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      1 /*
      2  * Copyright 2005 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ANDROID_PIXELFLINGER_SHARED_BUFFER_H
     18 #define ANDROID_PIXELFLINGER_SHARED_BUFFER_H
     19 
     20 #include <stdint.h>
     21 #include <sys/types.h>
     22 
     23 // ---------------------------------------------------------------------------
     24 
     25 namespace android {
     26 namespace tinyutils {
     27 
     28 class SharedBuffer
     29 {
     30 public:
     31 
     32     /* flags to use with release() */
     33     enum {
     34         eKeepStorage = 0x00000001
     35     };
     36 
     37     /*! allocate a buffer of size 'size' and acquire() it.
     38      *  call release() to free it.
     39      */
     40     static          SharedBuffer*           alloc(size_t size);
     41 
     42     /*! free the memory associated with the SharedBuffer.
     43      * Fails if there are any users associated with this SharedBuffer.
     44      * In other words, the buffer must have been release by all its
     45      * users.
     46      */
     47     static          ssize_t                 dealloc(const SharedBuffer* released);
     48 
     49     //! get the SharedBuffer from the data pointer
     50     static  inline  const SharedBuffer*     sharedBuffer(const void* data);
     51 
     52     //! access the data for read
     53     inline          const void*             data() const;
     54 
     55     //! access the data for read/write
     56     inline          void*                   data();
     57 
     58     //! get size of the buffer
     59     inline          size_t                  size() const;
     60 
     61     //! get back a SharedBuffer object from its data
     62     static  inline  SharedBuffer*           bufferFromData(void* data);
     63 
     64     //! get back a SharedBuffer object from its data
     65     static  inline  const SharedBuffer*     bufferFromData(const void* data);
     66 
     67     //! get the size of a SharedBuffer object from its data
     68     static  inline  size_t                  sizeFromData(const void* data);
     69 
     70     //! edit the buffer (get a writtable, or non-const, version of it)
     71                     SharedBuffer*           edit() const;
     72 
     73     //! edit the buffer, resizing if needed
     74                     SharedBuffer*           editResize(size_t size) const;
     75 
     76     //! like edit() but fails if a copy is required
     77                     SharedBuffer*           attemptEdit() const;
     78 
     79     //! resize and edit the buffer, loose it's content.
     80                     SharedBuffer*           reset(size_t size) const;
     81 
     82     //! acquire/release a reference on this buffer
     83                     void                    acquire() const;
     84 
     85     /*! release a reference on this buffer, with the option of not
     86      * freeing the memory associated with it if it was the last reference
     87      * returns the previous reference count
     88      */
     89                     int32_t                 release(uint32_t flags = 0) const;
     90 
     91     //! returns wether or not we're the only owner
     92     inline          bool                    onlyOwner() const;
     93 
     94 
     95 private:
     96         inline SharedBuffer() { }
     97         inline ~SharedBuffer() { }
     98         inline SharedBuffer(const SharedBuffer&);
     99 
    100         // 16 bytes. must be sized to preserve correct alingment.
    101         mutable int32_t        mRefs;
    102                 size_t         mSize;
    103                 uint32_t       mReserved[2];
    104 };
    105 
    106 // ---------------------------------------------------------------------------
    107 
    108 const SharedBuffer* SharedBuffer::sharedBuffer(const void* data) {
    109     return data ? reinterpret_cast<const SharedBuffer *>(data)-1 : 0;
    110 }
    111 
    112 const void* SharedBuffer::data() const {
    113     return this + 1;
    114 }
    115 
    116 void* SharedBuffer::data() {
    117     return this + 1;
    118 }
    119 
    120 size_t SharedBuffer::size() const {
    121     return mSize;
    122 }
    123 
    124 SharedBuffer* SharedBuffer::bufferFromData(void* data)
    125 {
    126     return ((SharedBuffer*)data)-1;
    127 }
    128 
    129 const SharedBuffer* SharedBuffer::bufferFromData(const void* data)
    130 {
    131     return ((const SharedBuffer*)data)-1;
    132 }
    133 
    134 size_t SharedBuffer::sizeFromData(const void* data)
    135 {
    136     return (((const SharedBuffer*)data)-1)->mSize;
    137 }
    138 
    139 bool SharedBuffer::onlyOwner() const {
    140     return (mRefs == 1);
    141 }
    142 
    143 } // namespace tinyutils
    144 } // namespace android
    145 
    146 // ---------------------------------------------------------------------------
    147 
    148 #endif // ANDROID_PIXELFLINGER_SHARED_BUFFER_H
    149