code: Observable<File> mergeLogs(@NonNull File mergedFile) {
  
          return Observable.fromCallable(() -> {
              synchronized (sharedLock) {
                  try {
                      mergeFiles(mergedFile);
                  } catch (Exception e) {
                      e.printStackTrace();
                  } finally {
                      sharedLock.notifyAll();
                  }
              }
              return mergedFile;
          }).subscribeOn(Schedulers.from(executor));
      }
docs: Create observable returning same file that was passed as a parameter but with merged content of internal log files.
  
  @param mergedFile Instance of a file to merge logs into.
  @return Observable returning an instance of a file with logs merged into.