Thu, 14 Dec 2000 Eric Peterson wrote:
> Hi,
>
> I'm trying to use RT-Linux (2.2) RT-FIFOs, and I have come up against an
> apparent limitation with them: they only allow one writer (on the Linux
> side) to open the FIFO. I would like multiple processes to be able to
> open (and write to) a single RT task via a FIFO.
>
> Any suggestions?
There is an inherent implementation/semantics issue with multiple writer FIFOs;
how do you guarantee that data from writers is not mixed up?
1) Require writers to use a single write() call for data blocks that
need to be contiguous.
- Implementation mess for the "writer sleeps on full buffer"
case.
- Breaks if the writer uses buffered write operations, such as
stdio fwrite().
- Requires some kind of multi-open extension, similar to that
used by some sound drivers.
- This design is not POSIX compliant...
2) Design an API extension that deals with multiple writers using some
higher level approach than the write() interface.
- This actually doesn't change anything, except that it doesn't
fool users into believing that they're dealing with a POSIX
compliant interface.
- It doesn't even help you much in cleaning up the
implementation.
In short, you probably shouldn't use the RT-FIFO interface at all for multiple
writers - sockets or QNX style messages would probably be more right for the
job. Unfortunately, I'm not enough up to date with RTL to point you at
available solutions, but I think there are some.
//David
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