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Diffstat (limited to 'ipc/chromium/src/base/message_pump.h')
| -rw-r--r-- | ipc/chromium/src/base/message_pump.h | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/ipc/chromium/src/base/message_pump.h b/ipc/chromium/src/base/message_pump.h new file mode 100644 index 000000000..08bdbe30a --- /dev/null +++ b/ipc/chromium/src/base/message_pump.h @@ -0,0 +1,143 @@ +/* -*- 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. + +#ifndef BASE_MESSAGE_PUMP_H_ +#define BASE_MESSAGE_PUMP_H_ + +#include "nsISupportsImpl.h" + +class nsIEventTarget; + +namespace base { + +class TimeTicks; + +class MessagePump { + public: + NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MessagePump) + + // 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(TimeTicks* 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; + }; + + // 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; + // + // 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 cycles between calling DoInternalWork, DoWork, + // and DoDelayedWork methods. This helps ensure that neither work queue + // starves the other. This is 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; + + // This method may only called from the thread that called Run. + // + // Ensure that DoWork will be called if a nested loop is entered. + // If a MessagePump can already guarantee that DoWork will be called + // "reasonably soon", this method can be a no-op to avoid expensive + // atomic tests and/or syscalls required for ScheduleWork(). + virtual void ScheduleWorkForNestedLoop() { ScheduleWork(); }; + + // 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 TimeTicks& delayed_work_time) = 0; + + // If returned, just use the nsThread. + virtual nsIEventTarget* GetXPCOMThread() + { + return nullptr; + } + +protected: + virtual ~MessagePump() {}; +}; + +} // namespace base + +#endif // BASE_MESSAGE_PUMP_H_ |