Avoid calling gettext() in signal handlers.

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

diff --git a/src/fe_utils/cancel.c b/src/fe_utils/cancel.c
index 49bdc6aca197f7519fa3d90ff1a864b1d959c821..d430866758f887ad805e7b8f0d9213401bfdd089 100644 (file)
--- a/src/fe_utils/cancel.c
+++ b/src/fe_utils/cancel.c
@@ -42,6 +42,13 @@
  */
 static PGcancel *volatile cancelConn = NULL;
 
+/*
+ * Predetermined localized error strings --- needed to avoid trying
+ * to call gettext() from a signal handler.
+ */
+static const char *cancel_sent_msg = NULL;
+static const char *cancel_not_sent_msg = NULL;
+
 /*
  * CancelRequested is set when we receive SIGINT (or local equivalent).
  * There is no provision in this module for resetting it; but applications
@@ -158,11 +165,11 @@ handle_sigint(SIGNAL_ARGS)
    {
        if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
        {
-           write_stderr(_("Cancel request sent\n"));
+           write_stderr(cancel_sent_msg);
        }
        else
        {
-           write_stderr(_("Could not send cancel request: "));
+           write_stderr(cancel_not_sent_msg);
            write_stderr(errbuf);
        }
    }
@@ -179,6 +186,9 @@ void
 setup_cancel_handler(void (*callback) (void))
 {
    cancel_callback = callback;
+   cancel_sent_msg = _("Cancel request sent\n");
+   cancel_not_sent_msg = _("Could not send cancel request: ");
+
    pqsignal(SIGINT, handle_sigint);
 }
 
@@ -203,11 +213,11 @@ consoleHandler(DWORD dwCtrlType)
        {
            if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
            {
-               write_stderr(_("Cancel request sent\n"));
+               write_stderr(cancel_sent_msg);
            }
            else
            {
-               write_stderr(_("Could not send cancel request: "));
+               write_stderr(cancel_not_sent_msg);
                write_stderr(errbuf);
            }
        }
@@ -225,6 +235,8 @@ void
 setup_cancel_handler(void (*callback) (void))
 {
    cancel_callback = callback;
+   cancel_sent_msg = _("Cancel request sent\n");
+   cancel_not_sent_msg = _("Could not send cancel request: ");
 
    InitializeCriticalSection(&cancelConnLock);