Restore errno if signal handler changes it

It's way too easy to forget to "local $!" in signal handlers and
changing $! when signal hits between two ops is probably never useful.

1 files changed, 30 insertions, 0 deletions

diff --git a/t/io/errnosig.t b/t/io/errnosig.t
new file mode 100644
index 0000000000..8effcf1144
--- /dev/null
+++ b/t/io/errnosig.t
@@ -0,0 +1,30 @@
+#!./perl
+
+BEGIN {
+    chdir 't' if -d 't';
+    @INC = qw(. ../lib);
+}
+
+require Config; import Config;
+require "test.pl";
+plan(tests => 1);
+
+SKIP: {
+    skip("Alarm not supported", 1) unless exists $Config{'d_alarm'};
+
+    $SIG{ALRM} = sub {
+        # We could call anything that modifies $! here, but
+        # this way we can be sure that it isn't the same
+        # errno as interrupted sleep() would return, and are
+        # able to check it thereafter.
+        $! = -1;
+    };
+
+    alarm 1;
+    sleep 2;
+
+    # Interrupted sleeps sets errno to EAGAIN, but signal
+    # that # hits after it (if safe signal handling is enabled)
+    # causes a routing that modifies $! to be run afterwards
+    isnt($! + 0, -1, 'Signal does not modify $!');
+}