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

[David J Myers]

Since switching to MHD_USE_THREAD_PER_CONNECTION, after the system has been
running for a number of hours, I'm getting the following error message:-
"Failed to create a thread: Resource temporarily unavailable"
I can't tell if this a shortage of memory resources or thread handles or
what.
Is there something I need to do to cause threads to be destroyed after use? 
BR
David



-----Original Message-----
From: Christian Grothoff [mailto:address@hidden 
Sent: 01 February 2013 10:55
To: David J Myers
Cc: 'libmicrohttpd development and user mailinglist'
Subject: Re: ContentReaderCallback has changed behaviour in latest releases

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
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