[geos-devel] Proposal: Thread safe CAPI

[Frank Warmerdam]

>> On Tue, Oct 14, 2008 at 11:12 AM, Chuck Thibert
>> <charles.thibert at ingres.com> wrote:
>>> Hi,
>>>
>>> I have been prototyping a thread safe CAPI.  I have attached a simple
>>> proposal/design intent.  I have sample executables and test data that
>>> will illustrate the thread issues but I don't want to flood the mailing
>>> list with them.  If the proposal attached looks decent to you all I'll
>>> create a new ticket and attach the code I have to that.

Chuck,

As defined, the GEOSHandle structure is public.  This means any change
in the layout or items in the GEOSHandle structure cannot be changed
without altering the ABI.

I would like to suggest altering the approach so that the structure
structure is allocated internally by initGEOS_TS() and only an opaque
handle would be returned.

eg.

   typedef void *GEOSHandle_t;

   GEOSHandle_t initGEOS_TS( GEOSMessageHandler notice_function,
                             GEOSMessageHandler error_function);

   void finishGEOS_TS( GEOSHandle_t *handle );

I think we should also at this point consider whether there is anything
else that we want to be able to control on a per-thread-context basis.
For instance, currently the C API only offers use of the default
geometry factory.  Would there be reasons to provide access to others?
Also, given recent discussions, allowing overloading of the memory
allocator might be of interest.

I'm quite supportive of this thread safety change, and the approach
seems quite practical. I'd like to see a "proper" RFC written up in
Trac and voted on.

PS. It isn't very important, but I think a name like GEOSContext_t
or even GEOSContextHandle_t would be better than GEOSHandle_t.  The
object is essentially an execution context/environment.

PPS. I'm not sure why there are GEOSversion_TS() and GEOS_jtsport_TS()
function that operate exactly like the non-TS version. I'd like to
suggest we only implement _TS() versions of function that need the
handle/context to operate.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent