text: /*
  
  Copyright (c) 2006-2015, Arvid Norberg
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:
  
      * Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.
      * Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in
        the documentation and/or other materials provided with the distribution.
      * Neither the name of the author nor the names of its
        contributors may be used to endorse or promote products derived
        from this software without specific prior written permission.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE.
  
  */
  
  #ifndef TORRENT_FILE_POOL_HPP
  #define TORRENT_FILE_POOL_HPP
  
  #include <map>
  #include "libtorrent/file.hpp"
  #include "libtorrent/time.hpp"
  #include "libtorrent/thread.hpp"
  #include "libtorrent/file_storage.hpp"
  #include "libtorrent/aux_/time.hpp"
  
  namespace libtorrent
  {
  	struct pool_file_status
  	{
  		// the index of the file this entry refers to into the ``file_storage``
  		// file list of this torrent. This starts indexing at 0.
  		int file_index;
  
  		// a (high precision) timestamp of when the file was last used.
  		time_point last_use;
  
  		// ``open_mode`` is a bitmask of the file flags this file is currently opened with. These
  		// are the flags used in the ``file::open()`` function. This enum is defined as a member
  		// of the ``file`` class.
  		// 
  		// ::
  		// 
  		// 	enum
  		// 	{
  		// 		read_only = 0,
  		// 		write_only = 1,
  		// 		read_write = 2,
  		// 		rw_mask = 3,
  		// 		no_buffer = 4,
  		// 		sparse = 8,
  		// 		no_atime = 16,
  		// 		random_access = 32,
  		// 		lock_file = 64,
  		// 	};
  		// 
  		// Note that the read/write mode is not a bitmask. The two least significant bits are used
  		// to represent the read/write mode. Those bits can be masked out using the ``rw_mask`` constant.
  		int open_mode;
  	};
  
  	// this is an internal cache of open file handles. It's primarily used by
  	// storage_interface implementations. It provides semi weak guarantees of
  	// not opening more file handles than specified. Given multiple threads,
  	// each with the ability to lock a file handle (via smart pointer), there
  	// may be windows where more file handles are open.
  	struct TORRENT_EXPORT file_pool : boost::noncopyable
  	{
  		// ``size`` specifies the number of allowed files handles
  		// to hold open at any given time.
  		file_pool(int size = 40);
  		~file_pool();
  
  		// return an open file handle to file at ``file_index`` in the
  		// file_storage ``fs`` opened at save path ``p``. ``m`` is the
  		// file open mode (see file::open_mode_t).
  		file_handle open_file(void* st, std::string const& p
  			, int file_index, file_storage const& fs, int m, error_code& ec);
  		// release all files belonging to the specified storage_interface (``st``)
  		// the overload that takes ``file_index`` releases only the file with
  		// that index in storage ``st``.
  		void release(void* st = NULL);
  		void release(void* st, int file_index);
  
  		// update the allowed number of open file handles to ``size``.
  		void resize(int size);
  
  		// returns the current limit of number of allowed open file handles held
  		// by the file_pool.
  		int size_limit() const { return m_size; }
  
  		// internal
  		void set_low_prio_io(bool b) { m_low_prio_io = b; }
  		void get_status(std::vector<pool_file_status>* files, void* st) const;
  
  #if TORRENT_USE_ASSERTS
  		bool assert_idle_files(void* st) const;
  
  		// remember that this storage has had
  		// its files deleted. We may not open any
  		// files from it again
  		void mark_deleted(file_storage const& fs);
  #endif
  
  	private:
  
  		void remove_oldest(mutex::scoped_lock& l);
  
  		int m_size;
  		bool m_low_prio_io;
  
  		struct lru_file_entry
  		{
  			lru_file_entry(): key(0), last_use(aux::time_now()), mode(0) {}
  			mutable file_handle file_ptr;
  			void* key;
  			time_point last_use;
  			int mode;
  		};
  
  		// maps storage pointer, file index pairs to the
  		// lru entry for the file
  		typedef std::map<std::pair<void*, int>, lru_file_entry> file_set;
  		
  		file_set m_files;
  #if TORRENT_USE_ASSERTS
  		std::vector<std::pair<std::string, void const*> > m_deleted_storages;
  #endif
  		mutable mutex m_mutex;
  	};
  }
  
  #endif
  