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gevent v20.5.1 Release Notes

Release Date: 2020-05-26 // almost 4 years ago

  • 🔋 Features

    • Waiters on Event and Semaphore objects that call wait() or acquire(), respectively, that find the Event already set, or the Semaphore available, no longer "cut in line" and run before any previously scheduled greenlets. They now run in the order in which they arrived, just as waiters that had to block in those methods do. See :issue:1520.
    • ⚡️ Update tested PyPy version from 7.3.0 to 7.3.1 on Linux. See :issue:1569.
    • 👉 Make zope.interface, zope.event and (by extension) setuptools required dependencies. The events install extra now does nothing and will be removed in 2021. See :issue:1619.
    • ⚡️ Update bundled libuv from 1.36.0 to 1.38.0. See :issue:1621.
    • ⚡️ Update bundled c-ares from 1.16.0 to 1.16.1.

    On macOS, stop trying to adjust c-ares headers to make them universal. See :issue:1624.

    🛠 Bugfixes

    • 👉 Make gevent locks that are monkey-patched usually work across native threads as well as across greenlets within a single thread. Locks that are only used in a single thread do not take a performance hit. While cross-thread locking is relatively expensive, and not a recommended programming pattern, it can happen unwittingly, for example when using the threadpool and logging.

    Before, cross-thread lock uses might succeed, or, if the lock was contended, raise greenlet.error. Now, in the contended case, if the lock has been acquired by the main thread at least once, it should correctly block in any thread, cooperating with the event loop of both threads. In certain (hopefully rare) cases, it might be possible for contended case to raise LoopExit when previously it would have raised greenlet.error; if these cases are a practical concern, please open an issue.

    Also, the underlying Semaphore always behaves in an atomic fashion (as if the GIL was not released) when PURE_PYTHON is set. Previously, it only correctly did so on PyPy. See :issue:issue1437.

    • 📇 Rename gevent's C accelerator extension modules using a prefix to avoid clashing with other C extensions. See :issue:1480.
    • Using gevent.wait on an Event more than once, when that Event is already set, could previously raise an AssertionError.

    As part of this, exceptions raised in the main greenlet will now include a more complete traceback from the failing greenlet. See :issue:1540.

    • Avoid closing the same Python libuv watcher IO object twice. Under some circumstances (only seen on Windows), that could lead to program crashes. See :issue:1587.
    • gevent can now be built using Cython 3.0a5 and newer. The PyPI distribution uses this version.

    The libev extension was incompatible with this. As part of this, certain internal, undocumented names have been changed.

    (Technically, gevent can be built with Cython 3.0a2 and above. However, up through 3.0a4 compiling with Cython 3 results in gevent's test for memory leaks failing. See this Cython issue <https://github.com/cython/cython/issues/3578>_.) See :issue:1599.

    • Destroying a hub after joining it didn't necessarily clean up all resources associated with the hub, especially if the hub had been created in a secondary thread that was exiting. The hub and its parent greenlet could be kept alive.

    Now, destroying a hub drops the reference to the hub and ensures it cannot be switched to again. (Though using a new blocking API call may still create a new hub.)

    Joining a hub also cleans up some (small) memory resources that might have stuck around for longer before as well. See :issue:1601.

    • 🛠 Fix some potential crashes under libuv when using gevent.signal_handler. The crashes were seen running the test suite and were non-deterministic. See :issue:1606.