threaded-safe exception handling?

I'm thinking of implementing exception handling in C and extractly I have written a simple one. But it's not threaded-safe. Can you have me fix it, or is there any similar implementation for exception handling?

Code:

---

int __cm_jmp_pos = 0;
jmp_buf __cm_jmp_buf[128];

/* exception */
/******************************************************************************/
#define cm_try_begin() \
    do { \
        extern jmp_buf __cm_jmp_buf[128]; \
        extern int __cm_jmp_pos; \
        int __jmp_ret; \
        if((__jmp_ret = setjmp(__cm_jmp_buf[__cm_jmp_pos++])) == 0) \
        {

#define cm_try_catch(exception) \
        } \
        else if(__jmp_ret == (exception)) \
        { \
            extern int __cm_jmp_pos; \
            __cm_jmp_pos--; \

#define cm_try_end() \
        } \
        else \
        { \
            extern int __cm_jmp_pos; \
            __cm_jmp_pos--; \
            cm_try_throw(__jmp_ret); \
        } \
    } while(0)

#define cm_try_throw(exception) \
    do { \
        extern jmp_buf __cm_jmp_buf[128]; \
        extern int __cm_jmp_pos; \
        if(__cm_jmp_pos > 0) \
        { \
            longjmp(__cm_jmp_buf[__cm_jmp_pos - 1], (exception)); \
        } \
        else \
        { \
            fprintf(stderr, "unhandled exception %d at file %s, line %d\n", \
                    (exception), \
                    __FILE__, \
                    __LINE__); \
            exit(EXIT_FAILURE); \
        } \
    } while(0)

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Unrelated to your question, but you should not use names that have leading underscores. In most cases these are reserved for the implementation (in all cases two leading underscores are reserved). Your compiler, for example, is allowed to create something called __cm_jmp_buf for its own uses because it knows you're not supposed to. You can use another convention to mean "hands off", such as trailing underscores, or what have you.

If you are on Windows platforms ... You should also investigate how their native SEH works...

Structured Exception Handling (Windows)

You will most likely discover that most of what you're doing is already implemented as a native part of the OS.

Quote:

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Originally Posted by CommonTater

If you are on Windows platforms ... You should also investigate how their native SEH works...

Structured Exception Handling (Windows)

You will most likely discover that most of what you're doing is already implemented as a native part of the OS.

---

working under linux...

The simplest way to make what you already have thread-safe is to use a thread-specific array instead of a global array.

Every time I've tried implementing or using such a system in C I've always hated it. Down this path is madness ;)

I think exceptions were one of the things that killed cfront, the original "pretranslator" that turned C++ code into something that was compileable by a C compiler. It's probably best that you learn from that failure.

Quote:

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Down this path is madness

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QFT

It is true that some problems led to the abandonment of "CFront", but the C++ exception handling mechanism is possible within standard C. The Comeau C/C++ produces such a bit of code.

Such a beast will however require a lot more than what anyone could manage using nothing but the C standard preprocessor.

And personally, I think using jump tables is starting at madness, who knows where you may end up?

Soma