Re: Examples of concurrent coproc usage?

[Carl Edquist]

On Thu, 18 Apr 2024, Martin D Kealey wrote:

> On Wed, 17 Apr 2024, Chet Ramey wrote:
>
> > It has to do it that way to find the delimiter on a non-seekable file 
> > descriptor, since it has to leave everything it didn't consume 
> > available on stdin.
>
> Has anyone tried asking any of the kernel teams (Linux, BSD, or other) 
> to add a new system call such as readln() or readd()?

You mean, specifically in order to implement a slightly-more-efficient 
'read' builtin in the shell?


> I envisage this working like stty cooked mode works on a tty, except it 
> would also work on files, pipes, and sockets: you'd get back *at most* 
> as many bytes as you ask for, but you may get fewer if a delimiter is 
> found. The delimiter is consumed (and returned in the buffer), but 
> everything following a delimiter is left available for a subsequent 
> read.

One downside is you'd end up with a system call for each token, which is 
only a little bit better than the 'read' builtin read(2)'ing 1 byte at a 
time.  If your program / shell script is going to be processing a long 
stream of tokens, it's just going to be more efficient to read(2) a block 
at a time and do the tokenizing in userspace.  And with any luck you can 
find an appropriate command line utility to do that for you, rather than 
relying on the shell's 'read' builtin.

(Or for your own programs, use getline(3)/getdelim(3), as Chet mentioned.)

Carl