From 39562775d907170ef82a2d64ba57a25f1312c508 Mon Sep 17 00:00:00 2001
From: Jon Chambers <jon@signal.org>
Date: Wed, 3 Aug 2022 15:28:23 -0400
Subject: [PATCH] Use a fixed-size thread pool for sending FCM notifications

---
 .../textsecuregcm/WhisperServerService.java   |  4 +--
 .../textsecuregcm/push/FcmSender.java         | 33 +++++++++++++++----
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
index 84f27b6b0..9a31242fc 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
@@ -381,7 +381,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
     ScheduledExecutorService websocketScheduledExecutor           = environment.lifecycle().scheduledExecutorService(name(getClass(), "websocket-%d")).threads(8).build();
     ExecutorService          keyspaceNotificationDispatchExecutor = environment.lifecycle().executorService(name(getClass(), "keyspaceNotification-%d")).maxThreads(16).workQueue(keyspaceNotificationDispatchQueue).build();
     ExecutorService          apnSenderExecutor                    = environment.lifecycle().executorService(name(getClass(), "apnSender-%d")).maxThreads(1).minThreads(1).build();
-    ExecutorService          gcmSenderExecutor                    = environment.lifecycle().executorService(name(getClass(), "gcmSender-%d")).maxThreads(1).minThreads(1).build();
+    ExecutorService          fcmSenderExecutor                    = environment.lifecycle().executorService(name(getClass(), "fcmSender-%d")).maxThreads(32).minThreads(32).build();
     ExecutorService          backupServiceExecutor                = environment.lifecycle().executorService(name(getClass(), "backupService-%d")).maxThreads(1).minThreads(1).build();
     ExecutorService          storageServiceExecutor               = environment.lifecycle().executorService(name(getClass(), "storageService-%d")).maxThreads(1).minThreads(1).build();
 
@@ -448,7 +448,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
     DispatchManager            dispatchManager            = new DispatchManager(pubSubClientFactory, Optional.empty());
     PubSubManager              pubSubManager              = new PubSubManager(pubsubClient, dispatchManager);
     APNSender                  apnSender                  = new APNSender(apnSenderExecutor, config.getApnConfiguration());
-    FcmSender                  fcmSender                  = new FcmSender(gcmSenderExecutor, config.getFcmConfiguration().credentials());
+    FcmSender                  fcmSender                  = new FcmSender(fcmSenderExecutor, config.getFcmConfiguration().credentials());
     ApnFallbackManager         apnFallbackManager         = new ApnFallbackManager(pushSchedulerCluster, apnSender, accountsManager);
     PushNotificationManager    pushNotificationManager    = new PushNotificationManager(accountsManager, apnSender, fcmSender, apnFallbackManager);
     RateLimiters               rateLimiters               = new RateLimiters(config.getLimitsConfiguration(), rateLimitersCluster);
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/push/FcmSender.java b/service/src/main/java/org/whispersystems/textsecuregcm/push/FcmSender.java
index 402c982f7..536293565 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/push/FcmSender.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/push/FcmSender.java
@@ -5,19 +5,25 @@
 
 package org.whispersystems.textsecuregcm.push;
 
+import static org.whispersystems.textsecuregcm.metrics.MetricsUtil.name;
+
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutureCallback;
 import com.google.api.core.ApiFutures;
 import com.google.auth.oauth2.GoogleCredentials;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.util.concurrent.MoreExecutors;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import com.google.firebase.FirebaseApp;
 import com.google.firebase.FirebaseOptions;
+import com.google.firebase.ThreadManager;
 import com.google.firebase.messaging.AndroidConfig;
 import com.google.firebase.messaging.FirebaseMessaging;
 import com.google.firebase.messaging.FirebaseMessagingException;
 import com.google.firebase.messaging.Message;
 import com.google.firebase.messaging.MessagingErrorCode;
+import io.micrometer.core.instrument.Metrics;
+import io.micrometer.core.instrument.Timer;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
@@ -25,13 +31,10 @@ import java.time.Duration;
 import java.time.Instant;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutorService;
-import io.micrometer.core.instrument.Metrics;
-import io.micrometer.core.instrument.Timer;
+import java.util.concurrent.ThreadFactory;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import static org.whispersystems.textsecuregcm.metrics.MetricsUtil.name;
-
 public class FcmSender implements PushNotificationSender {
 
   private final ExecutorService executor;
@@ -43,11 +46,27 @@ public class FcmSender implements PushNotificationSender {
 
   public FcmSender(ExecutorService executor, String credentials) throws IOException {
     try (final ByteArrayInputStream credentialInputStream = new ByteArrayInputStream(credentials.getBytes(StandardCharsets.UTF_8))) {
-      FirebaseOptions options = FirebaseOptions.builder()
+      FirebaseApp.initializeApp(FirebaseOptions.builder()
           .setCredentials(GoogleCredentials.fromStream(credentialInputStream))
-          .build();
+          .setThreadManager(new ThreadManager() {
+            @Override
+            protected ExecutorService getExecutor(final FirebaseApp app) {
+              return executor;
+            }
 
-      FirebaseApp.initializeApp(options);
+            @Override
+            protected void releaseExecutor(final FirebaseApp app, final ExecutorService executor) {
+              // Do nothing; the executor service is managed by Dropwizard
+            }
+
+            @Override
+            protected ThreadFactory getThreadFactory() {
+              return new ThreadFactoryBuilder()
+                  .setNameFormat("firebase-%d")
+                  .build();
+            }
+          })
+          .build());
     }
 
     this.executor = executor;