array.cc

/* Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

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   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

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/**
  @file mysys/array.cc
  Handling of arrays that can grow dynamically.
*/

#include <string.h>
#include <sys/types.h>

#include "my_alloc.h"
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_macros.h"
#include "my_sys.h"
#include "mysql/psi/psi_memory.h"
#include "mysql/service_mysql_alloc.h"

/*
  Initiate dynamic array

  SYNOPSIS
    my_init_dynamic_array()
      array		Pointer to an array
      element_size	Size of element
      init_buffer       Initial buffer pointer
      init_alloc	Number of initial elements
      alloc_increment	Increment for adding new elements

  DESCRIPTION
    init_dynamic_array() initiates array and allocate space for
    init_alloc eilements.
    Array is usable even if space allocation failed, hence, the
    function never returns true.
    Static buffers must begin immediately after the array structure.

  RETURN VALUE
    false	Ok
*/

bool my_init_dynamic_array(DYNAMIC_ARRAY *array, PSI_memory_key psi_key,
                           uint element_size, void *init_buffer,
                           uint init_alloc, uint alloc_increment) {
  DBUG_ENTER("my_init_dynamic_array");
  if (!alloc_increment) {
    alloc_increment = MY_MAX((8192 - MALLOC_OVERHEAD) / element_size, 16);
    if (init_alloc > 8 && alloc_increment > init_alloc * 2)
      alloc_increment = init_alloc * 2;
  }

  if (!init_alloc) {
    init_alloc = alloc_increment;
    init_buffer = 0;
  }
  array->elements = 0;
  array->max_element = init_alloc;
  array->alloc_increment = alloc_increment;
  array->size_of_element = element_size;
  array->m_psi_key = psi_key;
  if ((array->buffer = static_cast<uchar *>(init_buffer))) DBUG_RETURN(false);
  /*
    Since the dynamic array is usable even if allocation fails here malloc
    should not throw an error
  */
  if (!(array->buffer =
            (uchar *)my_malloc(psi_key, element_size * init_alloc, MYF(0))))
    array->max_element = 0;
  DBUG_RETURN(false);
}

/*
  Insert element at the end of array. Allocate memory if needed.

  SYNOPSIS
    insert_dynamic()
      array
      element

  RETURN VALUE
    true	Insert failed
    false	Ok
*/

bool insert_dynamic(DYNAMIC_ARRAY *array, const void *element) {
  uchar *buffer;
  if (array->elements == array->max_element) { /* Call only when nessesary */
    if (!(buffer = static_cast<uchar *>(alloc_dynamic(array)))) return true;
  } else {
    buffer = array->buffer + (array->elements * array->size_of_element);
    array->elements++;
  }
  memcpy(buffer, element, (size_t)array->size_of_element);
  return false;
}

/*
  Alloc space for next element(s)

  SYNOPSIS
    alloc_dynamic()
      array

  DESCRIPTION
    alloc_dynamic() checks if there is empty space for at least
    one element if not tries to allocate space for alloc_increment
    elements at the end of array.

  RETURN VALUE
    pointer	Pointer to empty space for element
    0		Error
*/

void *alloc_dynamic(DYNAMIC_ARRAY *array) {
  if (array->elements == array->max_element) {
    char *new_ptr;
    if (array->buffer == (uchar *)(array + 1)) {
      /*
        In this senerio, the buffer is statically preallocated,
        so we have to create an all-new malloc since we overflowed
      */
      if (!(new_ptr = (char *)my_malloc(
                array->m_psi_key,
                (array->max_element + array->alloc_increment) *
                    array->size_of_element,
                MYF(MY_WME))))
        return 0;
      memcpy(new_ptr, array->buffer, array->elements * array->size_of_element);
    } else if (!(new_ptr = (char *)my_realloc(
                     array->m_psi_key, array->buffer,
                     (array->max_element + array->alloc_increment) *
                         array->size_of_element,
                     MYF(MY_WME | MY_ALLOW_ZERO_PTR))))
      return 0;
    array->buffer = (uchar *)new_ptr;
    array->max_element += array->alloc_increment;
  }
  return array->buffer + (array->elements++ * array->size_of_element);
}

/*
  Pop last element from array.

  SYNOPSIS
    pop_dynamic()
      array

  RETURN VALUE
    pointer	Ok
    0		Array is empty
*/

void *pop_dynamic(DYNAMIC_ARRAY *array) {
  if (array->elements)
    return array->buffer + (--array->elements * array->size_of_element);
  return 0;
}

void claim_dynamic(DYNAMIC_ARRAY *array) {
  /*
    Check for a static buffer
  */
  if (array->buffer == (uchar *)(array + 1)) return;

  my_claim(array->buffer);
}

/*
  Empty array by freeing all memory

  SYNOPSIS
    delete_dynamic()
      array	Array to be deleted
*/

void delete_dynamic(DYNAMIC_ARRAY *array) {
  /*
    Just mark as empty if we are using a static buffer
  */
  if (array->buffer == (uchar *)(array + 1))
    array->elements = 0;
  else if (array->buffer) {
    my_free(array->buffer);
    array->buffer = 0;
    array->elements = array->max_element = 0;
  }
}

/*
  Free unused memory

  SYNOPSIS
    freeze_size()
      array	Array to be freed

*/

void freeze_size(DYNAMIC_ARRAY *array) {
  uint elements = MY_MAX(array->elements, 1);

  /*
    Do nothing if we are using a static buffer
  */
  if (array->buffer == (uchar *)(array + 1)) return;

  if (array->buffer && array->max_element != elements) {
    array->buffer =
        (uchar *)my_realloc(array->m_psi_key, array->buffer,
                            elements * array->size_of_element, MYF(MY_WME));
    array->max_element = elements;
  }
}