/* Copyright (c) 2000, 2025, Oracle and/or its affiliates.
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is designed to work with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have either included with
   the program or referenced in the documentation.

   Without limiting anything contained in the foregoing, this file,
   which is part of C Driver for MySQL (Connector/C), is also subject to the
   Universal FOSS Exception, version 1.0, a copy of which can be found at
   http://oss.oracle.com/licenses/universal-foss-exception.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
 * @file mysys/my_alloc.cc
 * Implementation of MEM_ROOT.
 *
 * This file follows Google coding style.
 */

#include <sys/types.h>
#include <algorithm>
#include <cassert>
#include <cstdarg>
#include <cstring>
#include <iterator>

#include "memory_debugging.h"
#include "my_alloc.h"
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_pointer_arithmetic.h"
#include "my_sys.h"
#include "mysql/service_mysql_alloc.h"
#include "mysys_err.h"
#include "template_utils.h"

// For instrumented code: Always use malloc(); never reuse a chunk.
// This gives a lot more memory chunks, each with a red-zone around them.
#if defined(HAVE_VALGRIND) || defined(HAVE_ASAN)
static constexpr bool MEM_ROOT_SINGLE_CHUNKS = true;
#else
static constexpr bool MEM_ROOT_SINGLE_CHUNKS = false;
#endif

MEM_ROOT::Block *MEM_ROOT::AllocBlock(size_t wanted_length,
                                      size_t minimum_length) {
  DBUG_TRACE;

  size_t length = std::max(wanted_length, ALIGN_SIZE(minimum_length));
  if (m_max_capacity != 0) {
    size_t bytes_left;
    if (m_allocated_size > m_max_capacity) {
      bytes_left = 0;
    } else {
      bytes_left = m_max_capacity - m_allocated_size;
    }
    if (length > bytes_left) {
      if (m_error_for_capacity_exceeded) {
        my_error(EE_CAPACITY_EXCEEDED, MYF(0),
                 static_cast<ulonglong>(m_max_capacity));
        // NOTE: No early return; we will abort the query at the next safe
        // point. We also don't go down to minimum_length, as this will give a
        // new block on every subsequent Alloc() (of which there might be
        // many, since we don't know when the next safe point will be).
      } else if (minimum_length <= bytes_left) {
        // Make one final chunk with all that we have left.
        length = bytes_left;
      } else {
        // We don't have enough memory left to satisfy minimum_length.
        return nullptr;
      }
    }
  }

  const size_t bytes_to_alloc = length + ALIGN_SIZE(sizeof(Block));
  auto *new_block = static_cast<Block *>(
      my_malloc(m_psi_key, bytes_to_alloc, MYF(MY_WME | ME_FATALERROR)));
  if (new_block == nullptr) {
    if (m_error_handler) (m_error_handler)();
    return nullptr;
  }
  TRASH(new_block, bytes_to_alloc);
  new_block->end = pointer_cast<char *>(new_block) + bytes_to_alloc;

  m_allocated_size += length;

  // Make the default block size 50% larger next time.
  // This ensures O(1) total mallocs (assuming Clear() is not called).
  if (!MEM_ROOT_SINGLE_CHUNKS) {
    m_block_size += m_block_size / 2;
  }
  return new_block;
}

void *MEM_ROOT::AllocSlow(size_t length) {
  DBUG_TRACE;
  DBUG_PRINT("enter", ("root: %p", this));

  // We need to allocate a new block to satisfy this allocation;
  // otherwise, the fast path in Alloc() would not have sent us here.
  // We plan to allocate a block of <block_size> bytes; see if that
  // would be enough or not.
  if (length >= m_block_size || MEM_ROOT_SINGLE_CHUNKS) {
    // The next block we'd allocate would _not_ be big enough
    // (or we're in Valgrind/ASAN mode, and want everything in single chunks).
    // Allocate an entirely new block, not disturbing anything;
    // since the new block isn't going to be used for the next allocation
    // anyway, we can just as well keep the previous one.
    Block *new_block =
        AllocBlock(/*wanted_length=*/length, /*minimum_length=*/length);
    if (new_block == nullptr) return nullptr;

    if (m_current_block == nullptr) {
      // This is the only block, so it has to be the current block, too.
      // However, it will be full, so we won't be allocating from it
      // unless ClearForReuse() is called.
      new_block->prev = nullptr;
      m_current_block = new_block;
      m_current_free_end = new_block->end;
      m_current_free_start = m_current_free_end;
    } else {
      // Insert the new block in the second-to-last position.
      new_block->prev = m_current_block->prev;
      m_current_block->prev = new_block;
    }

    return pointer_cast<char *>(new_block) + ALIGN_SIZE(sizeof(*new_block));
  }
  // The normal case: Throw away the current block, allocate a new block,
  // and use that to satisfy the new allocation.
  if (ForceNewBlock(/*minimum_length=*/length)) {
    return nullptr;
  }
  char *new_mem = m_current_free_start;
  m_current_free_start += length;
  return new_mem;
}

bool MEM_ROOT::ForceNewBlock(size_t minimum_length) {
  if (MEM_ROOT_SINGLE_CHUNKS) {
    assert(m_block_size == m_orig_block_size);
  }
  Block *new_block = AllocBlock(/*wanted_length=*/ALIGN_SIZE(m_block_size),
                                minimum_length);  // Will modify block_size.
  if (new_block == nullptr) return true;

  new_block->prev = m_current_block;
  m_current_block = new_block;

  char *new_mem =
      pointer_cast<char *>(new_block) + ALIGN_SIZE(sizeof(*new_block));
  m_current_free_start = new_mem;
  m_current_free_end = new_block->end;
  return false;
}

void MEM_ROOT::Clear() {
  DBUG_TRACE;
  DBUG_PRINT("enter", ("root: %p", this));

  // Already cleared, or memset() to zero, so just ignore.
  if (m_current_block == nullptr) return;

  Block *start = m_current_block;

  m_current_block = nullptr;
  m_block_size = m_orig_block_size;
  m_current_free_start = &s_dummy_target;
  m_current_free_end = &s_dummy_target;
  m_allocated_size = 0;

  FreeBlocks(start);
}

void MEM_ROOT::ClearForReuse() {
  DBUG_TRACE;

  if (MEM_ROOT_SINGLE_CHUNKS) {
    Clear();
    return;
  }

  // Already cleared, or memset() to zero, so just ignore.
  if (m_current_block == nullptr) return;

  // Keep the last block, which is usually the biggest one.
  m_current_free_start = pointer_cast<char *>(m_current_block) +
                         ALIGN_SIZE(sizeof(*m_current_block));
  Block *start = m_current_block->prev;
  m_current_block->prev = nullptr;
  m_allocated_size = m_current_free_end - m_current_free_start;
  TRASH(m_current_free_start, m_allocated_size);

  FreeBlocks(start);
}

void MEM_ROOT::FreeBlocks(Block *start) {
  // The MEM_ROOT might be allocated on itself, so make sure we don't
  // touch it after we've started freeing.
  for (Block *block = start; block != nullptr;) {
    Block *prev = block->prev;
    TRASH(block, std::distance(pointer_cast<char *>(block), block->end));
    my_free(block);
    block = prev;
  }
}

void MEM_ROOT::Claim(bool claim) {
  DBUG_TRACE;
  DBUG_PRINT("enter", ("root: %p", this));

  for (Block *block = m_current_block; block != nullptr; block = block->prev) {
    my_claim(block, claim);
  }
}

/*
 * Allocate many pointers at the same time.
 *
 * DESCRIPTION
 *   ptr1, ptr2, etc all point into big allocated memory area.
 *
 * SYNOPSIS
 *   multi_alloc_root()
 *     root               Memory root
 *     ptr1, length1      Multiple arguments terminated by a NULL pointer
 *     ptr2, length2      ...
 *     ...
 *     NULL
 *
 * RETURN VALUE
 *   A pointer to the beginning of the allocated memory block
 *   in case of success or NULL if out of memory.
 */

void *multi_alloc_root(MEM_ROOT *root, ...) {
  va_list args;
  char **ptr, *start, *res;
  size_t tot_length, length;
  DBUG_TRACE;

  va_start(args, root);
  tot_length = 0;
  while ((ptr = va_arg(args, char **))) {
    length = va_arg(args, uint);
    tot_length += ALIGN_SIZE(length);
  }
  va_end(args);

  if (!(start = static_cast<char *>(root->Alloc(tot_length))))
    return nullptr; /* purecov: inspected */

  va_start(args, root);
  res = start;
  while ((ptr = va_arg(args, char **))) {
    *ptr = res;
    length = va_arg(args, uint);
    res += ALIGN_SIZE(length);
  }
  va_end(args);
  return (void *)start;
}

char *strdup_root(MEM_ROOT *root, const char *str) {
  return strmake_root(root, str, strlen(str));
}

char *safe_strdup_root(MEM_ROOT *root, const char *str) {
  return str ? strdup_root(root, str) : nullptr;
}

char *strmake_root(MEM_ROOT *root, const char *str, size_t len) {
  char *pos;
  if ((pos = static_cast<char *>(root->Alloc(len + 1)))) {
    if (len > 0) memcpy(pos, str, len);
    pos[len] = 0;
  }
  return pos;
}

void *memdup_root(MEM_ROOT *root, const void *str, size_t len) {
  char *pos;
  if ((pos = static_cast<char *>(root->Alloc(len)))) {
    memcpy(pos, str, len);
  }
  return pos;
}

char MEM_ROOT::s_dummy_target;
