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/*
* Copyright 2003-2021 The Music Player Daemon Project
* http://www.musicpd.org
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* 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 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 Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifndef MPD_REMOTE_TAG_CACHE_HXX
#define MPD_REMOTE_TAG_CACHE_HXX
#include "input/RemoteTagScanner.hxx"
#include "tag/Tag.hxx"
#include "event/DeferEvent.hxx"
#include "thread/Mutex.hxx"
#include <boost/intrusive/list.hpp>
#include <boost/intrusive/unordered_set.hpp>
#include <string>
class RemoteTagCacheHandler;
/**
* A cache for tags received via #RemoteTagScanner.
*/
class RemoteTagCache final {
static constexpr size_t MAX_SIZE = 4096;
RemoteTagCacheHandler &handler;
DeferEvent defer_invoke_handler;
Mutex mutex;
struct Item final
: public boost::intrusive::unordered_set_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>>,
public boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>>,
RemoteTagHandler
{
RemoteTagCache &parent;
const std::string uri;
std::unique_ptr<RemoteTagScanner> scanner;
Tag tag;
template<typename U>
Item(RemoteTagCache &_parent, U &&_uri) noexcept
:parent(_parent), uri(std::forward<U>(_uri)) {}
/* virtual methods from RemoteTagHandler */
void OnRemoteTag(Tag &&tag) noexcept override;
void OnRemoteTagError(std::exception_ptr e) noexcept override;
struct Hash : std::hash<std::string> {
using std::hash<std::string>::operator();
gcc_pure
std::size_t operator()(const Item &item) const noexcept {
return std::hash<std::string>::operator()(item.uri);
}
};
struct Equal {
gcc_pure
bool operator()(const Item &a,
const Item &b) const noexcept {
return a.uri == b.uri;
}
gcc_pure
bool operator()(const std::string &a,
const Item &b) const noexcept {
return a == b.uri;
}
};
};
typedef boost::intrusive::list<Item,
boost::intrusive::constant_time_size<false>> ItemList;
/**
* These items have been resolved completely (successful or
* failed). All callbacks have been invoked. The oldest
* comes first in the list, and is the first one to be evicted
* if the cache is full.
*/
ItemList idle_list;
/**
* A #RemoteTagScanner instances is currently busy on fetching
* information, and we're waiting for our #RemoteTagHandler
* methods to be invoked.
*/
ItemList waiting_list;
/**
* These items have just been resolved, and the
* #RemoteTagCacheHandler is about to be invoked. After that,
* they will be moved to the #idle_list.
*/
ItemList invoke_list;
typedef boost::intrusive::unordered_set<Item,
boost::intrusive::hash<Item::Hash>,
boost::intrusive::equal<Item::Equal>,
boost::intrusive::constant_time_size<true>> KeyMap;
std::array<typename KeyMap::bucket_type, 127> buckets;
KeyMap map;
public:
RemoteTagCache(EventLoop &event_loop,
RemoteTagCacheHandler &_handler) noexcept;
~RemoteTagCache() noexcept;
void Lookup(const std::string &uri) noexcept;
private:
void InvokeHandlers() noexcept;
void ScheduleInvokeHandlers() noexcept {
defer_invoke_handler.Schedule();
}
void ItemResolved(Item &item) noexcept;
};
#endif
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