Java Reference
In-Depth Information
ence queue. The phantom reference and the resource object are then
stored into a map. This map serves two purposes: First, it keeps all the
phantom reference objects reachable; second it provides an easy way to
find the actual resource object associated with each phantom reference.
(The alternative would be to subclass
PhantomReference
and store the
Re-
source
object in a field.)
The resource manager uses a separate "reaper" thread to process re-
sources when the key has become unreachable. The
shutdown
method
"turns off" the resource manager by allowing the reaper to terminate
(in response to the interruption) and causing
geTResource
calls to throw
IllegalStateException
. In this simple design, any references enqueued
after shutdown will not be processed. The actual reaper thread looks like
this:
class ReaperThread extends Thread {
public void run() {
// run until interrupted
while (true) {
try {
Reference<?> ref = queue.remove();
Resource res = null;
synchronized(ResourceManager.this) {
res = refs.get(ref);
refs.remove(ref);
}
res.release();
ref.clear();
}
catch (InterruptedException ex) {
break; // all done
}
}
}
}
