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_remote_debugging: write_sample advances the timestamp before writing the sample #158550
Description
Bug report
(found while thinking about how to address the code review from #157228)
The timestamp is advanced before the stack is built:
If there's a failure, such as:
cpython/Lib/profiling/sampling/sample.py
Lines 180 to 184 in 763b6ed
Then the timestamps for the thread is shifted. That's a hard corruption for a delta-based format.
Reproduction
maurycy@gimel cpython-315 (main e580c88?) % cat repro.py
import _remote_debugging
w = _remote_debugging.BinaryWriter("/tmp/o.bin", 1000, 0)
try:
w.write_sample([(0, [(1, 0, [(42, None, "f", None)])])], 5000)
except TypeError:
pass
w.write_sample([(0, [(1, 0, [("a.py", None, "f", None)])])], 6000)
w.finalize()
class C:
def collect(self, frames, timestamps_us=None, **kw):
print(timestamps_us)
_remote_debugging.BinaryReader("/tmp/o.bin").replay(C())
maurycy@gimel cpython-315 (main e580c88?) % ./python.exe repro.py
[1000]Another repro could involve _testcapi.set_nomemory, incorrect unicode etc.
CPython versions tested on:
CPython main branch, 3.15
Operating systems tested on:
macOS
Activity
maurycy commented on Oct 5, 2026
Duplicated by #152892 and #158830