Make sure blocked task is dequeued before refreshing cluster info

Author: nicktindall

server/src/internalClusterTest/java/org/elasticsearch/cluster/routing/allocation/decider/WriteLoadConstraintDeciderIT.java

@@ -285,15 +285,20 @@ public void testMaxQueueLatencyMetricIsPublished() {
         final String dataNodeToDelay = randomFrom(dataNodes);
         final ThreadPool threadPoolToDelay = internalCluster().getInstance(ThreadPool.class, dataNodeToDelay);
 
-        // Fill the write thread pool and block a task for some time
+        // Fill the write thread pool
         final int writeThreadPoolSize = threadPoolToDelay.info(ThreadPool.Names.WRITE).getMax();
         final var latch = new CountDownLatch(1);
         final var writeThreadPool = threadPoolToDelay.executor(ThreadPool.Names.WRITE);
-        range(0, writeThreadPoolSize + 1).forEach(i -> writeThreadPool.execute(() -> safeAwait(latch)));
+        range(0, writeThreadPoolSize).forEach(i -> writeThreadPool.execute(() -> safeAwait(latch)));
+        // Submit a task that will be blocked
+        final var blockedTask = writeThreadPool.submit(() -> {
+            // Doesnt need to do anything
+        });
         final long delayMillis = randomIntBetween(100, 200);
         safeSleep(delayMillis);
         // Unblock the pool
         latch.countDown();
+        safeGet(blockedTask);
 
         refreshClusterInfo(masterName);
         mostRecentQueueLatencyMetrics = getMostRecentQueueLatencyMetrics(dataNodes);