Port thread safety/performance optimizations from #1992

src/main/java/fr/xephi/authme/util/AtomicIntervalCounter.java

@@ -0,0 +1,53 @@
+package fr.xephi.authme.util;
+
+/**
+ * A thread-safe interval counter, allows to detect if an event happens more than 'threshold' times
+ * in the given 'interval'.
+ */
+public class AtomicIntervalCounter {
+    private final int threshold;
+    private final int interval;
+    private int count;
+    private long lastInsert;
+
+    /**
+     * Constructs a new counter.
+     *
+     * @param threshold the threshold value of the counter.
+     * @param interval the counter interval in milliseconds.
+     */
+    public AtomicIntervalCounter(int threshold, int interval) {
+        this.threshold = threshold;
+        this.interval = interval;
+        reset();
+    }
+
+    /**
+     * Resets the counter count.
+     */
+    public synchronized void reset() {
+        count = 0;
+        lastInsert = 0;
+    }
+
+    /**
+     * Increments the counter and returns true if the current count has reached the threshold value
+     * in the given interval, this will also reset the count value.
+     *
+     * @return true if the count has reached the threshold value.
+     */
+    public synchronized boolean handle() {
+        long now = System.currentTimeMillis();
+        if (now - lastInsert > interval) {
+            count = 1;
+        } else {
+            count++;
+        }
+        if (count > threshold) {
+            reset();
+            return true;
+        }
+        lastInsert = now;
+        return false;
+    }
+}