Synchronize message updates and message operations

app/src/main/java/eu/faircode/email/ServiceSynchronize.java

@@ -97,13 +97,13 @@ import androidx.lifecycle.Observer;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 
 public class ServiceSynchronize extends LifecycleService {
+    private final Object lock = new Object();
     private ExecutorService executor = Executors.newSingleThreadExecutor();
 
     private static final int NOTIFICATION_SYNCHRONIZE = 1;
     private static final int NOTIFICATION_UNSEEN = 2;
 
     private static final long NOOP_INTERVAL = 9 * 60 * 1000L; // ms
-    private static final int FETCH_BATCH_SIZE = 10;
     private static final int ATTACHMENT_BUFFER_SIZE = 8192; // bytes
 
     static final String ACTION_PROCESS_OPERATIONS = BuildConfig.APPLICATION_ID + ".PROCESS_OPERATIONS";
@@ -607,6 +607,7 @@ public class ServiceSynchronize extends LifecycleService {
         ifolder.addMessageCountListener(new MessageCountAdapter() {
             @Override
             public void messagesAdded(MessageCountEvent e) {
+                synchronized (lock) {
                     try {
                         Log.i(Helper.TAG, folder.name + " messages added");
                         for (Message imessage : e.getMessages())
@@ -625,9 +626,11 @@ public class ServiceSynchronize extends LifecycleService {
                         }
                     }
                 }
+            }
 
             @Override
             public void messagesRemoved(MessageCountEvent e) {
+                synchronized (lock) {
                     try {
                         Log.i(Helper.TAG, folder.name + " messages removed");
                         for (Message imessage : e.getMessages())
@@ -653,6 +656,7 @@ public class ServiceSynchronize extends LifecycleService {
                         }
                     }
                 }
+            }
         });
 
         // Fetch e-mail
@@ -664,6 +668,7 @@ public class ServiceSynchronize extends LifecycleService {
         ifolder.addMessageChangedListener(new MessageChangedListener() {
             @Override
             public void messageChanged(MessageChangedEvent e) {
+                synchronized (lock) {
                     try {
                         Log.i(Helper.TAG, folder.name + " message changed");
                         synchronizeMessage(folder, ifolder, (IMAPMessage) e.getMessage());
@@ -684,6 +689,7 @@ public class ServiceSynchronize extends LifecycleService {
                         }
                     }
                 }
+            }
         });
 
         // Keep alive
@@ -734,6 +740,7 @@ public class ServiceSynchronize extends LifecycleService {
     }
 
     private void processOperations(EntityFolder folder, Session isession, IMAPStore istore, IMAPFolder ifolder) throws MessagingException, JSONException, IOException {
+        synchronized (lock) {
             try {
                 Log.i(Helper.TAG, folder.name + " start process");
 
@@ -812,6 +819,7 @@ public class ServiceSynchronize extends LifecycleService {
                 Log.i(Helper.TAG, folder.name + " end process");
             }
         }
+    }
 
     private void doSeen(EntityFolder folder, IMAPFolder ifolder, EntityMessage message, JSONArray jargs) throws MessagingException, JSONException {
         // Mark message (un)seen