lock sync at saving

lib/src/lightclient.rs

@@ -592,20 +592,27 @@ impl LightClient {
             }
         }        
 
-        let mut file_buffer = BufWriter::with_capacity(
-            1_000_000, // 1 MB write buffer
-            File::create(self.config.get_wallet_path()).unwrap());
-        
-            let r = match self.wallet.write().unwrap().write(&mut file_buffer) {
-            Ok(_) => Ok(()),
-            Err(e) => {
-                let err = format!("ERR: {}", e);
-                error!("{}", err);
-                Err(e.to_string())
-            }
-        };
+        let r;
+        {
+            // Prevent any overlapping syncs during save, and don't save in the middle of a sync
+            let _lock = self.sync_lock.lock().unwrap();
+
+            let wallet = self.wallet.write().unwrap();
+            let mut file_buffer = BufWriter::with_capacity(
+                1_000_000, // 1 MB write buffer
+                File::create(self.config.get_wallet_path()).unwrap());
 
-        file_buffer.flush().map_err(|e| format!("{}", e))?;
+                r = match wallet.write(&mut file_buffer) {
+                    Ok(_) => Ok(()),
+                    Err(e) => {
+                        let err = format!("ERR: {}", e);
+                        error!("{}", err);
+                        Err(e.to_string())
+                    }
+                };
+
+                file_buffer.flush().map_err(|e| format!("{}", e))?;
+            }
 
         r
     }