electron/atom/browser/relauncher.h

// Copyright (c) 2016 GitHub, Inc.
// Use of this source code is governed by the MIT license that can be
// found in the LICENSE file.

#ifndef ATOM_BROWSER_RELAUNCHER_H_
#define ATOM_BROWSER_RELAUNCHER_H_

// relauncher implements main browser application relaunches across platforms.
// 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.
//
// 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>

#include "base/command_line.h"

#if defined(OS_WIN)
#include "base/process/process_handle.h"
#endif

namespace content {
struct MainFunctionParams;
}

namespace relauncher {

using CharType = base::CommandLine::CharType;
using StringType = base::CommandLine::StringType;
using StringVector = base::CommandLine::StringVector;

// 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 StringVector& argv);

// Identical to RelaunchApp, but uses |helper| as the path to the relauncher
// process, and allows additional arguments to be supplied to the relauncher
// process in relauncher_args. 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 base::FilePath& helper,
                           const StringVector& relauncher_args,
                           const StringVector& args);

// The entry point from ChromeMain into the relauncher process.
int RelauncherMain(const content::MainFunctionParams& main_parameters);

namespace internal {

#if defined(OS_POSIX)
// The "magic" file descriptor that the relauncher process' write side of the
// pipe shows up on. Chosen to avoid conflicting with stdin, stdout, and
// stderr.
extern const int kRelauncherSyncFD;
#endif

// The "type" argument identifying a relauncher process ("--type=relauncher").
extern const CharType* kRelauncherTypeArg;

// The argument separating arguments intended for the relauncher process from
// those intended for the relaunched process. "---" is chosen instead of "--"
// because CommandLine interprets "--" as meaning "end of switches", but
// for many purposes, the relauncher process' CommandLine ought to interpret
// arguments intended for the relaunched process, to get the correct settings
// for such things as logging and the user-data-dir in case it affects crash
// reporting.
extern const CharType* kRelauncherArgSeparator;

#if defined(OS_WIN)
StringType GetWaitEventName(base::ProcessId pid);

StringType ArgvToCommandLineString(const StringVector& argv);
#endif

// In the relauncher process, performs the necessary synchronization steps
// with the parent by setting up a kqueue to watch for it to exit, writing a
// byte to the pipe, and then waiting for the exit notification on the kqueue.
// If anything fails, this logs a message and returns immediately. In those
// situations, it can be assumed that something went wrong with the parent
// process and the best recovery approach is to attempt relaunch anyway.
void RelauncherSynchronizeWithParent();

int LaunchProgram(const StringVector& relauncher_args,
                  const StringVector& argv);

}  // namespace internal

}  // namespace relauncher

#endif  // ATOM_BROWSER_RELAUNCHER_H_