Improve throttle.

Author: javadev

src/main/java/com/github/underscore/U.java

@@ -2068,30 +2068,63 @@ public Void get() {
     }
 
     public static <T> Supplier<T> throttle(final Supplier<T> function, final int waitMilliseconds) {
-        class ThrottleFunction implements Supplier<T> {
+        class ThrottleLater implements Supplier<T> {
             private final Supplier<T> localFunction;
-            private long previous;
             private java.util.concurrent.ScheduledFuture<T> timeout;
+            private long previous;
+
+            ThrottleLater(final Supplier<T> function) {
+                this.localFunction = function;
+            }
+
+            @Override
+            public T get() {
+                previous = now();
+                timeout = null;
+                return localFunction.get();
+            }
+
+            java.util.concurrent.ScheduledFuture<T> getTimeout() {
+                return timeout;
+            }
+
+            void setTimeout(java.util.concurrent.ScheduledFuture<T> timeout) {
+                this.timeout = timeout;
+            }
+
+            long getPrevious() {
+                return previous;
+            }
+
+            void setPrevious(long previous) {
+                this.previous = previous;
+            }
+        }
+
+        class ThrottleFunction implements Supplier<T> {
+            private final Supplier<T> localFunction;
+            private final ThrottleLater throttleLater;
 
             ThrottleFunction(final Supplier<T> function) {
                 this.localFunction = function;
+                this.throttleLater = new ThrottleLater(function);
             }
 
             @Override
             public T get() {
                 final long now = now();
-                if (previous == 0L) {
-                    previous = now;
+                if (throttleLater.getPrevious() == 0L) {
+                    throttleLater.setPrevious(now);
                 }
-                final long remaining = waitMilliseconds - (now - previous);
+                final long remaining = waitMilliseconds - (now - throttleLater.getPrevious());
+                T result = null;
                 if (remaining <= 0) {
-                    clearTimeout(timeout);
-                    previous = now;
-                    localFunction.get();
-                } else {
-                    timeout = delay(localFunction, waitMilliseconds);
+                    throttleLater.setPrevious(now);
+                    result = localFunction.get();
+                } else if (throttleLater.getTimeout() == null) {
+                    throttleLater.setTimeout(delay(throttleLater, waitMilliseconds));
                 }
-                return null;
+                return result;
             }
         }
         return new ThrottleFunction(function);

src/test/java/com/github/underscore/FunctionsTest.java

@@ -116,13 +116,14 @@ public void throttle() {
         final Integer[] counter = new Integer[] {0};
         Supplier<Void> incr = new Supplier<Void>() { public Void get() {
             counter[0]++; return null; } };
-        final Supplier<Void> throttleIncr = U.throttle(incr, 50);
+        final Supplier<Void> throttleIncr = U.throttle(incr, 30);
         throttleIncr.get();
         throttleIncr.get();
         U.delay(throttleIncr, 16);
         U.delay(new Supplier<Void>() {
             public Void get() {
                 assertEquals("incr was throttled", 1, counter[0].intValue());
+                throttleIncr.get();
                 return null;
             }
         }, 60);