Wrapper for peer network operations that need to acquire and release resource locks.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4780 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/presents/peer/server/PeerManager.java

@@ -109,6 +109,25 @@ public class PeerManager
         public void apply (NodeObject nodeobj);
     }
 
+    /**
+     * Wraps an operation that needs a shared resource lock to be acquired before it can be
+     * performed, and released after it completes. Used by {@link #performWithLock}.
+     */
+    public static interface LockedOperation
+    {
+        /**
+         * Called when the resource lock was acquired successfully. The lock will be released
+         * immediately after this function call finishes. 
+         */
+        public void run ();
+
+        /**
+         * Called when the resource lock was not acquired successfully, with the name of the peer
+         * who is holding the lock (or null in case of a generic failure).
+         */
+        public void fail (String peerName);
+    }
+    
     /**
      * Creates a peer manager which will create a {@link NodeRepository} which will be used to
      * publish our existence and discover the other nodes.
@@ -502,6 +521,34 @@ public class PeerManager
         return null;
     }
 
+    /**
+     * Tries to acquire the resource lock and, if successful, performs the operation and releases
+     * the lock; if unsuccessful, calls the operation's failure handler. Please note: the lock will
+     * be released immediately after the operation. 
+     */
+    public void performWithLock (final NodeObject.Lock lock, final LockedOperation operation)
+    {
+        acquireLock(lock, new ResultListener<String>() {
+            public void requestCompleted (String nodeName) {
+                if (getNodeObject().nodeName.equals(nodeName)) {
+                    // lock acquired successfully - perform the operation, and release the lock.
+                    operation.run();
+                    releaseLock(lock, new ResultListener.NOOP<String>());
+                } else {
+                    // some other peer beat us to it
+                    operation.fail(nodeName);
+                    if (nodeName == null) {
+                        log.warning("Lock acquired by null? [lock=" + lock + "].");
+                    }
+                }
+            }
+            public void requestFailed (Exception cause) {
+                log.log(Level.WARNING, "Lock acquisition failed [lock=" + lock + "].", cause);
+                operation.fail(null);
+            }
+        });
+    }
+
     /**
      * Adds an observer to notify when this peer has been forced to drop a lock immediately.
      */