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