malloc_allocator.h

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/* Copyright (c) 2014, 2025, Oracle and/or its affiliates.
 
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   it under the terms of the GNU General Public License, version 2.0,
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef MALLOC_ALLOCATOR_INCLUDED
#define MALLOC_ALLOCATOR_INCLUDED
 
#include <assert.h>
#include <limits>
#include <new>
#include <utility>  // std::forward
 
#include "my_sys.h"
#include "mysql/service_mysql_alloc.h"
#include "sql/psi_memory_key.h"
 
/**
  Malloc_allocator is a C++ STL memory allocator based on my_malloc/my_free.
 
  This allows for P_S instrumentation of memory allocation done by
  internally by STL container classes.
 
  Example usage:
  vector<int, Malloc_allocator<int>>
    v((Malloc_allocator<int>(PSI_NOT_INSTRUMENTED)));
 
  If the type is complicated, you can just write Malloc_allocator<>(psi_key)
  as a shorthand for Malloc_allocator<My_complicated_type>(psi_key), as all
  Malloc_allocator instances are implicitly convertible to each other
  and there is a default template parameter.
 
  @note allocate() throws std::bad_alloc() similarly to the default
  STL memory allocator. This is necessary - STL functions which allocates
  memory expects it. Otherwise these functions will try to use the memory,
  leading to segfaults if memory allocation was not successful.
 
  @note This allocator cannot be used for std::basic_string with RHEL 6/7
  because of this bug:
  https://bugzilla.redhat.com/show_bug.cgi?id=1546704
  "Define _GLIBCXX_USE_CXX11_ABI gets ignored by gcc in devtoolset-7"
*/
 
template <class T = void *>
class Malloc_allocator {
  // This cannot be const if we want to be able to swap.
  PSI_memory_key m_key;
 
 public:
  typedef T value_type;
  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;
 
  pointer address(reference r) const { return &r; }
  const_pointer address(const_reference r) const { return &r; }
 
  explicit Malloc_allocator(PSI_memory_key key) : m_key(key) {}
 
  template <class U>
  Malloc_allocator(const Malloc_allocator<U> &other [[maybe_unused]])
      : m_key(other.psi_key()) {}
 
  template <class U>
  Malloc_allocator &operator=(const Malloc_allocator<U> &other
                              [[maybe_unused]]) {
    assert(m_key == other.psi_key());  // Don't swap key.
  }
 
  pointer allocate(size_type n, const_pointer hint [[maybe_unused]] = nullptr) {
    if (n == 0) return nullptr;
    if (n > max_size()) throw std::bad_alloc();
 
    pointer p = static_cast<pointer>(
        my_malloc(m_key, n * sizeof(T), MYF(MY_WME | ME_FATALERROR)));
    if (p == nullptr) throw std::bad_alloc();
    return p;
  }
 
  void deallocate(pointer p, size_type) { my_free(p); }
 
  template <class U, class... Args>
  void construct(U *p, Args &&...args) {
    assert(p != nullptr);
    try {
      ::new ((void *)p) U(std::forward<Args>(args)...);
    } catch (...) {
      assert(false);  // Constructor should not throw an exception.
    }
  }
 
  void destroy(pointer p) {
    assert(p != nullptr);
    try {
      p->~T();
    } catch (...) {
      assert(false);  // Destructor should not throw an exception
    }
  }
 
  size_type max_size() const {
    return std::numeric_limits<size_t>::max() / sizeof(T);
  }
 
  template <class U>
  struct rebind {
    typedef Malloc_allocator<U> other;
  };
 
  PSI_memory_key psi_key() const { return m_key; }
};
 
template <class T>
bool operator==(const Malloc_allocator<T> &a1, const Malloc_allocator<T> &a2) {
  return a1.psi_key() == a2.psi_key();
}
 
template <class T>
bool operator!=(const Malloc_allocator<T> &a1, const Malloc_allocator<T> &a2) {
  return a1.psi_key() != a2.psi_key();
}
 
#endif  // MALLOC_ALLOCATOR_INCLUDED