text: // Copyright (C) 2000, 2001 Stephen Cleary
  //
  // Distributed under the Boost Software License, Version 1.0. (See
  // accompanying file LICENSE_1_0.txt or copy at
  // http://www.boost.org/LICENSE_1_0.txt)
  //
  // See http://www.boost.org for updates, documentation, and revision history.
  
  #ifndef BOOST_POOL_HPP
  #define BOOST_POOL_HPP
  
  #include <boost/config.hpp>  // for workarounds
  
  // std::less, std::less_equal, std::greater
  #include <functional>
  // new[], delete[], std::nothrow
  #include <new>
  // std::size_t, std::ptrdiff_t
  #include <cstddef>
  // std::malloc, std::free
  #include <cstdlib>
  // std::invalid_argument
  #include <exception>
  // std::max
  #include <algorithm>
  
  #include <boost/pool/poolfwd.hpp>
  
  // boost::details::pool::ct_lcm
  #include <boost/pool/detail/ct_gcd_lcm.hpp>
  // boost::details::pool::lcm
  #include <boost/pool/detail/gcd_lcm.hpp>
  // boost::simple_segregated_storage
  #include <boost/pool/simple_segregated_storage.hpp>
  
  #ifdef BOOST_NO_STDC_NAMESPACE
   namespace std { using ::malloc; using ::free; }
  #endif
  
  // There are a few places in this file where the expression "this->m" is used.
  // This expression is used to force instantiation-time name lookup, which I am
  //   informed is required for strict Standard compliance.  It's only necessary
  //   if "m" is a member of a base class that is dependent on a template
  //   parameter.
  // Thanks to Jens Maurer for pointing this out!
  
  namespace boost {
  
  struct default_user_allocator_new_delete
  {
    typedef std::size_t size_type;
    typedef std::ptrdiff_t difference_type;
  
    static char * malloc(const size_type bytes)
    { return new (std::nothrow) char[bytes]; }
    static void free(char * const block)
    { delete [] block; }
  };
  
  struct default_user_allocator_malloc_free
  {
    typedef std::size_t size_type;
    typedef std::ptrdiff_t difference_type;
  
    static char * malloc(const size_type bytes)
    { return reinterpret_cast<char *>(std::malloc(bytes)); }
    static void free(char * const block)
    { std::free(block); }
  };
  
  namespace details {
  
  // PODptr is a class that pretends to be a "pointer" to different class types
  //  that don't really exist.  It provides member functions to access the "data"
  //  of the "object" it points to.  Since these "class" types are of variable
  //  size, and contains some information at the *end* of its memory (for
  //  alignment reasons), PODptr must contain the size of this "class" as well as
  //  the pointer to this "object".
  template <typename SizeType>
  class PODptr
  {
    public:
      typedef SizeType size_type;
  
    private:
      char * ptr;
      size_type sz;
  
      char * ptr_next_size() const
      { return (ptr + sz - sizeof(size_type)); }
      char * ptr_next_ptr() const
      {
        return (ptr_next_size() -
            pool::ct_lcm<sizeof(size_type), sizeof(void *)>::value);
      }
  
    public:
      PODptr(char * const nptr, const size_type nsize)
      :ptr(nptr), sz(nsize) { }
      PODptr()
      :ptr(0), sz(0) { }
  
      bool valid() const { return (begin() != 0); }
      void invalidate() { begin() = 0; }
      char * & begin() { return ptr; }
      char * begin() const { return ptr; }
      char * end() const { return ptr_next_ptr(); }
      size_type total_size() const { return sz; }
      size_type element_size() const
      {
        return (sz - sizeof(size_type) -
            pool::ct_lcm<sizeof(size_type), sizeof(void *)>::value);
      }
  
      size_type & next_size() const
      { return *(reinterpret_cast<size_type *>(ptr_next_size())); }
      char * & next_ptr() const
      { return *(reinterpret_cast<char **>(ptr_next_ptr())); }
  
      PODptr next() const
      { return PODptr<size_type>(next_ptr(), next_size()); }
      void next(const PODptr & arg) const
      {
        next_ptr() = arg.begin();
        next_size() = arg.total_size();
      }
  };
  
  } // namespace details
  
  template <typename UserAllocator>
  class pool: protected simple_segregated_storage<
      typename UserAllocator::size_type>
  {
    public:
      typedef UserAllocator user_allocator;
      typedef typename UserAllocator::size_type size_type;
      typedef typename UserAllocator::difference_type difference_type;
  
    private:
      BOOST_STATIC_CONSTANT(unsigned, min_alloc_size =
          (::boost::details::pool::ct_lcm<sizeof(void *), sizeof(size_type)>::value) );
  
      // Returns 0 if out-of-memory
      // Called if malloc/ordered_malloc needs to resize the free list
      void * malloc_need_resize();
      void * ordered_malloc_need_resize();
  
    protected:
      details::PODptr<size_type> list;
  
      simple_segregated_storage<size_type> & store() { return *this; }
      const simple_segregated_storage<size_type> & store() const { return *this; }
      const size_type requested_size;
      size_type next_size;
  
      // finds which POD in the list 'chunk' was allocated from
      details::PODptr<size_type> find_POD(void * const chunk) const;
  
      // is_from() tests a chunk to determine if it belongs in a block
      static bool is_from(void * const chunk, char * const i,
          const size_type sizeof_i)
      {
        // We use std::less_equal and std::less to test 'chunk'
        //  against the array bounds because standard operators
        //  may return unspecified results.
        // This is to ensure portability.  The operators < <= > >= are only
        //  defined for pointers to objects that are 1) in the same array, or
        //  2) subobjects of the same object [5.9/2].
        // The functor objects guarantee a total order for any pointer [20.3.3/8]
  //WAS:
  //      return (std::less_equal<void *>()(static_cast<void *>(i), chunk)
  //          && std::less<void *>()(chunk,
  //              static_cast<void *>(i + sizeof_i)));
        std::less_equal<void *> lt_eq;
        std::less<void *> lt;
        return (lt_eq(i, chunk) && lt(chunk, i + sizeof_i));
      }
  
      size_type alloc_size() const
      {
        const unsigned min_size = min_alloc_size;
        return details::pool::lcm<size_type>(requested_size, min_size);
      }
  
      // for the sake of code readability :)
      static void * & nextof(void * const ptr)
      { return *(static_cast<void **>(ptr)); }
  
    public:
      // The second parameter here is an extension!
      // pre: npartition_size != 0 && nnext_size != 0
      explicit pool(const size_type nrequested_size,
          const size_type nnext_size = 32)
      :list(0, 0), requested_size(nrequested_size), next_size(nnext_size)
      { }
  
      ~pool() { purge_memory(); }
  
      // Releases memory blocks that don't have chunks allocated
      // pre: lists are ordered
      //  Returns true if memory was actually deallocated
      bool release_memory();
  
      // Releases *all* memory blocks, even if chunks are still allocated
      //  Returns true if memory was actually deallocated
      bool purge_memory();
  
      // These functions are extensions!
      size_type get_next_size() const { return next_size; }
      void set_next_size(const size_type nnext_size) { next_size = nnext_size; }
  
      // Both malloc and ordered_malloc do a quick inlined check first for any
      //  free chunks.  Only if we need to get another memory block do we call
      //  the non-inlined *_need_resize() functions.
      // Returns 0 if out-of-memory
      void * malloc()
      {
        // Look for a non-empty storage
        if (!store().empty())
          return store().malloc();
        return malloc_need_resize();
      }
  
      void * ordered_malloc()
      {
        // Look for a non-empty storage
        if (!store().empty())
          return store().malloc();
        return ordered_malloc_need_resize();
      }
  
      // Returns 0 if out-of-memory
      // Allocate a contiguous section of n chunks
      void * ordered_malloc(size_type n);
  
      // pre: 'chunk' must have been previously
      //        returned by *this.malloc().
      void free(void * const chunk)
      { store().free(chunk); }
  
      // pre: 'chunk' must have been previously
      //        returned by *this.malloc().
      void ordered_free(void * const chunk)
      { store().ordered_free(chunk); }
  
      // pre: 'chunk' must have been previously
      //        returned by *this.malloc(n).
      void free(void * const chunks, const size_type n)
      {
        const size_type partition_size = alloc_size();
        const size_type total_req_size = n * requested_size;
        const size_type num_chunks = total_req_size / partition_size +
            static_cast<bool>(total_req_size % partition_size);
  
        store().free_n(chunks, num_chunks, partition_size);
      }
  
      // pre: 'chunk' must have been previously
      //        returned by *this.malloc(n).
      void ordered_free(void * const chunks, const size_type n)
      {
        const size_type partition_size = alloc_size();
        const size_type total_req_size = n * requested_size;
        const size_type num_chunks = total_req_size / partition_size +
            static_cast<bool>(total_req_size % partition_size);
  
        store().ordered_free_n(chunks, num_chunks, partition_size);
      }
  
      // is_from() tests a chunk to determine if it was allocated from *this
      bool is_from(void * const chunk) const
      {
        return (find_POD(chunk).valid());
      }
  };
  
  template <typename UserAllocator>
  bool pool<UserAllocator>::release_memory()
  {
    // This is the return value: it will be set to true when we actually call
    //  UserAllocator::free(..)
    bool ret = false;
  
    // This is a current & previous iterator pair over the memory block list
    details::PODptr<size_type> ptr = list;
    details::PODptr<size_type> prev;
  
    // This is a current & previous iterator pair over the free memory chunk list
    //  Note that "prev_free" in this case does NOT point to the previous memory
    //  chunk in the free list, but rather the last free memory chunk before the
    //  current block.
    void * free = this->first;
    void * prev_free = 0;
  
    const size_type partition_size = alloc_size();
  
    // Search through all the all the allocated memory blocks
    while (ptr.valid())
    {
      // At this point:
      //  ptr points to a valid memory block
      //  free points to either:
      //    0 if there are no more free chunks
      //    the first free chunk in this or some next memory block
      //  prev_free points to either:
      //    the last free chunk in some previous memory block
      //    0 if there is no such free chunk
      //  prev is either:
      //    the PODptr whose next() is ptr
      //    !valid() if there is no such PODptr
  
      // If there are no more free memory chunks, then every remaining
      //  block is allocated out to its fullest capacity, and we can't
      //  release any more memory
      if (free == 0)
        return ret;
  
      // We have to check all the chunks.  If they are *all* free (i.e., present
      //  in the free list), then we can free the block.
      bool all_chunks_free = true;
  
      // Iterate 'i' through all chunks in the memory block
      // if free starts in the memory block, be careful to keep it there
      void * saved_free = free;
      for (char * i = ptr.begin(); i != ptr.end(); i += partition_size)
      {
        // If this chunk is not free
        if (i != free)
        {
          // We won't be able to free this block
          all_chunks_free = false;
  
          // free might have travelled outside ptr
          free = saved_free;
          // Abort searching the chunks; we won't be able to free this
          //  block because a chunk is not free.
          break;
        }
  
        // We do not increment prev_free because we are in the same block
        free = nextof(free);
      }
  
      // post: if the memory block has any chunks, free points to one of them
      // otherwise, our assertions above are still valid
  
      const details::PODptr<size_type> next = ptr.next();
  
      if (!all_chunks_free)
      {
        if (is_from(free, ptr.begin(), ptr.element_size()))
        {
          std::less<void *> lt;
          void * const end = ptr.end();
          do
          {
            prev_free = free;
            free = nextof(free);
          } while (free && lt(free, end));
        }
        // This invariant is now restored:
        //     free points to the first free chunk in some next memory block, or
        //       0 if there is no such chunk.
        //     prev_free points to the last free chunk in this memory block.
        
        // We are just about to advance ptr.  Maintain the invariant:
        // prev is the PODptr whose next() is ptr, or !valid()
        // if there is no such PODptr
        prev = ptr;
      }
      else
      {
        // All chunks from this block are free
  
        // Remove block from list
        if (prev.valid())
          prev.next(next);
        else
          list = next;
  
        // Remove all entries in the free list from this block
        if (prev_free != 0)
          nextof(prev_free) = free;
        else
          this->first = free;
  
        // And release memory
        UserAllocator::free(ptr.begin());
        ret = true;
      }
  
      // Increment ptr
      ptr = next;
    }
  
    return ret;
  }
  
  template <typename UserAllocator>
  bool pool<UserAllocator>::purge_memory()
  {
    details::PODptr<size_type> iter = list;
  
    if (!iter.valid())
      return false;
  
    do
    {
      // hold "next" pointer
      const details::PODptr<size_type> next = iter.next();
  
      // delete the storage
      UserAllocator::free(iter.begin());
  
      // increment iter
      iter = next;
    } while (iter.valid());
  
    list.invalidate();
    this->first = 0;
  
    return true;
  }
  
  template <typename UserAllocator>
  void * pool<UserAllocator>::malloc_need_resize()
  {
    // No memory in any of our storages; make a new storage,
    const size_type partition_size = alloc_size();
    const size_type POD_size = next_size * partition_size +
        details::pool::ct_lcm<sizeof(size_type), sizeof(void *)>::value + sizeof(size_type);
    char * const ptr = UserAllocator::malloc(POD_size);
    if (ptr == 0)
      return 0;
    const details::PODptr<size_type> node(ptr, POD_size);
    next_size <<= 1;
  
    //  initialize it,
    store().add_block(node.begin(), node.element_size(), partition_size);
  
    //  insert it into the list,
    node.next(list);
    list = node;
  
    //  and return a chunk from it.
    return store().malloc();
  }
  
  template <typename UserAllocator>
  void * pool<UserAllocator>::ordered_malloc_need_resize()
  {
    // No memory in any of our storages; make a new storage,
    const size_type partition_size = alloc_size();
    const size_type POD_size = next_size * partition_size +
        details::pool::ct_lcm<sizeof(size_type), sizeof(void *)>::value + sizeof(size_type);
    char * const ptr = UserAllocator::malloc(POD_size);
    if (ptr == 0)
      return 0;
    const details::PODptr<size_type> node(ptr, POD_size);
    next_size <<= 1;
  
    //  initialize it,
    //  (we can use "add_block" here because we know that
    //  the free list is empty, so we don't have to use
    //  the slower ordered version)
    store().add_block(node.begin(), node.element_size(), partition_size);
  
    //  insert it into the list,
    //   handle border case
    if (!list.valid() || std::greater<void *>()(list.begin(), node.begin()))
    {
      node.next(list);
      list = node;
    }
    else
    {
      details::PODptr<size_type> prev = list;
  
      while (true)
      {
        // if we're about to hit the end or
        //  if we've found where "node" goes
        if (prev.next_ptr() == 0
            || std::greater<void *>()(prev.next_ptr(), node.begin()))
          break;
  
        prev = prev.next();
      }
  
      node.next(prev.next());
      prev.next(node);
    }
  
    //  and return a chunk from it.
    return store().malloc();
  }
  
  template <typename UserAllocator>
  void * pool<UserAllocator>::ordered_malloc(const size_type n)
  {
    const size_type partition_size = alloc_size();
    const size_type total_req_size = n * requested_size;
    const size_type num_chunks = total_req_size / partition_size +
        static_cast<bool>(total_req_size % partition_size);
  
    void * ret = store().malloc_n(num_chunks, partition_size);
  
    if (ret != 0)
      return ret;
  
    // Not enougn memory in our storages; make a new storage,
    BOOST_USING_STD_MAX();
    next_size = max BOOST_PREVENT_MACRO_SUBSTITUTION(next_size, num_chunks);
    const size_type POD_size = next_size * partition_size +
        details::pool::ct_lcm<sizeof(size_type), sizeof(void *)>::value + sizeof(size_type);
    char * const ptr = UserAllocator::malloc(POD_size);
    if (ptr == 0)
      return 0;
    const details::PODptr<size_type> node(ptr, POD_size);
  
    // Split up block so we can use what wasn't requested
    //  (we can use "add_block" here because we know that
    //  the free list is empty, so we don't have to use
    //  the slower ordered version)
    if (next_size > num_chunks)
      store().add_block(node.begin() + num_chunks * partition_size,
          node.element_size() - num_chunks * partition_size, partition_size);
  
    next_size <<= 1;
  
    //  insert it into the list,
    //   handle border case
    if (!list.valid() || std::greater<void *>()(list.begin(), node.begin()))
    {
      node.next(list);
      list = node;
    }
    else
    {
      details::PODptr<size_type> prev = list;
  
      while (true)
      {
        // if we're about to hit the end or
        //  if we've found where "node" goes
        if (prev.next_ptr() == 0
            || std::greater<void *>()(prev.next_ptr(), node.begin()))
          break;
  
        prev = prev.next();
      }
  
      node.next(prev.next());
      prev.next(node);
    }
  
    //  and return it.
    return node.begin();
  }
  
  template <typename UserAllocator>
  details::PODptr<typename pool<UserAllocator>::size_type>
  pool<UserAllocator>::find_POD(void * const chunk) const
  {
    // We have to find which storage this chunk is from.
    details::PODptr<size_type> iter = list;
    while (iter.valid())
    {
      if (is_from(chunk, iter.begin(), iter.element_size()))
        return iter;
      iter = iter.next();
    }
  
    return iter;
  }
  
  } // namespace boost
  
  #endif
  