Fix relaunches on the Mac

chrome/browser/mac/relauncher.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_MAC_RELAUNCHER_H_
+#define CHROME_BROWSER_MAC_RELAUNCHER_H_
+#pragma once
+
+// mac_relauncher implements main browser application relaunches on the Mac.
+// When a browser wants to relaunch itself, it can't simply fork off a new
+// process and exec a new browser from within. That leaves open a window
+// during which two browser applications might be running concurrently. If
+// that happens, each will wind up with a distinct Dock icon, which is
+// especially bad if the user expected the Dock icon to be persistent by
+// choosing Keep in Dock from the icon's contextual menu.
+//
+// mac_relauncher approaches this problem by introducing an intermediate
+// process (the "relauncher") in between the original browser ("parent") and
+// replacement browser ("relaunched"). The helper executable is used for the
+// relauncher process; because it's an LSUIElement, it doesn't get a Dock
+// icon and isn't visible as a running application at all. The parent will
+// start a relauncher process, giving it the "writer" side of a pipe that it
+// retains the "reader" end of. When the relauncher starts up, it will
+// establish a kqueue to wait for the parent to exit, and will then write to
+// the pipe. The parent, upon reading from the pipe, is free to exit. When the
+// relauncher is notified via its kqueue that the parent has exited, it
+// proceeds, launching the relaunched process. The handshake to synchronize
+// the parent with the relauncher is necessary to avoid races: the relauncher
+// needs to be sure that it's monitoring the parent and not some other process
+// in light of PID reuse, so the parent must remain alive long enough for the
+// relauncher to set up its kqueue.
+
+#include <string>
+#include <vector>
+
+struct MainFunctionParams;
+
+namespace mac_relauncher {
+
+// Relaunches the application using the helper application associated with the
+// currently running instance of Chrome in the parent browser process as the
+// executable for the relauncher process. |args| is an argv-style vector of
+// command line arguments of the form normally passed to execv. args[0] is
+// also the path to the relaunched process. Because the relauncher process
+// will ultimately launch the relaunched process via Launch Services, args[0]
+// may be either a pathname to an executable file or a pathname to an .app
+// bundle directory. The caller should exit soon after RelaunchApp returns
+// successfully. Returns true on success, although some failures can occur
+// after this function returns true if, for example, they occur within the
+// relauncher process. Returns false when the relaunch definitely failed.
+bool RelaunchApp(const std::vector<std::string>& args);
+
+// Identical to RelaunchApp, but uses |helper| as the path to the relauncher
+// process. Unlike args[0], |helper| must be a pathname to an executable file.
+// The helper path given must be from the same version of Chrome as the
+// running parent browser process, as there are no guarantees that the parent
+// and relauncher processes from different versions will be able to
+// communicate with one another. This variant can be useful to relaunch the
+// same version of Chrome from another location, using that location's helper.
+bool RelaunchAppWithHelper(const std::string& helper,
+                           const std::vector<std::string>& args);
+
+namespace internal {
+
+// The entry point from ChromeMain into the relauncher process. This is not a
+// user API. Don't call it if your name isn't ChromeMain.
+int RelauncherMain(const MainFunctionParams& main_parameters);
+
+}  // namespace internal
+
+}  // namespace mac_relauncher
+
+#endif  // CHROME_BROWSER_MAC_RELAUNCHER_H_