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/**
* Copyright (C) 2019-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 <memory>
#include "mongo/util/functional.h"
#include "mongo/util/future.h"
#include "mongo/util/out_of_line_executor.h"
#include "mongo/util/time_support.h"
#include "mongo/util/waitable.h"
namespace mongo {
class OperationContext;
namespace transport {
class NetworkingBaton;
} // namespace transport
class Baton;
using BatonHandle = std::shared_ptr<Baton>;
/**
* A Baton is lightweight executor, with parallel forward progress guarantees. Rather than
* asynchronously running tasks through one, the baton records the intent of those tasks and defers
* waiting and execution to a later call to run().
*
* Note: This occurs automatically when opCtx waiting on a condition variable.
*/
class Baton : public Waitable,
public OutOfLineExecutor,
public std::enable_shared_from_this<Baton> {
public:
virtual ~Baton() = default;
/**
* Detaches a baton from an associated opCtx.
*
* This invokes all callbacks currently inside the baton (from the detaching thread) with a void
* opCtx. Also, any calls to schedule after this point will immediately invoke their callback
* with a null opCtx.
*/
void detach() noexcept {
// We make this anchor so that deleting the shared_ptr inside opCtx doesn't remove the last
// reference to this type until we return from detach.
const auto anchor = shared_from_this();
detachImpl();
}
/**
* Schedules a callback to run on the baton.
*
* The function will be invoked in one of 3 ways:
* 1. With an opCtx inside run() (I.e. opCtx->waitForConditionOrInterrupt)
* 2. Without an opCtx inside detach()
* 3. Without an opCtx inside schedule() after detach()
*
* Note that the latter two cases are indistinguishable, so the callback should be safe to run
* inline if passed a nullptr. Examples of such work are logging, simple cleanup and
* rescheduling the task on another executor.
*/
void schedule(Task func) noexcept override = 0;
/**
* Returns a networking view of the baton, if this baton supports networking functionality
*/
virtual transport::NetworkingBaton* networking() noexcept {
return nullptr;
}
/**
* Marks the baton to wake up on client socket disconnect
*/
virtual void markKillOnClientDisconnect() noexcept = 0;
/**
* Holder for a SubBaton, detaches on destruction
*/
class SubBatonHolder {
friend Baton;
public:
SubBatonHolder(const SubBatonHolder&) = delete;
SubBatonHolder& operator=(const SubBatonHolder&) = delete;
SubBatonHolder(SubBatonHolder&& other)
: _mustDetach(other._mustDetach), _baton(std::move(other._baton)) {
other._mustDetach = false;
}
SubBatonHolder& operator=(SubBatonHolder&& other) {
if (_mustDetach) {
_baton->detach();
}
_mustDetach = other._mustDetach;
_baton = std::move(other._baton);
other._mustDetach = false;
return *this;
}
~SubBatonHolder() {
if (_mustDetach) {
_baton->detach();
}
}
const BatonHandle& operator*() const {
return _baton;
}
const BatonHandle& operator->() const {
return _baton;
}
void shutdown() {
if (!std::exchange(_mustDetach, false)) {
return;
}
_baton->detach();
}
private:
explicit SubBatonHolder(const BatonHandle& baton) : _baton(baton) {}
bool _mustDetach = true;
BatonHandle _baton;
};
/**
* Makes a sub baton for this baton. A valid sub baton should proxy requests to the underlying
* baton until it is detached. After that point, all jobs within the sub baton should be failed
* with a ShutdownInProgress status and all further work should be refused.
*
* NOTE: The held baton will not intercept networking() related calls. If you intend to use the
* baton in that mode, you should use this type with the ScopedTaskExecutor to handle
* cancellation of async networking operations.
*/
SubBatonHolder makeSubBaton();
private:
virtual void detachImpl() noexcept = 0;
};
} // namespace mongo
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