From e9b0829860614c07ec5397e7af1902d9c526aebc Mon Sep 17 00:00:00 2001
From: Jon Chambers <jon@signal.org>
Date: Fri, 9 Oct 2020 19:39:12 -0400
Subject: [PATCH] Report the maximum number of file descriptors allowed by the
 OS.

---
 .../textsecuregcm/WhisperServerService.java   |  2 ++
 .../metrics/MaxFileDescriptorGauge.java       | 23 +++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 service/src/main/java/org/whispersystems/textsecuregcm/metrics/MaxFileDescriptorGauge.java

diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
index 62cc389da..158a35af7 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
@@ -89,6 +89,7 @@ import org.whispersystems.textsecuregcm.metrics.FileDescriptorGauge;
 import org.whispersystems.textsecuregcm.metrics.FreeMemoryGauge;
 import org.whispersystems.textsecuregcm.metrics.GarbageCollectionCountGauge;
 import org.whispersystems.textsecuregcm.metrics.GarbageCollectionTimeGauge;
+import org.whispersystems.textsecuregcm.metrics.MaxFileDescriptorGauge;
 import org.whispersystems.textsecuregcm.metrics.MetricsApplicationEventListener;
 import org.whispersystems.textsecuregcm.metrics.NetworkReceivedGauge;
 import org.whispersystems.textsecuregcm.metrics.NetworkSentGauge;
@@ -451,6 +452,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
     environment.metrics().register(name(FileDescriptorGauge.class, "fd_count"), new FileDescriptorGauge());
     environment.metrics().register(name(GarbageCollectionCountGauge.class, "gc_count"), new GarbageCollectionCountGauge());
     environment.metrics().register(name(GarbageCollectionTimeGauge.class, "gc_time"), new GarbageCollectionTimeGauge());
+    environment.metrics().register(name(MaxFileDescriptorGauge.class, "max_fd_count"), new MaxFileDescriptorGauge());
   }
 
   private void registerExceptionMappers(Environment environment, WebSocketEnvironment<Account> webSocketEnvironment, WebSocketEnvironment<Account> provisioningEnvironment) {
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/metrics/MaxFileDescriptorGauge.java b/service/src/main/java/org/whispersystems/textsecuregcm/metrics/MaxFileDescriptorGauge.java
new file mode 100644
index 000000000..39b05fbdd
--- /dev/null
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/metrics/MaxFileDescriptorGauge.java
@@ -0,0 +1,23 @@
+package org.whispersystems.textsecuregcm.metrics;
+
+import com.codahale.metrics.Gauge;
+import com.sun.management.UnixOperatingSystemMXBean;
+
+import java.lang.management.ManagementFactory;
+
+/**
+ * A gauge that reports the maximum number of file descriptors allowed by the operating system.
+ */
+public class MaxFileDescriptorGauge implements Gauge<Long> {
+
+    private final UnixOperatingSystemMXBean unixOperatingSystemMXBean;
+
+    public MaxFileDescriptorGauge() {
+        this.unixOperatingSystemMXBean = (UnixOperatingSystemMXBean)ManagementFactory.getOperatingSystemMXBean();
+    }
+
+    @Override
+    public Long getValue() {
+        return unixOperatingSystemMXBean.getMaxFileDescriptorCount();
+    }
+}