Fix deadlock with web socket health monitor.

app/src/main/java/org/thoughtcrime/securesms/net/SignalWebSocketHealthMonitor.java

@@ -5,6 +5,7 @@ import android.app.Application;
 import androidx.annotation.NonNull;
 
 import org.greenrobot.eventbus.EventBus;
+import org.signal.core.util.ThreadUtil;
 import org.signal.core.util.logging.Log;
 import org.thoughtcrime.securesms.dependencies.ApplicationDependencies;
 import org.thoughtcrime.securesms.events.ReminderUpdateEvent;
@@ -17,6 +18,8 @@ import org.whispersystems.signalservice.api.websocket.HealthMonitor;
 import org.whispersystems.signalservice.api.websocket.WebSocketConnectionState;
 import org.whispersystems.signalservice.internal.websocket.WebSocketConnection;
 
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 
 import io.reactivex.rxjava3.schedulers.Schedulers;
@@ -35,11 +38,13 @@ public final class SignalWebSocketHealthMonitor implements HealthMonitor {
   private static final long KEEP_ALIVE_SEND_CADENCE              = TimeUnit.SECONDS.toMillis(WebSocketConnection.KEEPALIVE_TIMEOUT_SECONDS);
   private static final long MAX_TIME_SINCE_SUCCESSFUL_KEEP_ALIVE = KEEP_ALIVE_SEND_CADENCE * 3;
 
+  private final Executor executor = ThreadUtil.trace(Executors.newSingleThreadExecutor());
+
   private final Application     context;
   private       SignalWebSocket signalWebSocket;
   private final SleepTimer      sleepTimer;
 
-  private volatile KeepAliveSender keepAliveSender;
+  private KeepAliveSender keepAliveSender;
 
   private final HealthState identified   = new HealthState();
   private final HealthState unidentified = new HealthState();
@@ -50,6 +55,7 @@ public final class SignalWebSocketHealthMonitor implements HealthMonitor {
   }
 
   public void monitor(@NonNull SignalWebSocket signalWebSocket) {
+    executor.execute(() -> {
       Preconditions.checkNotNull(signalWebSocket);
       Preconditions.checkArgument(this.signalWebSocket == null, "monitor can only be called once");
 
@@ -68,9 +74,11 @@ public final class SignalWebSocketHealthMonitor implements HealthMonitor {
                      .observeOn(Schedulers.computation())
                      .distinctUntilChanged()
                      .subscribe(s -> onStateChange(s, unidentified));
+    });
   }
 
-  private synchronized void onStateChange(WebSocketConnectionState connectionState, HealthState healthState) {
+  private void onStateChange(WebSocketConnectionState connectionState, HealthState healthState) {
+    executor.execute(() -> {
       switch (connectionState) {
         case CONNECTED:
           TextSecurePreferences.setUnauthorizedReceived(context, false);
@@ -96,19 +104,23 @@ public final class SignalWebSocketHealthMonitor implements HealthMonitor {
         keepAliveSender.shutdown();
         keepAliveSender = null;
       }
+    });
   }
 
   @Override
   public void onKeepAliveResponse(long sentTimestamp, boolean isIdentifiedWebSocket) {
+    executor.execute(() -> {
       if (isIdentifiedWebSocket) {
         identified.lastKeepAliveReceived = System.currentTimeMillis();
       } else {
         unidentified.lastKeepAliveReceived = System.currentTimeMillis();
       }
+    });
   }
 
   @Override
   public void onMessageError(int status, boolean isIdentifiedWebSocket) {
+    executor.execute(() -> {
       if (status == 409) {
         HealthState healthState = (isIdentifiedWebSocket ? identified : unidentified);
         if (healthState.mismatchErrorTracker.addSample(System.currentTimeMillis())) {
@@ -116,6 +128,7 @@ public final class SignalWebSocketHealthMonitor implements HealthMonitor {
           signalWebSocket.forceNewWebSockets();
         }
       }
+    });
   }
 
   private boolean isKeepAliveNecessary() {