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rocksdb/thrift/lib/cpp/async/TUndelayedDestruction.h

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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
#ifndef THRIFT_ASYNC_TUNDELAYEDDESTRUCTION_H_
#define THRIFT_ASYNC_TUNDELAYEDDESTRUCTION_H_ 1
#include <cstdlib>
#include <type_traits>
#include <utility>
#include <cassert>
namespace apache { namespace thrift { namespace async {
/**
* A helper class to allow a TDelayedDestruction object to be instantiated on
* the stack.
*
* This class derives from an existing TDelayedDestruction type and makes the
* destructor public again. This allows objects of this type to be declared on
* the stack or directly inside another class. Normally TDelayedDestruction
* objects must be dynamically allocated on the heap.
*
* However, the trade-off is that you lose some of the protections provided by
* TDelayedDestruction::destroy(). TDelayedDestruction::destroy() will
* automatically delay destruction of the object until it is safe to do so.
* If you use TUndelayedDestruction, you become responsible for ensuring that
* you only destroy the object where it is safe to do so. Attempting to
* destroy a TUndelayedDestruction object while it has a non-zero destructor
* guard count will abort the program.
*/
template<typename TDD>
class TUndelayedDestruction : public TDD {
public:
// We want to expose all constructors provided by the parent class.
// C++11 adds constructor inheritance to support this. Unfortunately gcc
// does not implement constructor inheritance yet, so we have to fake it with
// variadic templates.
#if THRIFT_HAVE_CONSTRUCTOR_INHERITANCE
using TDD::TDD;
#else
// We unfortunately can't simulate constructor inheritance as well as I'd
// like.
//
// Ideally we would use std::enable_if<> and std::is_constructible<> to
// provide only constructor methods that are valid for our parent class.
// Unfortunately std::is_constructible<> doesn't work for types that aren't
// destructible. In gcc-4.6 it results in a compiler error. In the latest
// gcc code it looks like it has been fixed to return false. (The language
// in the standard seems to indicate that returning false is the correct
// behavior for non-destructible types, which is unfortunate.)
template<typename ...Args>
explicit TUndelayedDestruction(Args&& ...args)
: TDD(std::forward<Args>(args)...) {}
#endif
/**
* Public destructor.
*
* The caller is responsible for ensuring that the object is only destroyed
* where it is safe to do so. (i.e., when the destructor guard count is 0).
*
* The exact conditions for meeting this may be dependant upon your class
* semantics. Typically you are only guaranteed that it is safe to destroy
* the object directly from the event loop (e.g., directly from a
* TEventBase::LoopCallback), or when the event loop is stopped.
*/
virtual ~TUndelayedDestruction() {
// Crash if the caller is destroying us with outstanding destructor guards.
if (this->getDestructorGuardCount() != 0) {
abort();
}
// Invoke destroy. This is necessary since our base class may have
// implemented custom behavior in destroy().
this->destroy();
}
protected:
/**
* Override our parent's destroy() method to make it protected.
* Callers should use the normal destructor instead of destroy
*/
virtual void destroy() {
this->TDD::destroy();
}
virtual void destroyNow(bool delayed) {
// Do nothing. This will always be invoked from the call to destroy inside
// our destructor.
assert(!delayed);
// prevent unused variable warnings when asserts are compiled out.
(void)delayed;
}
private:
// Forbidden copy constructor and assignment operator
TUndelayedDestruction(TUndelayedDestruction const &) = delete;
TUndelayedDestruction& operator=(TUndelayedDestruction const &) = delete;
};
}}} // apache::thrift::async
#endif // THRIFT_ASYNC_TUNDELAYEDDESTRUCTION_H_