[Xenomai] --session= is not a recognized option when using Posix skin

[Xenomai] --session= is not a recognized option when using Posix skin

[Giulio Moro]

On Xenomai 3.0.5, if I compile a program with the posix skin and I try to run it with `--session=mySessionName`, it errors as it cannot find the `--session` option. This is strange, because main() is definitely getting wrapped: if I run `--help`, it does show some Xenomai command-line options:
--main-prio=<prio>		main thread priority
--print-buffer-size=<bytes>	size of a print relay buffer (16k)
--print-buffer-count=<num>	number of print relay buffers (4)
--print-buffer-syncdelay=<ms>	max delay of output synchronization (100 ms)
--cpu-affinity=<cpu[,cpu]...>	set CPU affinity of threads
--[no-]sanity			disable/enable sanity checks
--verbose[=level] 		set verbosity to desired level [=1]
--silent, --quiet 		same as --verbose=0
--trace[=level] 		set tracing to desired level [=1]
--version			get version information
--dump-config			dump configuration settings
--help				display help

When I build a program with the Alchemy skin, then `--session` works just fine, and `--help` displays a number of additional options:
--alchemy-clock-resolution=<ns> tick value (default 1ns, tickless)
--mem-pool-size=<size[K|M|G]> 	size of the main heap
--no-registry			suppress object registration
--shared-registry		enable public access to registry
--registry-root=<path>		root path of registry
--session=<label>[/<group>]	enable shared session

I am linking with `/usr/xenomai/bin/xeno-config --ldflags --skin=posix`, which gives the following on my system (Beaglebone Black, kernel 4.4.87)
-Wl,--no-as-needed -Wl,@/usr/xenomai/lib/cobalt.wrappers -Wl,@/usr/xenomai/lib/modechk.wrappers  /usr/xenomai/lib/xenomai/bootstrap.o -Wl,--wrap=main -Wl,--dynamic-list=/usr/xenomai/lib/dynlist.ld -L/usr/xenomai/lib -lcobalt -lmodechk -lpthread -lrt

Thanks,
Giulio

Re: [Xenomai] --session= is not a recognized option when using Posix skin

[Philippe Gerum]

On 10/06/2017 03:58 AM, Giulio Moro wrote:
> On Xenomai 3.0.5, if I compile a program with the posix skin and I try to run it with `--session=mySessionName`, it errors as it cannot find the `--session` option. This is strange, because main() is definitely getting wrapped: if I run `--help`, it does show some Xenomai command-line options:
> --main-prio=<prio>		main thread priority
> --print-buffer-size=<bytes>	size of a print relay buffer (16k)
> --print-buffer-count=<num>	number of print relay buffers (4)
> --print-buffer-syncdelay=<ms>	max delay of output synchronization (100 ms)
> --cpu-affinity=<cpu[,cpu]...>	set CPU affinity of threads
> --[no-]sanity			disable/enable sanity checks
> --verbose[=level] 		set verbosity to desired level [=1]
> --silent, --quiet 		same as --verbose=0
> --trace[=level] 		set tracing to desired level [=1]
> --version			get version information
> --dump-config			dump configuration settings
> --help				display help
> 
> When I build a program with the Alchemy skin, then `--session` works just fine, and `--help` displays a number of additional options:
> --alchemy-clock-resolution=<ns> tick value (default 1ns, tickless)
> --mem-pool-size=<size[K|M|G]> 	size of the main heap
> --no-registry			suppress object registration
> --shared-registry		enable public access to registry
> --registry-root=<path>		root path of registry
> --session=<label>[/<group>]	enable shared session
> 
> I am linking with `/usr/xenomai/bin/xeno-config --ldflags --skin=posix`, which gives the following on my system (Beaglebone Black, kernel 4.4.87)
> -Wl,--no-as-needed -Wl,@/usr/xenomai/lib/cobalt.wrappers -Wl,@/usr/xenomai/lib/modechk.wrappers  /usr/xenomai/lib/xenomai/bootstrap.o -Wl,--wrap=main -Wl,--dynamic-list=/usr/xenomai/lib/dynlist.ld -L/usr/xenomai/lib -lcobalt -lmodechk -lpthread -lrt
> 

This feature is implemented by the so-called "copperplate" interface
libalchemy depends on. The POSIX API does not depend on copperplate, so
you don't have support for multi-process sessions when linking against
libcobalt exclusively. See there http://xenomai.org/start-here/.

-- 
Philippe.

Re: [Xenomai] --session= is not a recognized option when using Posix skin

[Giulio Moro]

> The POSIX API does not depend on copperplate, so
> you don't have support for multi-process sessions when linking against
> libcobalt exclusively. 

Ok. All we need this for is to prevent multiple instances of our program to be started at the same time. What would you suggest as the best way to check for the existence of a given real-time task using the POSIX API? We could just grep /proc/xenomai/sched/stat, or is there a better solution?

Thanks,
Giulio

Re: [Xenomai] --session= is not a recognized option when using Posix skin

[Henning Schild]

On Sat, 7 Oct 2017 01:33:06 +0000
Giulio Moro <g.moro@qmul.ac.uk> wrote:

> > The POSIX API does not depend on copperplate, so
> > you don't have support for multi-process sessions when linking
> > against libcobalt exclusively.   
> 
> Ok. All we need this for is to prevent multiple instances of our
> program to be started at the same time. What would you suggest as the
> best way to check for the existence of a given real-time task using
> the POSIX API? We could just grep /proc/xenomai/sched/stat, or is
> there a better solution?

In the init-phase your process is probably not real-time yet. So you
can implement a PID-file-based singleton or something alike. Or offload
that task to systemd or whatever you use as init-system.

Henning

> Thanks,
> Giulio
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