Ungraceful handling of fatal flex errors

Peter Eisentraut <peter_e@gmx.net> writes:

A fatal scanner error (likely a memory exhaustion problem) causes a
straight exit() without clean up, which causes a system-wide restart.
This should fix it:

*** scan.l      2001/01/24 19:43:03     1.85
--- scan.l      2001/01/27 14:14:29
***************
*** 55,60 ****
--- 55,62 ----
/* No reason to constrain amount of data slurped per myinput() call. */
#define YY_READ_BUF_SIZE 16777216

+ #define YY_FATAL_ERROR(msg) elog(FATAL, "%s", (msg))
+
#else /* !FLEX_SCANNER */

#undef input

But you will now get an unavoidable

scan.c:2145: warning: `yy_fatal_error' defined but not used

I have a sneakier idea to avoid the warning. The yy_fatal_error routine
is defined as

(void) fprintf( stderr, "%s\n", msg );
exit( YY_EXIT_FAILURE );

and this is the only use of fprintf in the scan.c file. How about
leaving yy_fatal_error as the error subroutine, and insert

#define fprintf(file,fmt,msg) elog(FATAL, "%s", (msg))

regards, tom lane

scan.c:2145: warning: `yy_fatal_error' defined but not used

I have a sneakier idea to avoid the warning. [...]

#define fprintf(file,fmt,msg) elog(FATAL, "%s", (msg))

Meaning no disrespect : yuck... IMHO this is asking for trouble
whenever someone decides to use another yacc. One should never ever
use the preprocessor to do what it was originally intended for
:-). Why not just make a useless statement calling yy_fatal_error ?

--- scan.l.orig	Mon Jan 29 11:36:56 2001
+++ scan.l	Mon Jan 29 11:27:28 2001
@@ -532,6 +534,9 @@
 	   because input()/myinput() checks the non-nullness of parseCh
 	   to know when to pass the string to lex/flex */
 	parseCh = NULL;
+
+	/* Make a bogus use of yy_fatal_error to avoid spurious warning */
+	(void) &yy_fatal_error;

/* initialize literal buffer to a reasonable but expansible size */
literalalloc = 128;

--
<< Tout n'y est pas parfait, mais on y honore certainement les jardiniers >>

Dominique Quatravaux <dom@kilimandjaro.dyndns.org>

dom@idealx.com, dom@idealx.com writes:

#define fprintf(file,fmt,msg) elog(FATAL, "%s", (msg))

Meaning no disrespect : yuck... IMHO this is asking for trouble
whenever someone decides to use another yacc.

This is flex, not yacc, and our lexer has been flex-only for a long
time. It's possible that the hack would break in a future version
of flex, but I doubt it. What else is a lexer going to use fprintf
for?

regards, tom lane

This is flex, not yacc, and our lexer has been flex-only for a long
time. It's possible that the hack would break in a future version
of flex, but I doubt it. What else is a lexer going to use fprintf
for?

Hmm, well of course you are right... (and I could use some sleep too
:-). OK, this becomes a non-issue then.

--
<< Tout n'y est pas parfait, mais on y honore certainement les jardiniers >>

Dominique Quatravaux <dom@kilimandjaro.dyndns.org>