YARN-11816. Fix flaky test: TestCapacitySchedulerMultiNodes#testCheckRequestOnceForUnsatisfiedRequest. (#7659) Contributed by Tao Yang.

Signed-off-by: Shilun Fan <slfan1989@apache.org>

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/TestCapacitySchedulerMultiNodes.java

@@ -23,7 +23,6 @@ import static org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.C
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
 import static org.mockito.Mockito.when;
 
@@ -35,8 +34,10 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import org.apache.hadoop.test.GenericTestUtils;
 import org.apache.hadoop.thirdparty.com.google.common.collect.Iterators;
 
 import org.apache.hadoop.yarn.server.resourcemanager.RMContext;
@@ -625,7 +626,6 @@ public class TestCapacitySchedulerMultiNodes {
     // mock node tracker with 2000 nodes
     // to simulate the scenario where there are many nodes in the cluster
     List<FiCaSchedulerNode> mockNodes = new ArrayList<>();
-    long ss = System.currentTimeMillis();
     for (int i = 0; i < 2000; i++) {
       FiCaSchedulerNode node =
           TestUtils.getMockNode("host" + i + ":1234", "", 0, 10 * GB, 10);
@@ -660,26 +660,34 @@ public class TestCapacitySchedulerMultiNodes {
     // create an unsatisfied request which will reach the headroom
     am1.allocate("*", 2 * GB, 10, new ArrayList<>());
 
-    // verify that when headroom is reached for an unsatisfied request,
-    // scheduler should only check the request once before checking all nodes.
-    CandidateNodeSet<FiCaSchedulerNode> candidates =
-        new SimpleCandidateNodeSet<>(Collections.emptyMap(), "");
-    int numSchedulingCycles = 10;
-    long startTime = System.currentTimeMillis();
-    for (int i = 0; i < numSchedulingCycles; i++) {
-      spyCs.allocateContainersToNode(candidates, false);
+    List<Long> elapsedMsLst = new ArrayList<>();
+    try {
+      GenericTestUtils.waitFor(() -> {
+        // verify that when headroom is reached for an unsatisfied request,
+        // scheduler should only check the request once before checking all nodes.
+        CandidateNodeSet<FiCaSchedulerNode> candidates =
+            new SimpleCandidateNodeSet<>(Collections.emptyMap(), "");
+        int numSchedulingCycles = 10;
+        long startTime = System.currentTimeMillis();
+        for (int i = 0; i < numSchedulingCycles; i++) {
+          spyCs.allocateContainersToNode(candidates, false);
+        }
+        long avgElapsedMs =
+            (System.currentTimeMillis() - startTime) / numSchedulingCycles;
+        LOG.info("Average elapsed time for a scheduling cycle: {} ms",
+            avgElapsedMs);
+
+        elapsedMsLst.add(avgElapsedMs);
+        // verify that the scheduling cycle is less than 10ms,
+        // ideally the latency should be less than 2ms.
+        return avgElapsedMs < 10;
+      }, 500, 3000);
+    } catch (TimeoutException e) {
+      fail("Scheduling cycle expected to be less than 10ms, " +
+          "but took too long, elapsedMs:" + elapsedMsLst);
+    } finally {
+      rm.stop();
     }
-    long avgElapsedMs =
-        (System.currentTimeMillis() - startTime) / numSchedulingCycles;
-    LOG.info("Average elapsed time for a scheduling cycle: {} ms",
-        avgElapsedMs);
-    // verify that the scheduling cycle is less than 5ms,
-    // ideally the latency should be less than 2ms.
-    assertTrue(avgElapsedMs < 5,
-        String.format("%d ms elapsed in average for a scheduling cycle, " +
-            "expected to be less than 5ms.", avgElapsedMs));
-
-    rm.stop();
   }
 
   private static void moveReservation(CapacityScheduler cs,