ENG-25947: metrics empty response bug (#13)

* ENG-25948: Added descriptive message when port conflict occurs (instead of stacktrace). Prometheus output includes more useful host name as host_name label, e.g. tomaszs-mbp-2_localdomain instead of localhost. Logging of errors that could happen during Prometheus response generation.

* ENG-25947: Fixed concurrency issue when trying to iterate over synchronised HdrHistogram.

src/main/java/org/voltdb/meshmonitor/HistogramWithDelta.java

@@ -9,6 +9,8 @@
 
 import org.HdrHistogram.SynchronizedHistogram;
 
+import java.util.function.Consumer;
+
 public class HistogramWithDelta {
 
     private final ConsoleLogger logger;
@@ -34,7 +36,14 @@ public void recordValueWithExpectedInterval(long value, long expectedIntervalBet
         }
     }
 
-    public SynchronizedHistogram getCumulativeHistogram() {
+    public void getCumulativeHistogram(Consumer<SynchronizedHistogram> consumer) {
+        synchronized (histogram) {
+            consumer.accept(histogram);
+        }
+    }
+
+    // @VisibleForTesting
+    SynchronizedHistogram getCumulativeHistogram() {
         return histogram;
     }
 

src/main/java/org/voltdb/meshmonitor/metrics/MonitorStatsPrinter.java

@@ -7,11 +7,11 @@
  */
 package org.voltdb.meshmonitor.metrics;
 
-import java.net.InetSocketAddress;
-
 import org.voltdb.meshmonitor.MeshMonitorTimings;
 import org.voltdb.meshmonitor.Monitor;
 
+import java.net.InetSocketAddress;
+
 public class MonitorStatsPrinter {
 
     private final HistogramPrinter histogramPrinter;
@@ -24,19 +24,25 @@ public void print(StringBuilder output, Monitor monitor) {
         MeshMonitorTimings timings = monitor.getTimings();
         InetSocketAddress remoteId = monitor.getRemoteId();
 
-        histogramPrinter.printHistogram(output,
-                timings.receiveHistogram().getCumulativeHistogram(),
-                remoteId,
-                "receive_seconds");
-
-        histogramPrinter.printHistogram(output,
-                timings.deltaHistogram().getCumulativeHistogram(),
-                remoteId,
-                "delta_seconds");
-
-        histogramPrinter.printHistogram(output,
-                timings.sendHistogram().getCumulativeHistogram(),
-                remoteId,
-                "send_seconds");
+        timings.receiveHistogram().getCumulativeHistogram(histogram ->
+                histogramPrinter.printHistogram(output,
+                        histogram,
+                        remoteId,
+                        "receive_seconds")
+        );
+
+        timings.deltaHistogram().getCumulativeHistogram(histogram ->
+                histogramPrinter.printHistogram(output,
+                        histogram,
+                        remoteId,
+                        "delta_seconds")
+        );
+
+        timings.sendHistogram().getCumulativeHistogram(histogram -> {
+            histogramPrinter.printHistogram(output,
+                    histogram,
+                    remoteId,
+                    "send_seconds");
+        });
     }
 }

src/test/java/org/voltdb/meshmonitor/metrics/HistogramPrinterTest.java

@@ -7,7 +7,6 @@
  */
 package org.voltdb.meshmonitor.metrics;
 
-import org.HdrHistogram.SynchronizedHistogram;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.voltdb.meshmonitor.ConsoleLoggerTest;
@@ -20,25 +19,30 @@
 public class HistogramPrinterTest {
 
     private static final InetSocketAddress REMOTE_ID = new InetSocketAddress("remote.host.com", 8080);
-    private SynchronizedHistogram histogram;
+
+    private MeshMonitorTimings meshMonitorTimings;
 
     @BeforeEach
     void setUp() {
-        histogram = MeshMonitorTimings.createDefault(ConsoleLoggerTest.loggerForTest())
-                .deltaHistogram()
-                .getCumulativeHistogram();
+        meshMonitorTimings = MeshMonitorTimings.createDefault(ConsoleLoggerTest.loggerForTest());
     }
 
     @Test
     public void shouldPrintBasicHistogram() {
         // Given
-        histogram.recordValue(42L);
+        meshMonitorTimings
+                .deltaHistogram()
+                .recordValueWithExpectedInterval(42L, 42L);
 
         HistogramPrinter printer = new HistogramPrinter("host_name");
         StringBuilder actual = new StringBuilder();
 
         // When
-        printer.printHistogram(actual, histogram, REMOTE_ID, "empty_histogram");
+        meshMonitorTimings
+                .deltaHistogram()
+                .getCumulativeHistogram(histogram ->
+                        printer.printHistogram(actual, histogram, REMOTE_ID, "empty_histogram")
+                );
 
         // Then
         String result = actual.toString();
@@ -52,15 +56,27 @@ public void shouldPrintBasicHistogram() {
     @Test
     public void shouldFormatCumulativeBuckets() {
         // Given
-        histogram.recordValue(42L);
-        histogram.recordValue(420L);
-        histogram.recordValue(4200L);
+        meshMonitorTimings
+                .deltaHistogram()
+                .recordValueWithExpectedInterval(42L, 42L);
+
+        meshMonitorTimings
+                .deltaHistogram()
+                .recordValueWithExpectedInterval(420L, 420L);
+
+        meshMonitorTimings
+                .deltaHistogram()
+                .recordValueWithExpectedInterval(4200L, 4200L);
 
         HistogramPrinter printer = new HistogramPrinter("host_name");
         StringBuilder actual = new StringBuilder();
 
         // When
-        printer.printHistogram(actual, histogram, REMOTE_ID, "histogram");
+        meshMonitorTimings
+                .deltaHistogram()
+                .getCumulativeHistogram(histogram ->
+                        printer.printHistogram(actual, histogram, REMOTE_ID, "histogram")
+                );
 
         // Then
         String result = actual.toString();