src/content/child/child_thread.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/child/child_thread.h"
   6
   7 #include <signal.h>
   8
   9 #include <string>
  10
  11 #include "base/allocator/allocator_extension.h"
  12 #include "base/base_switches.h"
  13 #include "base/basictypes.h"
  14 #include "base/command_line.h"
  15 #include "base/debug/leak_annotations.h"
  16 #include "base/lazy_instance.h"
  17 #include "base/logging.h"
  18 #include "base/message_loop/message_loop.h"
  19 #include "base/message_loop/timer_slack.h"
  20 #include "base/process/kill.h"
  21 #include "base/process/process_handle.h"
  22 #include "base/strings/string_number_conversions.h"
  23 #include "base/strings/string_util.h"
  24 #include "base/synchronization/condition_variable.h"
  25 #include "base/synchronization/lock.h"
  26 #include "base/threading/thread_local.h"
  27 #include "base/tracked_objects.h"
  28 #include "components/tracing/child_trace_message_filter.h"
  29 #include "content/child/child_histogram_message_filter.h"
  30 #include "content/child/child_process.h"
  31 #include "content/child/child_resource_message_filter.h"
  32 #include "content/child/child_shared_bitmap_manager.h"
  33 #include "content/child/fileapi/file_system_dispatcher.h"
  34 #include "content/child/fileapi/webfilesystem_impl.h"
  35 #include "content/child/mojo/mojo_application.h"
  36 #include "content/child/power_monitor_broadcast_source.h"
  37 #include "content/child/quota_dispatcher.h"
  38 #include "content/child/quota_message_filter.h"
  39 #include "content/child/resource_dispatcher.h"
  40 #include "content/child/service_worker/service_worker_message_filter.h"
  41 #include "content/child/socket_stream_dispatcher.h"
  42 #include "content/child/thread_safe_sender.h"
  43 #include "content/child/websocket_dispatcher.h"
  44 #include "content/common/child_process_messages.h"
  45 #include "content/public/common/content_switches.h"
  46 #include "ipc/ipc_logging.h"
  47 #include "ipc/ipc_switches.h"
  48 #include "ipc/ipc_sync_channel.h"
  49 #include "ipc/ipc_sync_message_filter.h"
  50 #include "ipc/mojo/ipc_channel_mojo.h"
  51
  52 #if defined(OS_WIN)
  53 #include "content/common/handle_enumerator_win.h"
  54 #endif
  55
  56 #if defined(TCMALLOC_TRACE_MEMORY_SUPPORTED)
  57 #include "third_party/tcmalloc/chromium/src/gperftools/heap-profiler.h"
  58 #endif
  59
  60 using tracked_objects::ThreadData;
  61
  62 namespace content {
  63 namespace {
  64
  65 // How long to wait for a connection to the browser process before giving up.
  66 const int kConnectionTimeoutS = 15;
  67
  68 base::LazyInstance<base::ThreadLocalPointer<ChildThread> > g_lazy_tls =
  69     LAZY_INSTANCE_INITIALIZER;
  70
  71 // This isn't needed on Windows because there the sandbox's job object
  72 // terminates child processes automatically. For unsandboxed processes (i.e.
  73 // plugins), PluginThread has EnsureTerminateMessageFilter.
  74 #if defined(OS_POSIX)
  75
  76 // TODO(earthdok): Re-enable on CrOS http://crbug.com/360622
  77 #if (defined(ADDRESS_SANITIZER) || defined(LEAK_SANITIZER) || \
  78     defined(THREAD_SANITIZER)) && !defined(OS_CHROMEOS)
  79 // A thread delegate that waits for |duration| and then exits the process with
  80 // _exit(0).
  81 class WaitAndExitDelegate : public base::PlatformThread::Delegate {
  82  public:
  83   explicit WaitAndExitDelegate(base::TimeDelta duration)
  84       : duration_(duration) {}
  85   virtual ~WaitAndExitDelegate() OVERRIDE {}
  86
  87   virtual void ThreadMain() OVERRIDE {
  88     base::PlatformThread::Sleep(duration_);
  89     _exit(0);
  90   }
  91
  92  private:
  93   const base::TimeDelta duration_;
  94   DISALLOW_COPY_AND_ASSIGN(WaitAndExitDelegate);
  95 };
  96
  97 bool CreateWaitAndExitThread(base::TimeDelta duration) {
  98   scoped_ptr<WaitAndExitDelegate> delegate(new WaitAndExitDelegate(duration));
  99
 100   const bool thread_created =
 101       base::PlatformThread::CreateNonJoinable(0, delegate.get());
 102   if (!thread_created)
 103     return false;
 104
 105   // A non joinable thread has been created. The thread will either terminate
 106   // the process or will be terminated by the process. Therefore, keep the
 107   // delegate object alive for the lifetime of the process.
 108   WaitAndExitDelegate* leaking_delegate = delegate.release();
 109   ANNOTATE_LEAKING_OBJECT_PTR(leaking_delegate);
 110   ignore_result(leaking_delegate);
 111   return true;
 112 }
 113 #endif
 114
 115 class SuicideOnChannelErrorFilter : public IPC::MessageFilter {
 116  public:
 117   // IPC::MessageFilter
 118   virtual void OnChannelError() OVERRIDE {
 119     // For renderer/worker processes:
 120     // On POSIX, at least, one can install an unload handler which loops
 121     // forever and leave behind a renderer process which eats 100% CPU forever.
 122     //
 123     // This is because the terminate signals (ViewMsg_ShouldClose and the error
 124     // from the IPC sender) are routed to the main message loop but never
 125     // processed (because that message loop is stuck in V8).
 126     //
 127     // One could make the browser SIGKILL the renderers, but that leaves open a
 128     // large window where a browser failure (or a user, manually terminating
 129     // the browser because "it's stuck") will leave behind a process eating all
 130     // the CPU.
 131     //
 132     // So, we install a filter on the sender so that we can process this event
 133     // here and kill the process.
 134     // TODO(earthdok): Re-enable on CrOS http://crbug.com/360622
 135 #if (defined(ADDRESS_SANITIZER) || defined(LEAK_SANITIZER) || \
 136     defined(THREAD_SANITIZER)) && !defined(OS_CHROMEOS)
 137     // Some sanitizer tools rely on exit handlers (e.g. to run leak detection,
 138     // or dump code coverage data to disk). Instead of exiting the process
 139     // immediately, we give it 60 seconds to run exit handlers.
 140     CHECK(CreateWaitAndExitThread(base::TimeDelta::FromSeconds(60)));
 141 #if defined(LEAK_SANITIZER)
 142     // Invoke LeakSanitizer early to avoid detecting shutdown-only leaks. If
 143     // leaks are found, the process will exit here.
 144     __lsan_do_leak_check();
 145 #endif
 146 #else
 147     _exit(0);
 148 #endif
 149   }
 150
 151  protected:
 152   virtual ~SuicideOnChannelErrorFilter() {}
 153 };
 154
 155 #endif  // OS(POSIX)
 156
 157 #if defined(OS_ANDROID)
 158 ChildThread* g_child_thread = NULL;
 159
 160 // A lock protects g_child_thread.
 161 base::LazyInstance<base::Lock> g_lazy_child_thread_lock =
 162     LAZY_INSTANCE_INITIALIZER;
 163
 164 // base::ConditionVariable has an explicit constructor that takes
 165 // a base::Lock pointer as parameter. The base::DefaultLazyInstanceTraits
 166 // doesn't handle the case. Thus, we need our own class here.
 167 struct CondVarLazyInstanceTraits {
 168   static const bool kRegisterOnExit = true;
 169 #ifndef NDEBUG
 170   static const bool kAllowedToAccessOnNonjoinableThread = false;
 171 #endif
 172
 173   static base::ConditionVariable* New(void* instance) {
 174     return new (instance) base::ConditionVariable(
 175         g_lazy_child_thread_lock.Pointer());
 176   }
 177   static void Delete(base::ConditionVariable* instance) {
 178     instance->~ConditionVariable();
 179   }
 180 };
 181
 182 // A condition variable that synchronize threads initializing and waiting
 183 // for g_child_thread.
 184 base::LazyInstance<base::ConditionVariable, CondVarLazyInstanceTraits>
 185     g_lazy_child_thread_cv = LAZY_INSTANCE_INITIALIZER;
 186
 187 void QuitMainThreadMessageLoop() {
 188   base::MessageLoop::current()->Quit();
 189 }
 190
 191 #endif
 192
 193 }  // namespace
 194
 195 ChildThread::Options::Options()
 196     : channel_name(base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 197           switches::kProcessChannelID)),
 198       use_mojo_channel(false) {}
 199
 200 ChildThread::Options::Options(bool mojo)
 201     : channel_name(base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 202           switches::kProcessChannelID)),
 203       use_mojo_channel(mojo) {}
 204
 205
 206 ChildThread::ChildThreadMessageRouter::ChildThreadMessageRouter(
 207     IPC::Sender* sender)
 208     : sender_(sender) {}
 209
 210 bool ChildThread::ChildThreadMessageRouter::Send(IPC::Message* msg) {
 211   return sender_->Send(msg);
 212 }
 213
 214 ChildThread::ChildThread()
 215     : router_(this),
 216       channel_connected_factory_(this),
 217       in_browser_process_(false) {
 218   Init(Options());
 219 }
 220
 221 ChildThread::ChildThread(const Options& options)
 222     : router_(this),
 223       channel_connected_factory_(this),
 224       in_browser_process_(true) {
 225   Init(options);
 226 }
 227
 228 scoped_ptr<IPC::SyncChannel> ChildThread::CreateChannel(bool use_mojo_channel) {
 229   if (use_mojo_channel) {
 230     VLOG(1) << "Mojo is enabled on child";
 231     return IPC::SyncChannel::Create(
 232         IPC::ChannelMojo::CreateFactory(
 233             channel_name_,
 234             IPC::Channel::MODE_CLIENT,
 235             ChildProcess::current()->io_message_loop_proxy()),
 236         this,
 237         ChildProcess::current()->io_message_loop_proxy(),
 238         true,
 239         ChildProcess::current()->GetShutDownEvent());
 240   }
 241
 242   VLOG(1) << "Mojo is disabled on child";
 243   return IPC::SyncChannel::Create(
 244       channel_name_,
 245       IPC::Channel::MODE_CLIENT,
 246       this,
 247       ChildProcess::current()->io_message_loop_proxy(),
 248       true,
 249       ChildProcess::current()->GetShutDownEvent());
 250 }
 251
 252 void ChildThread::Init(const Options& options) {
 253   channel_name_ = options.channel_name;
 254
 255   g_lazy_tls.Pointer()->Set(this);
 256   on_channel_error_called_ = false;
 257   message_loop_ = base::MessageLoop::current();
 258 #ifdef IPC_MESSAGE_LOG_ENABLED
 259   // We must make sure to instantiate the IPC Logger *before* we create the
 260   // channel, otherwise we can get a callback on the IO thread which creates
 261   // the logger, and the logger does not like being created on the IO thread.
 262   IPC::Logging::GetInstance();
 263 #endif
 264   channel_ = CreateChannel(options.use_mojo_channel);
 265 #ifdef IPC_MESSAGE_LOG_ENABLED
 266   if (!in_browser_process_)
 267     IPC::Logging::GetInstance()->SetIPCSender(this);
 268 #endif
 269
 270   mojo_application_.reset(new MojoApplication);
 271
 272   sync_message_filter_ =
 273       new IPC::SyncMessageFilter(ChildProcess::current()->GetShutDownEvent());
 274   thread_safe_sender_ = new ThreadSafeSender(
 275       base::MessageLoopProxy::current().get(), sync_message_filter_.get());
 276
 277   resource_dispatcher_.reset(new ResourceDispatcher(this));
 278   socket_stream_dispatcher_.reset(new SocketStreamDispatcher());
 279   websocket_dispatcher_.reset(new WebSocketDispatcher);
 280   file_system_dispatcher_.reset(new FileSystemDispatcher());
 281
 282   histogram_message_filter_ = new ChildHistogramMessageFilter();
 283   resource_message_filter_ =
 284       new ChildResourceMessageFilter(resource_dispatcher());
 285
 286   service_worker_message_filter_ =
 287       new ServiceWorkerMessageFilter(thread_safe_sender_.get());
 288
 289   quota_message_filter_ =
 290       new QuotaMessageFilter(thread_safe_sender_.get());
 291   quota_dispatcher_.reset(new QuotaDispatcher(thread_safe_sender_.get(),
 292                                               quota_message_filter_.get()));
 293
 294   channel_->AddFilter(histogram_message_filter_.get());
 295   channel_->AddFilter(sync_message_filter_.get());
 296   channel_->AddFilter(resource_message_filter_.get());
 297   channel_->AddFilter(quota_message_filter_->GetFilter());
 298   channel_->AddFilter(service_worker_message_filter_->GetFilter());
 299
 300   if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
 301           switches::kSingleProcess)) {
 302     // In single process mode, browser-side tracing will cover the whole
 303     // process including renderers.
 304     channel_->AddFilter(new tracing::ChildTraceMessageFilter(
 305         ChildProcess::current()->io_message_loop_proxy()));
 306   }
 307
 308   // In single process mode we may already have a power monitor
 309   if (!base::PowerMonitor::Get()) {
 310     scoped_ptr<PowerMonitorBroadcastSource> power_monitor_source(
 311       new PowerMonitorBroadcastSource());
 312     channel_->AddFilter(power_monitor_source->GetMessageFilter());
 313
 314     power_monitor_.reset(new base::PowerMonitor(
 315         power_monitor_source.PassAs<base::PowerMonitorSource>()));
 316   }
 317
 318 #if defined(OS_POSIX)
 319   // Check that --process-type is specified so we don't do this in unit tests
 320   // and single-process mode.
 321   if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kProcessType))
 322     channel_->AddFilter(new SuicideOnChannelErrorFilter());
 323 #endif
 324
 325   int connection_timeout = kConnectionTimeoutS;
 326   std::string connection_override =
 327       base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 328           switches::kIPCConnectionTimeout);
 329   if (!connection_override.empty()) {
 330     int temp;
 331     if (base::StringToInt(connection_override, &temp))
 332       connection_timeout = temp;
 333   }
 334
 335   base::MessageLoop::current()->PostDelayedTask(
 336       FROM_HERE,
 337       base::Bind(&ChildThread::EnsureConnected,
 338                  channel_connected_factory_.GetWeakPtr()),
 339       base::TimeDelta::FromSeconds(connection_timeout));
 340
 341 #if defined(OS_ANDROID)
 342   {
 343     base::AutoLock lock(g_lazy_child_thread_lock.Get());
 344     g_child_thread = this;
 345   }
 346   // Signalling without locking is fine here because only
 347   // one thread can wait on the condition variable.
 348   g_lazy_child_thread_cv.Get().Signal();
 349 #endif
 350
 351 #if defined(TCMALLOC_TRACE_MEMORY_SUPPORTED)
 352   trace_memory_controller_.reset(new base::debug::TraceMemoryController(
 353       message_loop_->message_loop_proxy(),
 354       ::HeapProfilerWithPseudoStackStart,
 355       ::HeapProfilerStop,
 356       ::GetHeapProfile));
 357 #endif
 358
 359   shared_bitmap_manager_.reset(
 360       new ChildSharedBitmapManager(thread_safe_sender()));
 361 }
 362
 363 ChildThread::~ChildThread() {
 364 #ifdef IPC_MESSAGE_LOG_ENABLED
 365   IPC::Logging::GetInstance()->SetIPCSender(NULL);
 366 #endif
 367
 368   channel_->RemoveFilter(histogram_message_filter_.get());
 369   channel_->RemoveFilter(sync_message_filter_.get());
 370
 371   // The ChannelProxy object caches a pointer to the IPC thread, so need to
 372   // reset it as it's not guaranteed to outlive this object.
 373   // NOTE: this also has the side-effect of not closing the main IPC channel to
 374   // the browser process.  This is needed because this is the signal that the
 375   // browser uses to know that this process has died, so we need it to be alive
 376   // until this process is shut down, and the OS closes the handle
 377   // automatically.  We used to watch the object handle on Windows to do this,
 378   // but it wasn't possible to do so on POSIX.
 379   channel_->ClearIPCTaskRunner();
 380   g_lazy_tls.Pointer()->Set(NULL);
 381 }
 382
 383 void ChildThread::Shutdown() {
 384   // Delete objects that hold references to blink so derived classes can
 385   // safely shutdown blink in their Shutdown implementation.
 386   file_system_dispatcher_.reset();
 387   quota_dispatcher_.reset();
 388   WebFileSystemImpl::DeleteThreadSpecificInstance();
 389 }
 390
 391 void ChildThread::OnChannelConnected(int32 peer_pid) {
 392   channel_connected_factory_.InvalidateWeakPtrs();
 393 }
 394
 395 void ChildThread::OnChannelError() {
 396   set_on_channel_error_called(true);
 397   base::MessageLoop::current()->Quit();
 398 }
 399
 400 bool ChildThread::Send(IPC::Message* msg) {
 401   DCHECK(base::MessageLoop::current() == message_loop());
 402   if (!channel_) {
 403     delete msg;
 404     return false;
 405   }
 406
 407   return channel_->Send(msg);
 408 }
 409
 410 MessageRouter* ChildThread::GetRouter() {
 411   DCHECK(base::MessageLoop::current() == message_loop());
 412   return &router_;
 413 }
 414
 415 base::SharedMemory* ChildThread::AllocateSharedMemory(size_t buf_size) {
 416   return AllocateSharedMemory(buf_size, this);
 417 }
 418
 419 // static
 420 base::SharedMemory* ChildThread::AllocateSharedMemory(
 421     size_t buf_size,
 422     IPC::Sender* sender) {
 423   scoped_ptr<base::SharedMemory> shared_buf;
 424 #if defined(OS_WIN)
 425   shared_buf.reset(new base::SharedMemory);
 426   if (!shared_buf->CreateAndMapAnonymous(buf_size)) {
 427     NOTREACHED();
 428     return NULL;
 429   }
 430 #else
 431   // On POSIX, we need to ask the browser to create the shared memory for us,
 432   // since this is blocked by the sandbox.
 433   base::SharedMemoryHandle shared_mem_handle;
 434   if (sender->Send(new ChildProcessHostMsg_SyncAllocateSharedMemory(
 435                            buf_size, &shared_mem_handle))) {
 436     if (base::SharedMemory::IsHandleValid(shared_mem_handle)) {
 437       shared_buf.reset(new base::SharedMemory(shared_mem_handle, false));
 438       if (!shared_buf->Map(buf_size)) {
 439         NOTREACHED() << "Map failed";
 440         return NULL;
 441       }
 442     } else {
 443       NOTREACHED() << "Browser failed to allocate shared memory";
 444       return NULL;
 445     }
 446   } else {
 447     NOTREACHED() << "Browser allocation request message failed";
 448     return NULL;
 449   }
 450 #endif
 451   return shared_buf.release();
 452 }
 453
 454 bool ChildThread::OnMessageReceived(const IPC::Message& msg) {
 455   if (mojo_application_->OnMessageReceived(msg))
 456     return true;
 457
 458   // Resource responses are sent to the resource dispatcher.
 459   if (resource_dispatcher_->OnMessageReceived(msg))
 460     return true;
 461   if (socket_stream_dispatcher_->OnMessageReceived(msg))
 462     return true;
 463   if (websocket_dispatcher_->OnMessageReceived(msg))
 464     return true;
 465   if (file_system_dispatcher_->OnMessageReceived(msg))
 466     return true;
 467
 468   bool handled = true;
 469   IPC_BEGIN_MESSAGE_MAP(ChildThread, msg)
 470     IPC_MESSAGE_HANDLER(ChildProcessMsg_Shutdown, OnShutdown)
 471 #if defined(IPC_MESSAGE_LOG_ENABLED)
 472     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetIPCLoggingEnabled,
 473                         OnSetIPCLoggingEnabled)
 474 #endif
 475     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetProfilerStatus,
 476                         OnSetProfilerStatus)
 477     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetChildProfilerData,
 478                         OnGetChildProfilerData)
 479     IPC_MESSAGE_HANDLER(ChildProcessMsg_DumpHandles, OnDumpHandles)
 480     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetProcessBackgrounded,
 481                         OnProcessBackgrounded)
 482 #if defined(USE_TCMALLOC)
 483     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetTcmallocStats, OnGetTcmallocStats)
 484 #endif
 485     IPC_MESSAGE_UNHANDLED(handled = false)
 486   IPC_END_MESSAGE_MAP()
 487
 488   if (handled)
 489     return true;
 490
 491   if (msg.routing_id() == MSG_ROUTING_CONTROL)
 492     return OnControlMessageReceived(msg);
 493
 494   return router_.OnMessageReceived(msg);
 495 }
 496
 497 bool ChildThread::OnControlMessageReceived(const IPC::Message& msg) {
 498   return false;
 499 }
 500
 501 void ChildThread::OnShutdown() {
 502   base::MessageLoop::current()->Quit();
 503 }
 504
 505 #if defined(IPC_MESSAGE_LOG_ENABLED)
 506 void ChildThread::OnSetIPCLoggingEnabled(bool enable) {
 507   if (enable)
 508     IPC::Logging::GetInstance()->Enable();
 509   else
 510     IPC::Logging::GetInstance()->Disable();
 511 }
 512 #endif  //  IPC_MESSAGE_LOG_ENABLED
 513
 514 void ChildThread::OnSetProfilerStatus(ThreadData::Status status) {
 515   ThreadData::InitializeAndSetTrackingStatus(status);
 516 }
 517
 518 void ChildThread::OnGetChildProfilerData(int sequence_number) {
 519   tracked_objects::ProcessDataSnapshot process_data;
 520   ThreadData::Snapshot(false, &process_data);
 521
 522   Send(new ChildProcessHostMsg_ChildProfilerData(sequence_number,
 523                                                  process_data));
 524 }
 525
 526 void ChildThread::OnDumpHandles() {
 527 #if defined(OS_WIN)
 528   scoped_refptr<HandleEnumerator> handle_enum(
 529       new HandleEnumerator(
 530           base::CommandLine::ForCurrentProcess()->HasSwitch(
 531               switches::kAuditAllHandles)));
 532   handle_enum->EnumerateHandles();
 533   Send(new ChildProcessHostMsg_DumpHandlesDone);
 534 #else
 535   NOTIMPLEMENTED();
 536 #endif
 537 }
 538
 539 #if defined(USE_TCMALLOC)
 540 void ChildThread::OnGetTcmallocStats() {
 541   std::string result;
 542   char buffer[1024 * 32];
 543   base::allocator::GetStats(buffer, sizeof(buffer));
 544   result.append(buffer);
 545   Send(new ChildProcessHostMsg_TcmallocStats(result));
 546 }
 547 #endif
 548
 549 ChildThread* ChildThread::current() {
 550   return g_lazy_tls.Pointer()->Get();
 551 }
 552
 553 #if defined(OS_ANDROID)
 554 // The method must NOT be called on the child thread itself.
 555 // It may block the child thread if so.
 556 void ChildThread::ShutdownThread() {
 557   DCHECK(!ChildThread::current()) <<
 558       "this method should NOT be called from child thread itself";
 559   {
 560     base::AutoLock lock(g_lazy_child_thread_lock.Get());
 561     while (!g_child_thread)
 562       g_lazy_child_thread_cv.Get().Wait();
 563   }
 564   DCHECK_NE(base::MessageLoop::current(), g_child_thread->message_loop());
 565   g_child_thread->message_loop()->PostTask(
 566       FROM_HERE, base::Bind(&QuitMainThreadMessageLoop));
 567 }
 568 #endif
 569
 570 void ChildThread::OnProcessFinalRelease() {
 571   if (on_channel_error_called_) {
 572     base::MessageLoop::current()->Quit();
 573     return;
 574   }
 575
 576   // The child process shutdown sequence is a request response based mechanism,
 577   // where we send out an initial feeler request to the child process host
 578   // instance in the browser to verify if it's ok to shutdown the child process.
 579   // The browser then sends back a response if it's ok to shutdown. This avoids
 580   // race conditions if the process refcount is 0 but there's an IPC message
 581   // inflight that would addref it.
 582   Send(new ChildProcessHostMsg_ShutdownRequest);
 583 }
 584
 585 void ChildThread::EnsureConnected() {
 586   VLOG(0) << "ChildThread::EnsureConnected()";
 587   base::KillProcess(base::GetCurrentProcessHandle(), 0, false);
 588 }
 589
 590 void ChildThread::OnProcessBackgrounded(bool background) {
 591   // Set timer slack to maximum on main thread when in background.
 592   base::TimerSlack timer_slack = base::TIMER_SLACK_NONE;
 593   if (background)
 594     timer_slack = base::TIMER_SLACK_MAXIMUM;
 595   base::MessageLoop::current()->SetTimerSlack(timer_slack);
 596 }
 597
 598 }  // namespace content