Re: [PATCH] O_CLOEXEC not honored on Windows - handle inheritance chain

Hello Bryan,

13.12.2025 04:44, Tom Lane wrote:
> Thomas Munro<thomas(dot)munro(at)gmail(dot)com> writes:
>> Hearing nothing, pushed.
> fairywren is unimpressed:

Now that fairywren is pretty satisfied with the test, it has produced an
interesting failure [1]:
208/222 postgresql:test_cloexec / test_cloexec/001_cloexec                        ERROR 4.09s   exit status 1

regress_log_001_cloexec
[14:36:36.820](1.047s) 1..1
[14:36:36.821](0.001s) # Using test program:
C:\\tools\\xmsys64\\home\\pgrunner\\bf\\root\\REL_16_STABLE\\pgsql.build\\tmp_install\\tools\\xmsys64\\home\\pgrunner\\bf\\root\\REL_16_STABLE\\inst\\bin\\test_cloexec.exe
[14:36:37.445](0.624s) # Test program output:
[14:36:37.446](0.001s) # Child: Received HANDLE1=00000000000000B0 (should fail - O_CLOEXEC)
# Child: Received HANDLE2=00000000000000C0 (should work - no O_CLOEXEC)
# Child: Successfully wrote to HANDLE1
# Child: Successfully wrote to HANDLE2
# Child: HANDLE1 (O_CLOEXEC): ACCESSIBLE (BAD!)
# Child: HANDLE2 (no O_CLOEXEC): ACCESSIBLE (GOOD!)
# Child: Test FAILED - O_CLOEXEC not working correctly
# Parent: Opening test files...
# Parent: fd1=3 (O_CLOEXEC) -> HANDLE=00000000000000B0
# Parent: fd2=4 (no O_CLOEXEC) -> HANDLE=00000000000000C0
# Parent: Spawning child process...
# Parent: Command line:
"C:\\tools\\xmsys64\\home\\pgrunner\\bf\\root\\REL_16_STABLE\\pgsql.build\\tmp_install\\tools\\xmsys64\\home\\pgrunner\\bf\\root\\REL_16_STABLE\\inst\\bin\\test_cloexec.exe"
00000000000000B0 00000000000000C0
# Parent: Waiting for child process...
# Parent: Child exit code: 1
# Parent: FAILURE - O_CLOEXEC not working correctly
[14:36:37.447](0.002s) not ok 1 - O_CLOEXEC prevents handle inheritance
[14:36:37.448](0.001s) #   Failed test 'O_CLOEXEC prevents handle inheritance'
#   at C:/tools/xmsys64/home/pgrunner/bf/root/REL_16_STABLE/pgsql/src/test/modules/test_cloexec/t/001_cloexec.pl line 57.
[14:36:37.449](0.001s) # Looks like you failed 1 test of 1.

I've managed to reproduce it locally with:
--- a/src/test/modules/test_cloexec/t/001_cloexec.pl
+++ b/src/test/modules/test_cloexec/t/001_cloexec.pl
@@ -19,3 +19,3 @@ if (!$PostgreSQL::Test::Utils::windows_os)

-plan tests => 1;
+plan tests => 1000;

@@ -44,2 +44,4 @@ note("Using test program: $test_prog");

+for (my $i = 1; $i <= 1000; $i++)
+{
 my ($stdout, $stderr);
@@ -58,3 +60,3 @@ ok($result && $stdout =~ /SUCCESS.*O_CLOEXEC behavior verified/s,
    "O_CLOEXEC prevents handle inheritance");
-
+}
 done_testing();

and with the test cloned:
perl -i.bak -ne "print unless /test_cloexec_/" "src/test/modules/meson.build" && python3 -c "for i in
range(1,50+1):import os;import
shutil;sd=\"src/test/modules/test_cloexec/\";td=f\"src/test/modules/test_cloexec_{i}\";shutil.rmtree(td,ignore_errors=1);shutil.copytree(sd,
td);assert(os.system(f'perl -i.bak -pe
\"s#(subdir.\'test_cloexec\'.)#subdir(\'test_cloexec_{i}\'){chr(92)}n{chr(92)}1#\"
\"src/test/modules/meson.build\"')==0);assert(os.system(f'perl -i.bak -pe \"s#: \'test_cloexec\',#:
\'test_cloexec_{i}\',#\" \"{td}/meson.build\"')==0)"

meson test test_cloexec_*/001_cloexec --num-processes 50
failed for me as below:
Ok:                19
Fail:              31

# grep 'not ok' meson-logs/testlog.txt
not ok 541 - O_CLOEXEC prevents handle inheritance
not ok 303 - O_CLOEXEC prevents handle inheritance
not ok 798 - O_CLOEXEC prevents handle inheritance
not ok 901 - O_CLOEXEC prevents handle inheritance
not ok 634 - O_CLOEXEC prevents handle inheritance
not ok 640 - O_CLOEXEC prevents handle inheritance
not ok 770 - O_CLOEXEC prevents handle inheritance
not ok 938 - O_CLOEXEC prevents handle inheritance
not ok 420 - O_CLOEXEC prevents handle inheritance
not ok 674 - O_CLOEXEC prevents handle inheritance
not ok 114 - O_CLOEXEC prevents handle inheritance
not ok 649 - O_CLOEXEC prevents handle inheritance
not ok 51 - O_CLOEXEC prevents handle inheritance
not ok 692 - O_CLOEXEC prevents handle inheritance
not ok 874 - O_CLOEXEC prevents handle inheritance
not ok 955 - O_CLOEXEC prevents handle inheritance
not ok 690 - O_CLOEXEC prevents handle inheritance
not ok 33 - O_CLOEXEC prevents handle inheritance
not ok 116 - O_CLOEXEC prevents handle inheritance
not ok 398 - O_CLOEXEC prevents handle inheritance
not ok 773 - O_CLOEXEC prevents handle inheritance
not ok 2 - O_CLOEXEC prevents handle inheritance
not ok 253 - O_CLOEXEC prevents handle inheritance
not ok 10 - O_CLOEXEC prevents handle inheritance
not ok 902 - O_CLOEXEC prevents handle inheritance
not ok 848 - O_CLOEXEC prevents handle inheritance
not ok 832 - O_CLOEXEC prevents handle inheritance
not ok 38 - O_CLOEXEC prevents handle inheritance
not ok 986 - O_CLOEXEC prevents handle inheritance
not ok 688 - O_CLOEXEC prevents handle inheritance
not ok 872 - O_CLOEXEC prevents handle inheritance
not ok 582 - O_CLOEXEC prevents handle inheritance
not ok 816 - O_CLOEXEC prevents handle inheritance
not ok 277 - O_CLOEXEC prevents handle inheritance
not ok 570 - O_CLOEXEC prevents handle inheritance
not ok 691 - O_CLOEXEC prevents handle inheritance
not ok 871 - O_CLOEXEC prevents handle inheritance
not ok 770 - O_CLOEXEC prevents handle inheritance
not ok 108 - O_CLOEXEC prevents handle inheritance
not ok 610 - O_CLOEXEC prevents handle inheritance
not ok 866 - O_CLOEXEC prevents handle inheritance
not ok 909 - O_CLOEXEC prevents handle inheritance
not ok 276 - O_CLOEXEC prevents handle inheritance
not ok 190 - O_CLOEXEC prevents handle inheritance

It looks like HANDLE1 passed from parent to child can accidentally point
to a child slot occupied by some other writable object, not inherited from
parent.

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=fairywren&dt=2026-06-19%2013%3A28%3A44

Best regards,
Alexander