1 /*
2  * Copyright 2015 Google Inc.
3  *
4  * Use of this source code is governed by a BSD-style license that can be
5  * found in the LICENSE file.
6  */
7 
8 #ifndef SkRWBuffer_DEFINED
9 #define SkRWBuffer_DEFINED
10 
11 #include "SkRefCnt.h"
12 
13 struct SkBufferBlock;
14 struct SkBufferHead;
15 class SkRWBuffer;
16 class SkStreamAsset;
17 
18 /**
19  *  Contains a read-only, thread-sharable block of memory. To access the memory, the caller must
20  *  instantiate a local iterator, as the memory is stored in 1 or more contiguous blocks.
21  */
22 class SK_API SkROBuffer : public SkRefCnt {
23 public:
24     /**
25      *  Return the logical length of the data owned/shared by this buffer. It may be stored in
26      *  multiple contiguous blocks, accessible via the iterator.
27      */
size()28     size_t size() const { return fAvailable; }
29 
30     class SK_API Iter {
31     public:
32         Iter(const SkROBuffer*);
33 
34         void reset(const SkROBuffer*);
35 
36         /**
37          *  Return the current continuous block of memory, or nullptr if the iterator is exhausted
38          */
39         const void* data() const;
40 
41         /**
42          *  Returns the number of bytes in the current continguous block of memory, or 0 if the
43          *  iterator is exhausted.
44          */
45         size_t size() const;
46 
47         /**
48          *  Advance to the next contiguous block of memory, returning true if there is another
49          *  block, or false if the iterator is exhausted.
50          */
51         bool next();
52 
53     private:
54         const SkBufferBlock* fBlock;
55         size_t               fRemaining;
56         const SkROBuffer*    fBuffer;
57     };
58 
59 private:
60     SkROBuffer(const SkBufferHead* head, size_t available, const SkBufferBlock* fTail);
61     virtual ~SkROBuffer();
62 
63     const SkBufferHead*     fHead;
64     const size_t            fAvailable;
65     const SkBufferBlock*    fTail;
66 
67     friend class SkRWBuffer;
68 };
69 
70 /**
71  *  Accumulates bytes of memory that are "appended" to it, growing internal storage as needed.
72  *  The growth is done such that at any time in the writer's thread, an RBuffer or StreamAsset
73  *  can be snapped off (and safely passed to another thread). The RBuffer/StreamAsset snapshot
74  *  can see the previously stored bytes, but will be unaware of any future writes.
75  */
76 class SK_API SkRWBuffer {
77 public:
78     SkRWBuffer(size_t initialCapacity = 0);
79     ~SkRWBuffer();
80 
size()81     size_t size() const { return fTotalUsed; }
82 
83     /**
84      *  Append |length| bytes from |buffer|.
85      *
86      *  If the caller knows in advance how much more data they are going to append, they can
87      *  pass a |reserve| hint (representing the number of upcoming bytes *in addition* to the
88      *  current append), to minimize the number of internal allocations.
89      */
90     void append(const void* buffer, size_t length, size_t reserve = 0);
91 
92     SkROBuffer* newRBufferSnapshot() const;
93     SkStreamAsset* newStreamSnapshot() const;
94 
95 #ifdef SK_DEBUG
96     void validate() const;
97 #else
validate()98     void validate() const {}
99 #endif
100 
101 private:
102     SkBufferHead*   fHead;
103     SkBufferBlock*  fTail;
104     size_t          fTotalUsed;
105 };
106 
107 #endif
108