Re: [BUG] zsystem:34: flock: invalid timeout value: '0'

[Cedric Ware <cedric.ware__bml@xxxxxxxxxxxxxx>]

	Hello,

Bart Schaefer (Friday 2020-06-26):
> It's pretty obvious that the patch caused the change:
> 
> +               if (timeout < 1e-6 || timeout > 1073741823.) {
> +                   zwarnnam(nam, "flock: invalid timeout value: '%s'",
> +                            optarg);

Yes, sorry, didn't catch the 0 case.

> Similarly:
> 
> +               if (timeout_param.u.d < 1
> +                   || timeout_param.u.d > 0.999 * LONG_MAX) {
> +                   zwarnnam(nam, "flock: invalid interval value: '%s'",
> +                            optarg);

I don't think so.  This one is for the -i parameter, which is new,
it's not a behavior change.  And IMO it doesn't make sense to allow
a zero interval.

> I don't know enough about dealing with the float-valued time specs to be
> sure what to do about it, i.e., why a limit above zero was considered
> necessary or whether zero needs to be a special case.

I didn't want to allow specifying a timeout below 1 microsecond,
because that's the granularity of zsleep().  One could still allow it
but silently treat it as 0.  In any case, the 0 value itself should
indeed have been allowed.  Here's a quick patch below, I've tested it,
but I don't have time right now to do much more.

					Best regards,
					Cedric Ware.


diff --git a/Src/Modules/system.c b/Src/Modules/system.c
index 972aa0767..638fe029e 100644
--- a/Src/Modules/system.c
+++ b/Src/Modules/system.c
@@ -591,13 +591,16 @@ bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
 		    timeout_param.u.d : (double)timeout_param.u.l;
 
 		/*
+		 * timeout can be 0 (no wait) but not so small as to be
+		 * less than a microsecond.
 		 * timeout must not overflow time_t, but little is known
 		 * about this type's limits.  Conservatively limit to 2^30-1
 		 * (34 years).  Then it can only overflow if time_t is only
 		 * a 32-bit int and CLOCK_MONOTONIC is not supported, in which
 		 * case there is a Y2038 problem anyway.
 		 */
-		if (timeout < 1e-6 || timeout > 1073741823.) {
+		if (timeout != 0. &&
+		    (timeout < 1e-6 || timeout > 1073741823.)) {
 		    zwarnnam(nam, "flock: invalid timeout value: '%s'",
 			     optarg);
 		    return 1;
diff --git a/Test/V14system.ztst b/Test/V14system.ztst
index b8af96cda..06512fe05 100644
--- a/Test/V14system.ztst
+++ b/Test/V14system.ztst
@@ -13,7 +13,9 @@
 %test
 
   (
-    zsystem flock -t 0.1 -i 0.000001 $tst_dir/file
+    zsystem flock -t 0 -i 0.000001 $tst_dir/file   &&
+    zsystem flock -t 0.1 -i 0.000001 $tst_dir/file &&
+    zsystem flock -t 1 -i 0.000001 $tst_dir/file
   )
 0:zsystem flock valid time arguments