SharedBuffer.h revision dd7bc3319deb2b77c5d07a51b7d6cd7e11b5beb0 
1/*
2 *  SharedBuffer.h
3 *  Android
4 *
5 *  Copyright 2005 The Android Open Source Project
6 *
7 */
8
9#ifndef ANDROID_SHARED_BUFFER_H
10#define ANDROID_SHARED_BUFFER_H
11
12#include <stdint.h>
13#include <sys/types.h>
14
15// ---------------------------------------------------------------------------
16
17namespace android {
18
19class SharedBuffer
20{
21public:
22
23    /* flags to use with release() */
24    enum {
25        eKeepStorage = 0x00000001
26    };
27
28    /*! allocate a buffer of size 'size' and acquire() it.
29     *  call release() to free it.
30     */
31    static          SharedBuffer*           alloc(size_t size);
32
33    /*! free the memory associated with the SharedBuffer.
34     * Fails if there are any users associated with this SharedBuffer.
35     * In other words, the buffer must have been release by all its
36     * users.
37     */
38    static          ssize_t                 dealloc(const SharedBuffer* released);
39
40    //! get the SharedBuffer from the data pointer
41    static  inline  const SharedBuffer*     sharedBuffer(const void* data);
42
43    //! access the data for read
44    inline          const void*             data() const;
45
46    //! access the data for read/write
47    inline          void*                   data();
48
49    //! get size of the buffer
50    inline          size_t                  size() const;
51
52    //! get back a SharedBuffer object from its data
53    static  inline  SharedBuffer*           bufferFromData(void* data);
54
55    //! get back a SharedBuffer object from its data
56    static  inline  const SharedBuffer*     bufferFromData(const void* data);
57
58    //! get the size of a SharedBuffer object from its data
59    static  inline  size_t                  sizeFromData(const void* data);
60
61    //! edit the buffer (get a writtable, or non-const, version of it)
62                    SharedBuffer*           edit() const;
63
64    //! edit the buffer, resizing if needed
65                    SharedBuffer*           editResize(size_t size) const;
66
67    //! like edit() but fails if a copy is required
68                    SharedBuffer*           attemptEdit() const;
69
70    //! resize and edit the buffer, loose it's content.
71                    SharedBuffer*           reset(size_t size) const;
72
73    //! acquire/release a reference on this buffer
74                    void                    acquire() const;
75
76    /*! release a reference on this buffer, with the option of not
77     * freeing the memory associated with it if it was the last reference
78     * returns the previous reference count
79     */
80                    int32_t                 release(uint32_t flags = 0) const;
81
82    //! returns wether or not we're the only owner
83    inline          bool                    onlyOwner() const;
84
85
86private:
87        inline SharedBuffer() { }
88        inline ~SharedBuffer() { }
89        inline SharedBuffer(const SharedBuffer&);
90
91        // 16 bytes. must be sized to preserve correct alingment.
92        mutable int32_t        mRefs;
93                size_t         mSize;
94                uint32_t       mReserved[2];
95};
96
97// ---------------------------------------------------------------------------
98
99const SharedBuffer* SharedBuffer::sharedBuffer(const void* data) {
100    return data ? reinterpret_cast<const SharedBuffer *>(data)-1 : 0;
101}
102
103const void* SharedBuffer::data() const {
104    return this + 1;
105}
106
107void* SharedBuffer::data() {
108    return this + 1;
109}
110
111size_t SharedBuffer::size() const {
112    return mSize;
113}
114
115SharedBuffer* SharedBuffer::bufferFromData(void* data)
116{
117    return ((SharedBuffer*)data)-1;
118}
119
120const SharedBuffer* SharedBuffer::bufferFromData(const void* data)
121{
122    return ((const SharedBuffer*)data)-1;
123}
124
125size_t SharedBuffer::sizeFromData(const void* data)
126{
127    return (((const SharedBuffer*)data)-1)->mSize;
128}
129
130bool SharedBuffer::onlyOwner() const {
131    return (mRefs == 1);
132}
133
134}; // namespace android
135
136// ---------------------------------------------------------------------------
137
138#endif // ANDROID_VECTOR_H
139