Re: [libmicrohttpd] race condition on 0.9.73

[Evgeny Grin]

Hi José,

On 28.09.2021 18:44, José Bollo wrote:
> > Function MHD_run_wait() was added for upcoming version 0.9.74, but it
> > does not return flag "need to re-run". MHD_get_timeout() already
> > serves for this purpose.
>
> I finally had time to look at this new function. It can be improved by
> returning a status telling if something was processed or not instead of
> just ok/error. This would allow to call it with a timeout of 0 until
> nothing is done.

It would be easy to implement such kind of loop just inside this 
function, but the idea of MHD_run_wait() is to avoid locking of all 
system resources only for HTTP processing, therefore after making full 
round of processing of all connection, the function returns for any 
other processing by application.

With fast enough connection (or connections) and slow CPU it is possible 
that MHD_get_timeout() returns zero for some period of time when data is 
arriving faster that CPU is able to process it (or the response is being 
sent faster than the response is being generated). Especially if 
connection is HTTPS.
With MHD_run_wait() you can get some kind fair distribution of CPU time 
for HTTP processing and for other needs.

It is expected that application may have something to process without 
locking and return to MHD_run_wait() as soon as other data is processed.

MHD_get_timeout() gives you better indication whether something needs to 
be processed than flag "something was processed".
It would be possible that nothing was processed, but next timeout is 
zero because some connection has been just expired.

--
Wishes,
Evgeny

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