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