Don't run anti-entropy when under high load
Change-Id: I9e480708b9eced73da98e5c4cb27a18aeb08f09a
diff --git a/utils/misc/src/main/java/org/onlab/util/SlidingWindowCounter.java b/utils/misc/src/main/java/org/onlab/util/SlidingWindowCounter.java
new file mode 100644
index 0000000..5c14d95
--- /dev/null
+++ b/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;
+ }
+
+}