- Electron version: 1.1.0
- Operating system: Windows
- Use case: cleanup and reporting tasks executed on quit (headless), which may take time and should not prevent from opening a new instance.
- Proposed solutions:
  - new _app.releaseSingleInstance()_ API which free the singleInstance lock
  - replace _app.releaseSingleInstance()_ API by an event listener (which may be listened/unlistened)
  - [app.makeSingleInstance](https://github.com/electron/electron/blob/master/docs/api/app.md#appmakesingleinstancecallback) returns the result of the callback function. So we can choose to quit or not in a more accurate way.
  - Provide a communication channel between the new instance and the main one (in callback arguments)

atom/browser/api/atom_api_app.cc
*prevent_default = Emit("open-file", file_path);
}
void App::OnOpenURL(const std::string& url) {
  Emit("open-url", url);
}
void App::OnActivate(bool has_visible_windows) {
  Emit("activate", has_visible_windows);
}
void App::OnWillFinishLaunching() {
  Emit("will-finish-launching");
}
void App::OnFinishLaunching() {
  Emit("ready");
}
#if defined(OS_MACOSX)
void App::OnContinueUserActivity(
    bool* prevent_default,
    const std::string& type,
    const base::DictionaryValue& user_info) {
  *prevent_default = Emit("continue-activity", type, user_info);
}
#endif
void App::OnLogin(LoginHandler* login_handler) {