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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 <boost/optional.hpp>
#include <functional>
#include "mongo/platform/mutex.h"
#include "mongo/util/assert_util.h"
namespace mongo {
namespace repl {
/**
* RAII type that stores the result of callbacks written using the executor::TaskExecutor framework.
* Only the first result passed to setResultAndCancelRemainingWork_inlock() is saved.
* Calls '_onCompletion' on destruction with result.
* We use an invariant to ensure that a result has been provided by the caller at destruction.
*/
template <typename Result>
class CallbackCompletionGuard {
public:
/**
* Function to cancel remaining work in caller after setting '_result'.
* This function must be called while holding a lock on the caller's mutex.
*/
using CancelRemainingWorkInLockFn = std::function<void()>;
/**
* Callback function to pass result to caller at destruction.
*/
typedef std::function<void(const Result& result)> OnCompletionFn;
/**
* Constructor for this completion guard.
* 'cancelRemainingWorkInLock' is called after setting the result to cancel any outstanding
* work in the caller. 'cancelRemainingWorkInLock' must be called while holding a lock on the
* caller's mutex.
* 'onCompletion' is called with the result at destruction.
*/
CallbackCompletionGuard(const CancelRemainingWorkInLockFn& cancelRemainingWorkInLock,
const OnCompletionFn& onCompletion);
/**
* Invokes '_onCompletion' with the result.
* Aborts if:
* result is not set; or
* '_onCompletion' throws an exception.
*/
~CallbackCompletionGuard();
/**
* Sets result if called for the first time.
* Cancels remaining work in caller.
* Requires either a unique_lock or lock_guard to be passed in to ensure that we call
* _cancelRemainingWork_inlock()) while we have a lock on the callers's mutex.
*/
void setResultAndCancelRemainingWork_inlock(const stdx::lock_guard<Latch>& lock,
const Result& result);
void setResultAndCancelRemainingWork_inlock(const stdx::unique_lock<Latch>& lock,
const Result& result);
private:
/**
* Once we verified that we have the caller's lock, this function is called by both
* versions of setResultAndCancelRemainingWork_inlock() to set the result and cancel any
* remaining work in the caller.
*/
void _setResultAndCancelRemainingWork_inlock(const Result& result);
// Called at most once after setting '_result'.
const CancelRemainingWorkInLockFn _cancelRemainingWorkInLock;
// Called at destruction with '_result'.
const OnCompletionFn _onCompletion;
// _result is guarded by the mutex of the caller instance that owns this guard object.
boost::optional<Result> _result;
};
template <typename Result>
CallbackCompletionGuard<Result>::CallbackCompletionGuard(
const CancelRemainingWorkInLockFn& cancelRemainingWorkInLock,
const OnCompletionFn& onCompletion)
: _cancelRemainingWorkInLock(cancelRemainingWorkInLock), _onCompletion(onCompletion) {}
template <typename Result>
CallbackCompletionGuard<Result>::~CallbackCompletionGuard() {
invariant(_result);
// _onCompletion() must be called outside the caller's lock to avoid a deadlock.
// If '_onCompletion' throws an exception, the exception will be logged (by the terminate hook)
// and the program will abort.
_onCompletion(*_result);
}
template <typename Result>
void CallbackCompletionGuard<Result>::setResultAndCancelRemainingWork_inlock(
const stdx::lock_guard<Latch>& lock, const Result& result) {
_setResultAndCancelRemainingWork_inlock(result);
}
template <typename Result>
void CallbackCompletionGuard<Result>::setResultAndCancelRemainingWork_inlock(
const stdx::unique_lock<Latch>& lock, const Result& result) {
invariant(lock.owns_lock());
_setResultAndCancelRemainingWork_inlock(result);
}
template <typename Result>
void CallbackCompletionGuard<Result>::_setResultAndCancelRemainingWork_inlock(
const Result& result) {
if (_result) {
return;
}
_result = result;
// This is called at most once.
_cancelRemainingWorkInLock();
}
} // namespace repl
} // namespace mongo
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