Re: [PATCH] tee: Add --pipe-check to allow instantly detecting closed outputs

[Carl Edquist]

On Tue, 29 Nov 2022, Arsen Arsenović wrote:

> The issue here isn't the compilers hanging, it's tee living longer than 
> all the compilers do because it's stdin doesn't EOF (it'd be preferable 
> for it to only live as long as the last of the compilers).
>
> I can imagine attempting to implement this with enough pipe and fd 
> redirection magic, but I'm not sure how (in)elegant that becomes.

It sounds like one way or another you want to copy your endless but 
intermittent input to multiple output pipes, but you want to quit as soon 
as all the output pipes become broken.

To me, tee sounds like exactly the place to do that.  Otherwise, you'd 
have to add the broken-pipe detection (as in your patch) to your own 
program, along with the rest of tee's basic functionality  :)

It would be one thing if you controlled the programs that consume the 
input (you could have them handle 'heartbeats' in the input stream, and 
once these programs terminate, the heartbeats would trip on the broken 
pipe).  (However (in)elegant that becomes to implement...)

But if you don't have control over that, the fundamental problem is 
detecting broken pipes *without writing to them*, and I don't think that 
can be solved with any amount of extra pipes and fd redirection...

Carl