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_discardable_shared_memory_manager.h"
  30 #include "content/child/child_gpu_memory_buffer_manager.h"
  31 #include "content/child/child_histogram_message_filter.h"
  32 #include "content/child/child_process.h"
  33 #include "content/child/child_resource_message_filter.h"
  34 #include "content/child/child_shared_bitmap_manager.h"
  35 #include "content/child/fileapi/file_system_dispatcher.h"
  36 #include "content/child/fileapi/webfilesystem_impl.h"
  37 #include "content/child/geofencing/geofencing_message_filter.h"
  38 #include "content/child/mojo/mojo_application.h"
  39 #include "content/child/notifications/notification_dispatcher.h"
  40 #include "content/child/power_monitor_broadcast_source.h"
  41 #include "content/child/quota_dispatcher.h"
  42 #include "content/child/quota_message_filter.h"
  43 #include "content/child/resource_dispatcher.h"
  44 #include "content/child/service_worker/service_worker_message_filter.h"
  45 #include "content/child/thread_safe_sender.h"
  46 #include "content/child/websocket_dispatcher.h"
  47 #include "content/common/child_process_messages.h"
  48 #include "content/public/common/content_switches.h"
  49 #include "ipc/ipc_logging.h"
  50 #include "ipc/ipc_switches.h"
  51 #include "ipc/ipc_sync_channel.h"
  52 #include "ipc/ipc_sync_message_filter.h"
  53 #include "ipc/mojo/ipc_channel_mojo.h"
  54
  55 #if defined(OS_WIN)
  56 #include "content/common/handle_enumerator_win.h"
  57 #endif
  58
  59 #if defined(TCMALLOC_TRACE_MEMORY_SUPPORTED)
  60 #include "third_party/tcmalloc/chromium/src/gperftools/heap-profiler.h"
  61 #endif
  62
  63 using tracked_objects::ThreadData;
  64
  65 namespace content {
  66 namespace {
  67
  68 // How long to wait for a connection to the browser process before giving up.
  69 const int kConnectionTimeoutS = 15;
  70
  71 base::LazyInstance<base::ThreadLocalPointer<ChildThread> > g_lazy_tls =
  72     LAZY_INSTANCE_INITIALIZER;
  73
  74 // This isn't needed on Windows because there the sandbox's job object
  75 // terminates child processes automatically. For unsandboxed processes (i.e.
  76 // plugins), PluginThread has EnsureTerminateMessageFilter.
  77 #if defined(OS_POSIX)
  78
  79 // TODO(earthdok): Re-enable on CrOS http://crbug.com/360622
  80 #if (defined(ADDRESS_SANITIZER) || defined(LEAK_SANITIZER) || \
  81     defined(THREAD_SANITIZER)) && !defined(OS_CHROMEOS)
  82 // A thread delegate that waits for |duration| and then exits the process with
  83 // _exit(0).
  84 class WaitAndExitDelegate : public base::PlatformThread::Delegate {
  85  public:
  86   explicit WaitAndExitDelegate(base::TimeDelta duration)
  87       : duration_(duration) {}
  88   virtual ~WaitAndExitDelegate() override {}
  89
  90   virtual void ThreadMain() override {
  91     base::PlatformThread::Sleep(duration_);
  92     _exit(0);
  93   }
  94
  95  private:
  96   const base::TimeDelta duration_;
  97   DISALLOW_COPY_AND_ASSIGN(WaitAndExitDelegate);
  98 };
  99
 100 bool CreateWaitAndExitThread(base::TimeDelta duration) {
 101   scoped_ptr<WaitAndExitDelegate> delegate(new WaitAndExitDelegate(duration));
 102
 103   const bool thread_created =
 104       base::PlatformThread::CreateNonJoinable(0, delegate.get());
 105   if (!thread_created)
 106     return false;
 107
 108   // A non joinable thread has been created. The thread will either terminate
 109   // the process or will be terminated by the process. Therefore, keep the
 110   // delegate object alive for the lifetime of the process.
 111   WaitAndExitDelegate* leaking_delegate = delegate.release();
 112   ANNOTATE_LEAKING_OBJECT_PTR(leaking_delegate);
 113   ignore_result(leaking_delegate);
 114   return true;
 115 }
 116 #endif
 117
 118 class SuicideOnChannelErrorFilter : public IPC::MessageFilter {
 119  public:
 120   // IPC::MessageFilter
 121   void OnChannelError() override {
 122     // For renderer/worker processes:
 123     // On POSIX, at least, one can install an unload handler which loops
 124     // forever and leave behind a renderer process which eats 100% CPU forever.
 125     //
 126     // This is because the terminate signals (ViewMsg_ShouldClose and the error
 127     // from the IPC sender) are routed to the main message loop but never
 128     // processed (because that message loop is stuck in V8).
 129     //
 130     // One could make the browser SIGKILL the renderers, but that leaves open a
 131     // large window where a browser failure (or a user, manually terminating
 132     // the browser because "it's stuck") will leave behind a process eating all
 133     // the CPU.
 134     //
 135     // So, we install a filter on the sender so that we can process this event
 136     // here and kill the process.
 137     // TODO(earthdok): Re-enable on CrOS http://crbug.com/360622
 138 #if (defined(ADDRESS_SANITIZER) || defined(LEAK_SANITIZER) || \
 139     defined(THREAD_SANITIZER)) && !defined(OS_CHROMEOS)
 140     // Some sanitizer tools rely on exit handlers (e.g. to run leak detection,
 141     // or dump code coverage data to disk). Instead of exiting the process
 142     // immediately, we give it 60 seconds to run exit handlers.
 143     CHECK(CreateWaitAndExitThread(base::TimeDelta::FromSeconds(60)));
 144 #if defined(LEAK_SANITIZER)
 145     // Invoke LeakSanitizer early to avoid detecting shutdown-only leaks. If
 146     // leaks are found, the process will exit here.
 147     __lsan_do_leak_check();
 148 #endif
 149 #else
 150     _exit(0);
 151 #endif
 152   }
 153
 154  protected:
 155   ~SuicideOnChannelErrorFilter() override {}
 156 };
 157
 158 #endif  // OS(POSIX)
 159
 160 #if defined(OS_ANDROID)
 161 ChildThread* g_child_thread = NULL;
 162
 163 // A lock protects g_child_thread.
 164 base::LazyInstance<base::Lock> g_lazy_child_thread_lock =
 165     LAZY_INSTANCE_INITIALIZER;
 166
 167 // base::ConditionVariable has an explicit constructor that takes
 168 // a base::Lock pointer as parameter. The base::DefaultLazyInstanceTraits
 169 // doesn't handle the case. Thus, we need our own class here.
 170 struct CondVarLazyInstanceTraits {
 171   static const bool kRegisterOnExit = true;
 172 #ifndef NDEBUG
 173   static const bool kAllowedToAccessOnNonjoinableThread = false;
 174 #endif
 175
 176   static base::ConditionVariable* New(void* instance) {
 177     return new (instance) base::ConditionVariable(
 178         g_lazy_child_thread_lock.Pointer());
 179   }
 180   static void Delete(base::ConditionVariable* instance) {
 181     instance->~ConditionVariable();
 182   }
 183 };
 184
 185 // A condition variable that synchronize threads initializing and waiting
 186 // for g_child_thread.
 187 base::LazyInstance<base::ConditionVariable, CondVarLazyInstanceTraits>
 188     g_lazy_child_thread_cv = LAZY_INSTANCE_INITIALIZER;
 189
 190 void QuitMainThreadMessageLoop() {
 191   base::MessageLoop::current()->Quit();
 192 }
 193
 194 #endif
 195
 196 }  // namespace
 197
 198 ChildThread::Options::Options()
 199     : channel_name(base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 200           switches::kProcessChannelID)),
 201       use_mojo_channel(false) {}
 202
 203 ChildThread::Options::Options(bool mojo)
 204     : channel_name(base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 205           switches::kProcessChannelID)),
 206       use_mojo_channel(mojo) {}
 207
 208
 209 ChildThread::ChildThreadMessageRouter::ChildThreadMessageRouter(
 210     IPC::Sender* sender)
 211     : sender_(sender) {}
 212
 213 bool ChildThread::ChildThreadMessageRouter::Send(IPC::Message* msg) {
 214   return sender_->Send(msg);
 215 }
 216
 217 ChildThread::ChildThread()
 218     : router_(this),
 219       in_browser_process_(false),
 220       channel_connected_factory_(this) {
 221   Init(Options());
 222 }
 223
 224 ChildThread::ChildThread(const Options& options)
 225     : router_(this),
 226       in_browser_process_(true),
 227       channel_connected_factory_(this) {
 228   Init(options);
 229 }
 230
 231 scoped_ptr<IPC::SyncChannel> ChildThread::CreateChannel(bool use_mojo_channel) {
 232   if (use_mojo_channel) {
 233     VLOG(1) << "Mojo is enabled on child";
 234     return IPC::SyncChannel::Create(
 235         IPC::ChannelMojo::CreateClientFactory(channel_name_),
 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   websocket_dispatcher_.reset(new WebSocketDispatcher);
 279   file_system_dispatcher_.reset(new FileSystemDispatcher());
 280
 281   histogram_message_filter_ = new ChildHistogramMessageFilter();
 282   resource_message_filter_ =
 283       new ChildResourceMessageFilter(resource_dispatcher());
 284
 285   service_worker_message_filter_ =
 286       new ServiceWorkerMessageFilter(thread_safe_sender_.get());
 287
 288   quota_message_filter_ =
 289       new QuotaMessageFilter(thread_safe_sender_.get());
 290   quota_dispatcher_.reset(new QuotaDispatcher(thread_safe_sender_.get(),
 291                                               quota_message_filter_.get()));
 292   geofencing_message_filter_ =
 293       new GeofencingMessageFilter(thread_safe_sender_.get());
 294   notification_dispatcher_ =
 295       new NotificationDispatcher(thread_safe_sender_.get());
 296   channel_->AddFilter(histogram_message_filter_.get());
 297   channel_->AddFilter(sync_message_filter_.get());
 298   channel_->AddFilter(resource_message_filter_.get());
 299   channel_->AddFilter(quota_message_filter_->GetFilter());
 300   channel_->AddFilter(notification_dispatcher_->GetFilter());
 301   channel_->AddFilter(service_worker_message_filter_->GetFilter());
 302   channel_->AddFilter(geofencing_message_filter_->GetFilter());
 303
 304   if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
 305           switches::kSingleProcess)) {
 306     // In single process mode, browser-side tracing will cover the whole
 307     // process including renderers.
 308     channel_->AddFilter(new tracing::ChildTraceMessageFilter(
 309         ChildProcess::current()->io_message_loop_proxy()));
 310   }
 311
 312   // In single process mode we may already have a power monitor
 313   if (!base::PowerMonitor::Get()) {
 314     scoped_ptr<PowerMonitorBroadcastSource> power_monitor_source(
 315       new PowerMonitorBroadcastSource());
 316     channel_->AddFilter(power_monitor_source->GetMessageFilter());
 317
 318     power_monitor_.reset(new base::PowerMonitor(
 319         power_monitor_source.Pass()));
 320   }
 321
 322 #if defined(OS_POSIX)
 323   // Check that --process-type is specified so we don't do this in unit tests
 324   // and single-process mode.
 325   if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kProcessType))
 326     channel_->AddFilter(new SuicideOnChannelErrorFilter());
 327 #endif
 328
 329   int connection_timeout = kConnectionTimeoutS;
 330   std::string connection_override =
 331       base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 332           switches::kIPCConnectionTimeout);
 333   if (!connection_override.empty()) {
 334     int temp;
 335     if (base::StringToInt(connection_override, &temp))
 336       connection_timeout = temp;
 337   }
 338
 339   base::MessageLoop::current()->PostDelayedTask(
 340       FROM_HERE,
 341       base::Bind(&ChildThread::EnsureConnected,
 342                  channel_connected_factory_.GetWeakPtr()),
 343       base::TimeDelta::FromSeconds(connection_timeout));
 344
 345 #if defined(OS_ANDROID)
 346   {
 347     base::AutoLock lock(g_lazy_child_thread_lock.Get());
 348     g_child_thread = this;
 349   }
 350   // Signalling without locking is fine here because only
 351   // one thread can wait on the condition variable.
 352   g_lazy_child_thread_cv.Get().Signal();
 353 #endif
 354
 355 #if defined(TCMALLOC_TRACE_MEMORY_SUPPORTED)
 356   trace_memory_controller_.reset(new base::debug::TraceMemoryController(
 357       message_loop_->message_loop_proxy(),
 358       ::HeapProfilerWithPseudoStackStart,
 359       ::HeapProfilerStop,
 360       ::GetHeapProfile));
 361 #endif
 362
 363   shared_bitmap_manager_.reset(
 364       new ChildSharedBitmapManager(thread_safe_sender()));
 365
 366   gpu_memory_buffer_manager_.reset(
 367       new ChildGpuMemoryBufferManager(thread_safe_sender()));
 368
 369   discardable_shared_memory_manager_.reset(
 370       new ChildDiscardableSharedMemoryManager(thread_safe_sender()));
 371 }
 372
 373 ChildThread::~ChildThread() {
 374 #ifdef IPC_MESSAGE_LOG_ENABLED
 375   IPC::Logging::GetInstance()->SetIPCSender(NULL);
 376 #endif
 377
 378   channel_->RemoveFilter(histogram_message_filter_.get());
 379   channel_->RemoveFilter(sync_message_filter_.get());
 380
 381   // The ChannelProxy object caches a pointer to the IPC thread, so need to
 382   // reset it as it's not guaranteed to outlive this object.
 383   // NOTE: this also has the side-effect of not closing the main IPC channel to
 384   // the browser process.  This is needed because this is the signal that the
 385   // browser uses to know that this process has died, so we need it to be alive
 386   // until this process is shut down, and the OS closes the handle
 387   // automatically.  We used to watch the object handle on Windows to do this,
 388   // but it wasn't possible to do so on POSIX.
 389   channel_->ClearIPCTaskRunner();
 390   g_lazy_tls.Pointer()->Set(NULL);
 391 }
 392
 393 void ChildThread::Shutdown() {
 394   // Delete objects that hold references to blink so derived classes can
 395   // safely shutdown blink in their Shutdown implementation.
 396   file_system_dispatcher_.reset();
 397   quota_dispatcher_.reset();
 398   WebFileSystemImpl::DeleteThreadSpecificInstance();
 399 }
 400
 401 void ChildThread::OnChannelConnected(int32 peer_pid) {
 402   channel_connected_factory_.InvalidateWeakPtrs();
 403 }
 404
 405 void ChildThread::OnChannelError() {
 406   set_on_channel_error_called(true);
 407   base::MessageLoop::current()->Quit();
 408 }
 409
 410 bool ChildThread::Send(IPC::Message* msg) {
 411   DCHECK(base::MessageLoop::current() == message_loop());
 412   if (!channel_) {
 413     delete msg;
 414     return false;
 415   }
 416
 417   return channel_->Send(msg);
 418 }
 419
 420 MessageRouter* ChildThread::GetRouter() {
 421   DCHECK(base::MessageLoop::current() == message_loop());
 422   return &router_;
 423 }
 424
 425 base::SharedMemory* ChildThread::AllocateSharedMemory(size_t buf_size) {
 426   return AllocateSharedMemory(buf_size, this);
 427 }
 428
 429 // static
 430 base::SharedMemory* ChildThread::AllocateSharedMemory(
 431     size_t buf_size,
 432     IPC::Sender* sender) {
 433   scoped_ptr<base::SharedMemory> shared_buf;
 434 #if defined(OS_WIN)
 435   shared_buf.reset(new base::SharedMemory);
 436   if (!shared_buf->CreateAndMapAnonymous(buf_size)) {
 437     NOTREACHED();
 438     return NULL;
 439   }
 440 #else
 441   // On POSIX, we need to ask the browser to create the shared memory for us,
 442   // since this is blocked by the sandbox.
 443   base::SharedMemoryHandle shared_mem_handle;
 444   if (sender->Send(new ChildProcessHostMsg_SyncAllocateSharedMemory(
 445                            buf_size, &shared_mem_handle))) {
 446     if (base::SharedMemory::IsHandleValid(shared_mem_handle)) {
 447       shared_buf.reset(new base::SharedMemory(shared_mem_handle, false));
 448       if (!shared_buf->Map(buf_size)) {
 449         NOTREACHED() << "Map failed";
 450         return NULL;
 451       }
 452     } else {
 453       NOTREACHED() << "Browser failed to allocate shared memory";
 454       return NULL;
 455     }
 456   } else {
 457     NOTREACHED() << "Browser allocation request message failed";
 458     return NULL;
 459   }
 460 #endif
 461   return shared_buf.release();
 462 }
 463
 464 bool ChildThread::OnMessageReceived(const IPC::Message& msg) {
 465   if (mojo_application_->OnMessageReceived(msg))
 466     return true;
 467
 468   // Resource responses are sent to the resource dispatcher.
 469   if (resource_dispatcher_->OnMessageReceived(msg))
 470     return true;
 471   if (websocket_dispatcher_->OnMessageReceived(msg))
 472     return true;
 473   if (file_system_dispatcher_->OnMessageReceived(msg))
 474     return true;
 475
 476   bool handled = true;
 477   IPC_BEGIN_MESSAGE_MAP(ChildThread, msg)
 478     IPC_MESSAGE_HANDLER(ChildProcessMsg_Shutdown, OnShutdown)
 479 #if defined(IPC_MESSAGE_LOG_ENABLED)
 480     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetIPCLoggingEnabled,
 481                         OnSetIPCLoggingEnabled)
 482 #endif
 483     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetProfilerStatus,
 484                         OnSetProfilerStatus)
 485     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetChildProfilerData,
 486                         OnGetChildProfilerData)
 487     IPC_MESSAGE_HANDLER(ChildProcessMsg_DumpHandles, OnDumpHandles)
 488     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetProcessBackgrounded,
 489                         OnProcessBackgrounded)
 490 #if defined(USE_TCMALLOC)
 491     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetTcmallocStats, OnGetTcmallocStats)
 492 #endif
 493     IPC_MESSAGE_UNHANDLED(handled = false)
 494   IPC_END_MESSAGE_MAP()
 495
 496   if (handled)
 497     return true;
 498
 499   if (msg.routing_id() == MSG_ROUTING_CONTROL)
 500     return OnControlMessageReceived(msg);
 501
 502   return router_.OnMessageReceived(msg);
 503 }
 504
 505 bool ChildThread::OnControlMessageReceived(const IPC::Message& msg) {
 506   return false;
 507 }
 508
 509 void ChildThread::OnShutdown() {
 510   base::MessageLoop::current()->Quit();
 511 }
 512
 513 #if defined(IPC_MESSAGE_LOG_ENABLED)
 514 void ChildThread::OnSetIPCLoggingEnabled(bool enable) {
 515   if (enable)
 516     IPC::Logging::GetInstance()->Enable();
 517   else
 518     IPC::Logging::GetInstance()->Disable();
 519 }
 520 #endif  //  IPC_MESSAGE_LOG_ENABLED
 521
 522 void ChildThread::OnSetProfilerStatus(ThreadData::Status status) {
 523   ThreadData::InitializeAndSetTrackingStatus(status);
 524 }
 525
 526 void ChildThread::OnGetChildProfilerData(int sequence_number) {
 527   tracked_objects::ProcessDataSnapshot process_data;
 528   ThreadData::Snapshot(false, &process_data);
 529
 530   Send(new ChildProcessHostMsg_ChildProfilerData(sequence_number,
 531                                                  process_data));
 532 }
 533
 534 void ChildThread::OnDumpHandles() {
 535 #if defined(OS_WIN)
 536   scoped_refptr<HandleEnumerator> handle_enum(
 537       new HandleEnumerator(
 538           base::CommandLine::ForCurrentProcess()->HasSwitch(
 539               switches::kAuditAllHandles)));
 540   handle_enum->EnumerateHandles();
 541   Send(new ChildProcessHostMsg_DumpHandlesDone);
 542 #else
 543   NOTIMPLEMENTED();
 544 #endif
 545 }
 546
 547 #if defined(USE_TCMALLOC)
 548 void ChildThread::OnGetTcmallocStats() {
 549   std::string result;
 550   char buffer[1024 * 32];
 551   base::allocator::GetStats(buffer, sizeof(buffer));
 552   result.append(buffer);
 553   Send(new ChildProcessHostMsg_TcmallocStats(result));
 554 }
 555 #endif
 556
 557 ChildThread* ChildThread::current() {
 558   return g_lazy_tls.Pointer()->Get();
 559 }
 560
 561 #if defined(OS_ANDROID)
 562 // The method must NOT be called on the child thread itself.
 563 // It may block the child thread if so.
 564 void ChildThread::ShutdownThread() {
 565   DCHECK(!ChildThread::current()) <<
 566       "this method should NOT be called from child thread itself";
 567   {
 568     base::AutoLock lock(g_lazy_child_thread_lock.Get());
 569     while (!g_child_thread)
 570       g_lazy_child_thread_cv.Get().Wait();
 571   }
 572   DCHECK_NE(base::MessageLoop::current(), g_child_thread->message_loop());
 573   g_child_thread->message_loop()->PostTask(
 574       FROM_HERE, base::Bind(&QuitMainThreadMessageLoop));
 575 }
 576 #endif
 577
 578 void ChildThread::OnProcessFinalRelease() {
 579   if (on_channel_error_called_) {
 580     base::MessageLoop::current()->Quit();
 581     return;
 582   }
 583
 584   // The child process shutdown sequence is a request response based mechanism,
 585   // where we send out an initial feeler request to the child process host
 586   // instance in the browser to verify if it's ok to shutdown the child process.
 587   // The browser then sends back a response if it's ok to shutdown. This avoids
 588   // race conditions if the process refcount is 0 but there's an IPC message
 589   // inflight that would addref it.
 590   Send(new ChildProcessHostMsg_ShutdownRequest);
 591 }
 592
 593 void ChildThread::EnsureConnected() {
 594   VLOG(0) << "ChildThread::EnsureConnected()";
 595   base::KillProcess(base::GetCurrentProcessHandle(), 0, false);
 596 }
 597
 598 void ChildThread::OnProcessBackgrounded(bool background) {
 599   // Set timer slack to maximum on main thread when in background.
 600   base::TimerSlack timer_slack = base::TIMER_SLACK_NONE;
 601   if (background)
 602     timer_slack = base::TIMER_SLACK_MAXIMUM;
 603   base::MessageLoop::current()->SetTimerSlack(timer_slack);
 604 }
 605
 606 }  // namespace content