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/**
* Copyright (C) 2017 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/base/status_with.h"
#include "mongo/db/logical_session_id.h"
#include "mongo/db/logical_session_record.h"
#include "mongo/db/service_liason.h"
#include "mongo/db/sessions_collection.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/lru_cache.h"
namespace mongo {
/**
* A thread-safe cache structure for logical session records.
*
* The cache takes ownership of the passed-in ServiceLiason and
* SessionsCollection helper types.
*/
class LogicalSessionCache {
public:
using SessionList = std::list<LogicalSessionId>;
static constexpr int kLogicalSessionCacheDefaultCapacity = 10000;
static constexpr Minutes kLogicalSessionDefaultTimeout = Minutes(30);
static constexpr Minutes kLogicalSessionDefaultRefresh = Minutes(5);
/**
* An Options type to support the LogicalSessionCache.
*/
struct Options {
Options(){};
/**
* The number of session records to keep in the cache.
*/
int capacity = kLogicalSessionCacheDefaultCapacity;
/**
* A timeout value to use for sessions in the cache, in minutes.
*
* By default, this is set to 30 minutes.
*/
Minutes sessionTimeout = kLogicalSessionDefaultTimeout;
/**
* The interval over which the cache will refresh session records.
*
* By default, this is set to every 5 minutes. If the caller is
* setting the sessionTimeout by hand, it is suggested that they
* consider also setting the refresh interval accordingly.
*/
Minutes refreshInterval = kLogicalSessionDefaultRefresh;
};
/**
* Construct a new session cache.
*/
explicit LogicalSessionCache(std::unique_ptr<ServiceLiason> service,
std::unique_ptr<SessionsCollection> collection,
Options options = Options{});
LogicalSessionCache(const LogicalSessionCache&) = delete;
LogicalSessionCache operator=(const LogicalSessionCache&) = delete;
~LogicalSessionCache();
/**
* Returns the owner for the given session, or return an error if there
* is no authoritative record for this session.
*
* If the cache does not already contain a record for this session, this
* method may issue networking operations to obtain the record. Afterwards,
* the cache will keep the record for future use.
*
* This call will promote any record it touches to be the most-recently-used
* record in the cache.
*/
StatusWith<LogicalSessionRecord::Owner> getOwner(LogicalSessionId lsid);
/**
* Returns the owner for the given session if we already have its record in the
* cache. Do not fetch the record from the network if we do not already have it.
*
* This call will promote any record it touches to be the most-recently-used
* record in the cache.
*/
StatusWith<LogicalSessionRecord::Owner> getOwnerFromCache(LogicalSessionId lsid);
/**
* Inserts a new authoritative session record into the cache. This method will
* insert the authoritative record into the sessions collection. This method
* should only be used when starting new sessions and should not be used to
* insert records for existing sessions.
*/
Status startSession(LogicalSessionRecord authoritativeRecord);
/**
* Removes all local records in this cache. Does not remove the corresponding
* authoritative session records from the sessions collection.
*/
void clear();
private:
/**
* Internal methods to handle scheduling and perform refreshes for active
* session records contained within the cache.
*/
void _refresh();
/**
* Returns true if a record has passed its given expiration.
*/
bool _isDead(const LogicalSessionRecord& record, Date_t now) const;
/**
* Takes the lock and inserts the given record into the cache.
*/
boost::optional<LogicalSessionRecord> _addToCache(LogicalSessionRecord record);
const Minutes _refreshInterval;
const Minutes _sessionTimeout;
std::unique_ptr<ServiceLiason> _service;
std::unique_ptr<SessionsCollection> _sessionsColl;
stdx::mutex _cacheMutex;
LRUCache<LogicalSessionId, LogicalSessionRecord, LogicalSessionId::Hash> _cache;
};
} // namespace mongo
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