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Side by Side Diff: base/message_loop/message_pump.h

Issue 1647803004: Move base to DEPS (Closed) Base URL: git@github.com:domokit/mojo.git@master
Patch Set: Created 4 years, 10 months ago
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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #ifndef BASE_MESSAGE_LOOP_MESSAGE_PUMP_H_
6 #define BASE_MESSAGE_LOOP_MESSAGE_PUMP_H_
7
8 #include "base/base_export.h"
9 #include "base/basictypes.h"
10 #include "base/message_loop/timer_slack.h"
11 #include "base/threading/non_thread_safe.h"
12
13 namespace base {
14
15 class TimeTicks;
16
17 class BASE_EXPORT MessagePump : public NonThreadSafe {
18 public:
19 // Please see the comments above the Run method for an illustration of how
20 // these delegate methods are used.
21 class BASE_EXPORT Delegate {
22 public:
23 virtual ~Delegate() {}
24
25 // Called from within Run in response to ScheduleWork or when the message
26 // pump would otherwise call DoDelayedWork. Returns true to indicate that
27 // work was done. DoDelayedWork will still be called if DoWork returns
28 // true, but DoIdleWork will not.
29 virtual bool DoWork() = 0;
30
31 // Called from within Run in response to ScheduleDelayedWork or when the
32 // message pump would otherwise sleep waiting for more work. Returns true
33 // to indicate that delayed work was done. DoIdleWork will not be called
34 // if DoDelayedWork returns true. Upon return |next_delayed_work_time|
35 // indicates the time when DoDelayedWork should be called again. If
36 // |next_delayed_work_time| is null (per Time::is_null), then the queue of
37 // future delayed work (timer events) is currently empty, and no additional
38 // calls to this function need to be scheduled.
39 virtual bool DoDelayedWork(TimeTicks* next_delayed_work_time) = 0;
40
41 // Called from within Run just before the message pump goes to sleep.
42 // Returns true to indicate that idle work was done. Returning false means
43 // the pump will now wait.
44 virtual bool DoIdleWork() = 0;
45 };
46
47 MessagePump();
48 virtual ~MessagePump();
49
50 // The Run method is called to enter the message pump's run loop.
51 //
52 // Within the method, the message pump is responsible for processing native
53 // messages as well as for giving cycles to the delegate periodically. The
54 // message pump should take care to mix delegate callbacks with native
55 // message processing so neither type of event starves the other of cycles.
56 //
57 // The anatomy of a typical run loop:
58 //
59 // for (;;) {
60 // bool did_work = DoInternalWork();
61 // if (should_quit_)
62 // break;
63 //
64 // did_work |= delegate_->DoWork();
65 // if (should_quit_)
66 // break;
67 //
68 // TimeTicks next_time;
69 // did_work |= delegate_->DoDelayedWork(&next_time);
70 // if (should_quit_)
71 // break;
72 //
73 // if (did_work)
74 // continue;
75 //
76 // did_work = delegate_->DoIdleWork();
77 // if (should_quit_)
78 // break;
79 //
80 // if (did_work)
81 // continue;
82 //
83 // WaitForWork();
84 // }
85 //
86 // Here, DoInternalWork is some private method of the message pump that is
87 // responsible for dispatching the next UI message or notifying the next IO
88 // completion (for example). WaitForWork is a private method that simply
89 // blocks until there is more work of any type to do.
90 //
91 // Notice that the run loop cycles between calling DoInternalWork, DoWork,
92 // and DoDelayedWork methods. This helps ensure that none of these work
93 // queues starve the others. This is important for message pumps that are
94 // used to drive animations, for example.
95 //
96 // Notice also that after each callout to foreign code, the run loop checks
97 // to see if it should quit. The Quit method is responsible for setting this
98 // flag. No further work is done once the quit flag is set.
99 //
100 // NOTE: Care must be taken to handle Run being called again from within any
101 // of the callouts to foreign code. Native message pumps may also need to
102 // deal with other native message pumps being run outside their control
103 // (e.g., the MessageBox API on Windows pumps UI messages!). To be specific,
104 // the callouts (DoWork and DoDelayedWork) MUST still be provided even in
105 // nested sub-loops that are "seemingly" outside the control of this message
106 // pump. DoWork in particular must never be starved for time slices unless
107 // it returns false (meaning it has run out of things to do).
108 //
109 virtual void Run(Delegate* delegate) = 0;
110
111 // Quit immediately from the most recently entered run loop. This method may
112 // only be used on the thread that called Run.
113 virtual void Quit() = 0;
114
115 // Schedule a DoWork callback to happen reasonably soon. Does nothing if a
116 // DoWork callback is already scheduled. This method may be called from any
117 // thread. Once this call is made, DoWork should not be "starved" at least
118 // until it returns a value of false.
119 virtual void ScheduleWork() = 0;
120
121 // Schedule a DoDelayedWork callback to happen at the specified time,
122 // cancelling any pending DoDelayedWork callback. This method may only be
123 // used on the thread that called Run.
124 virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time) = 0;
125
126 // Sets the timer slack to the specified value.
127 virtual void SetTimerSlack(TimerSlack timer_slack);
128 };
129
130 } // namespace base
131
132 #endif // BASE_MESSAGE_LOOP_MESSAGE_PUMP_H_
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