when the event
is dispatched, using the EventDispatchThread.
This is a very useful mechanism for avoiding deadlocks. If
a thread is executing in a critical section (i.e., it has entered
one or more monitors), calling other synchronized code may
cause deadlocks. To avoid the potential deadlocks, an
ActiveEvent can be created to run the second section of
code at later time. If there is contention on the monitor,
the second thread will simply block until the first thread
has finished its work and exited its monitors.
For security reasons, it is often desirable to use an ActiveEvent
to avoid calling untrusted code from a critical thread. For
instance, peer implementations can use this facility to avoid
making calls into user code from a system thread. Doing so avoids
potential deadlocks and denial-of-service attacks. |
