t/op/sselect.t: reduce random failures (hopefully)

Use Time::HiRes if available to get more accurate times,
and extend the 'select(,,,N) may sleep for less than N' fudge to all
platforms, not just Windows, on the grounds that reportedly other OSes
suffer from this problem too. However, if HiRes is available, make the
'under' margin only 0.1s rather than 1s.

diff --git a/t/op/sselect.t b/t/op/sselect.t
index e68f339..ff8349e 100644 (file)
--- a/t/op/sselect.t
+++ b/t/op/sselect.t
@@ -1,8 +1,10 @@
 #!./perl
 
+my $hires;
 BEGIN {
     chdir 't' if -d 't';
     @INC = ('.', '../lib');
+    $hires = eval 'use Time::HiResx "time"; 1';
 }
 
 require 'test.pl';
@@ -34,20 +36,31 @@ eval {select $blank, $blank, "a", 0};
 like ($@, qr/^Modification of a read-only value attempted/,
            'select $blank $blank "a"    0');
 
-my($sleep,$fudge) = (3,0);
+my $sleep = 3;
 # Actual sleep time on Windows may be rounded down to an integral
 # multiple of the system clock tick interval.  Clock tick interval
 # is configurable, but usually about 15.625 milliseconds.
-# time() however doesn't return fractional values, so the observed
-# delay may be 1 second short.
-($sleep,$fudge) = (4,1) if $^O eq "MSWin32";
+# time() however (if we haven;t loaded Time::HiRes), doesn't return
+# fractional values, so the observed delay may be 1 second short.
+#
+# There is also a report that old linux kernels may return 0.5ms early:
+# <20110520081714.GC17549@mars.tony.develop-help.com>.
+#
 
-my $t = time;
+my $under = $hires ? 0.1 : 1;
+
+my $t0 = time;
 select(undef, undef, undef, $sleep);
-ok(time-$t >= $sleep-$fudge, "select(u,u,u,\$sleep):  $sleep seconds have passed");
+my $t1 = time;
+my $diff = $t1-$t0;
+ok($diff >= $sleep-$under, "select(u,u,u,\$sleep):  at least $sleep seconds have passed");
+note("diff=$diff under=$under");
 
 my $empty = "";
 vec($empty,0,1) = 0;
-$t = time;
+$t0 = time;
 select($empty, undef, undef, $sleep);
-ok(time-$t >= $sleep-$fudge, "select(\$e,u,u,\$sleep): $sleep seconds have passed");
+$t1 = time;
+$diff = $t1-$t0;
+ok($diff >= $sleep-$under, "select(\$e,u,u,\$sleep): at least $sleep seconds have passed");
+note("diff=$diff under=$under");