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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 "mongo/db/operation_context.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/duration.h"
#include "mongo/util/hierarchical_acquisition.h"
#include "mongo/util/time_support.h"
namespace mongo {
/**
* Allows waiting for a result returned from an asynchronous operation.
*/
template <class T>
class Notification {
public:
Notification() = default;
/**
* Creates a notification object, which has already been set. Calls to any of the getters will
* return immediately.
*/
explicit Notification(T value) : _value(value) {}
/**
* Returns true if the notification has been set (i.e., the call to get/waitFor would not
* block).
*/
explicit operator bool() const {
stdx::unique_lock<Latch> lock(_mutex);
return !!_value;
}
/**
* If the notification has been set, returns immediately. Otherwise blocks until it becomes set.
* If the wait is interrupted, throws an exception.
*/
T& get(OperationContext* opCtx) {
stdx::unique_lock<Latch> lock(_mutex);
opCtx->waitForConditionOrInterrupt(_condVar, lock, [this]() -> bool { return !!_value; });
return _value.get();
}
/**
* If the notification has been set, returns immediately. Otherwise blocks until it becomes set.
* This variant of get cannot be interrupted.
*/
T& get() {
stdx::unique_lock<Latch> lock(_mutex);
while (!_value) {
_condVar.wait(lock);
}
return _value.get();
}
/**
* Sets the notification result and wakes up any threads, which might be blocked in the wait
* call. Must only be called once for the lifetime of the notification.
*/
void set(T value) {
stdx::lock_guard<Latch> lock(_mutex);
invariant(!_value);
_value = std::move(value);
_condVar.notify_all();
}
/**
* If the notification is set, returns immediately. Otherwise, blocks until it either becomes
* set or the waitTimeout expires, whichever comes first. Returns true if the notification is
* set (in which case a subsequent call to get is guaranteed to not block) or false otherwise.
* If the wait is interrupted, throws an exception.
*/
bool waitFor(OperationContext* opCtx, Milliseconds waitTimeout) {
stdx::unique_lock<Latch> lock(_mutex);
return opCtx->waitForConditionOrInterruptFor(
_condVar, lock, waitTimeout, [&]() { return !!_value; });
}
private:
mutable Mutex _mutex =
MONGO_MAKE_LATCH(HierarchicalAcquisitionLevel(0), "Notification::_mutex");
stdx::condition_variable _condVar;
// Protected by mutex and only moves from not-set to set once
boost::optional<T> _value{boost::none};
};
template <>
class Notification<void> {
public:
explicit operator bool() const {
return _notification.operator bool();
}
void get(OperationContext* opCtx) {
_notification.get(opCtx);
}
void get() {
_notification.get();
}
void set() {
_notification.set(true);
}
bool waitFor(OperationContext* opCtx, Milliseconds waitTimeout) {
return _notification.waitFor(opCtx, waitTimeout);
}
private:
Notification<bool> _notification;
};
} // namespace mongo
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