Improve AbstractRegistration.isClosed() performance

The check for the registration being closed does not need to be
ordered with other access, except close(). Using VarHandles, we
can express the check in terms for getAcquire().

Change-Id: Idf685e8adafbe102c4c65f735d872a1f4b801188
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>

diff --git a/common/concepts/src/main/java/org/opendaylight/yangtools/concepts/AbstractRegistration.java b/common/concepts/src/main/java/org/opendaylight/yangtools/concepts/AbstractRegistration.java
index f0e6238e339a54dc52f1b576ac22e601f5509178..7f43bc9f4b588fb4ac2b6a4705ff18e568c5f3dd 100644 (file)
--- a/common/concepts/src/main/java/org/opendaylight/yangtools/concepts/AbstractRegistration.java
+++ b/common/concepts/src/main/java/org/opendaylight/yangtools/concepts/AbstractRegistration.java
@@ -9,16 +9,27 @@ package org.opendaylight.yangtools.concepts;
 
 import com.google.common.base.MoreObjects;
 import com.google.common.base.MoreObjects.ToStringHelper;
-import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
 
 /**
  * Utility registration handle. It is a convenience for register-style method which can return an AutoCloseable realized
  * by a subclass of this class. Invoking the close() method triggers unregistration of the state the method installed.
  */
 public abstract class AbstractRegistration implements Registration {
-    private static final AtomicIntegerFieldUpdater<AbstractRegistration> CLOSED_UPDATER =
-            AtomicIntegerFieldUpdater.newUpdater(AbstractRegistration.class, "closed");
-    private volatile int closed = 0;
+    private static final VarHandle CLOSED;
+
+    // All access needs to go through this handle
+    @SuppressWarnings("unused")
+    private volatile byte closed;
+
+    static {
+        try {
+            CLOSED = MethodHandles.lookup().findVarHandle(AbstractRegistration.class, "closed", byte.class);
+        } catch (ReflectiveOperationException e) {
+            throw new ExceptionInInitializerError(e);
+        }
+    }
 
     /**
      * Remove the state referenced by this registration. This method is guaranteed to be called at most once.
@@ -32,12 +43,14 @@ public abstract class AbstractRegistration implements Registration {
      * @return true if the registration was closed, false otherwise.
      */
     public final boolean isClosed() {
-        return closed != 0;
+        return (byte) CLOSED.getAcquire(this) != 0;
     }
 
     @Override
     public final void close() {
-        if (CLOSED_UPDATER.compareAndSet(this, 0, 1)) {
+        // We want full setVolatile() memory semantics here, as all state before calling this method
+        // needs to be visible
+        if (CLOSED.compareAndSet(this, (byte) 0, (byte) 1)) {
             removeRegistration();
         }
     }
@@ -48,6 +61,6 @@ public abstract class AbstractRegistration implements Registration {
     }
 
     protected ToStringHelper addToStringAttributes(final ToStringHelper toStringHelper) {
-        return toStringHelper.add("closed", closed);
+        return toStringHelper.add("closed", isClosed());
     }
 }