Allow setting droppedWarnFrequency=0 to disable logging dropped message warnings (#1086)

Allow setting droppedWarnFrequency=0 to disable logging dropped message warnings

Setting droppedWarnFrequency=0 was intended to disable logging of dropped events.

---------

Co-authored-by: Phil Clay <[email protected]>

Author: tommyulfsparre

src/main/java/net/logstash/logback/appender/AsyncDisruptorAppender.java

@@ -499,7 +499,7 @@ protected void append(Event event) {
                 // Log warning if we had drop before
                 //
                 long consecutiveDropped = this.consecutiveDroppedCount.get();
-                if (consecutiveDropped != 0 && this.consecutiveDroppedCount.compareAndSet(consecutiveDropped, 0L)) {
+                if (consecutiveDropped != 0 && this.consecutiveDroppedCount.compareAndSet(consecutiveDropped, 0L) && this.droppedWarnFrequency != 0) {
                     addWarn("Dropped " + consecutiveDropped + " total events due to ring buffer at max capacity [" + this.ringBufferSize + "]");
                 }
 
@@ -511,7 +511,7 @@ protected void append(Event event) {
                 // Log a warning status about the failure
                 //
                 long consecutiveDropped = this.consecutiveDroppedCount.incrementAndGet();
-                if ((consecutiveDropped % this.droppedWarnFrequency) == 1) {
+                if (this.droppedWarnFrequency != 0 && (consecutiveDropped % this.droppedWarnFrequency) == 1) {
                     addWarn("Dropped " + consecutiveDropped + " events (and counting...) due to ring buffer at max capacity [" + this.ringBufferSize + "]");
                 }
 
@@ -807,8 +807,7 @@ public boolean isAddDefaultStatusListener() {
     public void setAddDefaultStatusListener(boolean addDefaultStatusListener) {
         this.addDefaultStatusListener = addDefaultStatusListener;
     }
-    
-    
+
     private static boolean isPowerOfTwo(int x) {
         /* First x in the below expression is for the case when x is 0 */
         return x != 0 && ((x & (x - 1)) == 0);

src/test/java/net/logstash/logback/appender/AsyncDisruptorAppenderTest.java

@@ -200,8 +200,48 @@ public void testEventDroppedWhenFull() throws Exception {
             eventHandlerWaiter.countDown();
         }
     }
-    
-    
+
+
+    @Test
+    public void testDisableLoggedDroppedEvents() throws Exception {
+        final CountDownLatch eventHandlerWaiter = new CountDownLatch(1);
+        TestEventHandler eventHandler = new TestEventHandler(eventHandlerWaiter);
+
+        appender.setDroppedWarnFrequency(0); // disable logging dropped events
+        appender.setRingBufferSize(1);
+        appender.setAppendTimeout(toLogback(Duration.ZERO)); // no timeout - drop when full
+        appender.setEventHandler(eventHandler);
+        appender.start();
+
+        /*
+         * First event blocks the ring buffer until eventHandlerWaiter is released
+         */
+        appender.append(event1);
+        await().until(() -> eventHandlerWaiter.getCount() == 1); // wait until the handler is invoked before going any further
+
+        /*
+         * RingBuffer is full - second event is dropped and not logged
+         */
+        appender.append(event2);
+
+        /*
+         * Failed to append event...
+         */
+        verify(listener).eventAppendFailed(eq(appender), eq(event2), any());
+
+        /*
+         * Unblock the eventHandlerWaiter
+         */
+        eventHandlerWaiter.countDown();
+
+        /*
+         * Last event would have trigger another log event.
+         */
+        appender.append(event1);
+
+        assertThat(statusManager.getCopyOfStatusList()).hasSize(0);
+    }
+ 
     @SuppressWarnings("unchecked")
     @Test
     public void testEventHandlerThrowsException() throws Exception {