159 lines
4.3 KiB
C++
159 lines
4.3 KiB
C++
/*
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* Copyright 2012 Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* 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, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef FOLLY_SCOPEGUARD_H_
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#define FOLLY_SCOPEGUARD_H_
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#include <cstddef>
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#include <iostream>
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#include <functional>
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#include <new>
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//#include <glog/logging.h>
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#include "folly/Preprocessor.h"
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namespace folly {
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/**
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* ScopeGuard is a general implementation of the "Initilization is
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* Resource Acquisition" idiom. Basically, it guarantees that a function
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* is executed upon leaving the currrent scope unless otherwise told.
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*
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* The makeGuard() function is used to create a new ScopeGuard object.
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* It can be instantiated with a lambda function, a std::function<void()>,
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* a functor, or a void(*)() function pointer.
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*
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*
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* Usage example: Add a friend to memory iff it is also added to the db.
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*
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* void User::addFriend(User& newFriend) {
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* // add the friend to memory
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* friends_.push_back(&newFriend);
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*
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* // If the db insertion that follows fails, we should
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* // remove it from memory.
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* // (You could also declare this as "auto guard = makeGuard(...)")
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* ScopeGuard guard = makeGuard([&] { friends_.pop_back(); });
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*
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* // this will throw an exception upon error, which
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* // makes the ScopeGuard execute UserCont::pop_back()
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* // once the Guard's destructor is called.
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* db_->addFriend(GetName(), newFriend.GetName());
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*
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* // an exception was not thrown, so don't execute
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* // the Guard.
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* guard.dismiss();
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* }
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*
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* Examine ScopeGuardTest.cpp for some more sample usage.
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*
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* Stolen from:
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* Andrei's and Petru Marginean's CUJ article:
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* http://drdobbs.com/184403758
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* and the loki library:
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* http://loki-lib.sourceforge.net/index.php?n=Idioms.ScopeGuardPointer
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* and triendl.kj article:
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* http://www.codeproject.com/KB/cpp/scope_guard.aspx
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*/
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class ScopeGuardImplBase {
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public:
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void dismiss() noexcept {
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dismissed_ = true;
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}
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protected:
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ScopeGuardImplBase()
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: dismissed_(false) {}
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ScopeGuardImplBase(ScopeGuardImplBase&& other)
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: dismissed_(other.dismissed_) {
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other.dismissed_ = true;
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}
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bool dismissed_;
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};
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template<typename FunctionType>
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class ScopeGuardImpl : public ScopeGuardImplBase {
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public:
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explicit ScopeGuardImpl(const FunctionType& fn)
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: function_(fn) {}
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explicit ScopeGuardImpl(FunctionType&& fn)
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: function_(std::move(fn)) {}
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ScopeGuardImpl(ScopeGuardImpl&& other)
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: ScopeGuardImplBase(std::move(other)),
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function_(std::move(other.function_)) {
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}
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~ScopeGuardImpl() noexcept {
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if (!dismissed_) {
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execute();
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}
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}
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private:
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void* operator new(size_t) = delete;
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void execute() noexcept {
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try {
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function_();
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} catch (const std::exception& ex) {
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std::cout << "ScopeGuard cleanup function threw a " <<
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typeid(ex).name() << "exception: " << ex.what();
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} catch (...) {
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std::cout << "ScopeGuard cleanup function threw a non-exception object";
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}
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}
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FunctionType function_;
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};
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template<typename FunctionType>
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ScopeGuardImpl<typename std::decay<FunctionType>::type>
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makeGuard(FunctionType&& fn) {
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return ScopeGuardImpl<typename std::decay<FunctionType>::type>(
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std::forward<FunctionType>(fn));
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}
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/**
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* This is largely unneeded if you just use auto for your guards.
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*/
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typedef ScopeGuardImplBase&& ScopeGuard;
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namespace detail {
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/**
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* Internal use for the macro SCOPE_EXIT below
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*/
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enum class ScopeGuardOnExit {};
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template <typename FunctionType>
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ScopeGuardImpl<typename std::decay<FunctionType>::type>
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operator+(detail::ScopeGuardOnExit, FunctionType&& fn) {
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return ScopeGuardImpl<typename std::decay<FunctionType>::type>(
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std::forward<FunctionType>(fn));
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}
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} // namespace detail
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} // folly
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#define SCOPE_EXIT \
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auto FB_ANONYMOUS_VARIABLE(SCOPE_EXIT_STATE) \
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= ::folly::detail::ScopeGuardOnExit() + [&]
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#endif // FOLLY_SCOPEGUARD_H_
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