[bug-gawk] Behavior of fflush with SIGPIPE on stdout

[alexandre.ferrieux]

Hi,

After a recent OS upgrade on the only machine where I do heavy awk work, I got caught by a regression dated 2013 in 
gawk, namely the one about "ignored SIGPIPE".

Basically, what happens is that the ages-old unix idiom

        infinite-data-source | filter | head

fails if "filter" is a post-2013 gawk using explicit fflush().

Example:

        yes | awk '{print;fflush(stdout)}' | head

Of course this is a cooked example, but I guess you can imagine the real-life situations where explicit fflush() is 
needed, with appropriate task-dependent granularity, for performance and interactivity.


Looking at the comments in main.c, I do not see whether this regression was 
considered or not.
It rather looks like the idea of "writing to a pipe" was generally thought about in the context of additional fds 
("print ... | cmd"), but that the simple, obvious case of

        - gawk used as a unix filter
        - stdout is a pipe

was overlooked.

I assume this is just a shallow search on my part; thanks in advance for giving pointers to the relevant discussion and 
release notes announcing this regression, and the idiomatic ways to avoid it.

-Alex

PS: Note that crude versions of awk like "mawk" don't have the issue, but I 
need gawk for the obvious reasons.


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