[QGIS-Developer] QGIS Server plugins and thread safety

[Luigi Pirelli]

I didn't follow, shared cache is a solved problem for the server?
Luigi Pirelli

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On 19 November 2017 at 10:34, Alessandro Pasotti <apasotti at gmail.com> wrote:
> Hi,
>
> mi recent experiments with multi-threaded python wrappers for QGIS server
> showed a critical flaw in my original implementation of the server plugins.
>
> First, I want to stress that this is not a problem in FCGI server
> implementation but only if the server is used directly from python in a
> multi threaded server implementation.
>
> The problem is that the server interface that exposes the request handler is
> a static property of the interface, that is changed on every request.
> This means that there is a race condition in setting/accessing the handler
> from a plugin filter, and that a plugin filter might access to the handler
> for a wrong request.
>
> The solution is to pass the request handler (or the request and/or response
> objects depending on the filter) to the plugin filters and leave the
> interface for static properties only.
>
> This would be a big API change for the server interface and filters and I'm
> not sure we have time/resources to do that now.
>
> As an alternative we could simply document the issue and change the testing
> code to create a new server instance to server every request (to be
> verified, and with consitent performance degradation).
>
> What's your opinion about this issue?
>
> BTW,  tomorrow I'll file a ticket for this problem.
>
> --
> Alessandro Pasotti
> w3:   www.itopen.it
>
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