At Friday 6/10/2006 16:14, Thomas Heller wrote:
> Currently ctypes can't play well with any C code that requires
use of setjmp
> as part of its API.
> libpng is one of those libraries.
>
I didn't know that setjmp/longjmp is actually used by production libraries
for error handling.
Using setjmp to report errors in a general library is, uhm, a bit
crazy at least!
C programmers are certainly crazy people :)
How is this pattern used in C? Do you call setjump() before each api call,
or do you call setjump once, and then do all the api calls? What do you do
when setjmp() returns != 0? Exit the program? Log a message? How do you
determine which call failed? How do you pass the jmp_buf that you passed to
setjmp() to the api call?
The setjmp must be on scope when a longjmp is called. Since there is
no endjmp/canceljmp, this in the practice means that you have to call
setjmp in *every* function that calls another one which may issue a longjmp.
There are other alternatives in plain C (cexcept:
http://cexcept.sourceforge.net/) but that wont help you with ctypes.
For ctypes, the only solution I can think of is to invent a new calling
convention, which will call setjmp() first internally before calling the
libpng api function...
May be reasonable - a non-zero in setjmp would raise a Python
exception. But perhaps a new calling convention is not needed: as you
need a way to indicate *which* argument is the jmp_buf, just a new
argument type would suffice. If you encounter one such thing in the
function.argtypes list, that means a setjmp is needed before calling
the actual function.
Gabriel Genellina
Softlab SRL
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