1 //
2 // Copyright 2016 The ANGLE Project Authors. All rights reserved.
3 // Use of this source code is governed by a BSD-style license that can be
4 // found in the LICENSE file.
5 //
6 // Observer:
7 // Implements the Observer pattern for sending state change notifications
8 // from Subject objects to dependent Observer objects.
9 //
10 // See design document:
11 // https://docs.google.com/document/d/15Edfotqg6_l1skTEL8ADQudF_oIdNa7i8Po43k6jMd4/
12
13 #ifndef LIBANGLE_OBSERVER_H_
14 #define LIBANGLE_OBSERVER_H_
15
16 #include "common/FastVector.h"
17 #include "common/angleutils.h"
18
19 namespace angle
20 {
21 template <typename HaystackT, typename NeedleT>
IsInContainer(const HaystackT & haystack,const NeedleT & needle)22 bool IsInContainer(const HaystackT &haystack, const NeedleT &needle)
23 {
24 return std::find(haystack.begin(), haystack.end(), needle) != haystack.end();
25 }
26
27 using SubjectIndex = size_t;
28
29 // Messages are used to distinguish different Subject events that get sent to a single Observer.
30 // It could be possible to improve the handling by using different callback functions instead
31 // of a single handler function. But in some cases we want to share a single binding between
32 // Observer and Subject and handle different types of events.
33 enum class SubjectMessage
34 {
35 // Used by gl::VertexArray to notify gl::Context of a gl::Buffer binding count change. Triggers
36 // a validation cache update. Also used by gl::Texture to notify gl::Framebuffer of loops.
37 BindingChanged,
38
39 // Only the contents (pixels, bytes, etc) changed in this Subject. Distinct from the object
40 // storage.
41 ContentsChanged,
42
43 // Sent by gl::Sampler, gl::Texture, gl::Framebuffer and others to notifiy gl::Context. This
44 // flag indicates to call syncState before next use.
45 DirtyBitsFlagged,
46
47 // Generic state change message. Used in multiple places for different purposes.
48 SubjectChanged,
49
50 // Indicates a bound gl::Buffer is now mapped or unmapped. Passed from gl::Buffer, through
51 // gl::VertexArray, into gl::Context. Used to track validation.
52 SubjectMapped,
53 SubjectUnmapped,
54 // Indicates a bound buffer was reallocated when it was mapped, to prevent having to flush
55 // pending commands and waiting for the GPU to become idle.
56 InternalMemoryAllocationChanged,
57
58 // Indicates an external change to the default framebuffer.
59 SurfaceChanged,
60
61 // Indicates a separable program's textures or images changed in the ProgramExecutable.
62 ProgramTextureOrImageBindingChanged,
63 // Indicates a separable program was successfully re-linked.
64 ProgramRelinked,
65 // Indicates a separable program's sampler uniforms were updated.
66 SamplerUniformsUpdated,
67
68 // Indicates a Storage of back-end in gl::Texture has been released.
69 StorageReleased,
70
71 // Indicates that all pending updates are complete in the subject.
72 InitializationComplete,
73 };
74
75 // The observing class inherits from this interface class.
76 class ObserverInterface
77 {
78 public:
79 virtual ~ObserverInterface();
80 virtual void onSubjectStateChange(SubjectIndex index, SubjectMessage message) = 0;
81 };
82
83 class ObserverBindingBase
84 {
85 public:
ObserverBindingBase(ObserverInterface * observer,SubjectIndex subjectIndex)86 ObserverBindingBase(ObserverInterface *observer, SubjectIndex subjectIndex)
87 : mObserver(observer), mIndex(subjectIndex)
88 {}
~ObserverBindingBase()89 virtual ~ObserverBindingBase() {}
90
getObserver()91 ObserverInterface *getObserver() const { return mObserver; }
getSubjectIndex()92 SubjectIndex getSubjectIndex() const { return mIndex; }
93
onSubjectReset()94 virtual void onSubjectReset() {}
95
96 private:
97 ObserverInterface *mObserver;
98 SubjectIndex mIndex;
99 };
100
101 constexpr size_t kMaxFixedObservers = 8;
102
103 // Maintains a list of observer bindings. Sends update messages to the observer.
104 class Subject : NonCopyable
105 {
106 public:
107 Subject();
108 virtual ~Subject();
109
110 void onStateChange(SubjectMessage message) const;
111 bool hasObservers() const;
112 void resetObservers();
113
addObserver(ObserverBindingBase * observer)114 ANGLE_INLINE void addObserver(ObserverBindingBase *observer)
115 {
116 ASSERT(!IsInContainer(mObservers, observer));
117 mObservers.push_back(observer);
118 }
119
removeObserver(ObserverBindingBase * observer)120 ANGLE_INLINE void removeObserver(ObserverBindingBase *observer)
121 {
122 ASSERT(IsInContainer(mObservers, observer));
123 mObservers.remove_and_permute(observer);
124 }
125
126 private:
127 // Keep a short list of observers so we can allocate/free them quickly. But since we support
128 // unlimited bindings, have a spill-over list of that uses dynamic allocation.
129 angle::FastVector<ObserverBindingBase *, kMaxFixedObservers> mObservers;
130 };
131
132 // Keeps a binding between a Subject and Observer, with a specific subject index.
133 class ObserverBinding final : public ObserverBindingBase
134 {
135 public:
136 ObserverBinding(ObserverInterface *observer, SubjectIndex index);
137 ~ObserverBinding() override;
138 ObserverBinding(const ObserverBinding &other);
139 ObserverBinding &operator=(const ObserverBinding &other);
140
141 void bind(Subject *subject);
142
reset()143 ANGLE_INLINE void reset() { bind(nullptr); }
144
145 void onStateChange(SubjectMessage message) const;
146 void onSubjectReset() override;
147
getSubject()148 ANGLE_INLINE const Subject *getSubject() const { return mSubject; }
149
assignSubject(Subject * subject)150 ANGLE_INLINE void assignSubject(Subject *subject) { mSubject = subject; }
151
152 private:
153 Subject *mSubject;
154 };
155
156 } // namespace angle
157
158 #endif // LIBANGLE_OBSERVER_H_
159