Issue 36184: test_gdb.test_threads() is specific to _POSIX_THREADS, fail on FreeBSD

On my FreeBSD VM, _POSIX_THREADS is not defined:

sys.thread_info: sys.thread_info(name='pthread', lock='semaphore', version=None)

test_gdb fails with:

Verify that "py-bt" indicates threads that are waiting for the GIL ... FAIL

======================================================================
FAIL: test_threads (test.test_gdb.PyBtTests)
Verify that "py-bt" indicates threads that are waiting for the GIL
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/vstinner/prog/python/master/Lib/test/test_gdb.py", line 826, in test_threads
    self.assertIn('Waiting for the GIL', gdb_output)
AssertionError: 'Waiting for the GIL' not found in 'Breakpoint 1 at 0x49e5d0: file Python/bltinmodule.c, line 1203.\n[New LWP 100742 of process 68315]\n[New LWP 100749 of process 68315]\n[New LWP 100751 of process 68315]\n[New LWP 100766 of process 68315]\n\nThread 1 hit Breakpoint 1, builtin_id (self=, v=42) at Python/bltinmodule.c:1203\n1203\t    return PyLong_FromVoidPtr(v);\n\nThread 5 (LWP 100766 of process 68315):\nTraceback (most recent call first):\n  File "<string>", line 10, in run\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 917, in _bootstrap_inner\n    self.run()\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 885, in _bootstrap\n    self._bootstrap_inner()\n\nThread 4 (LWP 100751 of process 68315):\nTraceback (most recent call first):\n  File "<string>", line 10, in run\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 917, in _bootstrap_inner\n    self.run()\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 885, in _bootstrap\n    self._bootstrap_inner()\n\nThread 3 (LWP 100749 of process 68315):\nTraceback (most recent call first):\n  File "<string>", line 10, in run\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 917, in _bootstrap_inner\n    self.run()\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 885, in _bootstrap\n    self._bootstrap_inner()\n\nThread 2 (LWP 100742 of process 68315):\nTraceback (most recent call first):\n  File "<string>", line 10, in run\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 917, in _bootstrap_inner\n    self.run()\n  File "/usr/home/vstinner/prog/python/master/Lib/threading.py", line 885, in _bootstrap\n    self._bootstrap_inner()\n\nThread 1 (LWP 100559 of process 68315):\nTraceback (most recent call first):\n  <built-in method id of module object at remote 0x800bccde8>\n  File "<string>", line 18, in <module>\n'


=> 'Waiting for the GIL' cannot be found in the output, because python-gdb.py failed to detect that a threading is waiting for the GIL.


The problem can be found in Tools/gdb/libpython.py:

    def is_waiting_for_gil(self):
        '''Is this frame waiting on the GIL?'''
        # This assumes the _POSIX_THREADS version of Python/ceval_gil.h:
        name = self._gdbframe.name()
        if name:
            return 'pthread_cond_timedwait' in name

pthread_cond_timedwait() is too close to POSIX threads. We can make this function more portable by checking for 'take_gil' function instead.

Hi, I would like to try to solve this issue. Does this occur on the latest version of FreeBSD?

I am running FreeBSD 12. I don't recall the minor version (12.1 maybe?).

I was able to reproduce this on FreeBSD 12.0.

So I changed 'pthread_cond_timedwait' to 'take_gil' and this didn't seem to have an effect on the unit test.

I installed GDB 8.2 is that the same version you are using?

> So I changed 'pthread_cond_timedwait' to 'take_gil' and this didn't seem to have an effect on the unit test.

Maybe you forgot to run "make" to copy Tools/gdb/libpython.py as python-gdb.py.

Anyway, I wrote PR 18873 and I tested manually that it does fix test_gdb on FreeBSD. I tested "GNU gdb (GDB) 8.3.1 [GDB v8.3.1 for FreeBSD]" on FreeBSD 12.1-RELEASE-p2.

New changeset 6d0ee60740f2862a878f009671b1aaa75aeb0c2a by Victor Stinner in branch 'master':
bpo-36184: Port python-gdb.py to FreeBSD (GH-18873)
https://github.com/python/cpython/commit/6d0ee60740f2862a878f009671b1aaa75aeb0c2a

New changeset 1695836123609a8ae97f2cfbe180a028dcd650a3 by Miss Islington (bot) in branch '3.7':
bpo-36184: Port python-gdb.py to FreeBSD (GH-18873)
https://github.com/python/cpython/commit/1695836123609a8ae97f2cfbe180a028dcd650a3

New changeset 5854d451cb35ac38bc07b95afeb077e8a35d5c7d by Miss Islington (bot) in branch '3.8':
bpo-36184: Port python-gdb.py to FreeBSD (GH-18873)
https://github.com/python/cpython/commit/5854d451cb35ac38bc07b95afeb077e8a35d5c7d

For our future reference/selves, GDB (currently 9.1 w/ python bindings) is now installed on the two FreeBSD buildbot workers