/*

Copyright (c) 2006, 2009, 2013-2021, Arvid Norberg
Copyright (c) 2016, Alden Torres
Copyright (c) 2019, Steven Siloti
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_VIEW_POOL_HPP
#define TORRENT_FILE_VIEW_POOL_HPP

#include "libtorrent/config.hpp"

#if TORRENT_HAVE_MMAP || TORRENT_HAVE_MAP_VIEW_OF_FILE

#include <map>
#include <mutex>
#include <vector>
#include <memory>
#include <condition_variable>

#include "libtorrent/aux_/time.hpp"
#include "libtorrent/units.hpp"
#include "libtorrent/storage_defs.hpp"
#include "libtorrent/error_code.hpp"
#include "libtorrent/aux_/mmap.hpp"

#include "libtorrent/aux_/disable_warnings_push.hpp"

#define BOOST_BIND_NO_PLACEHOLDERS

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/sequenced_index.hpp>
#include <boost/multi_index/member.hpp>

#include <boost/intrusive/list.hpp>

#include "libtorrent/aux_/disable_warnings_pop.hpp"

namespace libtorrent {

class file_storage;
struct open_file_state;

namespace aux {

	namespace mi = boost::multi_index;

	TORRENT_EXTRA_EXPORT file_open_mode_t to_file_open_mode(open_mode_t, bool const mmapped);

	// this is an internal cache of open file mappings.
	struct TORRENT_EXTRA_EXPORT file_view_pool
	{
		// ``size`` specifies the number of allowed files handles
		// to hold open at any given time.
		explicit file_view_pool(int size = 40);
		~file_view_pool();

		file_view_pool(file_view_pool const&) = delete;
		file_view_pool& operator=(file_view_pool const&) = delete;

		std::tuple<std::int64_t, std::int64_t, std::int64_t, std::int64_t, std::int64_t> stats_counters() const
		{
			std::unique_lock<std::mutex> l(m_mutex);
			return {m_hits, m_misses, m_stalls, m_read_write_race, static_cast<std::int64_t>(m_files.size())};
		}

		// 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).
		std::shared_ptr<file_mapping>
		open_file(storage_index_t st, std::string const& p
			, file_index_t file_index, file_storage const& fs, open_mode_t m
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
			, std::shared_ptr<std::mutex> open_unmap_lock
#endif
			);

		// release all file views 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 release(storage_index_t st);
		void release(storage_index_t st, file_index_t 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 views held
		// by the file_view_pool.
		int size_limit() const { return m_size; }

		std::vector<open_file_state> get_status(storage_index_t st) const;

		void close_oldest();

#if TORRENT_HAVE_MAP_VIEW_OF_FILE
		void flush_next_file();
		void record_file_write(storage_index_t st, file_index_t file_index
			, uint64_t pages);
#endif

	private:

		std::shared_ptr<file_mapping> remove_oldest(std::unique_lock<std::mutex>&);

		int m_size;

		using file_id = std::pair<storage_index_t, file_index_t>;

		struct file_entry
		{
			file_entry(file_id k
				, string_view name
				, open_mode_t const m
				, std::int64_t const size
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
				, std::shared_ptr<std::mutex> open_unmap_lock
#endif
				)
				: key(k)
				, mapping(std::make_shared<file_mapping>(file_handle(name, size, m), m, size
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
					, open_unmap_lock
#endif
					))
				, mode(m)
			{}

			file_id key;
			std::shared_ptr<file_mapping> mapping;
			time_point last_use{aux::time_now()};
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
			std::uint64_t dirty_bytes;
#endif
			open_mode_t mode{};
		};

		using files_container = mi::multi_index_container<
			file_entry,
			mi::indexed_by<
			// look up files by (torrent, file) key
			mi::ordered_unique<mi::member<file_entry, file_id, &file_entry::key>>,
			// look up files by least recently used. New items are added to the
			// back, and old items are removed from the front.
			mi::sequenced<>
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
			// look up files with dirty pages
			, mi::ordered_non_unique<mi::member<file_entry, std::uint64_t, &file_entry::dirty_bytes>>
#endif
			>
		>;

		struct wait_open_entry
		{
			boost::intrusive::list_member_hook<> list_hook;

			std::condition_variable cond;

			// the open file is passed back to the waiting threads, just in case
			// the pool size is so small that it's otherwise evicted between
			// being notified and waking up to look for it.
			std::shared_ptr<file_mapping> mapping;

			// if opening the file fails, waiters are also notified but there
			// won't be a mapping. Then this error code is set.
			lt::storage_error error = {};
		};

		struct opening_file_entry
		{
			boost::intrusive::list_member_hook<> list_hook;

			file_id file_key;

			// the open mode for the file the thread is opening. A thread
			// needing a file opened in read-write mode should not wait for a
			// thread opening the file in read mode
			open_mode_t mode{};

			boost::intrusive::list<wait_open_entry
				, boost::intrusive::member_hook<wait_open_entry
				, boost::intrusive::list_member_hook<>
				, &wait_open_entry::list_hook>
			> waiters;
		};

		void notify_file_open(opening_file_entry& ofe, std::shared_ptr<file_mapping>, lt::storage_error const&);

		file_entry open_file_impl(std::string const& p
			, file_index_t file_index, file_storage const& fs
			, open_mode_t m, file_id file_key
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
			, std::shared_ptr<std::mutex> open_unmap_lock
#endif
			);

		// In order to avoid multiple threads opening the same file in parallel,
		// just to race to add it to the pool. This list, also protected by
		// m_mutex, contains files that one thread is currently opening. If
		// another thread also need this file, it can add itself to the waiters
		// list. The condition variable will then be notified when the file has
		// been opened.
		boost::intrusive::list<opening_file_entry
			, boost::intrusive::member_hook<opening_file_entry
			, boost::intrusive::list_member_hook<>
			, &opening_file_entry::list_hook>
			> m_opening_files;

		// maps storage pointer, file index pairs to the lru entry for the file
		files_container m_files;
		mutable std::mutex m_mutex;
		std::int64_t m_hits = 0;
		std::int64_t m_misses = 0;
		std::int64_t m_stalls = 0;
		std::int64_t m_read_write_race = 0;

		// the boost.multi-index container is not no-throw move constructable. In
		// order to destruct m_files without holding the mutex, we need this
		// separate pre-allocated container to move it into before releasing the
		// mutex and clearing it.
		files_container m_deferred_destruction;
		mutable std::mutex m_destruction_mutex;
	};

}
}

#endif // HAVE_MMAP || HAVE_MAP_VIEW_OF_FILE

#endif
