[gcc r13-7495] Support parallel testing in libgomp: fallback Perl 'flock' [PR66005]

[gcc r13-7495] Support parallel testing in libgomp: fallback Perl 'flock' [PR66005]

[Thomas Schwinge]

https://gcc.gnu.org/g:09124b7ed7709721e86556b4083ef40925d7489b

commit r13-7495-g09124b7ed7709721e86556b4083ef40925d7489b
Author: Thomas Schwinge <thomas@codesourcery.com>
Date:   Mon May 15 20:00:07 2023 +0200

    Support parallel testing in libgomp: fallback Perl 'flock' [PR66005]
    
    Follow-up to commit 6c3b30ef9e0578509bdaf59c13da4a212fe6c2ba
    "Support parallel testing in libgomp, part II [PR66005]"
    ("..., and enable if 'flock' is available for serializing execution testing"),
    where we saw:
    
    > On my Dell Precision 7530 laptop:
    >
    >     $ uname -srvi
    >     Linux 5.15.0-71-generic #78-Ubuntu SMP Tue Apr 18 09:00:29 UTC 2023 x86_64
    >     $ grep '^model name' < /proc/cpuinfo | uniq -c
    >          12 model name      : Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
    >     $ nvidia-smi -L
    >     GPU 0: Quadro P1000 (UUID: GPU-e043973b-b52a-d02b-c066-a8fdbf64e8ea)
    >
    > ... [...]: case (c) standard configuration, no offloading
    > configured, [...]
    
    >     $ \time make check-target-libgomp
    >
    > Case (c), baseline; [...]:
    >
    >     1180.98user 110.80system 19:36.40elapsed 109%CPU (0avgtext+0avgdata 505148maxresident)k
    >     1133.22user 111.08system 19:35.75elapsed 105%CPU (0avgtext+0avgdata 505212maxresident)k
    >
    > Case (c), parallelized [using 'flock']:
    >
    > [...]
    >     -j12 GCC_TEST_PARALLEL_SLOTS=12
    >     2591.04user 192.64system 4:44.98elapsed 976%CPU (0avgtext+0avgdata 505216maxresident)k
    >     2581.23user 195.21system 4:47.51elapsed 965%CPU (0avgtext+0avgdata 505212maxresident)k
    
    Quite the same when instead of 'flock' using this fallback Perl 'flock':
    
        2565.23user 194.35system 4:46.77elapsed 962%CPU (0avgtext+0avgdata 505216maxresident)k
        2549.38user 200.20system 4:46.08elapsed 961%CPU (0avgtext+0avgdata 505216maxresident)k
    
            PR testsuite/66005
            gcc/
            * doc/install.texi: Document (optional) Perl usage for parallel
            testing of libgomp.
            libgomp/
            * testsuite/lib/libgomp.exp: 'flock' through stdout.
            * testsuite/flock: New.
            * configure.ac (FLOCK): Point to that if no 'flock' available, but
            'perl' is.
            * configure: Regenerate.
    
    (cherry picked from commit 04abe1944d30eb18a2060cfcd9695d085f7b4752)

Diff:
---
 gcc/doc/install.texi              |  3 +++
 libgomp/configure                 | 42 +++++++++++++++++++++++++++++++++++++++
 libgomp/configure.ac              |  5 +++++
 libgomp/testsuite/flock           | 17 ++++++++++++++++
 libgomp/testsuite/lib/libgomp.exp |  4 +++-
 5 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index 928fc6b6d4b..b30d3691fe6 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -382,6 +382,9 @@ tables.
 
 Used by @command{automake}.
 
+If available, enables parallel testing of @samp{libgomp} in case that
+@command{flock} is not available.
+
 @end table
 
 Several support libraries are necessary to build GCC, some are required,
diff --git a/libgomp/configure b/libgomp/configure
index 489c9a00421..ed18809ff1c 100755
--- a/libgomp/configure
+++ b/libgomp/configure
@@ -16487,6 +16487,8 @@ $as_echo "unable to detect (assuming 1)" >&6; }
 fi
 
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for flock implementation" >&5
+$as_echo "$as_me: checking for flock implementation" >&6;}
 for ac_prog in flock
 do
   # Extract the first word of "$ac_prog", so it can be a program name with args.
@@ -16529,6 +16531,46 @@ fi
   test -n "$FLOCK" && break
 done
 
+# Fallback if 'perl' is available.
+if test -z "$FLOCK"; then
+  # Extract the first word of "perl", so it can be a program name with args.
+set dummy perl; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_prog_FLOCK+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$FLOCK"; then
+  ac_cv_prog_FLOCK="$FLOCK" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_prog_FLOCK="$srcdir/testsuite/flock"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+FLOCK=$ac_cv_prog_FLOCK
+if test -n "$FLOCK"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $FLOCK" >&5
+$as_echo "$FLOCK" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+fi
 
 # Get target configury.
 . ${srcdir}/configure.tgt
diff --git a/libgomp/configure.ac b/libgomp/configure.ac
index 0fab7168cfa..cc96e5b753b 100644
--- a/libgomp/configure.ac
+++ b/libgomp/configure.ac
@@ -339,7 +339,12 @@ fi
 AX_COUNT_CPUS
 AC_SUBST(CPU_COUNT)
 
+AC_MSG_NOTICE([checking for flock implementation])
 AC_CHECK_PROGS(FLOCK, flock)
+# Fallback if 'perl' is available.
+if test -z "$FLOCK"; then
+  AC_CHECK_PROG(FLOCK, perl, $srcdir/testsuite/flock)
+fi
 
 # Get target configury.
 . ${srcdir}/configure.tgt
diff --git a/libgomp/testsuite/flock b/libgomp/testsuite/flock
new file mode 100755
index 00000000000..71878b104f1
--- /dev/null
+++ b/libgomp/testsuite/flock
@@ -0,0 +1,17 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+# Only arguments '--exclusive 1' exactly are supported.
+(@ARGV == 2) or die;
+my $mode = shift;
+($mode eq "--exclusive") or die;
+my $fd = shift;
+($fd eq "1") or die;
+
+use Fcntl ':flock';
+
+open(my $fh, '>&=', 1) or die "open: $!";
+
+flock($fh, LOCK_EX) or die "flock: $!";
diff --git a/libgomp/testsuite/lib/libgomp.exp b/libgomp/testsuite/lib/libgomp.exp
index 8512f2c1e64..70e9b85eb9a 100644
--- a/libgomp/testsuite/lib/libgomp.exp
+++ b/libgomp/testsuite/lib/libgomp.exp
@@ -308,12 +308,14 @@ if ![info exists ::env(GCC_RUNTEST_PARALLELIZE_DIR)] {
     rename libgomp_load standard_libgomp_load
     proc libgomp_load { program args } {
 	# ... in order to serialize execution testing via an exclusive lock.
+	# We use stdout, as per <https://perldoc.perl.org/functions/flock>
+	# "[...] FILEHANDLE [...] be open with write intent to use LOCK_EX".
 	set lock_file ../lock
 	set lock_kind --exclusive
 	set lock_fd [open $lock_file a+]
 	set lock_clock_begin [clock seconds]
 	global FLOCK
-	exec $FLOCK $lock_kind 0 <@ $lock_fd
+	exec $FLOCK $lock_kind 1 >@ $lock_fd
 	set lock_clock_end [clock seconds]
 	verbose -log "Got ${FLOCK}('$lock_file', '$lock_kind') at [clock format $lock_clock_end] after [expr $lock_clock_end - $lock_clock_begin] s" 2