/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2017-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.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
+/*
+ * Author: Eric Niebler <eniebler@fb.com>
+ */
-#ifndef FOLLY_EXCEPTIONWRAPPER_H
-#define FOLLY_EXCEPTIONWRAPPER_H
+#pragma once
#include <cassert>
+#include <cstdint>
#include <exception>
+#include <iosfwd>
#include <memory>
-#include <folly/String.h>
-#include <folly/detail/ExceptionWrapper.h>
+#include <new>
+#include <type_traits>
+#include <typeinfo>
+#include <utility>
+
+#include <folly/Assume.h>
+#include <folly/CPortability.h>
+#include <folly/Demangle.h>
+#include <folly/ExceptionString.h>
+#include <folly/FBString.h>
+#include <folly/Traits.h>
+
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpragmas"
+#pragma GCC diagnostic ignored "-Wpotentially-evaluated-expression"
+// GCC gets confused about lambda scopes and issues shadow-local warnings for
+// parameters in totally different functions.
+#pragma GCC diagnostic ignored "-Wshadow-local"
+#pragma GCC diagnostic ignored "-Wshadow-compatible-local"
+#endif
+
+#define FOLLY_EXCEPTION_WRAPPER_H_INCLUDED
namespace folly {
-/*
- * Throwing exceptions can be a convenient way to handle errors. Storing
- * exceptions in an exception_ptr makes it easy to handle exceptions in a
- * different thread or at a later time. exception_ptr can also be used in a very
- * generic result/exception wrapper.
- *
- * However, there are some issues with throwing exceptions and
- * std::exception_ptr. These issues revolve around throw being expensive,
- * particularly in a multithreaded environment (see
- * ExceptionWrapperBenchmark.cpp).
- *
- * Imagine we have a library that has an API which returns a result/exception
- * wrapper. Let's consider some approaches for implementing this wrapper.
- * First, we could store a std::exception. This approach loses the derived
- * exception type, which can make exception handling more difficult for users
- * that prefer rethrowing the exception. We could use a folly::dynamic for every
- * possible type of exception. This is not very flexible - adding new types of
- * exceptions requires a change to the result/exception wrapper. We could use an
- * exception_ptr. However, constructing an exception_ptr as well as accessing
- * the error requires a call to throw. That means that there will be two calls
- * to throw in order to process the exception. For performance sensitive
- * applications, this may be unacceptable.
- *
- * exception_wrapper is designed to handle exception management for both
- * convenience and high performance use cases. make_exception_wrapper is
- * templated on derived type, allowing us to rethrow the exception properly for
- * users that prefer convenience. These explicitly named exception types can
- * therefore be handled without any peformance penalty. exception_wrapper is
- * also flexible enough to accept any type. If a caught exception is not of an
- * explicitly named type, then std::exception_ptr is used to preserve the
- * exception state. For performance sensitive applications, the accessor methods
- * can test or extract a pointer to a specific exception type with very little
- * overhead.
- *
- * Example usage:
- *
- * exception_wrapper globalExceptionWrapper;
- *
- * // Thread1
- * void doSomethingCrazy() {
- * int rc = doSomethingCrazyWithLameReturnCodes();
- * if (rc == NAILED_IT) {
- * globalExceptionWrapper = exception_wrapper();
- * } else if (rc == FACE_PLANT) {
- * globalExceptionWrapper = make_exception_wrapper<FacePlantException>();
- * } else if (rc == FAIL_WHALE) {
- * globalExceptionWrapper = make_exception_wrapper<FailWhaleException>();
- * }
- * }
- *
- * // Thread2: Exceptions are ok!
- * void processResult() {
- * try {
- * globalExceptionWrapper.throwException();
- * } catch (const FacePlantException& e) {
- * LOG(ERROR) << "FACEPLANT!";
- * } catch (const FailWhaleException& e) {
- * LOG(ERROR) << "FAILWHALE!";
- * }
- * }
- *
- * // Thread2: Exceptions are bad!
- * void processResult() {
- * auto ep = globalExceptionWrapper.get();
- * if (!ep.with_exception<FacePlantException>([&](
- * FacePlantException& faceplant) {
- * LOG(ERROR) << "FACEPLANT";
- * })) {
- * ep.with_exception<FailWhaleException>([&](
- * FailWhaleException& failwhale) {
- * LOG(ERROR) << "FAILWHALE!";
- * });
- * }
- * }
- *
- */
-class exception_wrapper {
- protected:
- template <typename Ex>
- struct optimize;
+#define FOLLY_REQUIRES_DEF(...) \
+ _t<std::enable_if<static_cast<bool>(__VA_ARGS__), long>>
- public:
- exception_wrapper() = default;
-
- // Implicitly construct an exception_wrapper from a qualifying exception.
- // See the optimize struct for details.
- template <typename Ex, typename =
- typename std::enable_if<optimize<typename std::decay<Ex>::type>::value>
- ::type>
- /* implicit */ exception_wrapper(Ex&& exn) {
- typedef typename std::decay<Ex>::type DEx;
- item_ = std::make_shared<DEx>(std::forward<Ex>(exn));
- throwfn_ = folly::detail::Thrower<DEx>::doThrow;
- }
+#define FOLLY_REQUIRES(...) FOLLY_REQUIRES_DEF(__VA_ARGS__) = __LINE__
- // The following two constructors are meant to emulate the behavior of
- // try_and_catch in performance sensitive code as well as to be flexible
- // enough to wrap exceptions of unknown type. There is an overload that
- // takes an exception reference so that the wrapper can extract and store
- // the exception's type and what() when possible.
- //
- // The canonical use case is to construct an all-catching exception wrapper
- // with minimal overhead like so:
- //
- // try {
- // // some throwing code
- // } catch (const std::exception& e) {
- // // won't lose e's type and what()
- // exception_wrapper ew{std::current_exception(), e};
- // } catch (...) {
- // // everything else
- // exception_wrapper ew{std::current_exception()};
- // }
- //
- // try_and_catch is cleaner and preferable. Use it unless you're sure you need
- // something like this instead.
- template <typename Ex>
- explicit exception_wrapper(std::exception_ptr eptr, Ex& exn) {
- assign_eptr(eptr, exn);
- }
+namespace exception_wrapper_detail {
- explicit exception_wrapper(std::exception_ptr eptr) {
- assign_eptr(eptr);
- }
+template <template <class> class T, class... As>
+using AllOf = StrictConjunction<T<As>...>;
- void throwException() const {
- if (throwfn_) {
- throwfn_(item_.get());
- } else if (eptr_) {
- std::rethrow_exception(eptr_);
- }
- }
+template <bool If, class T>
+using AddConstIf = _t<std::conditional<If, const T, T>>;
- explicit operator bool() const {
- return item_ || eptr_;
- }
+template <class Fn, class A>
+FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN
+auto fold(Fn&&, A&& a) {
+ return static_cast<A&&>(a);
+}
- // This implementation is similar to std::exception_ptr's implementation
- // where two exception_wrappers are equal when the address in the underlying
- // reference field both point to the same exception object. The reference
- // field remains the same when the exception_wrapper is copied or when
- // the exception_wrapper is "rethrown".
- bool operator==(const exception_wrapper& a) const {
- if (item_) {
- return a.item_ && item_.get() == a.item_.get();
- } else {
- return eptr_ == a.eptr_;
- }
- }
+template <class Fn, class A, class B, class... Bs>
+FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN
+auto fold(Fn&& fn, A&& a, B&& b, Bs&&... bs) {
+ return fold(
+ // This looks like a use of fn after a move of fn, but in reality, this is
+ // just a cast and not a move. That's because regardless of which fold
+ // overload is selected, fn gets bound to a &&. Had fold taken fn by value
+ // there would indeed be a problem here.
+ static_cast<Fn&&>(fn),
+ static_cast<Fn&&>(fn)(static_cast<A&&>(a), static_cast<B&&>(b)),
+ static_cast<Bs&&>(bs)...);
+}
- bool operator!=(const exception_wrapper& a) const {
- return !(*this == a);
- }
+} // namespace exception_wrapper_detail
+
+//! Throwing exceptions can be a convenient way to handle errors. Storing
+//! exceptions in an `exception_ptr` makes it easy to handle exceptions in a
+//! different thread or at a later time. `exception_ptr` can also be used in a
+//! very generic result/exception wrapper.
+//!
+//! However, there are some issues with throwing exceptions and
+//! `std::exception_ptr`. These issues revolve around `throw` being expensive,
+//! particularly in a multithreaded environment (see
+//! ExceptionWrapperBenchmark.cpp).
+//!
+//! Imagine we have a library that has an API which returns a result/exception
+//! wrapper. Let's consider some approaches for implementing this wrapper.
+//! First, we could store a `std::exception`. This approach loses the derived
+//! exception type, which can make exception handling more difficult for users
+//! that prefer rethrowing the exception. We could use a `folly::dynamic` for
+//! every possible type of exception. This is not very flexible - adding new
+//! types of exceptions requires a change to the result/exception wrapper. We
+//! could use an `exception_ptr`. However, constructing an `exception_ptr` as
+//! well as accessing the error requires a call to throw. That means that there
+//! will be two calls to throw in order to process the exception. For
+//! performance sensitive applications, this may be unacceptable.
+//!
+//! `exception_wrapper` is designed to handle exception management for both
+//! convenience and high performance use cases. `make_exception_wrapper` is
+//! templated on derived type, allowing us to rethrow the exception properly for
+//! users that prefer convenience. These explicitly named exception types can
+//! therefore be handled without any peformance penalty. `exception_wrapper` is
+//! also flexible enough to accept any type. If a caught exception is not of an
+//! explicitly named type, then `std::exception_ptr` is used to preserve the
+//! exception state. For performance sensitive applications, the accessor
+//! methods can test or extract a pointer to a specific exception type with very
+//! little overhead.
+//!
+//! \par Example usage:
+//! \par
+//! \code
+//! exception_wrapper globalExceptionWrapper;
+//!
+//! // Thread1
+//! void doSomethingCrazy() {
+//! int rc = doSomethingCrazyWithLameReturnCodes();
+//! if (rc == NAILED_IT) {
+//! globalExceptionWrapper = exception_wrapper();
+//! } else if (rc == FACE_PLANT) {
+//! globalExceptionWrapper = make_exception_wrapper<FacePlantException>();
+//! } else if (rc == FAIL_WHALE) {
+//! globalExceptionWrapper = make_exception_wrapper<FailWhaleException>();
+//! }
+//! }
+//!
+//! // Thread2: Exceptions are ok!
+//! void processResult() {
+//! try {
+//! globalExceptionWrapper.throwException();
+//! } catch (const FacePlantException& e) {
+//! LOG(ERROR) << "FACEPLANT!";
+//! } catch (const FailWhaleException& e) {
+//! LOG(ERROR) << "FAILWHALE!";
+//! }
+//! }
+//!
+//! // Thread2: Exceptions are bad!
+//! void processResult() {
+//! globalExceptionWrapper.handle(
+//! [&](FacePlantException& faceplant) {
+//! LOG(ERROR) << "FACEPLANT";
+//! },
+//! [&](FailWhaleException& failwhale) {
+//! LOG(ERROR) << "FAILWHALE!";
+//! },
+//! [](...) {
+//! LOG(FATAL) << "Unrecognized exception";
+//! });
+//! }
+//! \endcode
+class exception_wrapper final {
+ private:
+ struct AnyException : std::exception {
+ std::type_info const* typeinfo_;
+ template <class T>
+ /* implicit */ AnyException(T&& t) noexcept : typeinfo_(&typeid(t)) {}
+ };
- // This will return a non-nullptr only if the exception is held as a
- // copy. It is the only interface which will distinguish between an
- // exception held this way, and by exception_ptr. You probably
- // shouldn't use it at all.
- std::exception* getCopied() { return item_.get(); }
- const std::exception* getCopied() const { return item_.get(); }
-
- fbstring what() const {
- if (item_) {
- return exceptionStr(*item_);
- } else if (eptr_) {
- return estr_;
- } else {
- return fbstring();
- }
- }
+ template <class Fn>
+ struct arg_type_;
+ template <class Fn>
+ using arg_type = _t<arg_type_<Fn>>;
+
+ // exception_wrapper is implemented as a simple variant over four
+ // different representations:
+ // 0. Empty, no exception.
+ // 1. An small object stored in-situ.
+ // 2. A larger object stored on the heap and referenced with a
+ // std::shared_ptr.
+ // 3. A std::exception_ptr, together with either:
+ // a. A pointer to the referenced std::exception object, or
+ // b. A pointer to a std::type_info object for the referenced exception,
+ // or for an unspecified type if the type is unknown.
+ // This is accomplished with the help of a union and a pointer to a hand-
+ // rolled virtual table. This virtual table contains pointers to functions
+ // that know which field of the union is active and do the proper action.
+ // The class invariant ensures that the vtable ptr and the union stay in sync.
+ struct VTable {
+ void (*copy_)(exception_wrapper const*, exception_wrapper*);
+ void (*move_)(exception_wrapper*, exception_wrapper*);
+ void (*delete_)(exception_wrapper*);
+ void (*throw_)(exception_wrapper const*);
+ std::type_info const* (*type_)(exception_wrapper const*);
+ std::exception const* (*get_exception_)(exception_wrapper const*);
+ exception_wrapper (*get_exception_ptr_)(exception_wrapper const*);
+ };
- fbstring class_name() const {
- if (item_) {
- auto& i = *item_;
- return demangle(typeid(i));
- } else if (eptr_) {
- return ename_;
- } else {
- return fbstring();
- }
- }
+ [[noreturn]] static void onNoExceptionError();
- template <class Ex>
- bool is_compatible_with() const {
- if (item_) {
- return dynamic_cast<const Ex*>(item_.get());
- } else if (eptr_) {
- try {
- std::rethrow_exception(eptr_);
- } catch (std::exception& e) {
- return dynamic_cast<const Ex*>(&e);
- } catch (...) {
- // fall through
- }
- }
- return false;
- }
+ template <class Ret, class... Args>
+ static Ret noop_(Args...);
- // If this exception wrapper wraps an exception of type Ex, with_exception
- // will call f with the wrapped exception as an argument and return true, and
- // will otherwise return false.
- template <class Ex, class F>
- typename std::enable_if<
- std::is_base_of<std::exception, typename std::decay<Ex>::type>::value,
- bool>::type
- with_exception(F f) {
- return with_exception1<typename std::decay<Ex>::type>(f, this);
- }
+ static std::type_info const* uninit_type_(exception_wrapper const*);
- // Const overload
- template <class Ex, class F>
- typename std::enable_if<
- std::is_base_of<std::exception, typename std::decay<Ex>::type>::value,
- bool>::type
- with_exception(F f) const {
- return with_exception1<const typename std::decay<Ex>::type>(f, this);
- }
+ static VTable const uninit_;
- // Overload for non-exceptions. Always rethrows.
- template <class Ex, class F>
- typename std::enable_if<
- !std::is_base_of<std::exception, typename std::decay<Ex>::type>::value,
- bool>::type
- with_exception(F f) const {
- try {
- throwException();
- } catch (typename std::decay<Ex>::type& e) {
- f(e);
- return true;
- } catch (...) {
- // fall through
- }
- return false;
- }
+ template <class Ex>
+ using IsStdException = std::is_base_of<std::exception, _t<std::decay<Ex>>>;
+ template <bool B, class T>
+ using AddConstIf = exception_wrapper_detail::AddConstIf<B, T>;
+ template <class CatchFn>
+ using IsCatchAll =
+ std::is_same<arg_type<_t<std::decay<CatchFn>>>, AnyException>;
+
+ struct Unknown {};
+
+ // Sadly, with the gcc-4.9 platform, std::logic_error and std::runtime_error
+ // do not fit here. They also don't have noexcept copy-ctors, so the internal
+ // storage wouldn't be used anyway. For the gcc-5 platform, both logic_error
+ // and runtime_error can be safely stored internally.
+ struct Buffer {
+ using Storage =
+ _t<std::aligned_storage<2 * sizeof(void*), alignof(std::exception)>>;
+ Storage buff_;
+
+ Buffer() : buff_{} {}
+
+ template <class Ex, class DEx = _t<std::decay<Ex>>>
+ Buffer(in_place_t, Ex&& ex);
+ template <class Ex>
+ Ex& as() noexcept;
+ template <class Ex>
+ Ex const& as() const noexcept;
+ };
- std::exception_ptr getExceptionPtr() const {
- if (eptr_) {
- return eptr_;
- }
-
- try {
- throwException();
- } catch (...) {
- return std::current_exception();
- }
- return std::exception_ptr();
- }
+ enum class Placement { kInSitu, kOnHeap };
+ template <class T>
+ using PlacementOf = std::integral_constant<
+ Placement,
+ sizeof(T) <= sizeof(Buffer::Storage) &&
+ alignof(T) <= alignof(Buffer::Storage) &&
+ noexcept(T(std::declval<T&&>()))
+ ? Placement::kInSitu
+ : Placement::kOnHeap>;
+
+ using InSituTag = std::integral_constant<Placement, Placement::kInSitu>;
+ using OnHeapTag = std::integral_constant<Placement, Placement::kOnHeap>;
+
+ static std::exception const* as_exception_or_null_(std::exception const& ex);
+ static std::exception const* as_exception_or_null_(AnyException);
+
+ struct ExceptionPtr {
+ std::exception_ptr ptr_;
+ std::uintptr_t exception_or_type_; // odd for type_info
+ static_assert(
+ 1 < alignof(std::exception) && 1 < alignof(std::type_info),
+ "Surprise! std::exception and std::type_info don't have alignment "
+ "greater than one. as_int_ below will not work!");
+
+ static std::uintptr_t as_int_(std::exception const& e);
+ static std::uintptr_t as_int_(AnyException e);
+ bool has_exception_() const;
+ std::exception const* as_exception_() const;
+ std::type_info const* as_type_() const;
+ static void copy_(exception_wrapper const* from, exception_wrapper* to);
+ static void move_(exception_wrapper* from, exception_wrapper* to);
+ static void delete_(exception_wrapper* that);
+ [[noreturn]] static void throw_(exception_wrapper const* that);
+ static std::type_info const* type_(exception_wrapper const* that);
+ static std::exception const* get_exception_(exception_wrapper const* that);
+ static exception_wrapper get_exception_ptr_(exception_wrapper const* that);
+ static VTable const ops_;
+ };
-protected:
- template <typename Ex>
- struct optimize {
- static const bool value =
- std::is_base_of<std::exception, Ex>::value &&
- std::is_copy_assignable<Ex>::value &&
- !std::is_abstract<Ex>::value;
+ template <class Ex>
+ struct InPlace {
+ static void copy_(exception_wrapper const* from, exception_wrapper* to);
+ static void move_(exception_wrapper* from, exception_wrapper* to);
+ static void delete_(exception_wrapper* that);
+ [[noreturn]] static void throw_(exception_wrapper const* that);
+ static std::type_info const* type_(exception_wrapper const*);
+ static std::exception const* get_exception_(exception_wrapper const* that);
+ static exception_wrapper get_exception_ptr_(exception_wrapper const* that);
+ static constexpr VTable const ops_{copy_,
+ move_,
+ delete_,
+ throw_,
+ type_,
+ get_exception_,
+ get_exception_ptr_};
};
- template <typename Ex>
- void assign_eptr(std::exception_ptr eptr, Ex& e) {
- this->eptr_ = eptr;
- this->estr_ = exceptionStr(e).toStdString();
- this->ename_ = demangle(typeid(e)).toStdString();
- }
+ struct SharedPtr {
+ struct Base {
+ std::type_info const* info_;
+ Base() = default;
+ explicit Base(std::type_info const& info) : info_(&info) {}
+ virtual ~Base() {}
+ virtual void throw_() const = 0;
+ virtual std::exception const* get_exception_() const noexcept = 0;
+ virtual exception_wrapper get_exception_ptr_() const noexcept = 0;
+ };
+ template <class Ex>
+ struct Impl final : public Base {
+ Ex ex_;
+ Impl() = default;
+ explicit Impl(Ex const& ex) : Base{typeid(ex)}, ex_(ex) {}
+ explicit Impl(Ex&& ex)
+ : Base{typeid(ex)},
+ ex_(std::move(ex)){}[[noreturn]] void throw_() const override;
+ std::exception const* get_exception_() const noexcept override;
+ exception_wrapper get_exception_ptr_() const noexcept override;
+ };
+ std::shared_ptr<Base> ptr_;
+
+ static void copy_(exception_wrapper const* from, exception_wrapper* to);
+ static void move_(exception_wrapper* from, exception_wrapper* to);
+ static void delete_(exception_wrapper* that);
+ [[noreturn]] static void throw_(exception_wrapper const* that);
+ static std::type_info const* type_(exception_wrapper const* that);
+ static std::exception const* get_exception_(exception_wrapper const* that);
+ static exception_wrapper get_exception_ptr_(exception_wrapper const* that);
+ static VTable const ops_;
+ };
- void assign_eptr(std::exception_ptr eptr) {
- this->eptr_ = eptr;
- }
+ union {
+ Buffer buff_{};
+ ExceptionPtr eptr_;
+ SharedPtr sptr_;
+ };
+ VTable const* vptr_{&uninit_};
- // Optimized case: if we know what type the exception is, we can
- // store a copy of the concrete type, and a helper function so we
- // can rethrow it.
- std::shared_ptr<std::exception> item_;
- void (*throwfn_)(std::exception*){nullptr};
- // Fallback case: store the library wrapper, which is less efficient
- // but gets the job done. Also store exceptionPtr() the name of the
- // exception type, so we can at least get those back out without
- // having to rethrow.
- std::exception_ptr eptr_;
- std::string estr_;
- std::string ename_;
-
- template <class T, class... Args>
- friend exception_wrapper make_exception_wrapper(Args&&... args);
-
-private:
- // What makes this useful is that T can be exception_wrapper* or
- // const exception_wrapper*, and the compiler will use the
- // instantiation which works with F.
- template <class Ex, class F, class T>
- static bool with_exception1(F f, T* that) {
- if (that->item_) {
- if (auto ex = dynamic_cast<Ex*>(that->item_.get())) {
- f(*ex);
- return true;
- }
- } else if (that->eptr_) {
- try {
- std::rethrow_exception(that->eptr_);
- } catch (std::exception& e) {
- if (auto ex = dynamic_cast<Ex*>(&e)) {
- f(*ex);
- return true;
- }
- } catch (...) {
- // fall through
- }
- }
- return false;
- }
-};
+ template <class Ex, class DEx = _t<std::decay<Ex>>>
+ exception_wrapper(Ex&& ex, OnHeapTag);
-template <class T, class... Args>
-exception_wrapper make_exception_wrapper(Args&&... args) {
- exception_wrapper ew;
- ew.item_ = std::make_shared<T>(std::forward<Args>(args)...);
- ew.throwfn_ = folly::detail::Thrower<T>::doThrow;
- return ew;
-}
+ template <class Ex, class DEx = _t<std::decay<Ex>>>
+ exception_wrapper(Ex&& ex, InSituTag);
-// For consistency with exceptionStr() functions in String.h
-inline fbstring exceptionStr(const exception_wrapper& ew) {
- return ew.what();
-}
+ template <class T>
+ struct IsRegularExceptionType
+ : StrictConjunction<
+ std::is_copy_constructible<T>,
+ Negation<std::is_base_of<exception_wrapper, T>>,
+ Negation<std::is_abstract<T>>> {};
-/*
- * try_and_catch is a simple replacement for try {} catch(){} that allows you to
- * specify which derived exceptions you would like to catch and store in an
- * exception_wrapper.
- *
- * Because we cannot build an equivalent of std::current_exception(), we need
- * to catch every derived exception that we are interested in catching.
- *
- * Exceptions should be listed in the reverse order that you would write your
- * catch statements (that is, std::exception& should be first).
- *
- * NOTE: Although implemented as a derived class (for syntactic delight), don't
- * be confused - you should not pass around try_and_catch objects!
- *
- * Example Usage:
- *
- * // This catches my runtime_error and if I call throwException() on ew, it
- * // will throw a runtime_error
- * auto ew = folly::try_and_catch<std::exception, std::runtime_error>([=]() {
- * if (badThingHappens()) {
- * throw std::runtime_error("ZOMG!");
- * }
- * });
- *
- * // This will catch the exception and if I call throwException() on ew, it
- * // will throw a std::exception
- * auto ew = folly::try_and_catch<std::exception, std::runtime_error>([=]() {
- * if (badThingHappens()) {
- * throw std::exception();
- * }
- * });
- *
- * // This will not catch the exception and it will be thrown.
- * auto ew = folly::try_and_catch<std::runtime_error>([=]() {
- * if (badThingHappens()) {
- * throw std::exception();
- * }
- * });
- */
+ template <class CatchFn, bool IsConst = false>
+ struct ExceptionTypeOf;
+
+ template <bool IsConst>
+ struct HandleReduce;
+
+ template <bool IsConst>
+ struct HandleStdExceptReduce;
+
+ template <class This, class... CatchFns>
+ static void handle_(std::false_type, This& this_, CatchFns&... fns);
+
+ template <class This, class... CatchFns>
+ static void handle_(std::true_type, This& this_, CatchFns&... fns);
-template <typename... Exceptions>
-class try_and_catch;
+ template <class Ex, class This, class Fn>
+ static bool with_exception_(This& this_, Fn fn_);
-template <typename LastException, typename... Exceptions>
-class try_and_catch<LastException, Exceptions...> :
- public try_and_catch<Exceptions...> {
public:
- template <typename F>
- explicit try_and_catch(F&& fn) : Base() {
- call_fn(fn);
- }
+ //! Default-constructs an empty `exception_wrapper`
+ //! \post `type() == none()`
+ exception_wrapper() noexcept {}
+
+ //! Move-constructs an `exception_wrapper`
+ //! \post `*this` contains the value of `that` prior to the move
+ //! \post `that.type() == none()`
+ exception_wrapper(exception_wrapper&& that) noexcept;
+
+ //! Copy-constructs an `exception_wrapper`
+ //! \post `*this` contains a copy of `that`, and `that` is unmodified
+ //! \post `type() == that.type()`
+ exception_wrapper(exception_wrapper const& that);
+
+ //! Move-assigns an `exception_wrapper`
+ //! \pre `this != &that`
+ //! \post `*this` contains the value of `that` prior to the move
+ //! \post `that.type() == none()`
+ exception_wrapper& operator=(exception_wrapper&& that) noexcept;
+
+ //! Copy-assigns an `exception_wrapper`
+ //! \post `*this` contains a copy of `that`, and `that` is unmodified
+ //! \post `type() == that.type()`
+ exception_wrapper& operator=(exception_wrapper const& that);
+
+ ~exception_wrapper();
+
+ //! \pre `ptr` is empty, or it holds a reference to an exception that is not
+ //! derived from `std::exception`.
+ //! \post `!ptr || bool(*this)`
+ //! \post `hasThrownException() == true`
+ //! \post `type() == unknown()`
+ explicit exception_wrapper(std::exception_ptr ptr) noexcept;
+
+ //! \pre `ptr` holds a reference to `ex`.
+ //! \post `hasThrownException() == true`
+ //! \post `bool(*this)`
+ //! \post `type() == typeid(ex)`
+ template <class Ex>
+ exception_wrapper(std::exception_ptr ptr, Ex& ex);
+
+ //! \pre `typeid(ex) == typeid(typename decay<Ex>::type)`
+ //! \post `bool(*this)`
+ //! \post `hasThrownException() == false`
+ //! \post `type() == typeid(ex)`
+ //! \note Exceptions of types derived from `std::exception` can be implicitly
+ //! converted to an `exception_wrapper`.
+ template <
+ class Ex,
+ class Ex_ = _t<std::decay<Ex>>,
+ FOLLY_REQUIRES(
+ Conjunction<IsStdException<Ex_>, IsRegularExceptionType<Ex_>>())>
+ /* implicit */ exception_wrapper(Ex&& ex);
+
+ //! \pre `typeid(ex) == typeid(typename decay<Ex>::type)`
+ //! \post `bool(*this)`
+ //! \post `hasThrownException() == false`
+ //! \post `type() == typeid(ex)`
+ //! \note Exceptions of types not derived from `std::exception` can still be
+ //! used to construct an `exception_wrapper`, but you must specify
+ //! `folly::in_place` as the first parameter.
+ template <
+ class Ex,
+ class Ex_ = _t<std::decay<Ex>>,
+ FOLLY_REQUIRES(IsRegularExceptionType<Ex_>())>
+ exception_wrapper(in_place_t, Ex&& ex);
+
+ //! Swaps the value of `*this` with the value of `that`
+ void swap(exception_wrapper& that) noexcept;
+
+ //! \return `true` if `*this` is not holding an exception.
+ explicit operator bool() const noexcept;
+
+ //! \return `!bool(*this)`
+ bool operator!() const noexcept;
+
+ //! Make this `exception_wrapper` empty
+ //! \post `!*this`
+ void reset();
+
+ //! \return `true` if this `exception_wrapper` holds a reference to an
+ //! exception that was thrown (i.e., if it was constructed with
+ //! a `std::exception_ptr`, or if `to_exception_ptr()` was called on a
+ //! (non-const) reference to `*this`).
+ bool has_exception_ptr() const noexcept;
+
+ //! \return a pointer to the `std::exception` held by `*this`, if it holds
+ //! one; otherwise, returns `nullptr`.
+ //! \note This function does not mutate the `exception_wrapper` object.
+ //! \note This function never causes an exception to be thrown.
+ std::exception* get_exception() noexcept;
+ //! \overload
+ std::exception const* get_exception() const noexcept;
+
+ //! \return A `std::exception_ptr` that references either the exception held
+ //! by `*this`, or a copy of same.
+ //! \note This function may need to throw an exception to complete the action.
+ //! \note The non-const overload of this function mutates `*this` to cache the
+ //! computed `std::exception_ptr`; that is, this function may cause
+ //! `has_exception_ptr()` to change from `false` to `true`.
+ std::exception_ptr const& to_exception_ptr() noexcept;
+ //! \overload
+ std::exception_ptr to_exception_ptr() const noexcept;
+
+ //! \return the `typeid` of an unspecified type used by
+ //! `exception_wrapper::type()` to denote an empty `exception_wrapper`.
+ static std::type_info const& none() noexcept;
+ //! \return the `typeid` of an unspecified type used by
+ //! `exception_wrapper::type()` to denote an `exception_wrapper` that
+ //! holds an exception of unknown type.
+ static std::type_info const& unknown() noexcept;
+
+ //! Returns the `typeid` of the wrapped exception object. If there is no
+ //! wrapped exception object, returns `exception_wrapper::none()`. If
+ //! this instance wraps an exception of unknown type not derived from
+ //! `std::exception`, returns `exception_wrapper::unknown()`.
+ std::type_info const& type() const noexcept;
+
+ //! \return If `get_exception() != nullptr`, `class_name() + ": " +
+ //! get_exception()->what()`; otherwise, `class_name()`.
+ folly::fbstring what() const;
+
+ //! \return If `!*this`, the empty string; otherwise, if
+ //! `type() == unknown()`, the string `"<unknown exception>"`; otherwise,
+ //! the result of `type().name()` after demangling.
+ folly::fbstring class_name() const;
+
+ //! \tparam Ex The expression type to check for compatibility with.
+ //! \return `true` if and only if `*this` wraps an exception that would be
+ //! caught with a `catch(Ex const&)` clause.
+ //! \note If `*this` is empty, this function returns `false`.
+ template <class Ex>
+ bool is_compatible_with() const noexcept;
+
+ //! \pre `bool(*this)`
+ //! Throws the wrapped expression.
+ [[noreturn]] void throwException() const;
+
+ //! Call `fn` with the wrapped exception (if any), if `fn` can accept it.
+ //! \par Example
+ //! \code
+ //! exception_wrapper ew{std::runtime_error("goodbye cruel world")};
+ //!
+ //! assert( ew.with_exception([](std::runtime_error& e){/*...*/}) );
+ //!
+ //! assert( !ew.with_exception([](int& e){/*...*/}) );
+ //!
+ //! assert( !exception_wrapper{}.with_exception([](int& e){/*...*/}) );
+ //! \endcode
+ //! \tparam Ex Optionally, the type of the exception that `fn` accepts.
+ //! \tparam Fn The type of a monomophic function object.
+ //! \param fn A function object to call with the wrapped exception
+ //! \return `true` if and only if `fn` was called.
+ //! \note Optionally, you may explicitly specify the type of the exception
+ //! that `fn` expects, as in
+ //! \code
+ //! ew.with_exception<std::runtime_error>([](auto&& e) { /*...*/; });
+ //! \endcode
+ //! \note The handler may or may not be invoked with an active exception.
+ //! **Do not try to rethrow the exception with `throw;` from within your
+ //! handler -- that is, a throw expression with no operand.** This may
+ //! cause your process to terminate. (It is perfectly ok to throw from
+ //! a handler so long as you specify the exception to throw, as in
+ //! `throw e;`.)
+ template <class Ex = void const, class Fn>
+ bool with_exception(Fn fn);
+ //! \overload
+ template <class Ex = void const, class Fn>
+ bool with_exception(Fn fn) const;
+
+ //! Handle the wrapped expression as if with a series of `catch` clauses,
+ //! propagating the exception if no handler matches.
+ //! \par Example
+ //! \code
+ //! exception_wrapper ew{std::runtime_error("goodbye cruel world")};
+ //!
+ //! ew.handle(
+ //! [&](std::logic_error const& e) {
+ //! LOG(DFATAL) << "ruh roh";
+ //! ew.throwException(); // rethrow the active exception without
+ //! // slicing it. Will not be caught by other
+ //! // handlers in this call.
+ //! },
+ //! [&](std::exception const& e) {
+ //! LOG(ERROR) << ew.what();
+ //! });
+ //! \endcode
+ //! In the above example, any exception _not_ derived from `std::exception`
+ //! will be propagated. To specify a catch-all clause, pass a lambda that
+ //! takes a C-style elipses, as in:
+ //! \code
+ //! ew.handle(/*...* /, [](...) { /* handle unknown exception */ } )
+ //! \endcode
+ //! \pre `!*this`
+ //! \tparam CatchFns... A pack of unary monomorphic function object types.
+ //! \param fns A pack of unary monomorphic function objects to be treated as
+ //! an ordered list of potential exception handlers.
+ //! \note The handlers may or may not be invoked with an active exception.
+ //! **Do not try to rethrow the exception with `throw;` from within your
+ //! handler -- that is, a throw expression with no operand.** This may
+ //! cause your process to terminate. (It is perfectly ok to throw from
+ //! a handler so long as you specify the exception to throw, as in
+ //! `throw e;`.)
+ template <class... CatchFns>
+ void handle(CatchFns... fns);
+ //! \overload
+ template <class... CatchFns>
+ void handle(CatchFns... fns) const;
+};
- protected:
- typedef try_and_catch<Exceptions...> Base;
+template <class Ex>
+constexpr exception_wrapper::VTable exception_wrapper::InPlace<Ex>::ops_;
- try_and_catch() : Base() {}
+/**
+ * \return An `exception_wrapper` that wraps an instance of type `Ex`
+ * that has been constructed with arguments `std::forward<As>(as)...`.
+ */
+template <class Ex, typename... As>
+exception_wrapper make_exception_wrapper(As&&... as) {
+ return exception_wrapper{Ex{std::forward<As>(as)...}};
+}
- template <typename Ex>
- typename std::enable_if<!exception_wrapper::optimize<Ex>::value>::type
- assign_exception(Ex& e, std::exception_ptr eptr) {
- exception_wrapper::assign_eptr(eptr, e);
- }
+/**
+ * Inserts `ew.what()` into the ostream `sout`.
+ * \return `sout`
+ */
+template <class Ch>
+std::basic_ostream<Ch>& operator<<(
+ std::basic_ostream<Ch>& sout,
+ exception_wrapper const& ew) {
+ return sout << ew.what();
+}
- template <typename Ex>
- typename std::enable_if<exception_wrapper::optimize<Ex>::value>::type
- assign_exception(Ex& e, std::exception_ptr /*eptr*/) {
- this->item_ = std::make_shared<Ex>(e);
- this->throwfn_ = folly::detail::Thrower<Ex>::doThrow;
- }
+/**
+ * Swaps the value of `a` with the value of `b`.
+ */
+inline void swap(exception_wrapper& a, exception_wrapper& b) noexcept {
+ a.swap(b);
+}
- template <typename F>
- void call_fn(F&& fn) {
- try {
- Base::call_fn(std::move(fn));
- } catch (LastException& e) {
- if (typeid(e) == typeid(LastException&)) {
- assign_exception(e, std::current_exception());
- } else {
- exception_wrapper::assign_eptr(std::current_exception(), e);
- }
- }
- }
-};
+// For consistency with exceptionStr() functions in ExceptionString.h
+fbstring exceptionStr(exception_wrapper const& ew);
-template<>
-class try_and_catch<> : public exception_wrapper {
- public:
- try_and_catch() = default;
+namespace detail {
+template <typename F>
+inline exception_wrapper try_and_catch_(F&& f) {
+ return (f(), exception_wrapper());
+}
- protected:
- template <typename F>
- void call_fn(F&& fn) {
- fn();
+template <typename F, typename Ex, typename... Exs>
+inline exception_wrapper try_and_catch_(F&& f) {
+ try {
+ return try_and_catch_<F, Exs...>(std::forward<F>(f));
+ } catch (Ex& ex) {
+ return exception_wrapper(std::current_exception(), ex);
}
-};
}
+} // detail
+
+//! `try_and_catch` is a simple replacement for `try {} catch(){}`` that allows
+//! you to specify which derived exceptions you would like to catch and store in
+//! an `exception_wrapper`.
+//!
+//! Because we cannot build an equivalent of `std::current_exception()`, we need
+//! to catch every derived exception that we are interested in catching.
+//!
+//! Exceptions should be listed in the reverse order that you would write your
+//! catch statements (that is, `std::exception&` should be first).
+//!
+//! \par Example Usage:
+//! \code
+//! // This catches my runtime_error and if I call throwException() on ew, it
+//! // will throw a runtime_error
+//! auto ew = folly::try_and_catch<std::exception, std::runtime_error>([=]() {
+//! if (badThingHappens()) {
+//! throw std::runtime_error("ZOMG!");
+//! }
+//! });
+//!
+//! // This will catch the exception and if I call throwException() on ew, it
+//! // will throw a std::exception
+//! auto ew = folly::try_and_catch<std::exception, std::runtime_error>([=]() {
+//! if (badThingHappens()) {
+//! throw std::exception();
+//! }
+//! });
+//!
+//! // This will not catch the exception and it will be thrown.
+//! auto ew = folly::try_and_catch<std::runtime_error>([=]() {
+//! if (badThingHappens()) {
+//! throw std::exception();
+//! }
+//! });
+//! \endcode
+template <typename... Exceptions, typename F>
+exception_wrapper try_and_catch(F&& fn) {
+ return detail::try_and_catch_<F, Exceptions...>(std::forward<F>(fn));
+}
+} // folly
+
+#include <folly/ExceptionWrapper-inl.h>
+
+#undef FOLLY_REQUIRES
+#undef FOLLY_REQUIRES_DEF
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
#endif
projects / folly.git / blobdiff