Switch psql's TAP test for query cancellation to use IPC::Run::signal()

Previously, the test relied on a trick with a shell to retrieve the PID
of the psql session to be stopped with SIGINT, that was skipped on
Windows.  This commit changes the test to use IPC::Run::signal()
instead, which still does not work on Windows, but for a different
reason: SIGINT would stop the test before finishing.

This should allow the test to run on non-Windows platforms where PPID is
not supported (like NetBSD), spreading it a bit more across the
buildfarm.  And the logic of the test is simpler.

It is the first time in the tree that IPC::Run::signal() is used, so, as
a matter of safety (or just call that as me having cold feet), no
backpatch is done, at least for now.

Author: Yugo NAGATA
Reviewed-by: Fabien Coelho
Discussion: https://postgr.es/m/20230810125935.22c2922ea5250ba79358965b@sraoss.co.jp

Author: michaelpq

src/bin/psql/t/020_cancel.pl

@@ -10,55 +10,21 @@
 use Time::HiRes qw(usleep);
 
 # Test query canceling by sending SIGINT to a running psql
-#
-# There is, as of this writing, no documented way to get the PID of
-# the process from IPC::Run.  As a workaround, we have psql print its
-# own PID (which is the parent of the shell launched by psql) to a
-# file.
 if ($windows_os)
 {
-	plan skip_all => "cancel test requires a Unix shell";
+	plan skip_all => 'sending SIGINT on Windows terminates the test itself';
 }
 
-my $tempdir = PostgreSQL::Test::Utils::tempdir;
-
 my $node = PostgreSQL::Test::Cluster->new('main');
 $node->init;
 $node->start;
 
 local %ENV = $node->_get_env();
 
 my ($stdin, $stdout, $stderr);
-
-# Test whether shell supports $PPID.  It's part of POSIX, but some
-# pre-/non-POSIX shells don't support it (e.g., NetBSD).
-$stdin = "\\! echo \$PPID";
-IPC::Run::run([ 'psql', '-X', '-v', 'ON_ERROR_STOP=1' ],
-	'<', \$stdin, '>', \$stdout, '2>', \$stderr);
-$stdout =~ /^\d+$/ or skip "shell apparently does not support \$PPID", 2;
-
-# Now start the real test
 my $h = IPC::Run::start([ 'psql', '-X', '-v', 'ON_ERROR_STOP=1' ],
 	\$stdin, \$stdout, \$stderr);
 
-# Get the PID
-$stdout = '';
-$stderr = '';
-$stdin = "\\! echo \$PPID >$tempdir/psql.pid\n";
-pump $h while length $stdin;
-my $count;
-my $psql_pid;
-until (
-	-s "$tempdir/psql.pid"
-	  and
-	  ($psql_pid = PostgreSQL::Test::Utils::slurp_file("$tempdir/psql.pid"))
-	  =~ /^\d+\n/s)
-{
-	($count++ < 100 * $PostgreSQL::Test::Utils::timeout_default)
-	  or die "pid file did not appear";
-	usleep(10_000);
-}
-
 # Send sleep command and wait until the server has registered it
 $stdin = "select pg_sleep($PostgreSQL::Test::Utils::timeout_default);\n";
 pump $h while length $stdin;
@@ -67,7 +33,7 @@
 ) or die "timed out";
 
 # Send cancel request
-kill 'INT', $psql_pid;
+$h->signal('INT');
 
 my $result = finish $h;