/*
- * Copyright 2014 Facebook, Inc.
+ * Copyright 2016 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_EXCEPTIONWRAPPER_H
-#define FOLLY_EXCEPTIONWRAPPER_H
+#pragma once
-#include <cassert>
#include <exception>
#include <memory>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include <folly/ExceptionString.h>
+#include <folly/FBString.h>
#include <folly/detail/ExceptionWrapper.h>
namespace folly {
* 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. exception_wrapper is flexible enough to accept
- * any std::exception. For performance sensitive applications, exception_wrapper
- * exposes a get() function. These users can use dynamic_cast to retrieve
- * desired derived types (hence the decision to limit usage to just
- * std::exception instead of void*).
+ * 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:
*
*
* // Thread2: Exceptions are bad!
* void processResult() {
- * auto ep = globalExceptionWrapper.get();
- * if (ep) {
- * auto faceplant = dynamic_cast<FacePlantException*>(ep);
- * if (faceplant) {
- * LOG(ERROR) << "FACEPLANT";
- * } else {
- * auto failwhale = dynamic_cast<FailWhaleException*>(ep);
- * if (failwhale) {
+ * globalExceptionWrapper.with_exception(
+ * [&](FacePlantException& faceplant) {
+ * LOG(ERROR) << "FACEPLANT";
+ * }) ||
+ * globalExceptionWrapper.with_exception(
+ * [&](FailWhaleException& failwhale) {
* LOG(ERROR) << "FAILWHALE!";
- * }
- * }
- * }
+ * }) ||
+ * LOG(FATAL) << "Unrecognized exception";
* }
*
*/
class exception_wrapper {
+ protected:
+ template <typename Ex>
+ struct optimize;
+
public:
- exception_wrapper() : throwfn_(nullptr) { }
+ 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;
+ }
+
+ // 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);
+ }
+
+ explicit exception_wrapper(std::exception_ptr eptr) {
+ assign_eptr(eptr);
+ }
+
+ // If the exception_wrapper does not contain an exception, std::terminate()
+ // is invoked to assure the [[noreturn]] behaviour.
+ [[noreturn]] void throwException() const;
+
+ explicit operator bool() const {
+ return item_ || eptr_;
+ }
- void throwException() const {
- if (throwfn_) {
- throwfn_(item_.get());
+ // 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_;
}
}
- std::exception* get() { return item_.get(); }
- const std::exception* get() const { return item_.get(); }
+ bool operator!=(const exception_wrapper& a) const {
+ return !(*this == a);
+ }
+
+ // 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;
+ fbstring class_name() const;
+
+ 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 (typename std::decay<Ex>::type&) {
+ return true;
+ } catch (...) {
+ // fall through
+ }
+ }
+ return false;
+ }
- std::exception* operator->() { return get(); }
- const std::exception* operator->() const { return get(); }
+ template <class F>
+ bool with_exception(F&& f) {
+ using arg_type = typename functor_traits<F>::arg_type_decayed;
+ return with_exception<arg_type>(std::forward<F>(f));
+ }
+
+ template <class F>
+ bool with_exception(F&& f) const {
+ using arg_type = typename functor_traits<F>::arg_type_decayed;
+ return with_exception<const arg_type>(std::forward<F>(f));
+ }
- std::exception& operator*() { assert(get()); return *get(); }
- const std::exception& operator*() const { assert(get()); return *get(); }
+ // 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);
+ }
- explicit operator bool() const { return get(); }
+ // 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);
+ }
+
+ // 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 {
+ if (*this) {
+ throwException();
+ }
+ } catch (typename std::decay<Ex>::type& e) {
+ f(e);
+ return true;
+ } catch (...) {
+ // fall through
+ }
+ return false;
+ }
std::exception_ptr getExceptionPtr() const {
+ if (eptr_) {
+ return eptr_;
+ }
+
try {
- throwException();
+ if (*this) {
+ throwException();
+ }
} catch (...) {
return std::current_exception();
}
return std::exception_ptr();
}
- protected:
+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 <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();
+ }
+
+ void assign_eptr(std::exception_ptr eptr) {
+ this->eptr_ = eptr;
+ }
+
+ // 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*);
+ 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:
+ template <typename F>
+ struct functor_traits {
+ template <typename T>
+ struct impl;
+ template <typename C, typename R, typename A>
+ struct impl<R(C::*)(A)> { using arg_type = A; };
+ template <typename C, typename R, typename A>
+ struct impl<R(C::*)(A) const> { using arg_type = A; };
+ using functor_decayed = typename std::decay<F>::type;
+ using functor_op = decltype(&functor_decayed::operator());
+ using arg_type = typename impl<functor_op>::arg_type;
+ using arg_type_decayed = typename std::decay<arg_type>::type;
+ };
+
+ // 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 (Ex& e) {
+ f(e);
+ return true;
+ } catch (...) {
+ // fall through
+ }
+ }
+ return false;
+ }
};
template <class T, class... Args>
return ew;
}
+// For consistency with exceptionStr() functions in String.h
+fbstring exceptionStr(const exception_wrapper& ew);
+
/*
* 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
try_and_catch() : Base() {}
+ 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);
+ }
+
+ 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;
+ }
+
template <typename F>
void call_fn(F&& fn) {
try {
Base::call_fn(std::move(fn));
- } catch (const LastException& e) {
- this->item_ = std::make_shared<LastException>(e);
- this->throwfn_ = folly::detail::Thrower<LastException>::doThrow;
+ } catch (LastException& e) {
+ if (typeid(e) == typeid(LastException&)) {
+ assign_exception(e, std::current_exception());
+ } else {
+ exception_wrapper::assign_eptr(std::current_exception(), e);
+ }
}
}
};
template<>
class try_and_catch<> : public exception_wrapper {
public:
- try_and_catch() {}
+ try_and_catch() = default;
protected:
template <typename F>
fn();
}
};
-}
-#endif
+
+} // folly
projects / folly.git / blobdiff