Merge "Add metric monitoring Java deadlocks" into stable-2.16

2 files changed, 33 insertions, 0 deletions

diff --git a/Documentation/metrics.txt b/Documentation/metrics.txt
index f729f549da..cb3eb2179d 100644
--- a/Documentation/metrics.txt
+++ b/Documentation/metrics.txt
@@ -50,6 +50,8 @@ objects needing finalization.
 * `proc/jvm/thread/num_daemon_live`: Current live daemon threads count.
 * `proc/jvm/thread/num_peak_live`: Peak live thread count since the Java virtual machine started or peak was reset.
 * `proc/jvm/thread/num_total_started`: Total number of threads created and also started since the Java virtual machine started.
+* `proc/jvm/thread/num_deadlocked_threads`: Number of threads that are deadlocked waiting for object monitors or ownable synchronizers.
+   If deadlocks waiting for ownable synchronizers can be monitored depends on the capabilities of the used JVM.
 
 === Caches
 
diff --git a/java/com/google/gerrit/metrics/proc/ProcMetricModule.java b/java/com/google/gerrit/metrics/proc/ProcMetricModule.java
index be70b8c4e8..2395e3d622 100644
--- a/java/com/google/gerrit/metrics/proc/ProcMetricModule.java
+++ b/java/com/google/gerrit/metrics/proc/ProcMetricModule.java
@@ -235,5 +235,36 @@ public class ProcMetricModule extends MetricModule {
             .setGauge()
             .setUnit("threads"),
         thread::getTotalStartedThreadCount);
+    if (thread.isSynchronizerUsageSupported()) {
+      metrics.newCallbackMetric(
+          "proc/jvm/thread/num_deadlocked_threads",
+          Integer.class,
+          new Description(
+                  "number of threads that are deadlocked waiting for object monitors or ownable synchronizers")
+              .setGauge()
+              .setUnit("threads"),
+          () -> {
+            long[] deadlocked = thread.findDeadlockedThreads();
+            if (deadlocked == null) {
+              return 0;
+            }
+            return deadlocked.length;
+          });
+    } else {
+      metrics.newCallbackMetric(
+          "proc/jvm/thread/num_deadlocked_threads",
+          Integer.class,
+          new Description(
+                  "number of threads that are deadlocked waiting to acquire object monitors")
+              .setGauge()
+              .setUnit("threads"),
+          () -> {
+            long[] deadlocked = thread.findMonitorDeadlockedThreads();
+            if (deadlocked == null) {
+              return 0;
+            }
+            return deadlocked.length;
+          });
+    }
   }
 }