Introduce the ability to wait for the watcher process to initialize.

chrome/app/chrome_watcher_command_line_win.cc

 // Copyright (c) 2014 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.
 
 #include "chrome/app/chrome_watcher_command_line_win.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "chrome/common/chrome_switches.h"
 
 namespace {
+
+const char kOnIninitializedEventHandleSwitch[] = "on-initialized-event-handle";
 const char kParentHandleSwitch[] = "parent-handle";
+
+void AppendHandleSwitch(const std::string& switch_name,
+                        HANDLE handle,
+                        base::CommandLine* command_line) {
+  command_line->AppendSwitchASCII(
+      switch_name, base::UintToString(reinterpret_cast<unsigned int>(handle)));
+}
+
+HANDLE ReadHandleFromSwitch(const base::CommandLine& command_line,
+                            const std::string& switch_name) {
+  std::string switch_string = command_line.GetSwitchValueASCII(switch_name);
+  unsigned int switch_uint = 0;
+  if (switch_string.empty() ||
+      !base::StringToUint(switch_string, &switch_uint)) {
+    DLOG(ERROR) << "Missing or invalid " << switch_name << " argument.";
+    return nullptr;
+  }
+  return reinterpret_cast<HANDLE>(switch_uint);
+}
+
 }  // namespace
 
 base::CommandLine GenerateChromeWatcherCommandLine(
     const base::FilePath& chrome_exe,
-    HANDLE parent_process) {
+    HANDLE parent_process,
+    HANDLE on_initialized_event) {
   base::CommandLine command_line(chrome_exe);
   command_line.AppendSwitchASCII(switches::kProcessType, "watcher");
-  command_line.AppendSwitchASCII(
-      kParentHandleSwitch,
-      base::UintToString(reinterpret_cast<unsigned int>(parent_process)));
+  AppendHandleSwitch(kOnIninitializedEventHandleSwitch, on_initialized_event,
+                     &command_line);
+  AppendHandleSwitch(kParentHandleSwitch, parent_process, &command_line);
   return command_line;
 }
 
-base::win::ScopedHandle InterpretChromeWatcherCommandLine(
-    const base::CommandLine& command_line) {
-  std::string parent_handle_str =
-      command_line.GetSwitchValueASCII(kParentHandleSwitch);
-  unsigned parent_handle_uint = 0;
-  if (parent_handle_str.empty() ||
-      !base::StringToUint(parent_handle_str, &parent_handle_uint)) {
-    LOG(ERROR) << "Missing or invalid " << kParentHandleSwitch << " argument.";
-    return base::win::ScopedHandle();
+bool InterpretChromeWatcherCommandLine(
+    const base::CommandLine& command_line,
+    base::win::ScopedHandle* parent_process,
+    base::win::ScopedHandle* on_initialized_event) {
+  DCHECK(on_initialized_event);
+  DCHECK(parent_process);
+
+  // For consistency, always close any existing HANDLEs here.
+  on_initialized_event->Close();
+  parent_process->Close();
+
+  HANDLE parent_handle =
+      ReadHandleFromSwitch(command_line, kParentHandleSwitch);
+  HANDLE on_initialized_event_handle =
+      ReadHandleFromSwitch(command_line, kOnIninitializedEventHandleSwitch);
+
+  if (parent_handle) {
+    // Initial test of the handle, a zero PID indicates invalid handle, or not
+    // a process handle. In this case, parsing fails and we avoid closing the
+    // handle.
+    DWORD process_pid = ::GetProcessId(parent_handle);
+    if (process_pid == 0) {
+      DLOG(ERROR) << "Invalid " << kParentHandleSwitch
+                  << " argument. Can't get parent PID.";
+    } else {
+      parent_process->Set(parent_handle);
+    }
   }
 
-  HANDLE parent_process = reinterpret_cast<HANDLE>(parent_handle_uint);
-  // Initial test of the handle, a zero PID indicates invalid handle, or not
-  // a process handle. In this case, parsing fails and we avoid closing the
-  // handle.
-  DWORD process_pid = ::GetProcessId(parent_process);
-  if (process_pid == 0) {
-    LOG(ERROR) << "Invalid " << kParentHandleSwitch
-               << " argument. Can't get parent PID.";
-    return base::win::ScopedHandle();
+  if (on_initialized_event_handle) {
+    DWORD result = ::WaitForSingleObject(on_initialized_event_handle, 0);
+    if (result == WAIT_FAILED) {
+      DPLOG(ERROR)
+          << "Unexpected error while testing the initialization event.";
+    } else if (result != WAIT_TIMEOUT) {
+      DLOG(ERROR) << "Unexpected result while testing the initialization event "
+                     "with WaitForSingleObject: " << result;
+    } else {
+      on_initialized_event->Set(on_initialized_event_handle);
+    }
   }
 
-  return base::win::ScopedHandle(parent_process);
+  if (!on_initialized_event->IsValid() || !parent_process->IsValid()) {
+    // If one was valid and not the other, free the valid one.
+    on_initialized_event->Close();
+    parent_process->Close();
+    return false;
+  }
+
+  return true;
 }