[geos-devel] Thread safe error handling

Pepijn Van Eeckhoudt pepijn at vaneeckhoudt.net
Mon Sep 9 00:43:51 PDT 2013

Hi Sandro,

I had a more in depth look at the code to see how this code be done. My
proposal would be to add an extended message handler signature like

typedef void (*GEOSMessageHandler_r)(GEOSContextHandle_t *handle, void
*userData, const char *fmt, ...);

and accompanying init and set...handler functions. The only real problem
I ran into is that we wont be able to implement the old handlers in
terms of the new ones since they're both variadic functions. That
implies that we'll need a mode flag in struct GEOSContextHandleInternal
and add conditionals around the handle->NOTICE and handle->ERROR calls.

Does the above acceptable to you?
Which version of C/C++ can I use. I'm thinking of hiding the details of
handle->NOTICE and handle->ERROR in a macro, but that would require
variadic macro support (i.e., c99 and/or c++11).


On za, 2013-09-07 at 15:32 +0200, Sandro Santilli wrote:
> On Sat, Sep 07, 2013 at 01:23:25AM +0200, Pepijn Van Eeckhoudt wrote:
> > Hi,
> > 
> > I'm using GEOS via the C api in libgpkg to implement geometry functions. I got the basics working now, but it feels like I had to jump through a lot of hoops to get the error handling set up reliably. The main problem I had was that there's no way to associate user data with the error and notice callbacks. Since this library may be used in a multi-threaded context I ended up having to use thread-local storage to store the error message. This feels more complicated than it should be.
> > 
> > Is there a simpler way to achieve the same result with the current API that I might have missed?
> Not really. If you have ideas for extending the interface in a backward
> compatible way, a patch would be accepted.
> --strk;
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