fix up small race on g_signal_socket

chrome/common/service_process_util_posix.cc

 // 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.
 
 #include "chrome/common/service_process_util_posix.h"
 
 #include "base/basictypes.h"
 #include "base/eintr_wrapper.h"
 #include "base/message_loop_proxy.h"
 
@@ skipping 41 matching lines @@
     PLOG(ERROR) << "write";
   }
 }
 
 ServiceProcessState::StateData::StateData() : set_action_(false) {
   memset(sockets_, -1, sizeof(sockets_));
   memset(&old_action_, 0, sizeof(old_action_));
 }
 
 void ServiceProcessState::StateData::SignalReady() {
+  CHECK_EQ(g_signal_socket, -1);
   CHECK(MessageLoopForIO::current()->WatchFileDescriptor(
       sockets_[0], true, MessageLoopForIO::WATCH_READ,
       &watcher_, shut_down_monitor_.get()));
   g_signal_socket = sockets_[1];
 
   // Set up signal handler for SIGTERM.
   struct sigaction action;
   action.sa_sigaction = SigTermHandler;
   sigemptyset(&action.sa_mask);
   action.sa_flags = SA_SIGINFO;
@@ skipping 25 matching lines @@
   if (sockets_[1] != -1) {
     if (HANDLE_EINTR(close(sockets_[1]))) {
       PLOG(ERROR) << "close";
     }
   }
   if (set_action_) {
     if (sigaction(SIGTERM, &old_action_, NULL) < 0) {
       PLOG(ERROR) << "sigaction";
     }
   }
+  g_signal_socket = -1;
 }
 
 void ServiceProcessState::CreateState() {
   CHECK(!state_);
   state_ = new StateData;
 
   // Explicitly adding a reference here (and removing it in TearDownState)
   // because StateData is refcounted on Mac and Linux so that methods can
   // be called on other threads.
   // It is not refcounted on Windows at this time.
   state_->AddRef();
 }
 
 bool ServiceProcessState::SignalReady(
     base::MessageLoopProxy* message_loop_proxy, Task* shutdown_task) {
   CHECK(state_);
-  CHECK_EQ(g_signal_socket, -1);
 
   scoped_ptr<Task> scoped_shutdown_task(shutdown_task);
 #if defined(OS_LINUX)
   state_->running_lock_.reset(TakeServiceRunningLock(true));
   if (state_->running_lock_.get() == NULL) {
     return false;
   }
 #endif // OS_LINUX
   state_->shut_down_monitor_.reset(
       new ServiceProcessShutdownMonitor(scoped_shutdown_task.release()));
   if (pipe(state_->sockets_) < 0) {
     PLOG(ERROR) << "pipe";
     return false;
   }
   message_loop_proxy->PostTask(FROM_HERE,
       NewRunnableMethod(state_, &ServiceProcessState::StateData::SignalReady));
   return true;
 }
 
 void ServiceProcessState::TearDownState() {
-  g_signal_socket = -1;
   if (state_) {
     state_->Release();
     state_ = NULL;
   }
 }