bm_tornado_http crashes on PyPy 3.11: "BufferError: Existing exports of data: object cannot be re-sized" #510

Bug report

Benchmark: tornado_http
Interpreter: PyPy 3.11 (3.11.17) — CPython is unaffected
pyperformance version: 1.14.0
tornado version: 6.5.2
Environment: GitHub Actions ubuntu-latest, matrix entry python: pypy-3.11

Description

Running python -m pyperformance run -b all --debug-single-value (what the
test_run_and_show test does in CI) fails only on PyPy because bm_tornado_http
dies:

1 benchmarks failed:
- tornado_http (Benchmark died)

The benchmark crashes with BufferError: Existing exports of data: object cannot be re-sized, raised from tornado's IOStream._consume where del self._read_buffer[:loc] resizes a buffer that PyPy considers to still have an
active export. tornado then closes the connection, the client sees
HTTPStreamClosedError: Stream closed, and the benchmark process exits non-zero.

Traceback

File ".../tornado/iostream.py", line 993, in _consume
    del self._read_buffer[:loc]
BufferError: Existing exports of data: object cannot be re-sized
Uncaught exception, closing connection.
...
File ".../bm_tornado_http/run_benchmark.py", line 74, in run_client
tornado.simple_httpclient.HTTPStreamClosedError: Stream closed
...
RuntimeError: Benchmark died

Reproducibility

Not a flake — it reproduces on every pypy-3.11 CI run. Both a recent pull-request
run and the main branch run fail identically on tornado_http, so this is
independent of any in-flight change.

Notes

• BufferError: Existing exports of data: object cannot be re-sized is a PyPy
  buffer-protocol behavior: slice-deleting a buffer that still has an active
  export (e.g. a memoryview) is rejected, where CPython does not enforce it here.
• Existing issues version 0.8.0 - tornado_http with --track-memory does not terminate #53 ("tornado_http with --track-memory does not terminate"),
  tornado fails with 3.8.0b2 on Windows #61 ("tornado fails with 3.8.0b2 on Windows") and Django and Tornado benchmarks broken on Python 3.9 #76 ("Django and Tornado
  benchmarks broken on Python 3.9") are different problems.