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// cursor_manager.h
/**
* Copyright (C) 2013 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/db/clientcursor.h"
#include "mongo/db/invalidation_type.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/record_id.h"
#include "mongo/platform/unordered_set.h"
#include "mongo/util/concurrency/mutex.h"
namespace mongo {
class OperationContext;
class PseudoRandom;
class PlanExecutor;
/**
* A container which owns ClientCursor objects. This class is used to create, access, and delete
* ClientCursors. It is also responsible for allocating the cursor ids that are passed back to
* clients.
*
* In addition to managing the lifetime of ClientCursors, the CursorManager is responsible for
* notifying yielded queries of write operations and collection drops. For this reason, query
* PlanExecutor objects which are not contained within a ClientCursor are also registered with the
* CursorManager. Query executors must be registered with the CursorManager, either as a bare
* PlanExecutor or inside a ClientCursor (but cannot be registered in both ways).
*
* There is a CursorManager per-collection and a global CursorManager. The global CursorManager owns
* cursors whose lifetime is not tied to that of the collection and which do not need to receive
* notifications about writes for a particular collection. In contrast, cursors owned by a
* collection's CursorManager, unless pinned, are destroyed when the collection is destroyed. Such
* cursors receive notifications about writes to the collection.
*
* Callers must hold the collection lock in at least MODE_IS in order to access a collection's
* CursorManager, which guards against the CursorManager being concurrently deleted due to a
* catalog-level operation such as a collection drop. No locks are required to access the global
* cursor manager.
*
* The CursorManager is internally synchronized; operations on a given collection may call methods
* concurrently on that collection's CursorManager.
*
* See clientcursor.h for more information.
*/
class CursorManager {
public:
CursorManager(StringData ns);
/**
* Destroys the CursorManager. Managed cursors which are not pinned are destroyed. Ownership of
* pinned cursors is transferred to the corresponding ClientCursorPin.
*/
~CursorManager();
/**
* Kills all managed query executors and ClientCursors.
*
* 'collectionGoingAway' indicates whether the Collection instance is being deleted. This could
* be because the db is being closed, or the collection/db is being dropped. When passing
* a 'collectionGoingAway' value of true, callers must have exclusive access to the collection
* (i.e. must have the collection, database, or global resource locked in MODE_X).
*
* The 'reason' is the motivation for invalidating all cursors. This will be used for error
* reporting and logging when an operation finds that the cursor it was operating on has been
* killed.
*/
void invalidateAll(bool collectionGoingAway, const std::string& reason);
/**
* Broadcast a document invalidation to all relevant PlanExecutor(s). invalidateDocument
* must called *before* the provided RecordId is about to be deleted or mutated.
*/
void invalidateDocument(OperationContext* txn, const RecordId& dl, InvalidationType type);
/**
* Destroys cursors that have been inactive for too long.
*
* Returns the number of cursors that were timed out.
*/
std::size_t timeoutCursors(int millisSinceLastCall);
/**
* Register an executor so that it can be notified of deletion/invalidation during yields.
* Must be called before an executor yields. If an executor is registered inside a
* ClientCursor it must not be itself registered; the two are mutually exclusive.
*/
void registerExecutor(PlanExecutor* exec);
/**
* Remove an executor from the registry.
*/
void deregisterExecutor(PlanExecutor* exec);
/**
* Constructs a new ClientCursor according to the given 'cursorParams'. The cursor is atomically
* registered with the manager and returned in pinned state.
*/
ClientCursorPin registerCursor(const ClientCursorParams& cursorParams);
/**
* Constructs and pins a special ClientCursor used to track sharding state for the given
* collection. See range_preserver.h for more details.
*/
ClientCursorPin registerRangePreserverCursor(const Collection* collection);
/**
* Pins and returns the cursor with the given id.
*
* Returns ErrorCodes::CursorNotFound if the cursor does not exist.
*
* Throws a UserException if the cursor is already pinned. Callers need not specially handle
* this error, as it should only happen if a misbehaving client attempts to simultaneously issue
* two operations against the same cursor id.
*/
StatusWith<ClientCursorPin> pinCursor(CursorId id);
/**
* Returns an OK status if the cursor was successfully erased.
*
* Returns error code CursorNotFound if the cursor id is not owned by this manager. Returns
* error code OperationFailed if attempting to erase a pinned cursor.
*
* If 'shouldAudit' is true, will perform audit logging.
*/
Status eraseCursor(OperationContext* txn, CursorId id, bool shouldAudit);
/**
* Returns true if the space of cursor ids that cursor manager is responsible for includes
* the given cursor id. Otherwise, returns false.
*
* The return value of this method does not indicate any information about whether or not a
* cursor actually exists with the given cursor id.
*/
bool ownsCursorId(CursorId cursorId) const;
void getCursorIds(std::set<CursorId>* openCursors) const;
/**
* Returns the number of ClientCursors currently registered. Excludes any registered bare
* PlanExecutors.
*/
std::size_t numCursors() const;
static CursorManager* getGlobalCursorManager();
static int eraseCursorGlobalIfAuthorized(OperationContext* txn, int n, const char* ids);
static bool eraseCursorGlobalIfAuthorized(OperationContext* txn, CursorId id);
static bool eraseCursorGlobal(OperationContext* txn, CursorId id);
/**
* Deletes inactive cursors from the global cursor manager and from all per-collection cursor
* managers. Returns the number of cursors that were timed out.
*/
static std::size_t timeoutCursorsGlobal(OperationContext* txn, int millisSinceLastCall);
private:
friend class ClientCursorPin;
CursorId _allocateCursorId_inlock();
void _deregisterCursor_inlock(ClientCursor* cc);
ClientCursorPin _registerCursor_inlock(
std::unique_ptr<ClientCursor, ClientCursor::Deleter> clientCursor);
void deregisterCursor(ClientCursor* cc);
void unpin(ClientCursor* cursor);
NamespaceString _nss;
unsigned _collectionCacheRuntimeId;
std::unique_ptr<PseudoRandom> _random;
mutable SimpleMutex _mutex;
typedef unordered_set<PlanExecutor*> ExecSet;
ExecSet _nonCachedExecutors;
typedef std::map<CursorId, ClientCursor*> CursorMap;
CursorMap _cursors;
};
} // namespace mongo
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