[Jack-Devel] Port number limitation

John Rigg jd at jrigg.co.uk
Wed Aug 21 22:52:13 CEST 2019


On Mon, Aug 19, 2019 at 08:54:04PM +0200, Hannes Helmholz wrote:
> I have noticed the JACK server limitation of port numbers in some
> specific applications ("Maximum number of output ports is reached for
> application ref = 2"). I have noticed the "-p" / "--port-max" parameter
> and was able to artificially scale down or up the available number. But,
> I seem to have reached and upper limit at around 800. Due to possibly
> already existing ports like system input and output I am not certain of
> the exact number.

jack_lsp should show a list of all ports.
 
> To be fair, the available number is high enough for general use cases
> (also for me). But in these certain conditions it definitely limits my
> possibilities without an apparent workaround.
> 
> Is there a way monitor if the port-max is passed correctly? Or where the
> limitation arises otherwise? Or how to possibly circumvent it?

In jack2 (don't know about jack1) PORT_NUM_MAX is set in
JackConstants.h. It's currently set to 4096.

There are other numbers in JackConstants.h like DRIVER_PORT_NUM
(currently 256 which is too small for multiple MADI cards,
for example).

If you can't get enough ports you might have to raise one or
more of those numbers and recompile.

John



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