It seems highly unlikely that gettext() can be relied on to be
async-signal-safe. psql used to understand that, but someone got
it wrong long ago in the src/bin/scripts/ version of handle_sigint,
and then the bad idea was perpetuated when those two versions were
unified into src/fe_utils/cancel.c.
I'm unsure why there have not been field complaints about this
... maybe gettext() is signal-safe once it's translated at least
one message? But we have no business assuming any such thing.
In cancel.c (v13 and up), I preserved our ability to localize
"Cancel request sent" messages by invoking gettext() before
the signal handler is set up. In earlier branches I just made
src/bin/scripts/ not localize those messages, as psql did then.
(Just for extra unsafety, the src/bin/scripts/ version was
invoking fprintf() from a signal handler. Sigh.)
Noted while fixing signal-safety issues in PQcancel() itself.
Back-patch to all supported branches.
Discussion: https://postgr.es/m/2937814.1641960929@sss.pgh.pa.us
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