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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <windows.h>
#include <list>
#include "base/message_pump.h"
#include "base/observer_list.h"
#include "base/scoped_handle.h"
#include "base/time.h"
namespace base {
// MessagePumpWin serves as the base for specialized versions of the MessagePump
// for Windows. It provides basic functionality like handling of observers and
// controlling the lifetime of the message pump.
class MessagePumpWin : public MessagePump {
// An Observer is an object that receives global notifications from the
// MessageLoop.
// NOTE: An Observer implementation should be extremely fast!
class Observer {
virtual ~Observer() {}
// This method is called before processing a message.
// The message may be undefined in which case msg.message is 0
virtual void WillProcessMessage(const MSG& msg) = 0;
// This method is called when control returns from processing a UI message.
// The message may be undefined in which case msg.message is 0
virtual void DidProcessMessage(const MSG& msg) = 0;
// Dispatcher is used during a nested invocation of Run to dispatch events.
// If Run is invoked with a non-NULL Dispatcher, MessageLoop does not
// dispatch events (or invoke TranslateMessage), rather every message is
// passed to Dispatcher's Dispatch method for dispatch. It is up to the
// Dispatcher to dispatch, or not, the event.
// The nested loop is exited by either posting a quit, or returning false
// from Dispatch.
class Dispatcher {
virtual ~Dispatcher() {}
// Dispatches the event. If true is returned processing continues as
// normal. If false is returned, the nested loop exits immediately.
virtual bool Dispatch(const MSG& msg) = 0;
MessagePumpWin() : have_work_(0), state_(NULL) {}
virtual ~MessagePumpWin() {}
// Add an Observer, which will start receiving notifications immediately.
void AddObserver(Observer* observer);
// Remove an Observer. It is safe to call this method while an Observer is
// receiving a notification callback.
void RemoveObserver(Observer* observer);
// Give a chance to code processing additional messages to notify the
// message loop observers that another message has been processed.
void WillProcessMessage(const MSG& msg);
void DidProcessMessage(const MSG& msg);
// Like MessagePump::Run, but MSG objects are routed through dispatcher.
void RunWithDispatcher(Delegate* delegate, Dispatcher* dispatcher);
// MessagePump methods:
virtual void Run(Delegate* delegate) { RunWithDispatcher(delegate, NULL); }
virtual void Quit();
struct RunState {
Delegate* delegate;
Dispatcher* dispatcher;
// Used to flag that the current Run() invocation should return ASAP.
bool should_quit;
// Used to count how many Run() invocations are on the stack.
int run_depth;
virtual void DoRunLoop() = 0;
int GetCurrentDelay() const;
ObserverList<Observer> observers_;
// The time at which delayed work should run.
TimeTicks delayed_work_time_;
// A boolean value used to indicate if there is a kMsgDoWork message pending
// in the Windows Message queue. There is at most one such message, and it
// can drive execution of tasks when a native message pump is running.
LONG have_work_;
// State for the current invocation of Run.
RunState* state_;
// MessagePumpForUI extends MessagePumpWin with methods that are particular to a
// MessageLoop instantiated with TYPE_UI.
// MessagePumpForUI implements a "traditional" Windows message pump. It contains
// a nearly infinite loop that peeks out messages, and then dispatches them.
// Intermixed with those peeks are callouts to DoWork for pending tasks, and
// DoDelayedWork for pending timers. When there are no events to be serviced,
// this pump goes into a wait state. In most cases, this message pump handles
// all processing.
// However, when a task, or windows event, invokes on the stack a native dialog
// box or such, that window typically provides a bare bones (native?) message
// pump. That bare-bones message pump generally supports little more than a
// peek of the Windows message queue, followed by a dispatch of the peeked
// message. MessageLoop extends that bare-bones message pump to also service
// Tasks, at the cost of some complexity.
// The basic structure of the extension (refered to as a sub-pump) is that a
// special message, kMsgHaveWork, is repeatedly injected into the Windows
// Message queue. Each time the kMsgHaveWork message is peeked, checks are
// made for an extended set of events, including the availability of Tasks to
// run.
// After running a task, the special message kMsgHaveWork is again posted to
// the Windows Message queue, ensuring a future time slice for processing a
// future event. To prevent flooding the Windows Message queue, care is taken
// to be sure that at most one kMsgHaveWork message is EVER pending in the
// Window's Message queue.
// There are a few additional complexities in this system where, when there are
// no Tasks to run, this otherwise infinite stream of messages which drives the
// sub-pump is halted. The pump is automatically re-started when Tasks are
// queued.
// A second complexity is that the presence of this stream of posted tasks may
// prevent a bare-bones message pump from ever peeking a WM_PAINT or WM_TIMER.
// Such paint and timer events always give priority to a posted message, such as
// kMsgHaveWork messages. As a result, care is taken to do some peeking in
// between the posting of each kMsgHaveWork message (i.e., after kMsgHaveWork
// is peeked, and before a replacement kMsgHaveWork is posted).
// NOTE: Although it may seem odd that messages are used to start and stop this
// flow (as opposed to signaling objects, etc.), it should be understood that
// the native message pump will *only* respond to messages. As a result, it is
// an excellent choice. It is also helpful that the starter messages that are
// placed in the queue when new task arrive also awakens DoRunLoop.
class MessagePumpForUI : public MessagePumpWin {
virtual ~MessagePumpForUI();
// MessagePump methods:
virtual void ScheduleWork();
virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time);
// Applications can call this to encourage us to process all pending WM_PAINT
// messages. This method will process all paint messages the Windows Message
// queue can provide, up to some fixed number (to avoid any infinite loops).
void PumpOutPendingPaintMessages();
virtual void DoRunLoop();
bool ProcessNextWindowsMessage();
void InitMessageWnd();
void WaitForWork();
void HandleWorkMessage();
void HandleTimerMessage();
bool ProcessMessageHelper(const MSG& msg);
bool ProcessPumpReplacementMessage();
// A hidden message-only window.
HWND message_hwnd_;
static LRESULT CALLBACK WndProcThunk(HWND hwnd, UINT message, WPARAM wparam,
LPARAM lparam);
// MessagePumpForIO extends MessagePumpWin with methods that are particular to a
// MessageLoop instantiated with TYPE_IO. This version of MessagePump does not
// deal with Windows mesagges, and instead has a Run loop based on Completion
// Ports so it is better suited for IO operations.
class MessagePumpForIO : public MessagePumpWin {
struct IOContext;
// Clients interested in receiving OS notifications when asynchronous IO
// operations complete should implement this interface and register themselves
// with the message pump.
// Typical use #1:
// // Use only when there are no user's buffers involved on the actual IO,
// // so that all the cleanup can be done by the message pump.
// class MyFile : public IOHandler {
// MyFile() {
// ...
// context_ = new IOContext;
// context_->handler = this;
// message_pump->RegisterIOHandler(file_, this);
// }
// ~MyFile() {
// if (pending_) {
// // By setting the handler to NULL, we're asking for this context
// // to be deleted when received, without calling back to us.
// context_->handler = NULL;
// } else {
// delete context_;
// }
// }
// virtual void OnIOCompleted(IOContext* context, DWORD bytes_transfered,
// DWORD error) {
// pending_ = false;
// }
// void DoSomeIo() {
// ...
// // The only buffer required for this operation is the overlapped
// // structure.
// ConnectNamedPipe(file_, &context_->overlapped);
// pending_ = true;
// }
// bool pending_;
// IOContext* context_;
// HANDLE file_;
// };
// Typical use #2:
// class MyFile : public IOHandler {
// MyFile() {
// ...
// message_pump->RegisterIOHandler(file_, this);
// }
// // Plus some code to make sure that this destructor is not called
// // while there are pending IO operations.
// ~MyFile() {
// }
// virtual void OnIOCompleted(IOContext* context, DWORD bytes_transfered,
// DWORD error) {
// ...
// delete context;
// }
// void DoSomeIo() {
// ...
// IOContext* context = new IOContext;
// // This is not used for anything. It just prevents the context from
// // being considered "abandoned".
// context->handler = this;
// ReadFile(file_, buffer, num_bytes, &read, &context->overlapped);
// }
// HANDLE file_;
// };
// Typical use #3:
// Same as the previous example, except that in order to deal with the
// requirement stated for the destructor, the class calls WaitForIOCompletion
// from the destructor to block until all IO finishes.
// ~MyFile() {
// while(pending_)
// message_pump->WaitForIOCompletion(INFINITE, this);
// }
class IOHandler {
virtual ~IOHandler() {}
// This will be called once the pending IO operation associated with
// |context| completes. |error| is the Win32 error code of the IO operation
// (ERROR_SUCCESS if there was no error). |bytes_transfered| will be zero
// on error.
virtual void OnIOCompleted(IOContext* context, DWORD bytes_transfered,
DWORD error) = 0;
// The extended context that should be used as the base structure on every
// overlapped IO operation. |handler| must be set to the registered IOHandler
// for the given file when the operation is started, and it can be set to NULL
// before the operation completes to indicate that the handler should not be
// called anymore, and instead, the IOContext should be deleted when the OS
// notifies the completion of this operation. Please remember that any buffers
// involved with an IO operation should be around until the callback is
// received, so this technique can only be used for IO that do not involve
// additional buffers (other than the overlapped structure itself).
struct IOContext {
OVERLAPPED overlapped;
IOHandler* handler;
virtual ~MessagePumpForIO() {}
// MessagePump methods:
virtual void ScheduleWork();
virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time);
// Register the handler to be used when asynchronous IO for the given file
// completes. The registration persists as long as |file_handle| is valid, so
// |handler| must be valid as long as there is pending IO for the given file.
void RegisterIOHandler(HANDLE file_handle, IOHandler* handler);
// Waits for the next IO completion that should be processed by |filter|, for
// up to |timeout| milliseconds. Return true if any IO operation completed,
// regardless of the involved handler, and false if the timeout expired. If
// the completion port received any message and the involved IO handler
// matches |filter|, the callback is called before returning from this code;
// if the handler is not the one that we are looking for, the callback will
// be postponed for another time, so reentrancy problems can be avoided.
// External use of this method should be reserved for the rare case when the
// caller is willing to allow pausing regular task dispatching on this thread.
bool WaitForIOCompletion(DWORD timeout, IOHandler* filter);
struct IOItem {
IOHandler* handler;
IOContext* context;
DWORD bytes_transfered;
DWORD error;
virtual void DoRunLoop();
void WaitForWork();
bool MatchCompletedIOItem(IOHandler* filter, IOItem* item);
bool GetIOItem(DWORD timeout, IOItem* item);
bool ProcessInternalIOItem(const IOItem& item);
// The completion port associated with this thread.
ScopedHandle port_;
// This list will be empty almost always. It stores IO completions that have
// not been delivered yet because somebody was doing cleanup.
std::list<IOItem> completed_io_;
} // namespace base