rocksdb/thrift/folly/ScopeGuard.h
Dhruba Borthakur b40ad060e0 Implement the FB-Assoc API via thrift.
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2012-08-01 16:18:24 -07:00

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/*
* Copyright 2012 Facebook, Inc.
*
* Licensed 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 FOLLY_SCOPEGUARD_H_
#define FOLLY_SCOPEGUARD_H_
#include <cstddef>
#include <iostream>
#include <functional>
#include <new>
//#include <glog/logging.h>
#include "folly/Preprocessor.h"
namespace folly {
/**
* ScopeGuard is a general implementation of the "Initilization is
* Resource Acquisition" idiom. Basically, it guarantees that a function
* is executed upon leaving the currrent scope unless otherwise told.
*
* The makeGuard() function is used to create a new ScopeGuard object.
* It can be instantiated with a lambda function, a std::function<void()>,
* a functor, or a void(*)() function pointer.
*
*
* Usage example: Add a friend to memory iff it is also added to the db.
*
* void User::addFriend(User& newFriend) {
* // add the friend to memory
* friends_.push_back(&newFriend);
*
* // If the db insertion that follows fails, we should
* // remove it from memory.
* // (You could also declare this as "auto guard = makeGuard(...)")
* ScopeGuard guard = makeGuard([&] { friends_.pop_back(); });
*
* // this will throw an exception upon error, which
* // makes the ScopeGuard execute UserCont::pop_back()
* // once the Guard's destructor is called.
* db_->addFriend(GetName(), newFriend.GetName());
*
* // an exception was not thrown, so don't execute
* // the Guard.
* guard.dismiss();
* }
*
* Examine ScopeGuardTest.cpp for some more sample usage.
*
* Stolen from:
* Andrei's and Petru Marginean's CUJ article:
* http://drdobbs.com/184403758
* and the loki library:
* http://loki-lib.sourceforge.net/index.php?n=Idioms.ScopeGuardPointer
* and triendl.kj article:
* http://www.codeproject.com/KB/cpp/scope_guard.aspx
*/
class ScopeGuardImplBase {
public:
void dismiss() noexcept {
dismissed_ = true;
}
protected:
ScopeGuardImplBase()
: dismissed_(false) {}
ScopeGuardImplBase(ScopeGuardImplBase&& other)
: dismissed_(other.dismissed_) {
other.dismissed_ = true;
}
bool dismissed_;
};
template<typename FunctionType>
class ScopeGuardImpl : public ScopeGuardImplBase {
public:
explicit ScopeGuardImpl(const FunctionType& fn)
: function_(fn) {}
explicit ScopeGuardImpl(FunctionType&& fn)
: function_(std::move(fn)) {}
ScopeGuardImpl(ScopeGuardImpl&& other)
: ScopeGuardImplBase(std::move(other)),
function_(std::move(other.function_)) {
}
~ScopeGuardImpl() noexcept {
if (!dismissed_) {
execute();
}
}
private:
void* operator new(size_t) = delete;
void execute() noexcept {
try {
function_();
} catch (const std::exception& ex) {
std::cout << "ScopeGuard cleanup function threw a " <<
typeid(ex).name() << "exception: " << ex.what();
} catch (...) {
std::cout << "ScopeGuard cleanup function threw a non-exception object";
}
}
FunctionType function_;
};
template<typename FunctionType>
ScopeGuardImpl<typename std::decay<FunctionType>::type>
makeGuard(FunctionType&& fn) {
return ScopeGuardImpl<typename std::decay<FunctionType>::type>(
std::forward<FunctionType>(fn));
}
/**
* This is largely unneeded if you just use auto for your guards.
*/
typedef ScopeGuardImplBase&& ScopeGuard;
namespace detail {
/**
* Internal use for the macro SCOPE_EXIT below
*/
enum class ScopeGuardOnExit {};
template <typename FunctionType>
ScopeGuardImpl<typename std::decay<FunctionType>::type>
operator+(detail::ScopeGuardOnExit, FunctionType&& fn) {
return ScopeGuardImpl<typename std::decay<FunctionType>::type>(
std::forward<FunctionType>(fn));
}
} // namespace detail
} // folly
#define SCOPE_EXIT \
auto FB_ANONYMOUS_VARIABLE(SCOPE_EXIT_STATE) \
= ::folly::detail::ScopeGuardOnExit() + [&]
#endif // FOLLY_SCOPEGUARD_H_