Re: Why sourcing a file is not faster than doing a loop with eval, zle -N

[Bart Schaefer <schaefer@brasslantern.com>]

This is now WELL into zsh-workers territory, please direct replies there
rather than to the -users list.

On Jun 19,  5:16pm, Stephane Chazelas wrote:
}
} That defeats a benefit of stdio saving read() systems calls by
} reading in chunk if we end up doing one system call per byte
} anyway.

Unfortunately we need to read from stdio one byte at a time, and
as far as I know there is no way to "ask" stdio whether it is still
working on a buffer, or is instead going to refill its buffer (and
therefore possibly block) on the next attempted getc() -- and to
find out would likely be more expensive than doing the system call.

Also stdio is *itself* not re-entrant, so we have to control signals
around all stdio operations.

Just to demonstrate why the signal handling is necessary; consider
this:

% echo $(trap '' INT; sleep 100)

That shell is now un-interruptible for 100 seconds, because readoutput()
does not do signal management around its fgetc() calls.  Worse, if you
type ^Z the sleep is silently suspended and the parent is hung forever.