1 files changed, 89 insertions, 0 deletions
diff --git a/zookeeper-server/src/main/java/org/apache/zookeeper/server/watch/WatchStats.java b/zookeeper-server/src/main/java/org/apache/zookeeper/server/watch/WatchStats.java
new file mode 100644
index 000000000..fd0c0259e
--- /dev/null
+++ b/zookeeper-server/src/main/java/org/apache/zookeeper/server/watch/WatchStats.java
@@ -0,0 +1,89 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.zookeeper.server.watch;
+
+/**
+ * Statistics for multiple different watches on one node.
+ */
+public final class WatchStats {
+    private static final WatchStats[] WATCH_STATS = new WatchStats[] {
+            new WatchStats(0), // NONE
+            new WatchStats(1), // STANDARD
+            new WatchStats(2), // PERSISTENT
+            new WatchStats(3), // STANDARD + PERSISTENT
+            new WatchStats(4), // PERSISTENT_RECURSIVE
+            new WatchStats(5), // STANDARD + PERSISTENT_RECURSIVE
+            new WatchStats(6), // PERSISTENT + PERSISTENT_RECURSIVE
+            new WatchStats(7), // STANDARD + PERSISTENT + PERSISTENT_RECURSIVE
+    };
+
+    /**
+     * Stats that have no watchers attached.
+     *
+     * <p>This could be used as start point to compute new stats using {@link #addMode(WatcherMode)}.
+     */
+    public static final WatchStats NONE = WATCH_STATS[0];
+
+    private final int flags;
+
+    private WatchStats(int flags) {
+        this.flags = flags;
+    }
+
+    private static int modeToFlag(WatcherMode mode) {
+        return 1 << mode.ordinal();
+    }
+
+    /**
+     * Compute stats after given mode attached to node.
+     *
+     * @param mode watcher mode
+     * @return a new stats if given mode is not attached to this node before, otherwise old stats
+     */
+    public WatchStats addMode(WatcherMode mode) {
+        int flags = this.flags | modeToFlag(mode);
+        return WATCH_STATS[flags];
+    }
+
+    /**
+     * Compute stats after given mode removed from node.
+     *
+     * @param mode watcher mode
+     * @return null if given mode is the last attached mode, otherwise a new stats
+     */
+    public WatchStats removeMode(WatcherMode mode) {
+        int mask = ~modeToFlag(mode);
+        int flags = this.flags & mask;
+        if (flags == 0) {
+            return NONE;
+        }
+        return WATCH_STATS[flags];
+    }
+
+    /**
+     * Check whether given mode is attached to this node.
+     *
+     * @param mode watcher mode
+     * @return true if given mode is attached to this node.
+     */
+    public boolean hasMode(WatcherMode mode) {
+        int flags = modeToFlag(mode);
+        return (this.flags & flags) != 0;
+    }
+}