From a2c4d3fe954a276cab4b93669758c17e6c475ebe Mon Sep 17 00:00:00 2001
From: Chris Eager <chris@signal.org>
Date: Wed, 16 Feb 2022 13:58:02 -0800
Subject: [PATCH] Use a strong reference to the application shutdown gauge

---
 .../textsecuregcm/WhisperServerService.java      |  2 +-
 .../metrics/ApplicationShutdownMonitor.java      | 16 +++++++++++-----
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
index 048587fbd..ef721fe7a 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
@@ -727,7 +727,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
 
     environment.healthChecks().register("cacheCluster", new RedisClusterHealthCheck(cacheCluster));
 
-    environment.lifecycle().manage(new ApplicationShutdownMonitor());
+    environment.lifecycle().manage(new ApplicationShutdownMonitor(Metrics.globalRegistry));
 
     environment.metrics().register(name(CpuUsageGauge.class, "cpu"), new CpuUsageGauge(3, TimeUnit.SECONDS));
     environment.metrics().register(name(FreeMemoryGauge.class, "free_memory"), new FreeMemoryGauge());
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/metrics/ApplicationShutdownMonitor.java b/service/src/main/java/org/whispersystems/textsecuregcm/metrics/ApplicationShutdownMonitor.java
index 8402c30c5..b9f13df8a 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/metrics/ApplicationShutdownMonitor.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/metrics/ApplicationShutdownMonitor.java
@@ -5,12 +5,14 @@
 
 package org.whispersystems.textsecuregcm.metrics;
 
-import io.dropwizard.lifecycle.Managed;
-import io.micrometer.core.instrument.Metrics;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 import static com.codahale.metrics.MetricRegistry.name;
 
+import io.dropwizard.lifecycle.Managed;
+import io.micrometer.core.instrument.Gauge;
+import io.micrometer.core.instrument.MeterRegistry;
+import java.util.concurrent.atomic.AtomicBoolean;
+
 /**
  * A managed monitor that reports whether the application is shutting down as a metric. That metric can then be used in
  * conjunction with other indicators to conditionally fire or suppress alerts.
@@ -19,8 +21,12 @@ public class ApplicationShutdownMonitor implements Managed {
 
   private final AtomicBoolean shuttingDown = new AtomicBoolean(false);
 
-  public ApplicationShutdownMonitor() {
-    Metrics.gauge(name(getClass().getSimpleName(), "shuttingDown"), shuttingDown, b -> b.get() ? 1 : 0);
+  public ApplicationShutdownMonitor(final MeterRegistry meterRegistry) {
+    // without a strong reference to the gauge’s value supplier, shutdown garbage collection
+    // might prevent the final value from being reported
+    Gauge.builder(name(getClass().getSimpleName(), "shuttingDown"), () -> shuttingDown.get() ? 1 : 0)
+        .strongReference(true)
+        .register(meterRegistry);
   }
 
   @Override