Make ChildProcessHost::DoLaunch() not touch a random set of things on a different thread.

(AFAICT, everything was "safe", except for the race condition noted in
OutOfProcessNativeRunner::~OutOfProcessNativeRunner(). That race
condition still exists, but at least now it's more predictable and not
as bad, and it should now be possible to fix Join().)

R=yzshen@chromium.org

Review URL: https://codereview.chromium.org/1146273002

shell/child_process_host.cc

diff --git a/shell/child_process_host.cc b/shell/child_process_host.cc
index 647f8fd..3759df8 100644
--- a/shell/child_process_host.cc
+++ b/shell/child_process_host.cc
@@ -17,6 +17,7 @@
 #include "base/task_runner.h"
 #include "base/task_runner_util.h"
 #include "mojo/edk/embedder/embedder.h"
+#include "mojo/edk/embedder/platform_channel_pair.h"
 #include "mojo/public/cpp/system/message_pipe.h"
 #include "shell/child_switches.h"
 #include "shell/context.h"
@@ -24,6 +25,15 @@
 
 namespace shell {
 
+struct ChildProcessHost::LaunchData {
+  LaunchData() {}
+  ~LaunchData() {}
+
+  base::FilePath child_path;
+  mojo::embedder::PlatformChannelPair platform_channel_pair;
+  std::string child_connection_id;
+};
+
 ChildProcessHost::ChildProcessHost(Context* context)
     : context_(context), channel_info_(nullptr) {
 }
@@ -35,12 +45,14 @@
 void ChildProcessHost::Start() {
   DCHECK(!child_process_.IsValid());
 
+  scoped_ptr<LaunchData> launch_data(new LaunchData());
+  launch_data->child_path = context_->mojo_shell_child_path();
+
   // TODO(vtl): Add something for |slave_info|.
   mojo::embedder::ScopedPlatformHandle platform_handle_for_channel;
-  std::string child_connection_id;
   mojo::embedder::ConnectToSlave(
-      nullptr, platform_channel_pair_.PassServerHandle(),
-      &platform_handle_for_channel, &child_connection_id);
+      nullptr, launch_data->platform_channel_pair.PassServerHandle(),
+      &platform_handle_for_channel, &launch_data->child_connection_id);
 
   mojo::ScopedMessagePipeHandle handle(mojo::embedder::CreateChannel(
       platform_handle_for_channel.Pass(), context_->task_runners()->io_runner(),
@@ -53,7 +65,7 @@
   CHECK(base::PostTaskAndReplyWithResult(
       context_->task_runners()->blocking_pool(), FROM_HERE,
       base::Bind(&ChildProcessHost::DoLaunch, base::Unretained(this),
-                 child_connection_id),
+                 base::Passed(&launch_data)),
       base::Bind(&ChildProcessHost::DidStart, base::Unretained(this))));
 }
 
@@ -84,14 +96,17 @@
   controller_->ExitNow(exit_code);
 }
 
-void ChildProcessHost::DidStart(bool success) {
+void ChildProcessHost::DidStart(base::Process child_process) {
   DVLOG(2) << "ChildProcessHost::DidStart()";
+  DCHECK(!child_process_.IsValid());
 
-  if (!success) {
+  if (!child_process.IsValid()) {
     LOG(ERROR) << "Failed to start app child process";
     AppCompleted(MOJO_RESULT_UNKNOWN);
     return;
   }
+
+  child_process_ = child_process.Pass();
 }
 
 // Callback for |mojo::embedder::CreateChannel()|.
@@ -103,32 +118,31 @@
   channel_info_ = channel_info;
 }
 
-bool ChildProcessHost::DoLaunch(const std::string& child_connection_id) {
+base::Process ChildProcessHost::DoLaunch(scoped_ptr<LaunchData> launch_data) {
   static const char* kForwardSwitches[] = {
       switches::kTraceToConsole, switches::kV, switches::kVModule,
   };
 
-  base::CommandLine child_command_line(context_->mojo_shell_child_path());
+  base::CommandLine child_command_line(launch_data->child_path);
   child_command_line.CopySwitchesFrom(*base::CommandLine::ForCurrentProcess(),
                                       kForwardSwitches,
                                       arraysize(kForwardSwitches));
   child_command_line.AppendSwitchASCII(switches::kChildConnectionId,
-                                       child_connection_id);
+                                       launch_data->child_connection_id);
 
   mojo::embedder::HandlePassingInformation handle_passing_info;
-  platform_channel_pair_.PrepareToPassClientHandleToChildProcess(
+  launch_data->platform_channel_pair.PrepareToPassClientHandleToChildProcess(
       &child_command_line, &handle_passing_info);
 
   base::LaunchOptions options;
   options.fds_to_remap = &handle_passing_info;
   DVLOG(2) << "Launching child with command line: "
            << child_command_line.GetCommandLineString();
-  child_process_ = base::LaunchProcess(child_command_line, options);
-  if (!child_process_.IsValid())
-    return false;
-
-  platform_channel_pair_.ChildProcessLaunched();
-  return true;
+  base::Process child_process =
+      base::LaunchProcess(child_command_line, options);
+  if (child_process.IsValid())
+    launch_data->platform_channel_pair.ChildProcessLaunched();
+  return child_process.Pass();
 }
 
 void ChildProcessHost::AppCompleted(int32_t result) {

shell/child_process_host.h

diff --git a/shell/child_process_host.h b/shell/child_process_host.h
index d5e4562..79fb292 100644
--- a/shell/child_process_host.h
+++ b/shell/child_process_host.h
@@ -10,9 +10,9 @@
 #include <string>
 
 #include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/process/process.h"
 #include "mojo/edk/embedder/channel_info_forward.h"
-#include "mojo/edk/embedder/platform_channel_pair.h"
 #include "mojo/edk/embedder/scoped_platform_handle.h"
 #include "mojo/public/cpp/bindings/error_handler.h"
 #include "shell/child_controller.mojom.h"
@@ -60,13 +60,17 @@
 
   // TODO(vtl): This is virtual, so tests can override it, but really |Start()|
   // should take a callback (see above) and this should be private.
-  virtual void DidStart(bool success);
+  virtual void DidStart(base::Process child_process);
 
  private:
+  struct LaunchData;
+
   // Callback for |mojo::embedder::CreateChannel()|.
   void DidCreateChannel(mojo::embedder::ChannelInfo* channel_info);
 
-  bool DoLaunch(const std::string& child_connection_id);
+  // Note: This is probably executed on a different thread (namely, using the
+  // blocking pool).
+  base::Process DoLaunch(scoped_ptr<LaunchData> launch_data);
 
   void AppCompleted(int32_t result);
 
@@ -74,7 +78,6 @@
   void OnConnectionError() override;
 
   Context* const context_;
-  mojo::embedder::PlatformChannelPair platform_channel_pair_;
 
   ChildControllerPtr controller_;
   mojo::embedder::ChannelInfo* channel_info_;

shell/child_process_host_unittest.cc

diff --git a/shell/child_process_host_unittest.cc b/shell/child_process_host_unittest.cc
index bb1817b..d4dc4a8 100644
--- a/shell/child_process_host_unittest.cc
+++ b/shell/child_process_host_unittest.cc
@@ -25,9 +25,9 @@
   explicit TestChildProcessHost(Context* context) : ChildProcessHost(context) {}
   ~TestChildProcessHost() override {}
 
-  void DidStart(bool success) override {
-    EXPECT_TRUE(success);
-    ChildProcessHost::DidStart(success);
+  void DidStart(base::Process child_process) override {
+    EXPECT_TRUE(child_process.IsValid());
+    ChildProcessHost::DidStart(child_process.Pass());
     base::MessageLoop::current()->QuitWhenIdle();
   }