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// 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.
#ifndef BASE_MESSAGE_LOOP_H_
#define BASE_MESSAGE_LOOP_H_
#pragma once
#include <queue>
#include <string>
#include "base/base_api.h"
#include "base/basictypes.h"
#include "base/memory/ref_counted.h"
#include "base/message_pump.h"
#include "base/observer_list.h"
#include "base/synchronization/lock.h"
#include "base/task.h"
#if defined(OS_WIN)
// We need this to declare base::MessagePumpWin::Dispatcher, which we should
// really just eliminate.
#include "base/message_pump_win.h"
#elif defined(OS_POSIX)
#include "base/message_pump_libevent.h"
#if !defined(OS_MACOSX)
#include "base/message_pump_glib.h"
typedef struct _XDisplay Display;
#endif
#endif
#if defined(TOUCH_UI)
#include "base/message_pump_glib_x_dispatch.h"
#endif
namespace base {
class Histogram;
}
// 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 or those
// managed by TimerManager. 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:
// bool old_state = MessageLoop::current()->NestableTasksAllowed();
// MessageLoop::current()->SetNestableTasksAllowed(true);
// HRESULT hr = DoDragDrop(...); // Implicitly runs a modal message loop here.
// MessageLoop::current()->SetNestableTasksAllowed(old_state);
// // 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_API MessageLoop : public base::MessagePump::Delegate {
public:
#if defined(OS_WIN)
typedef base::MessagePumpWin::Dispatcher Dispatcher;
typedef base::MessagePumpForUI::Observer Observer;
#elif !defined(OS_MACOSX)
#if defined(TOUCH_UI)
typedef base::MessagePumpGlibXDispatcher Dispatcher;
#else
typedef base::MessagePumpForUI::Dispatcher Dispatcher;
#endif
typedef base::MessagePumpForUI::Observer 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_IO
// This type of ML also supports asynchronous IO. See also
// MessageLoopForIO.
//
enum Type {
TYPE_DEFAULT,
TYPE_UI,
TYPE_IO
};
// 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);
~MessageLoop();
// Returns the MessageLoop object for the current thread, or null if none.
static MessageLoop* current();
static void EnableHistogrammer(bool enable_histogrammer);
// A DestructionObserver is notified when the current MessageLoop is being
// destroyed. These obsevers 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_API 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().
//
// 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, Task* task);
void PostDelayedTask(
const tracked_objects::Location& from_here, Task* task, int64 delay_ms);
void PostNonNestableTask(
const tracked_objects::Location& from_here, Task* task);
void PostNonNestableDelayedTask(
const tracked_objects::Location& from_here, Task* task, int64 delay_ms);
// 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) {
PostNonNestableTask(from_here, new DeleteTask<T>(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) {
PostNonNestableTask(from_here, new ReleaseTask<T>(object));
}
// Run the message loop.
void Run();
// 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 RunAllPending();
// Signals the Run method to return after it is done processing all pending
// messages. This method may only be called on the same thread that called
// Run, and Run must still be on the call stack.
//
// Use QuitTask 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 quiting, so be careful!
//
void Quit();
// This method is a variant of Quit, that does not wait for pending messages
// to be processed before returning from Run.
void QuitNow();
// Invokes Quit on the current MessageLoop when run. Useful to schedule an
// arbitrary MessageLoop to Quit.
class QuitTask : public Task {
public:
virtual void Run() {
MessageLoop::current()->Quit();
}
};
// 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_; }
// 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.
//
// 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_;
};
// Enables or disables the restoration during an exception of the unhandled
// exception filter that was active when Run() was called. This can happen
// if some third party code call SetUnhandledExceptionFilter() and never
// restores the previous filter.
void set_exception_restoration(bool restore) {
exception_restoration_ = restore;
}
// 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_API TaskObserver {
public:
TaskObserver();
// This method is called before processing a task.
virtual void WillProcessTask(const Task* task) = 0;
// This method is called after processing a task.
virtual void DidProcessTask(const Task* 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);
// Returns true if the message loop has high resolution timers enabled.
// Provided for testing.
bool high_resolution_timers_enabled() {
#if defined(OS_WIN)
return !high_resolution_timer_expiration_.is_null();
#else
return true;
#endif
}
// When we go into high resolution timer mode, we will stay in hi-res mode
// for at least 1s.
static const int kHighResolutionTimerModeLeaseTimeMs = 1000;
// Asserts that the MessageLoop is "idle".
void AssertIdle() const;
#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
//----------------------------------------------------------------------------
protected:
struct RunState {
// Used to count how many Run() invocations are on the stack.
int run_depth;
// Used to record that Quit() was called, or that we should quit the pump
// once it becomes idle.
bool quit_received;
#if !defined(OS_MACOSX)
Dispatcher* dispatcher;
#endif
};
class AutoRunState : RunState {
public:
explicit AutoRunState(MessageLoop* loop);
~AutoRunState();
private:
MessageLoop* loop_;
RunState* previous_state_;
};
// This structure is copied around by value.
struct PendingTask {
PendingTask(Task* task, bool nestable)
: task(task), sequence_num(0), nestable(nestable) {
}
// Used to support sorting.
bool operator<(const PendingTask& other) const;
Task* task; // The task to run.
base::TimeTicks delayed_run_time; // The time when the task should be run.
int sequence_num; // Secondary sort key for run time.
bool nestable; // OK to dispatch from a nested loop.
};
class TaskQueue : public std::queue<PendingTask> {
public:
void Swap(TaskQueue* queue) {
c.swap(queue->c); // Calls std::deque::swap
}
};
typedef std::priority_queue<PendingTask> DelayedTaskQueue;
#if defined(OS_WIN)
base::MessagePumpWin* pump_win() {
return static_cast<base::MessagePumpWin*>(pump_.get());
}
#elif defined(OS_POSIX)
base::MessagePumpLibevent* pump_libevent() {
return static_cast<base::MessagePumpLibevent*>(pump_.get());
}
#endif
// A function to encapsulate all the exception handling capability in the
// stacks around the running of a main message loop. It will run the message
// loop in a SEH try block or not depending on the set_SEH_restoration()
// flag invoking respectively RunInternalInSEHFrame() or RunInternal().
void RunHandler();
#if defined(OS_WIN)
__declspec(noinline) void RunInternalInSEHFrame();
#endif
// A surrounding stack frame around the running of the message loop that
// supports all saving and restoring of state, as is needed for any/all (ugly)
// recursive calls.
void RunInternal();
// Called to process any delayed non-nestable tasks.
bool ProcessNextDelayedNonNestableTask();
// Runs the specified task and deletes it.
void RunTask(Task* 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);
// Load tasks from the incoming_queue_ into work_queue_ if the latter is
// empty. The former requires a lock to access, while the latter is directly
// accessible on this thread.
void ReloadWorkQueue();
// 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();
// Post a task to our incomming queue.
void PostTask_Helper(const tracked_objects::Location& from_here, Task* task,
int64 delay_ms, bool nestable);
// 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 occurence 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);
// base::MessagePump::Delegate methods:
virtual bool DoWork();
virtual bool DoDelayedWork(base::TimeTicks* next_delayed_work_time);
virtual bool DoIdleWork();
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_.
base::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_;
scoped_refptr<base::MessagePump> pump_;
ObserverList<DestructionObserver> destruction_observers_;
// A recursion block that prevents accidentally running additonal tasks when
// insider a (accidentally induced?) nested message pump.
bool nestable_tasks_allowed_;
bool exception_restoration_;
std::string thread_name_;
// A profiling histogram showing the counts of various messages and events.
base::Histogram* message_histogram_;
// A null terminated list which creates an incoming_queue of tasks that are
// acquired under a mutex for processing on this instance's thread. These
// tasks have not yet been sorted out into items for our work_queue_ vs
// items that will be handled by the TimerManager.
TaskQueue incoming_queue_;
// Protect access to incoming_queue_.
mutable base::Lock incoming_queue_lock_;
RunState* state_;
#if defined(OS_WIN)
base::TimeTicks high_resolution_timer_expiration_;
// Should be set to true before calling Windows APIs like TrackPopupMenu, etc
// which enter a modal message loop.
bool os_modal_loop_;
#endif
// The next sequence number to use for delayed tasks.
int next_sequence_num_;
ObserverList<TaskObserver> task_observers_;
private:
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_API MessageLoopForUI : public MessageLoop {
public:
MessageLoopForUI() : MessageLoop(TYPE_UI) {
}
// Returns the MessageLoopForUI of the current thread.
static MessageLoopForUI* current() {
MessageLoop* loop = MessageLoop::current();
#ifdef ANDROID
DCHECK_EQ(static_cast<int>(MessageLoop::TYPE_UI),
static_cast<int>(loop->type()));
#else
DCHECK_EQ(MessageLoop::TYPE_UI, loop->type());
#endif
return static_cast<MessageLoopForUI*>(loop);
}
#if defined(OS_WIN)
void DidProcessMessage(const MSG& message);
#endif // defined(OS_WIN)
#if defined(USE_X11)
// Returns the Xlib Display that backs the MessagePump for this MessageLoop.
//
// This allows for raw access to the X11 server in situations where our
// abstractions do not provide enough power.
//
// Be careful how this is used. The MessagePump in general expects
// exclusive access to the Display. Calling things like XNextEvent() will
// likely break things in subtle, hard to detect, ways.
Display* GetDisplay();
#endif // defined(OS_X11)
#if !defined(OS_MACOSX)
// Please see message_pump_win/message_pump_glib for definitions of these
// methods.
void AddObserver(Observer* observer);
void RemoveObserver(Observer* observer);
void Run(Dispatcher* dispatcher);
protected:
// TODO(rvargas): Make this platform independent.
base::MessagePumpForUI* pump_ui() {
return static_cast<base::MessagePumpForUI*>(pump_.get());
}
#endif // !defined(OS_MACOSX)
};
// 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_API MessageLoopForIO : public MessageLoop {
public:
#if defined(OS_WIN)
typedef base::MessagePumpForIO::IOHandler IOHandler;
typedef base::MessagePumpForIO::IOContext IOContext;
typedef base::MessagePumpForIO::IOObserver IOObserver;
#elif defined(OS_POSIX)
typedef base::MessagePumpLibevent::Watcher Watcher;
typedef base::MessagePumpLibevent::FileDescriptorWatcher
FileDescriptorWatcher;
typedef base::MessagePumpLibevent::IOObserver IOObserver;
enum Mode {
WATCH_READ = base::MessagePumpLibevent::WATCH_READ,
WATCH_WRITE = base::MessagePumpLibevent::WATCH_WRITE,
WATCH_READ_WRITE = base::MessagePumpLibevent::WATCH_READ_WRITE
};
#endif
MessageLoopForIO() : MessageLoop(TYPE_IO) {
}
// Returns the MessageLoopForIO of the current thread.
static MessageLoopForIO* current() {
MessageLoop* loop = MessageLoop::current();
#ifdef ANDROID
DCHECK_EQ(static_cast<int>(MessageLoop::TYPE_IO),
static_cast<int>(loop->type()));
#else
DCHECK_EQ(MessageLoop::TYPE_IO, loop->type());
#endif
return static_cast<MessageLoopForIO*>(loop);
}
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_handle, IOHandler* handler);
bool WaitForIOCompletion(DWORD timeout, IOHandler* filter);
protected:
// TODO(rvargas): Make this platform independent.
base::MessagePumpForIO* pump_io() {
return static_cast<base::MessagePumpForIO*>(pump_.get());
}
#elif defined(OS_POSIX)
// Please see MessagePumpLibevent for definition.
bool WatchFileDescriptor(int fd,
bool persistent,
Mode mode,
FileDescriptorWatcher *controller,
Watcher *delegate);
private:
base::MessagePumpLibevent* pump_io() {
return static_cast<base::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);
#endif // BASE_MESSAGE_LOOP_H_