cpp/src/common/allocator/stl_allocator.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * License); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

#ifndef COMMON_ALLOCATOR_STL_ALLOCATOR_H
#define COMMON_ALLOCATOR_STL_ALLOCATOR_H

#include "alloc_base.h"

namespace common {

template <class T, AllocModID Mid, class TAllocator = BaseAllocator>
class StlAllocator {
   public:
    typedef size_t size_type;
    typedef ptrdiff_t difference_type;
    typedef T *pointer;
    typedef const T *const_pointer;
    typedef T &reference;
    typedef const T &const_reference;
    typedef T value_type;

    /*
     * rebind provides a way to obtain an allocator for a different type.
     * For example, std::list will alloc object Node<T> beside alloc object T.
     */
    template <class U>
    struct rebind {
        typedef StlAllocator<U, Mid, TAllocator> other;
    };

    StlAllocator() {}
    StlAllocator(const StlAllocator &) {}

    template <class T2, AllocModID Mid2>
    StlAllocator(const StlAllocator<T2, Mid2, TAllocator> &) {}

    StlAllocator(TAllocator base_allocator) : base_allocator_(base_allocator) {}

    pointer address(reference x) const { return &x; }
    const_pointer address(const_reference x) { return &x; }

    pointer allocate(size_type n, const void *hint = 0) {
        return (pointer)base_allocator_.alloc(n * sizeof(T), Mid);
    };
    void deallocate(void *p, size_type) { base_allocator_.free(p); }
    size_type max_size() const { return uint32_t(-1); }

    void construct(pointer p, const T &val) { new ((T *)p) T(val); }
    void destroy(pointer p) { p->~T(); }

   private:
    TAllocator base_allocator_;
};

/*
 * According to the manual, allocator is stateless.
 * Although we define a base_allocator_ here, but base_allocator_ is also
 * stateless. so '==' is always true and '!=' is always false. refer to
 * https://en.cppreference.com/w/cpp/memory/allocator/operator_cmp.
 */
template <class T1, AllocModID Mid1, class T2, AllocModID Mid2>
bool operator==(const StlAllocator<T1, Mid1> &a1,
                const StlAllocator<T2, Mid2> &a2) {
    return true;
}

template <class T1, AllocModID Mid1, class T2, AllocModID Mid2>
bool operator!=(const StlAllocator<T1, Mid1> &a1,
                const StlAllocator<T2, Mid2> &a2) {
    return false;
}

}  // end namespace common
#endif  // COMMON_ALLOCATOR_STL_ALLOCATOR_H