// Copyright 2013 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.
#ifndef BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_
#define BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_
#include <queue>
#include <string>
#include "base/base_export.h"
#include "base/basictypes.h"
#include "base/callback_forward.h"
#include "base/location.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/message_loop/incoming_task_queue.h"
#include "base/message_loop/message_loop_proxy.h"
#include "base/message_loop/message_loop_proxy_impl.h"
#include "base/message_loop/message_pump.h"
#include "base/observer_list.h"
#include "base/pending_task.h"
#include "base/sequenced_task_runner_helpers.h"
#include "base/synchronization/lock.h"
#include "base/time/time.h"
#include "base/tracking_info.h"
// TODO(sky): these includes should not be necessary. Nuke them.
#if defined(OS_WIN)
#include "base/message_loop/message_pump_win.h"
#elif defined(OS_IOS)
#include "base/message_loop/message_pump_io_ios.h"
#elif defined(OS_POSIX)
#include "base/message_loop/message_pump_libevent.h"
#if !defined(OS_MACOSX) && !defined(OS_ANDROID)
#if defined(USE_AURA) && defined(USE_X11) && !defined(OS_NACL)
#include "base/message_loop/message_pump_x11.h"
#elif defined(USE_OZONE) && !defined(OS_NACL)
#include "base/message_loop/message_pump_ozone.h"
#elif !defined(OS_ANDROID_HOST)
#define USE_GTK_MESSAGE_PUMP
#include "base/message_loop/message_pump_gtk.h"
#if defined(TOOLKIT_GTK)
#include "base/message_loop/message_pump_x11.h"
#endif
#endif
#endif
#endif
namespace base {
class HistogramBase;
class MessagePumpObserver;
class RunLoop;
class ThreadTaskRunnerHandle;
#if defined(OS_ANDROID)
class MessagePumpForUI;
#elif defined(OS_ANDROID_HOST)
typedef MessagePumpLibevent MessagePumpForUI;
#endif
class WaitableEvent;
// A MessageLoop is used to process events for a particular thread. There is
// at most one MessageLoop instance per thread.
//
// Events include at a minimum Task instances submitted to PostTask and its
// variants. Depending on the type of message pump used by the MessageLoop
// other events such as UI messages may be processed. On Windows APC calls (as
// time permits) and signals sent to a registered set of HANDLEs may also be
// processed.
//
// NOTE: Unless otherwise specified, a MessageLoop's methods may only be called
// on the thread where the MessageLoop's Run method executes.
//
// NOTE: MessageLoop has task reentrancy protection. This means that if a
// task is being processed, a second task cannot start until the first task is
// finished. Reentrancy can happen when processing a task, and an inner
// message pump is created. That inner pump then processes native messages
// which could implicitly start an inner task. Inner message pumps are created
// with dialogs (DialogBox), common dialogs (GetOpenFileName), OLE functions
// (DoDragDrop), printer functions (StartDoc) and *many* others.
//
// Sample workaround when inner task processing is needed:
// HRESULT hr;
// {
// MessageLoop::ScopedNestableTaskAllower allow(MessageLoop::current());
// hr = DoDragDrop(...); // Implicitly runs a modal message loop.
// }
// // Process |hr| (the result returned by DoDragDrop()).
//
// Please be SURE your task is reentrant (nestable) and all global variables
// are stable and accessible before calling SetNestableTasksAllowed(true).
//
class BASE_EXPORT MessageLoop : public MessagePump::Delegate {
public:
#if defined(USE_AURA)
typedef MessagePumpObserver Observer;
#elif defined(USE_GTK_MESSAGE_PUMP)
typedef MessagePumpGdkObserver Observer;
#endif
// A MessageLoop has a particular type, which indicates the set of
// asynchronous events it may process in addition to tasks and timers.
//
// TYPE_DEFAULT
// This type of ML only supports tasks and timers.
//
// TYPE_UI
// This type of ML also supports native UI events (e.g., Windows messages).
// See also MessageLoopForUI.
//
// TYPE_GPU
// This type of ML also supports native UI events for use in the GPU
// process. On Linux this will always be an X11 ML (as compared with the
// sometimes-GTK ML in the browser process).
//
// TYPE_IO
// This type of ML also supports asynchronous IO. See also
// MessageLoopForIO.
//
// TYPE_JAVA
// This type of ML is backed by a Java message handler which is responsible
// for running the tasks added to the ML. This is only for use on Android.
// TYPE_JAVA behaves in essence like TYPE_UI, except during construction
// where it does not use the main thread specific pump factory.
//
// TYPE_CUSTOM
// MessagePump was supplied to constructor.
//
enum Type {
TYPE_DEFAULT,
TYPE_UI,
TYPE_CUSTOM,
#if defined(TOOLKIT_GTK)
TYPE_GPU,
#endif
TYPE_IO,
#if defined(OS_ANDROID)
TYPE_JAVA,
#endif // defined(OS_ANDROID)
};
// Normally, it is not necessary to instantiate a MessageLoop. Instead, it
// is typical to make use of the current thread's MessageLoop instance.
explicit MessageLoop(Type type = TYPE_DEFAULT);
// Creates a TYPE_CUSTOM MessageLoop with the supplied MessagePump, which must
// be non-NULL.
explicit MessageLoop(scoped_ptr<base::MessagePump> pump);
virtual ~MessageLoop();
// Returns the MessageLoop object for the current thread, or null if none.
static MessageLoop* current();
static void EnableHistogrammer(bool enable_histogrammer);
typedef scoped_ptr<MessagePump> (MessagePumpFactory)();
// Uses the given base::MessagePumpForUIFactory to override the default
// MessagePump implementation for 'TYPE_UI'. Returns true if the factory
// was successfully registered.
static bool InitMessagePumpForUIFactory(MessagePumpFactory* factory);
// Creates the default MessagePump based on |type|. Caller owns return
// value.
static scoped_ptr<MessagePump> CreateMessagePumpForType(Type type);
// A DestructionObserver is notified when the current MessageLoop is being
// destroyed. These observers are notified prior to MessageLoop::current()
// being changed to return NULL. This gives interested parties the chance to
// do final cleanup that depends on the MessageLoop.
//
// NOTE: Any tasks posted to the MessageLoop during this notification will
// not be run. Instead, they will be deleted.
//
class BASE_EXPORT DestructionObserver {
public:
virtual void WillDestroyCurrentMessageLoop() = 0;
protected:
virtual ~DestructionObserver();
};
// Add a DestructionObserver, which will start receiving notifications
// immediately.
void AddDestructionObserver(DestructionObserver* destruction_observer);
// Remove a DestructionObserver. It is safe to call this method while a
// DestructionObserver is receiving a notification callback.
void RemoveDestructionObserver(DestructionObserver* destruction_observer);
// The "PostTask" family of methods call the task's Run method asynchronously
// from within a message loop at some point in the future.
//
// With the PostTask variant, tasks are invoked in FIFO order, inter-mixed
// with normal UI or IO event processing. With the PostDelayedTask variant,
// tasks are called after at least approximately 'delay_ms' have elapsed.
//
// The NonNestable variants work similarly except that they promise never to
// dispatch the task from a nested invocation of MessageLoop::Run. Instead,
// such tasks get deferred until the top-most MessageLoop::Run is executing.
//
// The MessageLoop takes ownership of the Task, and deletes it after it has
// been Run().
//
// PostTask(from_here, task) is equivalent to
// PostDelayedTask(from_here, task, 0).
//
// NOTE: These methods may be called on any thread. The Task will be invoked
// on the thread that executes MessageLoop::Run().
void PostTask(const tracked_objects::Location& from_here,
const Closure& task);
void PostDelayedTask(const tracked_objects::Location& from_here,
const Closure& task,
TimeDelta delay);
void PostNonNestableTask(const tracked_objects::Location& from_here,
const Closure& task);
void PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
const Closure& task,
TimeDelta delay);
// A variant on PostTask that deletes the given object. This is useful
// if the object needs to live until the next run of the MessageLoop (for
// example, deleting a RenderProcessHost from within an IPC callback is not
// good).
//
// NOTE: This method may be called on any thread. The object will be deleted
// on the thread that executes MessageLoop::Run(). If this is not the same
// as the thread that calls PostDelayedTask(FROM_HERE, ), then T MUST inherit
// from RefCountedThreadSafe<T>!
template <class T>
void DeleteSoon(const tracked_objects::Location& from_here, const T* object) {
base::subtle::DeleteHelperInternal<T, void>::DeleteViaSequencedTaskRunner(
this, from_here, object);
}
// A variant on PostTask that releases the given reference counted object
// (by calling its Release method). This is useful if the object needs to
// live until the next run of the MessageLoop, or if the object needs to be
// released on a particular thread.
//
// NOTE: This method may be called on any thread. The object will be
// released (and thus possibly deleted) on the thread that executes
// MessageLoop::Run(). If this is not the same as the thread that calls
// PostDelayedTask(FROM_HERE, ), then T MUST inherit from
// RefCountedThreadSafe<T>!
template <class T>
void ReleaseSoon(const tracked_objects::Location& from_here,
const T* object) {
base::subtle::ReleaseHelperInternal<T, void>::ReleaseViaSequencedTaskRunner(
this, from_here, object);
}
// Deprecated: use RunLoop instead.
// Run the message loop.
void Run();
// Deprecated: use RunLoop instead.
// Process all pending tasks, windows messages, etc., but don't wait/sleep.
// Return as soon as all items that can be run are taken care of.
void RunUntilIdle();
// TODO(jbates) remove this. crbug.com/131220. See QuitWhenIdle().
void Quit() { QuitWhenIdle(); }
// Deprecated: use RunLoop instead.
//
// Signals the Run method to return when it becomes idle. It will continue to
// process pending messages and future messages as long as they are enqueued.
// Warning: if the MessageLoop remains busy, it may never quit. Only use this
// Quit method when looping procedures (such as web pages) have been shut
// down.
//
// This method may only be called on the same thread that called Run, and Run
// must still be on the call stack.
//
// Use QuitClosure variants if you need to Quit another thread's MessageLoop,
// but note that doing so is fairly dangerous if the target thread makes
// nested calls to MessageLoop::Run. The problem being that you won't know
// which nested run loop you are quitting, so be careful!
void QuitWhenIdle();
// Deprecated: use RunLoop instead.
//
// This method is a variant of Quit, that does not wait for pending messages
// to be processed before returning from Run.
void QuitNow();
// TODO(jbates) remove this. crbug.com/131220. See QuitWhenIdleClosure().
static Closure QuitClosure() { return QuitWhenIdleClosure(); }
// Deprecated: use RunLoop instead.
// Construct a Closure that will call QuitWhenIdle(). Useful to schedule an
// arbitrary MessageLoop to QuitWhenIdle.
static Closure QuitWhenIdleClosure();
// Returns true if this loop is |type|. This allows subclasses (especially
// those in tests) to specialize how they are identified.
virtual bool IsType(Type type) const;
// Returns the type passed to the constructor.
Type type() const { return type_; }
// Optional call to connect the thread name with this loop.
void set_thread_name(const std::string& thread_name) {
DCHECK(thread_name_.empty()) << "Should not rename this thread!";
thread_name_ = thread_name;
}
const std::string& thread_name() const { return thread_name_; }
// Gets the message loop proxy associated with this message loop.
scoped_refptr<MessageLoopProxy> message_loop_proxy() {
return message_loop_proxy_;
}
// Enables or disables the recursive task processing. This happens in the case
// of recursive message loops. Some unwanted message loop may occurs when
// using common controls or printer functions. By default, recursive task
// processing is disabled.
//
// Please utilize |ScopedNestableTaskAllower| instead of calling these methods
// directly. In general nestable message loops are to be avoided. They are
// dangerous and difficult to get right, so please use with extreme caution.
//
// The specific case where tasks get queued is:
// - The thread is running a message loop.
// - It receives a task #1 and execute it.
// - The task #1 implicitly start a message loop, like a MessageBox in the
// unit test. This can also be StartDoc or GetSaveFileName.
// - The thread receives a task #2 before or while in this second message
// loop.
// - With NestableTasksAllowed set to true, the task #2 will run right away.
// Otherwise, it will get executed right after task #1 completes at "thread
// message loop level".
void SetNestableTasksAllowed(bool allowed);
bool NestableTasksAllowed() const;
// Enables nestable tasks on |loop| while in scope.
class ScopedNestableTaskAllower {
public:
explicit ScopedNestableTaskAllower(MessageLoop* loop)
: loop_(loop),
old_state_(loop_->NestableTasksAllowed()) {
loop_->SetNestableTasksAllowed(true);
}
~ScopedNestableTaskAllower() {
loop_->SetNestableTasksAllowed(old_state_);
}
private:
MessageLoop* loop_;
bool old_state_;
};
// Returns true if we are currently running a nested message loop.
bool IsNested();
// A TaskObserver is an object that receives task notifications from the
// MessageLoop.
//
// NOTE: A TaskObserver implementation should be extremely fast!
class BASE_EXPORT TaskObserver {
public:
TaskObserver();
// This method is called before processing a task.
virtual void WillProcessTask(const PendingTask& pending_task) = 0;
// This method is called after processing a task.
virtual void DidProcessTask(const PendingTask& pending_task) = 0;
protected:
virtual ~TaskObserver();
};
// These functions can only be called on the same thread that |this| is
// running on.
void AddTaskObserver(TaskObserver* task_observer);
void RemoveTaskObserver(TaskObserver* task_observer);
// When we go into high resolution timer mode, we will stay in hi-res mode
// for at least 1s.
static const int kHighResolutionTimerModeLeaseTimeMs = 1000;
#if defined(OS_WIN)
void set_os_modal_loop(bool os_modal_loop) {
os_modal_loop_ = os_modal_loop;
}
bool os_modal_loop() const {
return os_modal_loop_;
}
#endif // OS_WIN
// Can only be called from the thread that owns the MessageLoop.
bool is_running() const;
// Returns true if the message loop has high resolution timers enabled.
// Provided for testing.
bool IsHighResolutionTimerEnabledForTesting();
// Returns true if the message loop is "idle". Provided for testing.
bool IsIdleForTesting();
//----------------------------------------------------------------------------
protected:
#if defined(OS_WIN)
MessagePumpWin* pump_win() {
return static_cast<MessagePumpWin*>(pump_.get());
}
#elif defined(OS_POSIX) && !defined(OS_IOS)
MessagePumpLibevent* pump_libevent() {
return static_cast<MessagePumpLibevent*>(pump_.get());
}
#if defined(TOOLKIT_GTK)
friend class MessagePumpX11;
MessagePumpX11* pump_gpu() {
DCHECK_EQ(TYPE_GPU, type());
return static_cast<MessagePumpX11*>(pump_.get());
}
#endif
#endif
scoped_ptr<MessagePump> pump_;
private:
friend class internal::IncomingTaskQueue;
friend class RunLoop;
// Configures various members for the two constructors.
void Init();
// Invokes the actual run loop using the message pump.
void RunHandler();
// Called to process any delayed non-nestable tasks.
bool ProcessNextDelayedNonNestableTask();
// Runs the specified PendingTask.
void RunTask(const PendingTask& pending_task);
// Calls RunTask or queues the pending_task on the deferred task list if it
// cannot be run right now. Returns true if the task was run.
bool DeferOrRunPendingTask(const PendingTask& pending_task);
// Adds the pending task to delayed_work_queue_.
void AddToDelayedWorkQueue(const PendingTask& pending_task);
// Delete tasks that haven't run yet without running them. Used in the
// destructor to make sure all the task's destructors get called. Returns
// true if some work was done.
bool DeletePendingTasks();
// Creates a process-wide unique ID to represent this task in trace events.
// This will be mangled with a Process ID hash to reduce the likelyhood of
// colliding with MessageLoop pointers on other processes.
uint64 GetTaskTraceID(const PendingTask& task);
// Loads tasks from the incoming queue to |work_queue_| if the latter is
// empty.
void ReloadWorkQueue();
// Wakes up the message pump. Can be called on any thread. The caller is
// responsible for synchronizing ScheduleWork() calls.
void ScheduleWork(bool was_empty);
// Start recording histogram info about events and action IF it was enabled
// and IF the statistics recorder can accept a registration of our histogram.
void StartHistogrammer();
// Add occurrence of event to our histogram, so that we can see what is being
// done in a specific MessageLoop instance (i.e., specific thread).
// If message_histogram_ is NULL, this is a no-op.
void HistogramEvent(int event);
// MessagePump::Delegate methods:
virtual bool DoWork() OVERRIDE;
virtual bool DoDelayedWork(TimeTicks* next_delayed_work_time) OVERRIDE;
virtual bool DoIdleWork() OVERRIDE;
virtual void GetQueueingInformation(size_t* queue_size,
TimeDelta* queueing_delay) OVERRIDE;
const Type type_;
// A list of tasks that need to be processed by this instance. Note that
// this queue is only accessed (push/pop) by our current thread.
TaskQueue work_queue_;
// Contains delayed tasks, sorted by their 'delayed_run_time' property.
DelayedTaskQueue delayed_work_queue_;
// A recent snapshot of Time::Now(), used to check delayed_work_queue_.
TimeTicks recent_time_;
// A queue of non-nestable tasks that we had to defer because when it came
// time to execute them we were in a nested message loop. They will execute
// once we're out of nested message loops.
TaskQueue deferred_non_nestable_work_queue_;
ObserverList<DestructionObserver> destruction_observers_;
// A recursion block that prevents accidentally running additional tasks when
// insider a (accidentally induced?) nested message pump.
bool nestable_tasks_allowed_;
#if defined(OS_WIN)
// Should be set to true before calling Windows APIs like TrackPopupMenu, etc
// which enter a modal message loop.
bool os_modal_loop_;
#endif
std::string thread_name_;
// A profiling histogram showing the counts of various messages and events.
HistogramBase* message_histogram_;
RunLoop* run_loop_;
ObserverList<TaskObserver> task_observers_;
scoped_refptr<internal::IncomingTaskQueue> incoming_task_queue_;
// The message loop proxy associated with this message loop.
scoped_refptr<internal::MessageLoopProxyImpl> message_loop_proxy_;
scoped_ptr<ThreadTaskRunnerHandle> thread_task_runner_handle_;
template <class T, class R> friend class base::subtle::DeleteHelperInternal;
template <class T, class R> friend class base::subtle::ReleaseHelperInternal;
void DeleteSoonInternal(const tracked_objects::Location& from_here,
void(*deleter)(const void*),
const void* object);
void ReleaseSoonInternal(const tracked_objects::Location& from_here,
void(*releaser)(const void*),
const void* object);
DISALLOW_COPY_AND_ASSIGN(MessageLoop);
};
//-----------------------------------------------------------------------------
// MessageLoopForUI extends MessageLoop with methods that are particular to a
// MessageLoop instantiated with TYPE_UI.
//
// This class is typically used like so:
// MessageLoopForUI::current()->...call some method...
//
class BASE_EXPORT MessageLoopForUI : public MessageLoop {
public:
MessageLoopForUI() : MessageLoop(TYPE_UI) {
}
// Returns the MessageLoopForUI of the current thread.
static MessageLoopForUI* current() {
MessageLoop* loop = MessageLoop::current();
DCHECK(loop);
DCHECK_EQ(MessageLoop::TYPE_UI, loop->type());
return static_cast<MessageLoopForUI*>(loop);
}
static bool IsCurrent() {
MessageLoop* loop = MessageLoop::current();
return loop && loop->type() == MessageLoop::TYPE_UI;
}
#if defined(OS_IOS)
// On iOS, the main message loop cannot be Run(). Instead call Attach(),
// which connects this MessageLoop to the UI thread's CFRunLoop and allows
// PostTask() to work.
void Attach();
#endif
#if defined(OS_ANDROID)
// On Android, the UI message loop is handled by Java side. So Run() should
// never be called. Instead use Start(), which will forward all the native UI
// events to the Java message loop.
void Start();
#endif
#if !defined(OS_NACL) && (defined(TOOLKIT_GTK) || defined(USE_OZONE) || \
defined(OS_WIN) || defined(USE_X11))
// Please see message_pump_win/message_pump_glib for definitions of these
// methods.
void AddObserver(Observer* observer);
void RemoveObserver(Observer* observer);
#endif
protected:
#if defined(USE_X11)
friend class MessagePumpX11;
#endif
#if defined(USE_OZONE) && !defined(OS_NACL)
friend class MessagePumpOzone;
#endif
#if !defined(OS_MACOSX) && !defined(OS_ANDROID)
// TODO(rvargas): Make this platform independent.
MessagePumpForUI* pump_ui() {
return static_cast<MessagePumpForUI*>(pump_.get());
}
#endif
};
// Do not add any member variables to MessageLoopForUI! This is important b/c
// MessageLoopForUI is often allocated via MessageLoop(TYPE_UI). Any extra
// data that you need should be stored on the MessageLoop's pump_ instance.
COMPILE_ASSERT(sizeof(MessageLoop) == sizeof(MessageLoopForUI),
MessageLoopForUI_should_not_have_extra_member_variables);
//-----------------------------------------------------------------------------
// MessageLoopForIO extends MessageLoop with methods that are particular to a
// MessageLoop instantiated with TYPE_IO.
//
// This class is typically used like so:
// MessageLoopForIO::current()->...call some method...
//
class BASE_EXPORT MessageLoopForIO : public MessageLoop {
public:
#if defined(OS_WIN)
typedef MessagePumpForIO::IOHandler IOHandler;
typedef MessagePumpForIO::IOContext IOContext;
typedef MessagePumpForIO::IOObserver IOObserver;
#elif defined(OS_IOS)
typedef MessagePumpIOSForIO::Watcher Watcher;
typedef MessagePumpIOSForIO::FileDescriptorWatcher
FileDescriptorWatcher;
typedef MessagePumpIOSForIO::IOObserver IOObserver;
enum Mode {
WATCH_READ = MessagePumpIOSForIO::WATCH_READ,
WATCH_WRITE = MessagePumpIOSForIO::WATCH_WRITE,
WATCH_READ_WRITE = MessagePumpIOSForIO::WATCH_READ_WRITE
};
#elif defined(OS_POSIX)
typedef MessagePumpLibevent::Watcher Watcher;
typedef MessagePumpLibevent::FileDescriptorWatcher
FileDescriptorWatcher;
typedef MessagePumpLibevent::IOObserver IOObserver;
enum Mode {
WATCH_READ = MessagePumpLibevent::WATCH_READ,
WATCH_WRITE = MessagePumpLibevent::WATCH_WRITE,
WATCH_READ_WRITE = MessagePumpLibevent::WATCH_READ_WRITE
};
#endif
MessageLoopForIO() : MessageLoop(TYPE_IO) {
}
// Returns the MessageLoopForIO of the current thread.
static MessageLoopForIO* current() {
MessageLoop* loop = MessageLoop::current();
DCHECK_EQ(MessageLoop::TYPE_IO, loop->type());
return static_cast<MessageLoopForIO*>(loop);
}
static bool IsCurrent() {
MessageLoop* loop = MessageLoop::current();
return loop && loop->type() == MessageLoop::TYPE_IO;
}
void AddIOObserver(IOObserver* io_observer) {
pump_io()->AddIOObserver(io_observer);
}
void RemoveIOObserver(IOObserver* io_observer) {
pump_io()->RemoveIOObserver(io_observer);
}
#if defined(OS_WIN)
// Please see MessagePumpWin for definitions of these methods.
void RegisterIOHandler(HANDLE file, IOHandler* handler);
bool RegisterJobObject(HANDLE job, IOHandler* handler);
bool WaitForIOCompletion(DWORD timeout, IOHandler* filter);
protected:
// TODO(rvargas): Make this platform independent.
MessagePumpForIO* pump_io() {
return static_cast<MessagePumpForIO*>(pump_.get());
}
#elif defined(OS_IOS)
// Please see MessagePumpIOSForIO for definition.
bool WatchFileDescriptor(int fd,
bool persistent,
Mode mode,
FileDescriptorWatcher *controller,
Watcher *delegate);
private:
MessagePumpIOSForIO* pump_io() {
return static_cast<MessagePumpIOSForIO*>(pump_.get());
}
#elif defined(OS_POSIX)
// Please see MessagePumpLibevent for definition.
bool WatchFileDescriptor(int fd,
bool persistent,
Mode mode,
FileDescriptorWatcher* controller,
Watcher* delegate);
private:
MessagePumpLibevent* pump_io() {
return static_cast<MessagePumpLibevent*>(pump_.get());
}
#endif // defined(OS_POSIX)
};
// Do not add any member variables to MessageLoopForIO! This is important b/c
// MessageLoopForIO is often allocated via MessageLoop(TYPE_IO). Any extra
// data that you need should be stored on the MessageLoop's pump_ instance.
COMPILE_ASSERT(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
MessageLoopForIO_should_not_have_extra_member_variables);
} // namespace base
#endif // BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_