Package com.google.common.base

Class FinalizableReferenceQueue

java.lang.Object

com.google.common.base.FinalizableReferenceQueue

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

public class FinalizableReferenceQueue
extends java.lang.Object
implements java.io.Closeable

A reference queue with an associated background thread that dequeues references and invokes FinalizableReference.finalizeReferent() on them.

Keep a strong reference to this object until all of the associated referents have been finalized. If this object is garbage collected earlier, the backing thread will not invoke finalizeReferent() on the remaining references.

As an example of how this is used, imagine you have a class MyServer that creates a a ServerSocket, and you would like to ensure that the ServerSocket is closed even if the MyServer object is garbage-collected without calling its close method. You could use a finalizer to accomplish this, but that has a number of well-known problems. Here is how you might use this class instead:

 public class MyServer implements Closeable {
   private static final FinalizableReferenceQueue frq = new FinalizableReferenceQueue();
   // You might also share this between several objects.

   private static final Set<Reference<?>> references = Sets.newConcurrentHashSet();
   // This ensures that the FinalizablePhantomReference itself is not garbage-collected.

   private final ServerSocket serverSocket;

   private MyServer(...) {
     ...
     this.serverSocket = new ServerSocket(...);
     ...
   }

   public static MyServer create(...) {
     MyServer myServer = new MyServer(...);
     final ServerSocket serverSocket = myServer.serverSocket;
     Reference<?> reference = new FinalizablePhantomReference<MyServer>(myServer, frq) {
       @Override public void finalizeReferent() {
         references.remove(this):
         if (!serverSocket.isClosed()) {
           ...log a message about how nobody called close()...
           try {
             serverSocket.close();
           } catch (IOException e) {
             ...
           }
         }
       }
     };
     references.add(reference);
     return myServer;
   }

   @Override public void close() {
     serverSocket.close();
   }
 }
 

Since:

2.0 (imported from Google Collections Library)

Constructor Summary

Constructors

Constructor	Description
FinalizableReferenceQueue()	Constructs a new queue.

Method Summary

Modifier and Type	Method	Description
void	close()

Methods inherited from class java.lang.Object

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

Constructor Detail

FinalizableReferenceQueue

public FinalizableReferenceQueue()

Constructs a new queue.

Method Detail

close

public void close()

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable