Make push sender queue depth configurable or disable-able.

// FREEBIE

src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java

@@ -185,7 +185,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
     TwilioSmsSender          twilioSmsSender     = new TwilioSmsSender(config.getTwilioConfiguration());
     SmsSender                smsSender           = new SmsSender(twilioSmsSender);
     UrlSigner                urlSigner           = new UrlSigner(config.getS3Configuration());
-    PushSender               pushSender          = new PushSender(apnFallbackManager, pushServiceClient, websocketSender);
+    PushSender               pushSender          = new PushSender(apnFallbackManager, pushServiceClient, websocketSender, config.getPushConfiguration().getQueueSize());
     ReceiptSender            receiptSender       = new ReceiptSender(accountsManager, pushSender, federatedClientManager);
     FeedbackHandler          feedbackHandler     = new FeedbackHandler(pushServiceClient, accountsManager);
     Optional<byte[]>         authorizationKey    = config.getRedphoneConfiguration().getAuthorizationKey();

src/main/java/org/whispersystems/textsecuregcm/configuration/PushConfiguration.java

@@ -22,6 +22,10 @@ public class PushConfiguration {
   @NotEmpty
   private String password;
 
+  @JsonProperty
+  @Min(0)
+  private int queueSize = 200;
+
   public String getHost() {
     return host;
   }
@@ -37,4 +41,8 @@ public class PushConfiguration {
   public String getPassword() {
     return password;
   }
+
+  public int getQueueSize() {
+    return queueSize;
+  }
 }

src/main/java/org/whispersystems/textsecuregcm/push/PushSender.java

@@ -47,12 +47,16 @@ public class PushSender implements Managed {
   private final PushServiceClient          pushServiceClient;
   private final WebsocketSender            webSocketSender;
   private final BlockingThreadPoolExecutor executor;
+  private final int                        queueSize;
 
-  public PushSender(ApnFallbackManager apnFallbackManager, PushServiceClient pushServiceClient, WebsocketSender websocketSender) {
+  public PushSender(ApnFallbackManager apnFallbackManager, PushServiceClient pushServiceClient,
+                    WebsocketSender websocketSender, int queueSize)
+  {
     this.apnFallbackManager = apnFallbackManager;
     this.pushServiceClient  = pushServiceClient;
     this.webSocketSender    = websocketSender;
-    this.executor           = new BlockingThreadPoolExecutor(50, 200);
+    this.queueSize          = queueSize;
+    this.executor           = new BlockingThreadPoolExecutor(50, queueSize);
 
     SharedMetricRegistries.getOrCreate(Constants.METRICS_NAME)
                           .register(name(PushSender.class, "send_queue_depth"),
@@ -71,15 +75,16 @@ public class PushSender implements Managed {
       throw new NotPushRegisteredException("No delivery possible!");
     }
 
+    if (queueSize > 0) {
       executor.execute(new Runnable() {
         @Override
         public void run() {
-        if      (device.getGcmId() != null)   sendGcmMessage(account, device, message);
+          sendSynchronousMessage(account, device, message);
-        else if (device.getApnId() != null)   sendApnMessage(account, device, message);
-        else if (device.getFetchesMessages()) sendWebSocketMessage(account, device, message);
-        else                                  throw new AssertionError();
         }
       });
+    } else {
+      sendSynchronousMessage(account, device, message);
+    }
   }
 
   public void sendQueuedNotification(Account account, Device device, int messageQueueDepth)
@@ -94,6 +99,13 @@ public class PushSender implements Managed {
     return webSocketSender;
   }
 
+  private void sendSynchronousMessage(Account account, Device device, Envelope message) {
+    if      (device.getGcmId() != null)   sendGcmMessage(account, device, message);
+    else if (device.getApnId() != null)   sendApnMessage(account, device, message);
+    else if (device.getFetchesMessages()) sendWebSocketMessage(account, device, message);
+    else                                  throw new AssertionError();
+  }
+
   private void sendGcmMessage(Account account, Device device, Envelope message) {
     DeliveryStatus deliveryStatus = webSocketSender.sendMessage(account, device, message, WebsocketSender.Type.GCM);