Refactor PauseDetectorWrapper retrieval #1300

Previously, PauseDetectorWrapper was initialized once and a later loop attempted to retrieve the PauseDetector assuming that the previous code would had initialized the PauseDetector.

Due to concurrency it is possible that the PauseDetector instance is being released while another thread wants to obtain the PauseDetector. This gap could lead to infinite loops as the instance is never allocated. The refactored code include now the initialization so concurrent initialization/release are now properly guarded.

src/main/java/io/lettuce/core/metrics/DefaultCommandLatencyCollector.java

@@ -91,20 +91,25 @@ public void recordCommandLatency(SocketAddress local, SocketAddress remote, Prot
             return;
         }
 
-        if (PAUSE_DETECTOR_UPDATER.get(this) == null) {
-            if (PAUSE_DETECTOR_UPDATER.compareAndSet(this, null, GLOBAL_PAUSE_DETECTOR)) {
-                PAUSE_DETECTOR_UPDATER.get(this).retain();
+        PauseDetector pauseDetector;
+
+        do {
+            if (PAUSE_DETECTOR_UPDATER.get(this) == null) {
+                if (PAUSE_DETECTOR_UPDATER.compareAndSet(this, null, GLOBAL_PAUSE_DETECTOR)) {
+                    PAUSE_DETECTOR_UPDATER.get(this).retain();
+                }
             }
-        }
-        PauseDetector pauseDetector = ((DefaultPauseDetectorWrapper) PAUSE_DETECTOR_UPDATER.get(this)).getPauseDetector();
+            pauseDetector = ((DefaultPauseDetectorWrapper) PAUSE_DETECTOR_UPDATER.get(this)).getPauseDetector();
+        } while (pauseDetector == null);
 
+        PauseDetector pauseDetectorToUse = pauseDetector;
         Latencies latencies = latencyMetricsRef.get().computeIfAbsent(createId(local, remote, commandType), id -> {
 
             if (options.resetLatenciesAfterEvent()) {
-                return new Latencies(pauseDetector);
+                return new Latencies(pauseDetectorToUse);
             }
 
-            return new CummulativeLatencies(pauseDetector);
+            return new CummulativeLatencies(pauseDetectorToUse);
         });
 
         latencies.firstResponse.recordLatency(rangify(firstResponseLatency));
@@ -352,18 +357,10 @@ static class DefaultPauseDetectorWrapper implements PauseDetectorWrapper {
 
         /**
          * Obtain the current {@link PauseDetector}. Requires a call to {@link #retain()} first.
-         * 
+         *
          * @return
          */
         public PauseDetector getPauseDetector() {
-
-            for (;;) {
-
-                if (pauseDetector != null) {
-                    break;
-                }
-            }
-
             return pauseDetector;
         }