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// wiredtiger_session_cache.h
/**
* Copyright (C) 2014 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 <map>
#include <string>
#include <vector>
#include <boost/thread/shared_mutex.hpp>
#include <wiredtiger.h>
#include "mongo/stdx/mutex.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/util/concurrency/spin_lock.h"
namespace mongo {
class WiredTigerKVEngine;
/**
* This is a structure that caches 1 cursor for each uri.
* The idea is that there is a pool of these somewhere.
* NOT THREADSAFE
*/
class WiredTigerSession {
public:
/**
* Creates a new WT session on the specified connection.
*
* @param conn WT connection
* @param cachePartition If the session comes from the session cache, this indicates to
* which partition it should be returned. Value of -1 means it doesn't come from
* cache and that it should not be cached, but closed directly.
* @param epoch In which session cache cleanup epoch was this session instantiated. Value
* of -1 means that this value is not necessary since the session will not be
* cached.
*/
WiredTigerSession(WT_CONNECTION* conn, int cachePartition = -1, int epoch = -1);
~WiredTigerSession();
WT_SESSION* getSession() const { return _session; }
WT_CURSOR* getCursor(const std::string& uri,
uint64_t id,
bool forRecordStore);
void releaseCursor(uint64_t id, WT_CURSOR *cursor);
void closeAllCursors();
int cursorsOut() const { return _cursorsOut; }
static uint64_t genCursorId();
/**
* For "metadata:" cursors. Guaranteed never to collide with genCursorId() ids.
*/
static const uint64_t kMetadataCursorId = 0;
private:
friend class WiredTigerSessionCache;
typedef std::vector<WT_CURSOR*> Cursors;
typedef std::map<uint64_t, Cursors> CursorMap;
// Used internally by WiredTigerSessionCache
int _getEpoch() const { return _epoch; }
int _getCachePartition() const { return _cachePartition; }
const int _cachePartition;
const int _epoch;
WT_SESSION* _session; // owned
CursorMap _curmap; // owned
int _cursorsOut;
};
class WiredTigerSessionCache {
public:
WiredTigerSessionCache( WiredTigerKVEngine* engine );
WiredTigerSessionCache( WT_CONNECTION* conn );
~WiredTigerSessionCache();
WiredTigerSession* getSession();
void releaseSession( WiredTigerSession* session );
void closeAll();
void shuttingDown();
WT_CONNECTION* conn() const { return _conn; }
private:
typedef std::vector<WiredTigerSession*> SessionPool;
enum { NumSessionCachePartitions = 64 };
struct SessionCachePartition {
SessionCachePartition() : epoch(0) { }
~SessionCachePartition() {
invariant(pool.empty());
}
SpinLock lock;
int epoch;
SessionPool pool;
};
WiredTigerKVEngine* _engine; // not owned, might be NULL
WT_CONNECTION* _conn; // not owned
// Partitioned cache of WT sessions. The partition key is not important, but it is
// important that sessions be returned to the same partition they were taken from in order
// to have some form of balance between the partitions.
SessionCachePartition _cache[NumSessionCachePartitions];
// Regular operations take it in shared mode. Shutdown sets the _shuttingDown flag and
// then takes it in exclusive mode. This ensures that all threads, which would return
// sessions to the cache would leak them.
boost::shared_mutex _shutdownLock;
AtomicUInt32 _shuttingDown; // Used as boolean - 0 = false, 1 = true
};
}
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