Re: [libmicrohttpd] ContentReaderCallback has changed behaviour in latest releases

[Christian Grothoff]

On 02/01/2013 11:32 AM, David J Myers wrote:
> My server must stream to a number of concurrent clients. Does that not
> therefore mean that I need a multi-threaded mode, not the single-threaded
> external-select mode?
External-select can handle up to 1k concurrent clients.
> If I use the thread-per_connection mode, what is the consequence of
> returning zero from the callback instead of blocking? Does it create a new
> thread for the next callback?
No, MHD will just call the callback instantly again.
> If I use the thread-pool mode, I can't return zero from the callback, but
> what would be the consequence of blocking in this mode? This is my preferred
> mode.
In thread-pool mode, blocking would cause all other connections that are 
processed by the same thread to stall.  So that's the worst kind of 
behavior as the other connections might have data ready.  Thus, the 
thread pool mode must only be used if the callbacks are "virtually 
non-blocking" (by "virtually", I mean to say that I'd not necessarily 
count disk IO operations in this).  Note that *all* modes can support 
concurrent clients; the only fundamental limitation (with respect to 
performance) of the select/poll modes is that they only use a single core.


Happy hacking!

Christian