multidict 6.9.1

on Python PyPI

Bug fixes

• Fixed the C extension reading freed memory on free-threaded builds when a
  list handed to :py:meth:~multidict.MultiDict.update,
  :py:meth:~multidict.MultiDict.extend, :py:meth:~multidict.MultiDict.merge
  or the :py:class:~multidict.MultiDict and :py:class:~multidict.CIMultiDict
  constructors, a [key, value] item inside any iterable handed to them, or a
  list tested with in against :py:meth:~multidict.MultiDict.items, is
  changed by another thread; a call that catches the list shrinking under it
  now raises :py:exc:RuntimeError -- by :user:rodrigobnogueira.

  Related issues and pull requests on GitHub:
  #1437.

• Fixed a data race on the free-threaded build where a retired hash table's
  reader count used relaxed atomics, letting a lock-free get()/getone()/
  __getitem__() read race a concurrent free of that table. The reader-exit
  decrement and the drain's free check now use release/acquire ordering
  instead -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1481.

• Fixed a free-threaded build bug where two threads calling update(),
  merge(), or __setitem__() on the same key at the same time could lose
  the key entirely instead of just racing on which value wins. A decref of the
  replaced value could transiently suspend the writer's critical section,
  letting a second writer for the same key observe the first writer's
  in-progress entry as absent and, once both settled, mistake it for a stale
  duplicate and delete it. Every such decref is now deferred until the writer
  has released its critical section, so the window can no longer open.
  setdefault() had an unrelated instance of the same blind spot (it could
  insert a duplicate rather than recognizing an in-flight key), fixed alongside
  it -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1483.

• Fixed a free-threaded build bug where getall() and the items()/
  keys()/values() equality path could raise KeyError or report a
  present, never-deleted key as missing. A concurrent update()/extend()/
  __setitem__() call can have its critical section transiently suspended
  (a decref triggering a blocking allocator call) while an entry is marked as
  part of its own bookkeeping; a reader landing in that window used to treat
  the mark as "not found" instead of "still there, in flight" -- by
  :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1484.

• Fixed a reference leak in the C extension where operand | md.items()
  and md.items() - operand leaked one key and one value reference per
  element of operand, letting a large operand grow memory without bound
  (:gh:GHSA-54p9-h82j-f925 <aio-libs/multidict/security/advisories/GHSA-54p9-h82j-f925>)
  -- by :user:asvetlov.

  The issue was reported by :user:waydeshi.

  Related commits on GitHub:
  :commit:350b4a0.

• Fixed a segmentation fault on the standard (non-free-threaded) C extension
  build when a value type's __del__ released the GIL (for example by
  calling time.sleep()) while update(), merge(), __setitem__(),
  __delitem__(), pop(), popone(), or popall() was dropping a
  replaced or removed value. Py_BEGIN_CRITICAL_SECTION compiles to a no-op
  on this build, so nothing else was stopping a second thread from mutating the
  very same MultiDict concurrently once the GIL was released mid-mutation.
  Every such decref is now deferred until the mutation has fully finished, the
  same technique already used to close the analogous free-threaded-build race
  -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1489.

• Fixed the C extension reading freed memory while iterating a
  :py:class:~multidict.CIMultiDict whose keys are plain :py:class:str.
  Converting such a key to :py:class:~multidict.istr could run Python code
  (a :py:class:str subclass's __str__ or __del__) or, on free-threaded
  builds, suspend the iterator's critical section, after which the iterator read
  the entry again even though a concurrent mutation could already have freed it.
  As part of the fix, :py:meth:~multidict.MultiDict.copy and re-initializing
  from another multidict now assign a new version in the C extension instead of
  reusing the source's, matching the pure Python implementation
  -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1496.

• Fixed a use-after-free on the free-threaded build where a lock-free
  get(), [] or in could read a hash table that a concurrent
  resize had just retired and another reader was freeing
  -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1497.

Contributor-facing changes

• Removed a redundant include and a duplicated exclude line from
  MANIFEST.in; sdist contents are unchanged -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1478.

• Added .claudeignore file -- by :user:asvetlov

  Related issues and pull requests on GitHub:
  #1479.

• Scaled up the pure-Python pop(), popitem(), __delitem__(),
  add() and item-insertion benchmarks to do more work per measurement.
  Repeated CodSpeed runs on the same commit showed these particular
  benchmarks flagged as dominated by syscalls, understating their real
  cost and adding noise to the reported values; a larger working set
  amortizes that overhead -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1485.

• Replaced deprecated instrumentation codspeed mode with simulation -- by :user:asvetlov

  Related issues and pull requests on GitHub:
  #1493.

• Reorganized the mutating benchmarks (item insertion, update(),
  add() of the same key, pop(), popitem(), clear(),
  __delitem__() and __setitem__()) to copy a fresh multidict and
  apply the operation in a loop, like the add() and extend()
  benchmarks already do. The insertion, update() and clear()
  benchmarks previously mutated a single multidict shared across
  rounds, so only the first round measured the intended operation; the
  rest did a single copy per round, letting per-round overhead dominate
  -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1494.

• The repr() and view inequality benchmarks were updated to repeat their
  operation in a loop, like the other benchmarks, and the CodSpeed benchmark
  job was moved to Python 3.14 -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1498.

• Dropped -I from the AddressSanitizer test command in AGENTS.md
  and in the CI job. It implies -E, which made Python ignore
  PYTHONMALLOC=malloc, so small hash tables were still served from
  pymalloc arenas where use-after-free went undetected
  -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1499.

• The CI/CD workflow was updated to stop superseded runs of the same pull request
  when a new commit is pushed; runs on master, release branches, tags,
  the merge queue, and the daily schedule are never interrupted
  -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1500.

• The release job was changed to upload distributions and their signatures
  to the GitHub Release one file at a time, skipping assets that were
  already attached and retrying after a pause, so that a parallel upload
  burst no longer tripped the GitHub secondary rate limit
  -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1503.

Miscellaneous internal changes

• Corrected several comments in the free-threaded C extension that
  attributed critical-section suspension to a blocking PyMem_Malloc()
  call; allocation alone never suspends an acquired critical section, and
  the real risk at those sites is a decref running
  a finalizer or weakref callback. Also dropped a retry loop in
  md_clone_from_ht() that guarded against the same, non-existent
  allocation-triggered suspension -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1486.

• Changed the free-threaded build's deferred decref buffer, used by
  update() and __setitem__(), to a chain of fixed-size blocks
  with a large inline first block instead of a small inline array that
  was reallocated on growth -- by :user:asvetlov.

  Related issues and pull requests on GitHub:
  #1501.