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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 <memory>
#include "mongo/transport/transport_layer.h"
#include "mongo/util/functional.h"
#include "mongo/util/future.h"
#include "mongo/util/time_support.h"
#include "mongo/util/waitable.h"
namespace mongo {
class OperationContext;
namespace transport {
class TransportLayer;
class Session;
class ReactorTimer;
/**
* A Baton is basically a networking reactor, with limited functionality and no 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();
*
* Baton's provide a mechanism to allow consumers of a transport layer to execute IO themselves,
* rather than having this occur on another thread. This can improve performance by minimizing
* context switches, as well as improving the readability of stack traces by grounding async
* execution on top of a regular client call stack.
*/
class Baton : public Waitable {
public:
virtual ~Baton() = default;
/**
* Detaches a baton from an associated opCtx.
*/
virtual void detach() = 0;
/**
* Executes a callback on the baton via schedule. Returns a future which will execute on the
* baton runner.
*/
template <typename Callback>
Future<FutureContinuationResult<Callback>> execute(Callback&& cb) {
auto pf = makePromiseFuture<FutureContinuationResult<Callback>>();
schedule([ cb = std::forward<Callback>(cb), sp = pf.promise.share() ]() mutable {
sp.setWith(std::move(cb));
});
return std::move(pf.future);
}
/**
* Executes a callback on the baton.
*/
virtual void schedule(unique_function<void()> func) = 0;
/**
* Adds a session, returning a future which activates on read/write-ability of the session.
*/
enum class Type {
In,
Out,
};
virtual Future<void> addSession(Session& session, Type type) = 0;
/**
* Adds a timer, returning a future which activates after a deadline.
*/
virtual Future<void> waitUntil(const ReactorTimer& timer, Date_t expiration) = 0;
/**
* Cancels waiting on a session.
*
* Returns true if the session was in the baton to be cancelled.
*/
virtual bool cancelSession(Session& session) = 0;
/**
* Cancels waiting on a timer
*
* Returns true if the timer was in the baton to be cancelled.
*/
virtual bool cancelTimer(const ReactorTimer& timer) = 0;
};
using BatonHandle = std::shared_ptr<Baton>;
} // namespace transport
} // namespace mongo
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