1 files changed, 129 insertions, 0 deletions
diff --git a/framework/src/onos/utils/misc/src/main/java/org/onlab/util/SlidingWindowCounter.java b/framework/src/onos/utils/misc/src/main/java/org/onlab/util/SlidingWindowCounter.java
new file mode 100644
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--- /dev/null
+++ b/framework/src/onos/utils/misc/src/main/java/org/onlab/util/SlidingWindowCounter.java
@@ -0,0 +1,129 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed 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.onlab.util;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.stream.Collectors;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+/**
+ * Maintains a sliding window of value counts. The sliding window counter is
+ * initialized with a number of window slots. Calls to #incrementCount() will
+ * increment the value in the current window slot. Periodically the window
+ * slides and the oldest value count is dropped. Calls to #get() will get the
+ * total count for the last N window slots.
+ */
+public final class SlidingWindowCounter {
+
+    private volatile int headSlot;
+    private final int windowSlots;
+
+    private final List<AtomicLong> counters;
+
+    private final ScheduledExecutorService background;
+
+    private static final int SLIDE_WINDOW_PERIOD_SECONDS = 1;
+
+    /**
+     * Creates a new sliding window counter with the given total number of
+     * window slots.
+     *
+     * @param windowSlots total number of window slots
+     */
+    public SlidingWindowCounter(int windowSlots) {
+        checkArgument(windowSlots > 0, "Window size must be a positive integer");
+
+        this.windowSlots = windowSlots;
+        this.headSlot = 0;
+
+        // Initialize each item in the list to an AtomicLong of 0
+        this.counters = Collections.nCopies(windowSlots, 0)
+                .stream()
+                .map(AtomicLong::new)
+                .collect(Collectors.toCollection(ArrayList::new));
+
+        background = Executors.newSingleThreadScheduledExecutor();
+        background.scheduleWithFixedDelay(this::advanceHead, 0,
+                                          SLIDE_WINDOW_PERIOD_SECONDS, TimeUnit.SECONDS);
+    }
+
+    /**
+     * Releases resources used by the SlidingWindowCounter.
+     */
+    public void destroy() {
+        background.shutdownNow();
+    }
+
+    /**
+     * Increments the count of the current window slot by 1.
+     */
+    public void incrementCount() {
+        incrementCount(headSlot, 1);
+    }
+
+    /**
+     * Increments the count of the current window slot by the given value.
+     *
+     * @param value value to increment by
+     */
+    public void incrementCount(long value) {
+        incrementCount(headSlot, value);
+    }
+
+    private void incrementCount(int slot, long value) {
+        counters.get(slot).addAndGet(value);
+    }
+
+    /**
+     * Gets the total count for the last N window slots.
+     *
+     * @param slots number of slots to include in the count
+     * @return total count for last N slots
+     */
+    public long get(int slots) {
+        checkArgument(slots <= windowSlots,
+                      "Requested window must be less than the total window slots");
+
+        long sum = 0;
+
+        for (int i = 0; i < slots; i++) {
+            int currentIndex = headSlot - i;
+            if (currentIndex < 0) {
+                currentIndex = counters.size() + currentIndex;
+            }
+            sum += counters.get(currentIndex).get();
+        }
+
+        return sum;
+    }
+
+    void advanceHead() {
+        counters.get(slotAfter(headSlot)).set(0);
+        headSlot = slotAfter(headSlot);
+    }
+
+    private int slotAfter(int slot) {
+        return (slot + 1) % windowSlots;
+    }
+
+}