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// Copyright 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef BASE_MESSAGE_PUMP_H_
#define BASE_MESSAGE_PUMP_H_
#include "base/ref_counted.h"
class Time;
namespace base {
class MessagePump : public RefCountedThreadSafe<MessagePump> {
public:
// Please see the comments above the Run method for an illustration of how
// these delegate methods are used.
class Delegate {
public:
virtual ~Delegate() {}
// Called from within Run in response to ScheduleWork or when the message
// pump would otherwise call DoDelayedWork. Returns true to indicate that
// work was done. DoDelayedWork will not be called if DoWork returns true.
virtual bool DoWork() = 0;
// Called from within Run in response to ScheduleDelayedWork or when the
// message pump would otherwise sleep waiting for more work. Returns true
// to indicate that delayed work was done. DoIdleWork will not be called
// if DoDelayedWork returns true. Upon return |next_delayed_work_time|
// indicates the time when DoDelayedWork should be called again. If
// |next_delayed_work_time| is null (per Time::is_null), then the queue of
// future delayed work (timer events) is currently empty, and no additional
// calls to this function need to be scheduled.
virtual bool DoDelayedWork(Time* next_delayed_work_time) = 0;
// Called from within Run just before the message pump goes to sleep.
// Returns true to indicate that idle work was done.
virtual bool DoIdleWork() = 0;
};
virtual ~MessagePump() {}
// The Run method is called to enter the message pump's run loop.
//
// Within the method, the message pump is responsible for processing native
// messages as well as for giving cycles to the delegate periodically. The
// message pump should take care to mix delegate callbacks with native
// message processing so neither type of event starves the other of cycles.
//
// The anatomy of a typical run loop:
//
// for (;;) {
// bool did_work = DoInternalWork();
// if (should_quit_)
// break;
// did_work |= delegate_->DoWork();
// if (should_quit_)
// break;
// if (did_work)
// continue;
//
// did_work = delegate_->DoDelayedWork();
// if (should_quit_)
// break;
// if (did_work)
// continue;
//
// did_work = delegate_->DoIdleWork();
// if (should_quit_)
// break;
// if (did_work)
// continue;
//
// WaitForWork();
// }
//
// Here, DoInternalWork is some private method of the message pump that is
// responsible for dispatching the next UI message or notifying the next IO
// completion (for example). WaitForWork is a private method that simply
// blocks until there is more work of any type to do.
//
// Notice that the run loop alternates between calling DoInternalWork and
// calling the delegate's DoWork method. This helps ensure that neither work
// queue starves the other. However, DoDelayedWork may be starved. The
// implementation may decide to periodically let some DoDelayedWork calls go
// through if either DoInternalWork or DoWork is dominating the run loop.
// This can be important for message pumps that are used to drive animations,
// for example.
//
// Notice also that after each callout to foreign code, the run loop checks
// to see if it should quit. The Quit method is responsible for setting this
// flag. No further work is done once the quit flag is set.
//
// NOTE: Care must be taken to handle Run being called again from within any
// of the callouts to foreign code. Native message pumps may also need to
// deal with other native message pumps being run outside their control
// (e.g., the MessageBox API on Windows pumps UI messages!). To be specific,
// the callouts (DoWork and DoDelayedWork) MUST still be provided even in
// nested sub-loops that are "seemingly" outside the control of this message
// pump. DoWork in particular must never be starved for time slices unless
// it returns false (meaning it has run out of things to do).
//
virtual void Run(Delegate* delegate) = 0;
// Quit immediately from the most recently entered run loop. This method may
// only be used on the thread that called Run.
virtual void Quit() = 0;
// Schedule a DoWork callback to happen reasonably soon. Does nothing if a
// DoWork callback is already scheduled. This method may be called from any
// thread. Once this call is made, DoWork should not be "starved" at least
// until it returns a value of false.
virtual void ScheduleWork() = 0;
// Schedule a DoDelayedWork callback to happen at the specified time,
// cancelling any pending DoDelayedWork callback. This method may only be
// used on the thread that called Run.
virtual void ScheduleDelayedWork(const Time& delayed_work_time) = 0;
};
} // namespace base
#endif // BASE_MESSAGE_PUMP_H_
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