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/**
* Copyright (C) 2013 10gen 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/catalog/collection.h"
#include "mongo/db/query/plan_executor.h"
#include "mongo/util/elapsed_tracker.h"
namespace mongo {
class ClockSource;
class RecordFetcher;
class PlanYieldPolicy {
public:
PlanYieldPolicy(PlanExecutor* exec, PlanExecutor::YieldPolicy policy);
/**
* Only used in dbtests since we don't have access to a PlanExecutor. Since we don't have
* access to the PlanExecutor to grab a ClockSource from, we pass in a ClockSource directly
* in the constructor instead.
*/
PlanYieldPolicy(PlanExecutor::YieldPolicy policy, ClockSource* cs);
/**
* Used by YIELD_AUTO plan executors in order to check whether it is time to yield.
* PlanExecutors give up their locks periodically in order to be fair to other
* threads.
*/
bool shouldYield();
/**
* Resets the yield timer so that we wait for a while before yielding again.
*/
void resetTimer();
/**
* Used to cause a plan executor to release locks or storage engine state. The PlanExecutor must
* *not* be in saved state. Handles calls to save/restore state internally.
*
* If 'fetcher' is non-NULL, then we are yielding because the storage engine told us
* that we will page fault on this record. We use 'fetcher' to retrieve the record
* after we give up our locks.
*
* Returns true if the executor was restored successfully and is still alive. Returns false
* if the executor got killed during yield.
*/
bool yield(RecordFetcher* fetcher = NULL);
/**
* All calls to shouldYield() will return true until the next call to yield.
*/
void forceYield() {
dassert(canAutoYield());
_forceYield = true;
}
/**
* Returns true if there is a possibility that a collection lock will be yielded at some point
* during this PlanExecutor's lifetime.
*/
bool canReleaseLocksDuringExecution() const {
return _policy == PlanExecutor::YIELD_AUTO || _policy == PlanExecutor::YIELD_MANUAL;
}
/**
* Returns true if this yield policy performs automatic yielding. Note 'yielding' here refers to
* either releasing storage engine resources via abandonSnapshot() OR yielding LockManager
* locks.
*/
bool canAutoYield() const {
return _policy == PlanExecutor::YIELD_AUTO ||
_policy == PlanExecutor::WRITE_CONFLICT_RETRY_ONLY;
}
PlanExecutor::YieldPolicy getPolicy() const {
return _policy;
}
private:
const PlanExecutor::YieldPolicy _policy;
bool _forceYield;
ElapsedTracker _elapsedTracker;
// The plan executor which this yield policy is responsible for yielding. Must
// not outlive the plan executor.
PlanExecutor* const _planYielding;
};
} // namespace mongo
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