Re: Realtime safe signalling?

[Paul Davis <paul linuxaudiosystems com>]

>The writer of the manual could not guarantee how will write(2) behave,
>since the code is system-independent. Linux does protect pipe with
>a semaphore. On single-CPU, it can never be waited for unless the buffer

the FIFO semaphore is not the central issue, particular if the FIFO is
being used for single reader/single writer communication.

the problem is if the FIFO is created in a filesystem that is updating
metadata (such as modification time or a journal), where access to the
FIFO will require taking the filesystem lock too.

it is for this reason that all packaged version of JACK
(jackit.sf.net) create a tmpfs filesystem specifically as a place to
create the FIFOs used by jackd when communicating with clients. and
JACK is about as hard-RT as linux apps get.

--p