Bug report
Bug description:
I built libffi with TSAN and cpython (3.13 branch) with free-threading and TSAN. The following python code reports TSAN warnings:
import ctypes
import concurrent.futures
import threading
def test_ctypes():
@ctypes.CFUNCTYPE(ctypes.c_float, ctypes.c_float, ctypes.c_float)
def callback(a, b):
return a / 2 + b / 2
if __name__ == "__main__":
num_workers = 20
barrier = threading.Barrier(num_workers)
def closure():
barrier.wait()
test_ctypes()
with concurrent.futures.ThreadPoolExecutor(max_workers=num_workers) as executor:
futures = []
for i in range(num_workers):
futures.append(executor.submit(closure))
assert len(list(f.result() for f in futures)) == num_workersTSAN report exract:
WARNING: ThreadSanitizer: data race (pid=59410)
Read of size 8 at 0x7ffff618b6d0 by thread T2:
#0 dlmalloc /project/libffi/x86_64-pc-linux-gnu/../src/dlmalloc.c:4158:8 (libffi.so.8+0x58a5) (BuildId: 7b5c105b8eca23b7c54bb5eeab8b4ecf28fc7756)
#1 ffi_closure_alloc /project/libffi/x86_64-pc-linux-gnu/../src/closures.c:998:9 (libffi.so.8+0x56ec) (BuildId: 7b5c105b8eca23b7c54bb5eeab8b4ecf28fc7756)
#2 _ctypes_alloc_callback /project/cpython/./Modules/_ctypes/callbacks.c:367:20 (_ctypes.cpython-313t-x86_64-linux-gnu.so+0x1b435) (BuildId: e9fba41204b37973fe60945270803301c7df9615)
#3 PyCFuncPtr_new /project/cpython/./Modules/_ctypes/_ctypes.c:3955:13 (_ctypes.cpython-313t-x86_64-linux-gnu.so+0x18ba4) (BuildId: e9fba41204b37973fe60945270803301c7df9615)
More details on the build and the output: https://gist.github.com/vfdev-5/06b1c60713241e75773e9a92f2ecf135
The issue is with dlmalloc of libffi (reported here)
Discussing the issue with @colesbury and @Yhg1s on discord, Thomas proposed the following fix (agreed by Sam):
I still think the easy fix is to cause dlmalloc to do its initialization early, like during ctypes import time. Maybe just calling ffi_closure_alloc() (and immediately freeing) is enough.
CPython versions tested on:
3.13
Operating systems tested on:
Linux
Linked PRs
Bug report
Bug description:
I built libffi with TSAN and cpython (3.13 branch) with free-threading and TSAN. The following python code reports TSAN warnings:
TSAN report exract:
More details on the build and the output: https://gist.github.com/vfdev-5/06b1c60713241e75773e9a92f2ecf135
The issue is with dlmalloc of libffi (reported here)
Discussing the issue with @colesbury and @Yhg1s on discord, Thomas proposed the following fix (agreed by Sam):
CPython versions tested on:
3.13
Operating systems tested on:
Linux
Linked PRs