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/**
@file      mmap.hpp
@brief     class to manage memory-mapped files
@author    Robert van Engelen - engelen@genivia.com
@copyright (c) 2019-2022, Robert van Engelen, Genivia Inc. All rights reserved.
@copyright (c) BSD-3 License - see LICENSE.txt
*/

#ifndef MMAP_HPP
#define MMAP_HPP

#include "ugrep.hpp"

// --min-mmap and --max-mmap file size to allocate with mmap(), not greater than 4294967295LL, 0 disables mmap()
#ifndef MIN_MMAP_SIZE
# define MIN_MMAP_SIZE 16384LL // 16KB at minimum, smaller files are efficiently read in one go with read()
#endif
#ifndef MAX_MMAP_SIZE
# define MAX_MMAP_SIZE 1073741824LL // each worker thread may use up to 1GB mmap space but not more
#endif

#if defined(HAVE_MMAP) && MAX_MMAP_SIZE > 0
# include <sys/mman.h>
# include <sys/stat.h>
# include <limits>
# ifndef MAP_ANONYMOUS
#  define MAP_ANONYMOUS MAP_ANON
# endif
#endif

// manage mmap state
class MMap {

 public:

  MMap()
    :
      mmap_base(NULL),
      mmap_size(0)
  { }

  ~MMap()
  {
#if defined(HAVE_MMAP) && MAX_MMAP_SIZE > 0
    if (mmap_base != NULL)
      munmap(mmap_base, mmap_size);
#endif
  }

  // attempt to mmap the given file-based input, return true if successful with base and size
  bool file(reflex::Input& input, const char*& base, size_t& size)
  {
    base = NULL;
    size = 0;

#if defined(HAVE_MMAP) && MAX_MMAP_SIZE > 0

    // get current input file and check if its encoding is plain
    FILE *file = input.file();
    if (file == NULL || input.file_encoding() != reflex::Input::file_encoding::plain)
      return false;

    // is this a regular file that is not too large (for size_t)?
    int fd = fileno(file);
    struct stat buf;
    if (fstat(fd, &buf) != 0 || !S_ISREG(buf.st_mode) || static_cast<uint64_t>(buf.st_size) < MIN_MMAP_SIZE || static_cast<uint64_t>(buf.st_size) > static_cast<uint64_t>(std::numeric_limits<size_t>::max()))
      return false;

    // is this file not larger than --max-mmap?
    size = static_cast<size_t>(buf.st_size);
    if (size > flag_max_mmap)
      return false;

    // mmap the file and round requested size up to 4K (typical page size)
    if (mmap_base == NULL)
    {
      // allocate fixed mmap region to reuse
      mmap_size = (flag_max_mmap + 0xfff) & ~0xfffUL;
      mmap_base = mmap(NULL, mmap_size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);

      // files are sequentially read
      if (mmap_base == MAP_FAILED)
        mmap_base = NULL;
      else
        madvise(mmap_base, mmap_size, MADV_SEQUENTIAL);
    }

    if (mmap_base != NULL)
    {
      // mmap the (next) file to the fixed mmap region
      base = static_cast<const char*>(mmap_base = mmap(mmap_base, mmap_size, PROT_READ, MAP_FIXED | MAP_PRIVATE, fd, 0));

      // mmap OK?
      if (mmap_base != MAP_FAILED)
        return true;
    }

    // not OK
    mmap_base = NULL;
    mmap_size = 0;
    base = NULL;
    size = 0;

#else

    (void)input;

#endif

    return false;
  }

 protected:

  void  *mmap_base; // mmap() base address
  size_t mmap_size; // mmap() allocated size

};

#endif
