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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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/stdx/functional.h"
#include "mongo/util/elapsed_tracker.h"
namespace mongo {
class ClockSource;
class PlanYieldPolicy {
public:
virtual ~PlanYieldPolicy() {}
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);
/**
* Periodically returns true to indicate that it is time to check for interrupt (in the case of
* YIELD_AUTO and INTERRUPT_ONLY) or release locks or storage engine state (in the case of
* auto-yielding plans).
*/
virtual bool shouldYieldOrInterrupt();
/**
* Resets the yield timer so that we wait for a while before yielding/interrupting again.
*/
void resetTimer();
/**
* Used to cause a plan executor to check for interrupt (in the case of YIELD_AUTO and
* INTERRUPT_ONLY) or release locks or storage engine state (in the case of auto-yielding
* plans). The PlanExecutor must *not* be in saved state. Handles calls to save/restore state
* internally.
*
* Returns Status::OK() if the executor was restored successfully and is still alive. Returns
* ErrorCodes::QueryPlanKilled if the executor got killed during yield, and
* ErrorCodes::ExceededTimeLimit if the operation has exceeded the time limit.
*
* Calls 'whileYieldingFn' after relinquishing locks and before reacquiring the locks that have
* been relinquished.
*/
virtual Status yieldOrInterrupt(stdx::function<void()> whileYieldingFn = nullptr);
/**
* All calls to shouldYieldOrInterrupt() will return true until the next call to
* yieldOrInterrupt(). This must only be called for auto-yielding plans, to force a yield. It
* cannot be used to force an interrupt for INTERRUPT_ONLY plans.
*/
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 {
switch (_policy) {
case PlanExecutor::YIELD_AUTO:
case PlanExecutor::YIELD_MANUAL:
case PlanExecutor::ALWAYS_TIME_OUT:
case PlanExecutor::ALWAYS_MARK_KILLED: {
return true;
}
case PlanExecutor::NO_YIELD:
case PlanExecutor::WRITE_CONFLICT_RETRY_ONLY:
case PlanExecutor::INTERRUPT_ONLY: {
return false;
}
}
MONGO_UNREACHABLE;
}
/**
* 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 {
switch (_policy) {
case PlanExecutor::YIELD_AUTO:
case PlanExecutor::WRITE_CONFLICT_RETRY_ONLY:
case PlanExecutor::ALWAYS_TIME_OUT:
case PlanExecutor::ALWAYS_MARK_KILLED: {
return true;
}
case PlanExecutor::NO_YIELD:
case PlanExecutor::YIELD_MANUAL:
case PlanExecutor::INTERRUPT_ONLY:
return false;
}
MONGO_UNREACHABLE;
}
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;
// Returns true to indicate it's time to release locks or storage engine state.
bool shouldYield();
// Releases locks or storage engine state.
Status yield(stdx::function<void()> whileYieldingFn);
};
} // namespace mongo
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