@RequiresEdt
  protected boolean forceRediffSynchronously() {
    // most of performRediff implementations take ReadLock inside. If EDT is holding write lock - this will never happen,
    // and diff will not be calculated. This could happen for diff from FileDocumentManager.
    return ApplicationManager.getApplication().isWriteAccessAllowed();
  }
@RequiresEdt
  protected boolean forceRediffSynchronously()