Pipes and FIFOs

Hi all,
Just a quick question. I am pretty sure that both Pipe and FIFO IPC are
handled through Fsys buffers and do not use the physical disk, but would
like to confirm this. Does anyone know for sure that FIFOs are handled
using memory buffers and do not read and write to disk?

Thanks,
Marc.

Can’t be sure, but I think you are right. One thing I can say for sure though is
if you are not running Fsys (because you have no filesystem) you can still use
pipes by running Pipe (the pipe manager). In this case it couldn’t be writing to
the disk, could it?

Marc Desjardine wrote:

Hi all,
Just a quick question. I am pretty sure that both Pipe and FIFO IPC are
handled through Fsys buffers and do not use the physical disk, but would
like to confirm this. Does anyone know for sure that FIFOs are handled
using memory buffers and do not read and write to disk?

Thanks,
Marc.

I seem to recall long ago hearing Bill Flowers expound on
how Fsys would try to keep all FIFO data in buffers, but
that it was possble for data to be spilled to disk.
I’m not at all sure if this is/was true.


Previously, Marc Desjardine wrote in qdn.public.qnx4:

Hi all,
Just a quick question. I am pretty sure that both Pipe and FIFO IPC are
handled through Fsys buffers and do not use the physical disk, but would
like to confirm this. Does anyone know for sure that FIFOs are handled
using memory buffers and do not read and write to disk?

Thanks,
Marc.
\


Mitchell Schoenbrun --------- maschoen@pobox.com

Mitchell Schoenbrun <maschoen@pobox.com> wrote:

I seem to recall long ago hearing Bill Flowers expound on
how Fsys would try to keep all FIFO data in buffers, but
that it was possble for data to be spilled to disk.
I’m not at all sure if this is/was true.

It depends.

If you are running Pipe – the explicit pipe manager, all anonymous
pipes will go through it, and will never get spilled to disk.

If you are not runnign Pipe, or if you are using named pipes (FIFOs), your
data will go through Fsys. As such, the data in the will be put in Fsys’
cache. Most likely it will never be flushed to disk – but if the data
in the pipe gets really stale, and the rest of the Fsys cache gets demanded
for other use (heavy disk access), then it could happen.

-David

Previously, Marc Desjardine wrote in qdn.public.qnx4:
Hi all,
Just a quick question. I am pretty sure that both Pipe and FIFO IPC are
handled through Fsys buffers and do not use the physical disk, but would
like to confirm this. Does anyone know for sure that FIFOs are handled
using memory buffers and do not read and write to disk?

Thanks,
Marc.



\

Mitchell Schoenbrun --------- > maschoen@pobox.com


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