Core: include timestamp and params in hot threads

Include the timestamp and params (interval, busiestThreads,
ignoreIdleThreads), when hot threads were collected.

Closes #9773

src/main/java/org/elasticsearch/monitor/jvm/HotThreads.java

@@ -21,6 +21,8 @@ package org.elasticsearch.monitor.jvm;
 
 import org.apache.lucene.util.CollectionUtil;
 import org.elasticsearch.ElasticsearchIllegalArgumentException;
+import org.elasticsearch.common.joda.FormatDateTimeFormatter;
+import org.elasticsearch.common.joda.Joda;
 import org.elasticsearch.common.unit.TimeValue;
 
 import java.lang.management.ManagementFactory;
@@ -35,6 +37,8 @@ public class HotThreads {
 
     private static final Object mutex = new Object();
 
+    private static final FormatDateTimeFormatter DATE_TIME_FORMATTER = Joda.forPattern("dateOptionalTime");
+
     private int busiestThreads = 3;
     private TimeValue interval = new TimeValue(500, TimeUnit.MILLISECONDS);
     private TimeValue threadElementsSnapshotDelay = new TimeValue(10);
@@ -122,6 +126,17 @@ public class HotThreads {
 
     private String innerDetect() throws Exception {
         StringBuilder sb = new StringBuilder();
+
+        sb.append("Hot threads at ");
+        sb.append(DATE_TIME_FORMATTER.printer().print(System.currentTimeMillis()));
+        sb.append(", interval=");
+        sb.append(interval);
+        sb.append(", busiestThreads=");
+        sb.append(busiestThreads);
+        sb.append(", ignoreIdleThreads=");
+        sb.append(ignoreIdleThreads);
+        sb.append(":\n");
+
         ThreadMXBean threadBean = ManagementFactory.getThreadMXBean();
         boolean enabledCpu = false;
         try {

src/test/java/org/elasticsearch/action/admin/HotThreadsTest.java

@@ -163,4 +163,17 @@ public class HotThreadsTest extends ElasticsearchIntegrationTest {
         // The filtered stacks should be smaller than unfiltered ones:
         assertThat(totSizeIgnoreIdle, lessThan(totSizeAll));
     }
+
+    public void testTimestampAndParams() throws ExecutionException, InterruptedException {
+
+        NodesHotThreadsResponse response = client().admin().cluster().prepareNodesHotThreads().execute().get();
+
+        for (NodeHotThreads node : response.getNodesMap().values()) {
+            String result = node.getHotThreads();
+            assertTrue(result.indexOf("Hot threads at") != -1);
+            assertTrue(result.indexOf("interval=500ms") != -1);
+            assertTrue(result.indexOf("busiestThreads=3") != -1);
+            assertTrue(result.indexOf("ignoreIdleThreads=true") != -1);
+        }
+    }
 }