- 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.h
~App() override;
  
  void OnBeforeQuit(bool* prevent_default) override;
  void OnWillQuit(bool* prevent_default) override;
  void OnWindowAllClosed() override;
  void OnQuit() override;
  void OnOpenFile(bool* prevent_default, const std::string& file_path) override;
  void OnOpenURL(const std::string& url) override;
  void OnActivate(bool has_visible_windows) override;
  void OnWillFinishLaunching() override;
  void OnFinishLaunching() override;
  void OnLogin(LoginHandler* login_handler) override;
#if defined(OS_MACOSX)
  void OnContinueUserActivity(
      bool* prevent_default,
      const std::string& type,
      const base::DictionaryValue& user_info) override;
#endif
  
  void AllowCertificateError(
      content::WebContents* web_contents,
      int cert_error,
      const net::SSLInfo& ssl_info,
      const GURL& request_url,
      content::ResourceType resource_type,
      bool overridable,
      bool strict_enforcement,
      bool expired_previous_decision,
      const base::Callback<void(bool)>& callback,
      content::CertificateRequestResultType* request) override;