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Member "flatbuffers-23.1.21/include/flatbuffers/allocator.h" (21 Jan 2023, 2588 Bytes) of package /linux/misc/flatbuffers-23.1.21.tar.gz:


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    1 /*
    2  * Copyright 2021 Google Inc. All rights reserved.
    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 FLATBUFFERS_ALLOCATOR_H_
   18 #define FLATBUFFERS_ALLOCATOR_H_
   19 
   20 #include "flatbuffers/base.h"
   21 
   22 namespace flatbuffers {
   23 
   24 // Allocator interface. This is flatbuffers-specific and meant only for
   25 // `vector_downward` usage.
   26 class Allocator {
   27  public:
   28   virtual ~Allocator() {}
   29 
   30   // Allocate `size` bytes of memory.
   31   virtual uint8_t *allocate(size_t size) = 0;
   32 
   33   // Deallocate `size` bytes of memory at `p` allocated by this allocator.
   34   virtual void deallocate(uint8_t *p, size_t size) = 0;
   35 
   36   // Reallocate `new_size` bytes of memory, replacing the old region of size
   37   // `old_size` at `p`. In contrast to a normal realloc, this grows downwards,
   38   // and is intended specifcally for `vector_downward` use.
   39   // `in_use_back` and `in_use_front` indicate how much of `old_size` is
   40   // actually in use at each end, and needs to be copied.
   41   virtual uint8_t *reallocate_downward(uint8_t *old_p, size_t old_size,
   42                                        size_t new_size, size_t in_use_back,
   43                                        size_t in_use_front) {
   44     FLATBUFFERS_ASSERT(new_size > old_size);  // vector_downward only grows
   45     uint8_t *new_p = allocate(new_size);
   46     memcpy_downward(old_p, old_size, new_p, new_size, in_use_back,
   47                     in_use_front);
   48     deallocate(old_p, old_size);
   49     return new_p;
   50   }
   51 
   52  protected:
   53   // Called by `reallocate_downward` to copy memory from `old_p` of `old_size`
   54   // to `new_p` of `new_size`. Only memory of size `in_use_front` and
   55   // `in_use_back` will be copied from the front and back of the old memory
   56   // allocation.
   57   void memcpy_downward(uint8_t *old_p, size_t old_size, uint8_t *new_p,
   58                        size_t new_size, size_t in_use_back,
   59                        size_t in_use_front) {
   60     memcpy(new_p + new_size - in_use_back, old_p + old_size - in_use_back,
   61            in_use_back);
   62     memcpy(new_p, old_p, in_use_front);
   63   }
   64 };
   65 
   66 }  // namespace flatbuffers
   67 
   68 #endif  // FLATBUFFERS_ALLOCATOR_H_