LongJump.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#if (defined(__AUTORTFM) && __AUTORTFM)
 
#include "BuildMacros.h"
#include "Utils.h"
 
#include <setjmp.h>
 
#if AUTORTFM_PLATFORM_WINDOWS && AUTORTFM_ARCHITECTURE_X64 // We only have an Windows X64 implementation right now.
#define AUTORTFM_USE_SAVE_RESTORE_CONTEXT 1
#else
#define AUTORTFM_USE_SAVE_RESTORE_CONTEXT 0
#endif
 
namespace AutoRTFM
{
 
// setjmp/longjmp that doesn't do any unwinding (no C++ destructor calls, no messing with OS
// signal states - just saving/restoring CPU state). Although it's the setjmp/longjmp everyone
// knows and loves, it's exposed as a try/catch/throw API to make it less error-prone.
class FLongJump
{
public:
    FLongJump()
    {
        memset(this, 0, sizeof(*this));
    }
 
    template<typename TTryFunctor, typename TCatchFunctor>
    void TryCatch(const TTryFunctor& TryFunctor, const TCatchFunctor& CatchFunctor);
    
    [[noreturn]] void Throw();
    
private:
#if AUTORTFM_USE_SAVE_RESTORE_CONTEXT
    static bool SaveContext(void* Buffer);
    [[noreturn]] static void RestoreContext(void* Context);
    static constexpr size_t ContextSize = 256;
    static constexpr size_t ContextAlignment = 16;
    alignas(ContextAlignment) std::byte Context[ContextSize];
#else
    jmp_buf JmpBuf;
#endif
    bool bIsSet;
};
 
template<typename TTryFunctor, typename TCatchFunctor>
void FLongJump::TryCatch(const TTryFunctor& TryFunctor, const TCatchFunctor& CatchFunctor)
{
    AUTORTFM_ASSERT(!bIsSet);
#if AUTORTFM_USE_SAVE_RESTORE_CONTEXT
    if (!SaveContext(Context))
#elif AUTORTFM_PLATFORM_WINDOWS
    if (!setjmp(JmpBuf))
#else
    if (!_setjmp(JmpBuf))
#endif
    {
        bIsSet = true;
        TryFunctor();
        bIsSet = false;
    }
    else
    {
        AUTORTFM_ASSERT(bIsSet);
        bIsSet = false;
        CatchFunctor();
    }
}
 
inline void FLongJump::Throw()
{
    AUTORTFM_ASSERT(bIsSet);
#if AUTORTFM_USE_SAVE_RESTORE_CONTEXT
    RestoreContext(Context);
#elif AUTORTFM_PLATFORM_WINDOWS
    longjmp(JmpBuf, 1);
#else
    _longjmp(JmpBuf, 1);
#endif
}
 
} // namespace AutoRTFM
 
#endif // (defined(__AUTORTFM) && __AUTORTFM)