/*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2011-present Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* limitations under the License.
*/
-#ifndef FOLLY_SCOPEGUARD_H_
-#define FOLLY_SCOPEGUARD_H_
+#pragma once
#include <cstddef>
#include <functional>
#include <new>
+#include <type_traits>
+#include <utility>
-#include "folly/Preprocessor.h"
+#include <folly/Portability.h>
+#include <folly/Preprocessor.h>
+#include <folly/UncaughtExceptions.h>
namespace folly {
+namespace detail {
+
+class ScopeGuardImplBase {
+ public:
+ void dismiss() noexcept {
+ dismissed_ = true;
+ }
+
+ template <typename T>
+ FOLLY_ALWAYS_INLINE static void runAndWarnAboutToCrashOnException(
+ T& function) noexcept {
+ try {
+ function();
+ } catch (...) {
+ warnAboutToCrash();
+ std::terminate();
+ }
+ }
+
+ protected:
+ ScopeGuardImplBase() noexcept : dismissed_(false) {}
+
+ static ScopeGuardImplBase makeEmptyScopeGuard() noexcept {
+ return ScopeGuardImplBase{};
+ }
+
+ template <typename T>
+ static const T& asConst(const T& t) noexcept {
+ return t;
+ }
+
+ bool dismissed_;
+
+ private:
+ static void warnAboutToCrash() noexcept;
+};
+
+template <typename FunctionType>
+class ScopeGuardImpl : public ScopeGuardImplBase {
+ public:
+ explicit ScopeGuardImpl(FunctionType& fn) noexcept(
+ std::is_nothrow_copy_constructible<FunctionType>::value)
+ : ScopeGuardImpl(
+ asConst(fn),
+ makeFailsafe(std::is_nothrow_copy_constructible<FunctionType>{},
+ &fn)) {}
+
+ explicit ScopeGuardImpl(const FunctionType& fn) noexcept(
+ std::is_nothrow_copy_constructible<FunctionType>::value)
+ : ScopeGuardImpl(
+ fn,
+ makeFailsafe(std::is_nothrow_copy_constructible<FunctionType>{},
+ &fn)) {}
+
+ explicit ScopeGuardImpl(FunctionType&& fn) noexcept(
+ std::is_nothrow_move_constructible<FunctionType>::value)
+ : ScopeGuardImpl(
+ std::move_if_noexcept(fn),
+ makeFailsafe(std::is_nothrow_move_constructible<FunctionType>{},
+ &fn)) {}
+
+ ScopeGuardImpl(ScopeGuardImpl&& other) noexcept(
+ std::is_nothrow_move_constructible<FunctionType>::value)
+ : function_(std::move_if_noexcept(other.function_)) {
+ // If the above line attempts a copy and the copy throws, other is
+ // left owning the cleanup action and will execute it (or not) depending
+ // on the value of other.dismissed_. The following lines only execute
+ // if the move/copy succeeded, in which case *this assumes ownership of
+ // the cleanup action and dismisses other.
+ dismissed_ = other.dismissed_;
+ other.dismissed_ = true;
+ }
+
+ ~ScopeGuardImpl() noexcept {
+ if (!dismissed_) {
+ execute();
+ }
+ }
+
+ private:
+ static ScopeGuardImplBase makeFailsafe(std::true_type, const void*) noexcept {
+ return makeEmptyScopeGuard();
+ }
+
+ template <typename Fn>
+ static auto makeFailsafe(std::false_type, Fn* fn) noexcept
+ -> ScopeGuardImpl<decltype(std::ref(*fn))> {
+ return ScopeGuardImpl<decltype(std::ref(*fn))>{std::ref(*fn)};
+ }
+
+ template <typename Fn>
+ explicit ScopeGuardImpl(Fn&& fn, ScopeGuardImplBase&& failsafe)
+ : ScopeGuardImplBase{}, function_(std::forward<Fn>(fn)) {
+ failsafe.dismiss();
+ }
+
+ void* operator new(std::size_t) = delete;
+
+ void execute() noexcept {
+ runAndWarnAboutToCrashOnException(function_);
+ }
+
+ FunctionType function_;
+};
+
+template <typename F>
+using ScopeGuardImplDecay = ScopeGuardImpl<typename std::decay<F>::type>;
+
+} // namespace detail
+
/**
* ScopeGuard is a general implementation of the "Initialization is
* Resource Acquisition" idiom. Basically, it guarantees that a function
* a functor, or a void(*)() function pointer.
*
*
- * Usage example: Add a friend to memory iff it is also added to the db.
+ * Usage example: Add a friend to memory if and only if it is also added
+ * to the db.
*
* void User::addFriend(User& newFriend) {
* // add the friend to memory
*
* // 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(); });
+ * auto guard = makeGuard([&] { friends_.pop_back(); });
*
* // this will throw an exception upon error, which
* // makes the ScopeGuard execute UserCont::pop_back()
* 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) {}
+template <typename F>
+detail::ScopeGuardImplDecay<F> makeGuard(F&& f) noexcept(
+ noexcept(detail::ScopeGuardImplDecay<F>(static_cast<F&&>(f)))) {
+ return detail::ScopeGuardImplDecay<F>(static_cast<F&&>(f));
+}
- ScopeGuardImplBase(ScopeGuardImplBase&& other)
- : dismissed_(other.dismissed_) {
- other.dismissed_ = true;
- }
+namespace detail {
- bool dismissed_;
-};
+#if defined(FOLLY_EXCEPTION_COUNT_USE_CXA_GET_GLOBALS) || \
+ defined(FOLLY_EXCEPTION_COUNT_USE_GETPTD) || \
+ defined(FOLLY_EXCEPTION_COUNT_USE_STD)
-template<typename FunctionType>
-class ScopeGuardImpl : public ScopeGuardImplBase {
+/**
+ * ScopeGuard used for executing a function when leaving the current scope
+ * depending on the presence of a new uncaught exception.
+ *
+ * If the executeOnException template parameter is true, the function is
+ * executed if a new uncaught exception is present at the end of the scope.
+ * If the parameter is false, then the function is executed if no new uncaught
+ * exceptions are present at the end of the scope.
+ *
+ * Used to implement SCOPE_FAIL and SCOPE_SUCCESS below.
+ */
+template <typename FunctionType, bool ExecuteOnException>
+class ScopeGuardForNewException {
public:
- explicit ScopeGuardImpl(const FunctionType& fn)
- : function_(fn) {}
+ explicit ScopeGuardForNewException(const FunctionType& fn) : function_(fn) {}
- explicit ScopeGuardImpl(FunctionType&& fn)
- : function_(std::move(fn)) {}
+ explicit ScopeGuardForNewException(FunctionType&& fn)
+ : function_(std::move(fn)) {}
- ScopeGuardImpl(ScopeGuardImpl&& other)
- : ScopeGuardImplBase(std::move(other)),
- function_(std::move(other.function_)) {
- }
+ ScopeGuardForNewException(ScopeGuardForNewException&& other) = default;
- ~ScopeGuardImpl() noexcept {
- if (!dismissed_) {
- execute();
+ ~ScopeGuardForNewException() noexcept(ExecuteOnException) {
+ if (ExecuteOnException == (exceptionCounter_ < uncaught_exceptions())) {
+ if (ExecuteOnException) {
+ ScopeGuardImplBase::runAndWarnAboutToCrashOnException(function_);
+ } else {
+ function_();
+ }
}
}
-private:
- void* operator new(size_t) = delete;
+ private:
+ ScopeGuardForNewException(const ScopeGuardForNewException& other) = delete;
- void execute() noexcept { function_(); }
+ void* operator new(std::size_t) = delete;
FunctionType function_;
+ int exceptionCounter_{uncaught_exceptions()};
};
-template<typename FunctionType>
-ScopeGuardImpl<typename std::decay<FunctionType>::type>
-makeGuard(FunctionType&& fn) {
- return ScopeGuardImpl<typename std::decay<FunctionType>::type>(
+/**
+ * Internal use for the macro SCOPE_FAIL below
+ */
+enum class ScopeGuardOnFail {};
+
+template <typename FunctionType>
+ScopeGuardForNewException<typename std::decay<FunctionType>::type, true>
+operator+(detail::ScopeGuardOnFail, FunctionType&& fn) {
+ return
+ ScopeGuardForNewException<typename std::decay<FunctionType>::type, true>(
std::forward<FunctionType>(fn));
}
/**
- * This is largely unneeded if you just use auto for your guards.
+ * Internal use for the macro SCOPE_SUCCESS below
*/
-typedef ScopeGuardImplBase&& ScopeGuard;
+enum class ScopeGuardOnSuccess {};
+
+template <typename FunctionType>
+ScopeGuardForNewException<typename std::decay<FunctionType>::type, false>
+operator+(ScopeGuardOnSuccess, FunctionType&& fn) {
+ return
+ ScopeGuardForNewException<typename std::decay<FunctionType>::type, false>(
+ std::forward<FunctionType>(fn));
+}
+
+#endif // native uncaught_exception() supported
-namespace detail {
/**
* Internal use for the macro SCOPE_EXIT below
*/
}
} // namespace detail
-} // folly
+} // namespace folly
#define SCOPE_EXIT \
auto FB_ANONYMOUS_VARIABLE(SCOPE_EXIT_STATE) \
- = ::folly::detail::ScopeGuardOnExit() + [&]
+ = ::folly::detail::ScopeGuardOnExit() + [&]() noexcept
+
+#if defined(FOLLY_EXCEPTION_COUNT_USE_CXA_GET_GLOBALS) || \
+ defined(FOLLY_EXCEPTION_COUNT_USE_GETPTD) || \
+ defined(FOLLY_EXCEPTION_COUNT_USE_STD)
+#define SCOPE_FAIL \
+ auto FB_ANONYMOUS_VARIABLE(SCOPE_FAIL_STATE) \
+ = ::folly::detail::ScopeGuardOnFail() + [&]() noexcept
-#endif // FOLLY_SCOPEGUARD_H_
+#define SCOPE_SUCCESS \
+ auto FB_ANONYMOUS_VARIABLE(SCOPE_SUCCESS_STATE) \
+ = ::folly::detail::ScopeGuardOnSuccess() + [&]()
+#endif // native uncaught_exception() supported
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