Re: Multiple concurrent coprocesses

[Chet Ramey]

On 3/22/21 11:14 PM, Zachary Santer wrote:
>  > Something more than the trivial cases I've thrown at it. I'm interested in
>  > whether or not the code has deadlock problems in the presence of pipelines.
>
> I don't know if anonymous pipes 
> themselves always wait to fill a buffer before sending their contents on. 
> Am I getting your meaning, though? I don't see how this would be more of a 
> problem with multiple coprocesses than it is with one.

It's just more bookkeeping, and I'd want to make sure that bash takes
care of closing coproc file descriptors where necessary. I think it does,
but more real-world test cases are always nice.

Say you have a pipe file descriptor that's (inadvertently) shared by
more processes than intended. If that file descriptor is open for read,
the kernel won't send a SIGPIPE to a writer that anticipates getting
one. Similarly, if a stray file descriptor open for write exists, a
reader won't get the expected EOF. These situations can result in
deadlock.

The pipeline code passes around bitmaps of file descriptors to close to
handle this.

As I said, I think the multiple coprocs code takes care of these cases,
but it's good to be sure.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/