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/**
* @file llexception.h
* @author Nat Goodspeed
* @date 2016-06-29
* @brief Types needed for generic exception handling
*
* $LicenseInfo:firstyear=2016&license=viewerlgpl$
* Copyright (c) 2016, Linden Research, Inc.
* $/LicenseInfo$
*/
#if ! defined(LL_LLEXCEPTION_H)
#define LL_LLEXCEPTION_H
#include "always_return.h"
#include <stdexcept>
#include <boost/exception/exception.hpp>
#include <boost/throw_exception.hpp>
#include <boost/current_function.hpp>
// "Found someone who can comfort me
// But there are always exceptions..."
// - Empty Pages, Traffic, from John Barleycorn (1970)
// https://www.youtube.com/watch?v=dRH0CGVK7ic
/**
* LLException is intended as the common base class from which all
* viewer-specific exceptions are derived. Rationale for why it's derived from
* both std::exception and boost::exception is explained in
* tests/llexception_test.cpp.
*
* boost::current_exception_diagnostic_information() is quite wonderful: if
* all we need to do with an exception is log it, in most places we should
* catch (...) and log boost::current_exception_diagnostic_information().
* See CRASH_ON_UNHANDLED_EXCEPTION() and LOG_UNHANDLED_EXCEPTION() below.
*
* There may be circumstances in which it would be valuable to distinguish an
* exception explicitly thrown by viewer code from an exception thrown by
* (say) a third-party library. Catching (const LLException&) supports such
* usage. However, most of the value of this base class is in the
* diagnostic_information() available via Boost.Exception.
*/
struct LLException:
public std::runtime_error,
public boost::exception
{
LLException(const std::string& what):
std::runtime_error(what)
{}
};
/**
* The point of LLContinueError is to distinguish exceptions that need not
* terminate the whole viewer session. In general, an uncaught exception will
* be logged and will crash the viewer. However, though an uncaught exception
* derived from LLContinueError will still be logged, the viewer will attempt
* to continue processing.
*/
struct LLContinueError: public LLException
{
LLContinueError(const std::string& what):
LLException(what)
{}
};
/**
* Please use LLTHROW() to throw viewer exceptions whenever possible. This
* enriches the exception's diagnostic_information() with the source file,
* line and containing function of the LLTHROW() macro.
*/
#define LLTHROW(x) \
do { \
/* Capture the exception object 'x' by value. (Exceptions must */ \
/* be copyable.) It might seem simpler to use */ \
/* BOOST_THROW_EXCEPTION(annotate_exception_(x)) instead of */ \
/* three separate statements, but: */ \
/* - We want to throw 'x' with its original type, not just a */ \
/* reference to boost::exception. */ \
/* - To return x's original type, annotate_exception_() would */ \
/* have to be a template function. */ \
/* - We want annotate_exception_() to be opaque. */ \
/* We also might consider embedding BOOST_THROW_EXCEPTION() in */ \
/* our helper function, but we want the filename and line info */ \
/* embedded by BOOST_THROW_EXCEPTION() to be the throw point */ \
/* rather than always indicating the same line in */ \
/* llexception.cpp. */ \
auto exc{x}; \
annotate_exception_(exc); \
BOOST_THROW_EXCEPTION(exc); \
/* Use the classic 'do { ... } while (0)' macro trick to wrap */ \
/* our multiple statements. */ \
} while (0)
void annotate_exception_(boost::exception& exc);
/// Call this macro from a catch (...) clause
#define CRASH_ON_UNHANDLED_EXCEPTION(CONTEXT) \
crash_on_unhandled_exception_(__FILE__, __LINE__, BOOST_CURRENT_FUNCTION, CONTEXT)
void crash_on_unhandled_exception_(const char*, int, const char*, const std::string&);
/// Call this from a catch (const LLContinueError&) clause, or from a catch
/// (...) clause in which you do NOT want the viewer to crash.
#define LOG_UNHANDLED_EXCEPTION(CONTEXT) \
log_unhandled_exception_(__FILE__, __LINE__, BOOST_CURRENT_FUNCTION, CONTEXT)
void log_unhandled_exception_(const char*, int, const char*, const std::string&);
/*****************************************************************************
* Structured Exception Handling
*****************************************************************************/
// this is used in platform-generic code -- define outside #if LL_WINDOWS
struct Windows_SEH_exception: public LLException
{
Windows_SEH_exception(const std::string& what): LLException(what) {}
};
namespace LL
{
namespace seh
{
#if LL_WINDOWS //-------------------------------------------------------------
void fill_stacktrace(std::string& stacktrace, U32 code);
// wrapper around caller's U32 filter(U32 code, struct _EXCEPTION_POINTERS*)
// filter function: capture a stacktrace, if possible, before forwarding the
// call to the caller's filter() function
template <typename FILTER>
U32 filter_(std::string& stacktrace, FILTER&& filter,
U32 code, struct _EXCEPTION_POINTERS* exptrs)
{
// By the time the handler gets control, the stack has been unwound,
// so report the stack trace now at filter() time.
fill_stacktrace(stacktrace, code);
return std::forward<FILTER>(filter)(code, exptrs);
}
template <typename TRYCODE, typename FILTER, typename HANDLER>
auto catcher_inner(std::string& stacktrace,
TRYCODE&& trycode, FILTER&& filter, HANDLER&& handler)
{
__try
{
return std::forward<TRYCODE>(trycode)();
}
__except (filter_(stacktrace,
std::forward<FILTER>(filter),
GetExceptionCode(), GetExceptionInformation()))
{
return always_return<decltype(trycode())>(
std::forward<HANDLER>(handler), GetExceptionCode(), stacktrace);
}
}
// triadic variant specifies try(), filter(U32, struct _EXCEPTION_POINTERS*),
// handler(U32, const std::string& stacktrace)
// stacktrace may or may not be available
template <typename TRYCODE, typename FILTER, typename HANDLER>
auto catcher(TRYCODE&& trycode, FILTER&& filter, HANDLER&& handler)
{
// Construct and destroy this stacktrace string in the outer function
// because we can't do either in the function with __try/__except.
std::string stacktrace;
return catcher_inner(stacktrace,
std::forward<TRYCODE>(trycode),
std::forward<FILTER>(filter),
std::forward<HANDLER>(handler));
}
// common_filter() handles the typical case in which we want our handler
// clause to handle only Structured Exceptions rather than explicitly-thrown
// C++ exceptions
U32 common_filter(U32 code, struct _EXCEPTION_POINTERS*);
// dyadic variant specifies try(), handler(U32, stacktrace), assumes common_filter()
template <typename TRYCODE, typename HANDLER>
auto catcher(TRYCODE&& trycode, HANDLER&& handler)
{
return catcher(std::forward<TRYCODE>(trycode),
common_filter,
std::forward<HANDLER>(handler));
}
// monadic variant specifies try(), assumes default filter and handler
template <typename TRYCODE>
auto catcher(TRYCODE&& trycode)
{
return catcher(std::forward<TRYCODE>(trycode), rethrow);
}
[[noreturn]] void rethrow(U32 code, const std::string& stacktrace);
#else // not LL_WINDOWS -----------------------------------------------------
template <typename TRYCODE, typename FILTER, typename HANDLER>
auto catcher(TRYCODE&& trycode, FILTER&&, HANDLER&&)
{
return std::forward<TRYCODE>(trycode)();
}
template <typename TRYCODE, typename HANDLER>
auto catcher(TRYCODE&& trycode, HANDLER&&)
{
return std::forward<TRYCODE>(trycode)();
}
template <typename TRYCODE>
auto catcher(TRYCODE&& trycode)
{
return std::forward<TRYCODE>(trycode)();
}
#endif // not LL_WINDOWS -----------------------------------------------------
} // namespace LL::seh
} // namespace LL
#endif /* ! defined(LL_LLEXCEPTION_H) */
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