🤖 New build scheduled with the buildbot fleet by@hauntsaninja for commite196d3d 🤖

If you want to schedule another build, you need to add the🔨 test-with-buildbots label again.

I looked into the buildbot failures and they don't seem related to the changes I make here (full details below). Raspbian bot which failed post-merge on last PR, does pass here.

Investigating buildbot failures:

1. AMD64 Arch Linux Usan:
   - C compilation issue, seems unrelated to these changes
2. PPC64LE RHEL8 Refleaks
   - test.test_concurrent_futures.test_shutdown timed out after 3 hour 49 min
   - seems to be:test_concurrent_futures.test_shutdown: AssertionError: b'' != b'apple' #112542
3. test.test_asyncio.test_server.TestServer2.test_abort_clients failures
   • Also occur in main on same buildbots (ex.https://buildbot.python.org/#/builders/29/builds/6842)
   • AMD64 Fedora Stable Clang Installed
   • AMD64 Fedora Stable Clang PR
   • AMD64 Fedora Stable LTO + PGO
   • AMD64 Fedora Stable LTO PR
   • AMD64 Fedora Stable PR
   • note: I can get this same failure on my Arch Linux locally on main, may try investigating a bit more. Can't seem to find a issue for it currently.

Bots which failed aroundtest_asyncio should pass now with#123423

TheTests / Address sanitizer failure seems to be a case that needs to be handled, investigating it (anmmap shows up in the middle of the I/O calls). Could this get theno news tag (just changes pythontest. module pieces)

Could this get the "no news" label? (Internal changes). I think this is ready for a more full review again + run bots (merged current main in recently)

Recent changes:

1. AddressSanitizer + LeakSanitizer can't be used understrace /ptrace (And new versions print a very helpful hint about this), added a skip for that so "Tests / Address sanitizer" should pass now.
2. Updated forAvoid calling isatty() for most open() calls #90102 to validate the noisatty call

🤖 New build scheduled with the buildbot fleet by@hauntsaninja for commit9e8b23d 🤖

If you want to schedule another build, you need to add the🔨 test-with-buildbots label again.

Buildbots look fairly clean. Three failed (AMD64 Windows10 PR, ARM64 Windows Non-Debug PR, ARM64 Windows PR), all with issues inpegen (AttributeError: module 'token' has no attribute 'FSTRING_START'). Other Windows buildbots passed, and Windows Github action passed as well.

This does prevent additionalfstat andioctl/isatty calls which were the two big performance changes ingh-120754. The seek is in theory all that remains in there but not checked for, and the BufferedIO changes I'm working on should eliminate that. Will be a bit to even get a full approach+proposal around BufferedIO pieces, is refactoring how the middle layer of the I/O stack works and touches a lot more Python C internals (locks, critical sections, ...). With that will look at adding the "no unexpected calls" check, as well as likely add some tests around more specific optimized cases (ex. stdout/stderr just write/append+flush, stdin just read, ...).

All the newly added tests fail on Gentoo Linux with sandbox enabled. From a quick check, the test wrongly assumes that the first syscall reported bystrace would be anopen* call, but it doesn't even verify that — it just blindly takes the return value of the first syscall ever and assumes it would be fd.

If I add some prints to get the list of syscalls, I get e.g. the following:

Check that the set of system calls produced by the I/O stack is what ... StraceEvent(syscall='faccessat2', args=['AT_FDCWD', '"@test_1752124_tmp\\303\\246"', 'F_OK', 'AT_EACCESS'], returncode='0')StraceEvent(syscall='mmap', args=['NULL', '8208', 'PROT_READ|PROT_WRITE', 'MAP_PRIVATE|MAP_ANONYMOUS', '-1', '0'], returncode='0x7fe693892000')StraceEvent(syscall='mmap', args=['NULL', '8208', 'PROT_READ|PROT_WRITE', 'MAP_PRIVATE|MAP_ANONYMOUS', '-1', '0'], returncode='0x7fe693892000')StraceEvent(syscall='getcwd', args=['"/var/tmp/portage/dev-lang/python-3.14.0_alpha2/work/Python-3.14.0a2/build/test_python_1752124\\303\\246"', '8192'], returncode='96')StraceEvent(syscall='newfstatat', args=['AT_FDCWD', '"/var/tmp/portage/dev-lang/python-3.14.0_alpha2/work/Python-3.14.0a2/build/test_python_1752124\\303\\246"', '{st_mode=S_IFDIR|0755', 'st_size=38', '...}', 'AT_SYMLINK_NOFOLLOW'], returncode='0')StraceEvent(syscall='newfstatat', args=['AT_FDCWD', '"/var/tmp/portage/dev-lang/python-3.14.0_alpha2/work/Python-3.14.0a2/build/test_python_1752124\\303\\246"', '{st_mode=S_IFDIR|0755', 'st_size=38', '...}', 'AT_SYMLINK_NOFOLLOW'], returncode='0')StraceEvent(syscall='mmap', args=['NULL', '8208', 'PROT_READ|PROT_WRITE', 'MAP_PRIVATE|MAP_ANONYMOUS', '-1', '0'], returncode='0x7fe69388f000')StraceEvent(syscall='getcwd', args=['"/var/tmp/portage/dev-lang/python-3.14.0_alpha2/work/Python-3.14.0a2/build/test_python_1752124\\303\\246"', '1024'], returncode='96')StraceEvent(syscall='readlink', args=['"/var/tmp/portage/dev-lang/python-3.14.0_alpha2/work/Python-3.14.0a2/build/test_python_1752124\\303\\246/@test_1752124_tmp\\303\\246"', '0x7ffecf5289f0', '1023'], returncode='-1 EINVAL (Invalid argument)')StraceEvent(syscall='openat', args=['AT_FDCWD', '"@test_1752124_tmp\\303\\246"', 'O_RDONLY|O_CLOEXEC'], returncode='3')StraceEvent(syscall='fstat', args=['3', '{st_mode=S_IFREG|0644', 'st_size=13', '...}'], returncode='0')StraceEvent(syscall='lseek', args=['3', '0', 'SEEK_CUR'], returncode='0')StraceEvent(syscall='read', args=['3', '"Hello', 'World!"', '14'], returncode='13')StraceEvent(syscall='read', args=['3', '""', '1'], returncode='0')StraceEvent(syscall='close', args=['3'], returncode='0')

i.e. there's a bunch of extra "preparatory" calls before theopenat() you're expecting, that should be ignored.

Besides, given how fragile this thing is by design, there should be an easy way to disable it (e.g. via-u-strace).

It's broken on musl (without any special environment) too:

Check that the set of system calls produced by the I/O stack is what ... StraceEvent(syscall='open', args=['"@test_26640_tmp\\303\\246"', 'O_RDONLY|O_LARGEFILE|O_CLOEXEC'], returncode='3')StraceEvent(syscall='fcntl', args=['3', 'F_SETFD', 'FD_CLOEXEC'], returncode='0')StraceEvent(syscall='fstat', args=['3', '{st_mode=S_IFREG|0644', 'st_size=13', '...}'], returncode='0')StraceEvent(syscall='mmap', args=['NULL', '16384', 'PROT_READ|PROT_WRITE', 'MAP_PRIVATE|MAP_ANONYMOUS', '-1', '0'], returncode='0x7efd4027f000')StraceEvent(syscall='lseek', args=['3', '0', 'SEEK_CUR'], returncode='0')StraceEvent(syscall='read', args=['3', '"Hello', 'World!"', '14'], returncode='13')StraceEvent(syscall='read', args=['3', '""', '1'], returncode='0')StraceEvent(syscall='close', args=['3'], returncode='0')

Happy to work on making the state better on Gentoo. There are tradeoffs in the fragility, and I'm happy to iterate to get everything working well. Unfortunately not having a check like this has resulted in syscalls being re-added unintentionally (ex.bpo-21679 removed a double stat andgh-120754 removed a double stat again).

In the short term I think the--ignore /--ignorefile arguments should allow you to disable this individual test in the same spot you could add a-u argument to enable/disable specific test resources.

There looks like three cases to investigate/work on from this:

1. Test on Gentoo + Musl + make pass there (there's one extrammap which doesn't refer to the fd which appears).
2. Probably disable under gentoo + sandbox, it looks like in that environment significant runtime changes are introduced in the compiled binary. That there are twonewfstatat calls in that case worries me / will need to go investigate source.
3. Potentially add a specialized resource switch-u to enable/disable more broadly.

For 3, did anything intest_subprocess fail for you?test_vfork_used_when_expected uses the samestrace testing infrastructure.

For all three of those I think the standard python process is either open a new issue or reopen thegh-120754 one. Happy to open one so can track these changes and get a fix landed.

On a glibc system, onlytest_fileio tests failed. On musl, I haven't run other tests — just this one, since I suspect it'd be affected too.

Could you open the bug, please? I still have lots to do today.