BUG-5280: separate request sequence and transmit sequence

[controller.git] / opendaylight / md-sal / cds-access-client / src / main / java / org / opendaylight / controller / cluster / access / client / EmptyQueue.java

diff --git a/opendaylight/md-sal/cds-access-client/src/main/java/org/opendaylight/controller/cluster/access/client/EmptyQueue.java b/opendaylight/md-sal/cds-access-client/src/main/java/org/opendaylight/controller/cluster/access/client/EmptyQueue.java
new file mode 100644 (file)
index 0000000..31d863a
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+++ b/opendaylight/md-sal/cds-access-client/src/main/java/org/opendaylight/controller/cluster/access/client/EmptyQueue.java
@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2016 Cisco Systems, Inc. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.opendaylight.controller.cluster.access.client;
+
+import java.util.AbstractQueue;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.Queue;
+
+/**
+ * A specialized always-empty implementation of {@link java.util.Queue}. This implementation will always refuse new
+ * elements in its {@link #offer(Object)} method.
+
+ * @author Robert Varga
+ *
+ * @param <E> the type of elements held in this collection
+ */
+// TODO: move this class into yangtools.util
+final class EmptyQueue<T> extends AbstractQueue<T> {
+    private static final EmptyQueue<?> INSTANCE = new EmptyQueue<>();
+
+    private EmptyQueue() {
+        // No instances
+    }
+
+    @SuppressWarnings("unchecked")
+    static <T> Queue<T> getInstance() {
+        return (Queue<T>) INSTANCE;
+    }
+
+    @Override
+    public boolean offer(final T e) {
+        return false;
+    }
+
+    @Override
+    public T poll() {
+        return null;
+    }
+
+    @Override
+    public T peek() {
+        return null;
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return Collections.emptyIterator();
+    }
+
+    @Override
+    public int size() {
+        return 0;
+    }
+}
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