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  • v1.3.0 Changes

    May 11, 2018
    • πŸ‘€ Python 3.7 passes the automated memory leak checks. See :issue:1197.

    • ⚑️ Update autoconf's config.guess and config.sub to the latest versions for c-ares and libev.

    • :class:gevent.local.local subclasses that mix-in ABCs can be instantiated. Reported in :issue:1201 by Bob Jordan.

  • v1.3.b2 Changes

    May 03, 2018
    • 🏁 On Windows, CFFI is now a dependency so that the libuv backend really can be used by default.

    • πŸ›  Fix a bug detecting whether we can use the memory monitoring features when psutil is not installed.

    • 🐧 gevent.subprocess.Popen uses /proc/self/fd (on Linux) or /dev/fd (on BSD, including macOS) to find the file descriptors to close when close_fds is true. This matches an optimization added to Python 3 (and backports it to Python 2.7), making process spawning up to 9 times faster. Also, on Python 3, since Python 3.3 is no longer supported, we can also optimize the case where close_fds is false (not the default), making process spawning up to 38 times faster. Initially reported in :issue:1172 by Ofer Koren.

    • πŸ‘€ The bundled libuv is now 1.20.1, up from 1.19.2. See :issue:1177.

    • 🚚 The long-deprecated and undocumented module gevent.wsgi was removed.

    • βž• Add gevent.util.assert_switches to build on the monitoring functions. Fixes :issue:1182.

    • πŸ‘€ A started monitor thread for the active hub now survives a fork. See :issue:1185.

    • The greenlet tracer functions used for the various monitoring capabilities are now compiled with Cython for substantially lower overhead. See :pr:1190.

    • libuv now collects all pending watchers and runs their callbacks at the end of the loop iteration using UV_RUN_ONCE. This eliminates the need to patch libuv to be greenlet-safe. It also means that zero-duration timer watchers are actual timer watchers again (instead of being turned into check watchers); newly added zero-duration timers cannot block the event loop because they won't be run until a safe time.

    • βœ… Python 3.7.0b4 is now the tested and supported version of Python 3.7. PyPy 6.0 has been tested, although CI continues to use 5.10.

  • v1.3.b1 Changes

    April 13, 2018


    • πŸ— Cython 0.28.2 is now used to build gevent from a source checkout.

    • The bundled libuv is now 1.19.2, up from 1.18.0.

    πŸ‘ Platform Support

    • πŸ‘· Travis CI tests on Python 3.7.0b3.

    • 🏁 Windows now defaults to the libuv backend if CFFI is installed. See :issue:1163.

    πŸ› Bug Fixes

    • On Python 2, when monkey-patching threading.Event, also monkey-patch the underlying class, threading._Event. Some code may be type-checking for that. See :issue:1136.

    • πŸ›  Fix libuv io watchers polling for events that only stopped watchers are interested in, reducing CPU usage. Reported in :issue:1144 by wwqgtxx.

    ✨ Enhancements

    • βž• Add additional optimizations for spawning greenlets, making it faster than 1.3a2.

    • πŸ‘‰ Use strongly typed watcher callbacks in the libuv CFFI extensions. This prevents dozens of compiler warnings.

    • πŸ–¨ When gevent prints a timestamp as part of an error message, it is now in UTC format as specified by RFC3339.

    • Threadpool threads that exit now always destroy their hub (if one was created). This prevents some forms of resource leaks (notably visible as blocking functions reported by the new monitoring abilities).

    • Hub objects now include the value of their name attribute in their repr.

    • Pools for greenlets and threads have lower overhead, especially for map. See :pr:1153.

    • The undocumented, internal implementation classes IMap and IMapUnordered classes are now compiled with Cython, further reducing the overhead of [Thread]Pool.imap.

    • The classes gevent.event.Event and gevent.event.AsyncResult are compiled with Cython for improved performance, as is the gevent.queue module and gevent.hub.Waiter and certain time-sensitive parts of the hub itself. Please report any compatibility issues.

    • python -m gevent.monkey <script> accepts more values for <script>, including paths to packages or compiled bytecode. Reported in :issue:1157 by Eddie Linder.

    • βž• Add a simple event framework for decoupled communication. It uses :mod:zope.event if that is installed.

    • πŸ”Œ :mod:gevent.monkey has support for plugins in the form of event subscribers and setuptools entry points. See :pr:1158 and :issue:1162. setuptools must be installed at runtime for its entry points to function.

    Monitoring and Debugging

    • πŸ”§ Introduce the configuration variable gevent.config.track_greenlet_tree (aka GEVENT_TRACK_GREENLET_TREE) to allow disabling the greenlet tree features for applications where greenlet spawning is performance critical. This restores spawning performance to 1.2 levels.

    • βž• Add an optional monitoring thread for each hub. When enabled, this thread (by default) looks for greenlets that block the event loop for more than 0.1s. You can add your own periodic monitoring functions to this thread. Set GEVENT_MONITOR_THREAD_ENABLE to use it, and GEVENT_MAX_BLOCKING_TIME to configure the blocking interval.

    • The monitoring thread emits events when it detects certain conditions, like loop blocked or memory limits exceeded.

    • βž• Add settings for monitoring memory usage and emitting events when a threshold is exceeded and then corrected. gevent currently supplies no policy for what to do when memory exceeds the configured limit. psutil must be installed to use this. See :pr:1150.

  • v1.3.a2 Changes

    March 06, 2018


    • πŸ— Cython 0.28b1 or later is now required to build gevent from a source checkout (Cython is not required to build a source distribution from PyPI).

    • ⚑️ Update c-ares to 1.14.0. See :issue:1105.

    • gevent now requires the patched version of libuv it is distributed with. Building gevent with a non-embedded libuv, while not previously supported, is not possible now. See :issue:1126.

    πŸ‘ Platform Support

    • πŸ‘· Travis CI tests on Python 3.7.0b2 and PyPy 2.7 5.10.0 and PyPy 3.5 5.10.1.

    πŸ— Build Changes

    • πŸ›  Fix building from a source distribution (PyPI) without Cython installed.

    ✨ Enhancements

    • βž• Add the dnspython resolver as a lightweight alternative to c-ares. It is generally faster than c-ares and is supported on PyPy. c-ares may be deprecated in the future. See :pr:1088 and :issue:1103.

    • βž• Add the module :mod:gevent.time that can be imported instead of :mod:time, much like :mod:gevent.socket can be imported instead of :mod:socket. It contains gevent.sleep. This aids monkey-patching.

    • Simple subclasses of gevent.local.local now have the same (substantially improved) performance characteristics of plain gevent.local.local itself, making them 2 to 3 times faster than before. See :pr:1117. If there are any compatibility problems, please open issues.

    Monitoring and Debugging

    - Greenlet objects now keep track of their spawning parent greenlet
      and the code location that spawned them, in addition to maintaining
      a "spawn tree local" mapping. This adds some runtime overhead in
      relative terms, but absolute numbers are still relatively small.
      Based on a proposal from PayPal and comments by Mahmoud Hashemi and
      Kurt Rose. See :issue:`755` and :pr:`1115`. As always, feedback is
    - Greenlet objects now have a `minimal_ident
      <gevent.Greenlet.minimal_ident>` property. It functions
      similarly to ``Thread.ident`` or ``id`` by uniquely identifying the
      greenlet object while it remains alive, and it can be reused after
      the greenlet object is dead. It is different in that it is small and
      sequential. Based on a proposal from PayPal and comments by Mahmoud
      Hashemi and Kurt Rose. See :issue:`755`. As always, feedback is
    - `gevent.Greenlet` objects now have a ``
      attribute that is included in the default repr.
    - Include the values of `gevent.local.local` objects associated with
      each greenlet in `gevent.util.format_run_info`.
    - βž• Add `gevent.util.GreenletTree` to visualize the greenlet tree. This
      is used by `gevent.util.format_run_info`.
    - 🚦 Make :class:`gevnt.subprocess.Popen` accept the ``restore_signals``
      keyword argument on all versions of Python, and on Python 2 have it
      default to false. It previously defaulted to true on all versions;
      now it only defaults to true on Python 3. The standard library in
      Python 2 does not have this argument and its behaviour with regards
      to signals is undocumented, but there is code known to rely on
      signals not being restored under Python 2. Initial report and patch
      in :pr:`1063` by Florian Margaine.
    - πŸ‘ Allow :class:`gevent.subprocess.Popen` to accept the keyword
      arguments ``pass_fds`` and ``start_new_session`` under Python 2.
      They have always had the same default as Python 3, namely an empty
      tuple and false, but now are accessible to Python 2.
    - πŸ‘Œ Support the ``capture_output`` argument added to Python 3.7 in
    πŸ”§ Configuration
    - πŸ”§ Centralize all gevent configuration in an object at
      ``gevent.config``, allowing for gevent to be configured through code
      and not *necessarily* environment variables, and also provide a
      centralized place for documentation. See :issue:`1090`.
      - The new ``GEVENT_CORE_CFFI_ONLY`` environment variable has been
        replaced with the pre-existing ``GEVENT_LOOP`` environment
        variable. That variable may take the values ``libev-cext``,
        ``libev-cffi``, or ``libuv-cffi``, (or be a list in preference
        order, or be a dotted name; it may also be assigned to an
        object in Python code at ``gevent.config.loop``).
      - The ``GEVENTARES_SERVERS`` environment variable is deprecated in
        favor of ``GEVENT_RESOLVER_SERVERS``. See :issue:`1103`.
    πŸ› Bug Fixes
    - πŸ›  Fix calling ``shutdown`` on a closed socket. It was raising
      ``AttributeError``, now it once again raises the correct
      ``socket.error``. Reported in :issue:`1089` by AndrΓ© Cimander.
    - πŸ›  Fix an interpreter crash that could happen if two or more ``loop``
      objects referenced the default event loop and one of them was
      destroyed and then the other one destroyed or (in the libev C
      extension implementation only) deallocated (garbage collected). See
    - πŸ›  Fix a race condition in libuv child callbacks. See :issue:`1104`.
    Other Changes
    - The internal, undocumented module ``gevent._threading`` has been
    - The internal, undocumented class ``gevent._socket3._fileobject`` has
      been removed. See :issue:`1084`.
    - 0️⃣ Simplify handling of the libev default loop and the ``destroy()``
      method. The default loop, when destroyed, can again be requested and
      it will regenerate itself. The default loop is the only one that can
      receive child events.
    - πŸ‘‰ Make :meth:`gevent.socket.socket.sendall` up to ten times faster on
      PyPy3, through the same change that was applied in gevent 1.1b3 for PyPy2.
    - ⚠  Be more careful about issuing a warning about patching SSL on
      Python 2. See :issue:`1108`.
    - 🚦 Signal handling under PyPy with libuv is more reliable. See
    - The :mod:`gevent.greenlet` module is now compiled with Cython to
      offset any performance decrease due to :issue:`755`. Please open
      issues for any compatibility concerns. See :pr:`1115` and :pr:`1120`.
    - On CPython, allow the pure-Python implementations of
      `gevent.Greenlet`, `gevent.local` and `gevent.lock` to be
      used when the environment variable ``PURE_PYTHON`` is set. This is
      not recommended except for debugging and testing. See :issue:`1118`.
    - ⏱ :meth:`` now interprets a *timeout* of -1 the
      same as a *timeout* of *None* as the standard requires. Previously,
      on libuv this was interpreted the same as a *timeout* of 0. In
      addition, all *timeout* values less than zero are interpreted like
      *None* (as they always were under libev). See :issue:`1127`.
    - 0️⃣ Monkey-patching now defaults to patching ``threading.Event``.
  • v1.3.a1 Changes

    January 27, 2018


    • βœ… gevent is now built and tested with Cython 0.27. This is required for Python 3.7 support.

    • ⚑️ Update c-ares to 1.13.0. See :issue:990.

    πŸ‘ Platform Support

    • βž• Add initial support for Python 3.7a3. It has the same level of support as Python 3.6.

      • Using unreleased Cython 0.28 and greenlet 0.4.13; requires Python 3.7a3.
      • The async functions and classes have been renamed to async_ due to async becoming a keyword in Python 3.7. Aliases are still in place for older versions. See :issue:1047.
    • βœ… gevent is now tested on Python 3.6.4. This includes the following fixes and changes:

      • Errors raised from :mod:gevent.subprocess will have a filename attribute set.
      • The :class:threading.Timer class is now monkey-patched and can be joined. Previously on Python 3.4 and above, joining a Timer would hang the process.
      • :meth:gevent.ssl.SSLSocket.unwrap behaves more like the standard library, including returning a SSLSocket and allowing certain timeout-related SSL errors to propagate. The added standard library tests now passes.
      • :class:gevent.subprocess.Popen accepts a "path-like object" for the cwd parameter on all platforms. Previously this only worked on POSIX platforms under Python 3.6. Now it also works on Windows under Python 3.6 (as expected) and is backported to all previous versions.
    • ⚑️ Linux CI now tests on PyPy3 3.5-5.9.0, updated from PyPy3 3.5-5.7.1. See :issue:1001. PyPy2 has been updated to 5.9.0 from 5.7.1, Python 2.7 has been updated to 2.7.14 from 2.7.13, Python 3.4 is updated to 3.4.7 from 3.4.5, Python 3.5 is now 3.5.4 from 3.5.3, and Python 3.6 is now 3.6.4 from 3.6.0.

    • πŸ“š Drop support for Python 3.3. The documentation has only claimed support for 3.4+ since gevent 1.2 was released, and only 3.4+ has been tested. This merely removes the supporting Trove classifier and remaining test code. See :issue:997.

    • 🏁 PyPy is now known to run on Windows using the libuv backend, with caveats. See the section on libuv for more information.

    • πŸ”’ Due to security concerns, official support for Python 2.7.8 and earlier (without a modern SSL implementation) has been dropped. These versions are no longer tested with gevent, but gevent can still be installed on them. Supporting code will be removed in the next major version of gevent. See :issue:1073.

    πŸ— Build Changes

    • When building gevent from a source checkout (not a distributed source distribution), make is no longer required and the Makefile is not used. Neither is an external cython command. Instead, the cythonize function is used, as recommended by Cython. (The external commands were never required by source distributions.) See :issue:1076.

    • :class:gevent.local.local is compiled with Cython on CPython.

    • The Cython ares 'channel' class is no longer declared to be publicly accessible from a named C structure. Doing so caused a conflict with the c-ares header files.

    πŸ› Bug Fixes

    • If a single greenlet created and destroyed many :class:gevent.local.local objects without ever exiting, there would be a leak of the function objects intended to clean up the locals after the greenlet exited. Introduce a weak reference to avoid that. Reported in :issue:981 by Heungsub Lee.

    • 0️⃣ pywsgi also catches and ignores by default :const:errno.WSAECONNABORTED on Windows. Initial patch in :pr:999 by Jan van Valburg.

    • :meth:gevent.subprocess.Popen.communicate returns the correct type of str (not bytes) in universal newline mode under Python 3, or when an encoding has been specified. Initial patch in :pr:939 by William Grzybowski.

    • :meth:gevent.subprocess.Popen.communicate (and in general, accessing Popen.stdout and Popen.stderr) returns the correct type of str (bytes) in universal newline mode under Python 2. Previously it always returned unicode strings. Reported in :issue:1039 by Michal Petrucha.

    • :class:gevent.fileobject.FileObjectPosix returns native strings in universal newline mode on Python 2. This is consistent with what :class:.FileObjectThread does. See :issue:1039.

    • 🍎 socket.send() now catches EPROTOTYPE on macOS to handle a race condition during shutdown. Fixed in :pr:1035 by Jay Oster.

    • :func:gevent.socket.create_connection now properly cleans up open sockets if connecting or binding raises a :exc:BaseException like :exc:KeyboardInterrupt, :exc:greenlet.GreenletExit or :exc:gevent.timeout.Timeout. Reported in :issue:1044 by kochelmonster.

    Other Changes

    • ⏱ Pool.add now accepts blocking and timeout parameters, which function similarly to their counterparts in Semaphore. See :pr:1032 by Ron Rothman.

    • Defer adjusting the stdlib's list of active threads until threading is monkey patched. Previously this was done when :mod:gevent.threading was imported. That module is documented to be used as a helper for monkey patching, so this should generally function the same, but some applications ignore the documentation and directly import that module anyway.

    A positive consequence is that import gevent.threading, threading; threading.current_thread() will no longer return a DummyThread before monkey-patching. Another positive consequence is that PyPy will no longer print a KeyError on exit if :mod:gevent.threading was imported without monkey-patching.

    See :issue:984.

    • πŸ“‡ Specify the Requires-Python metadata for improved installation support in certain tools (setuptools v24.2.1 or newer is required). See :issue:995.

    • Monkey-patching after the :mod:ssl module has been imported now prints a warning because this can produce RecursionError.

    • :class:gevent.local.local objects are now approximately 3.5 times faster getting, setting and deleting attributes on PyPy. This involved implementing more of the attribute protocols directly. Please open an issue if you have any compatibility problems. See :issue:1020.

    • :class:gevent.local.local is compiled with Cython on CPython. It was already 5 to 6 times faster due to the work on :issue:1020, and compiling it with Cython makes it another 5 to 6 times faster, for a total speed up of about 35 times. It is now in the same ballpark as the native :class:threading.local class. It also uses one pointer less memory per object, and one pointer less memory per greenlet. See :pr:1024.

    • 🏁 More safely terminate subprocesses on Windows with :meth:gevent.subprocess.Popen.terminate. Reported in :issue:1023 by Giacomo Debidda.

    • gevent now uses cffi's "extern 'Python'" callbacks. These should be faster and more stable. This requires at least cffi 1.4.0. See :issue:1049.

    • ⏱ gevent now approximately tries to stick to a scheduling interval when running callbacks, instead of simply running a count of callbacks. The interval is determined by :func:gevent.getswitchinterval. On Python 3, this is the same as the thread switch interval. On Python 2, this defaults to 0.005s and can be changed with :func:gevent.setswitchinterval. This should result in more fair "scheduling" of greenlets, especially when gevent.sleep(0) or other busy callbacks are in use. The interval is checked every 50 callbacks to keep overhead low. See :issue:1072. With thanks to Arcadiy Ivanov and Antonio Cuni.


    • Add initial experimental support for using libuv as a backend instead of libev, controlled by setting the environment variable GEVENT_CORE_CFFI_ONLY=libuv before importing gevent. This suffers a number of limitations compared to libev, notably:

      • libuv support is not available in the manylinux wheels uploaded to PyPI. The manylinux specification requires glibc 2.5, while libuv requires glibc 2.12. Install from source to access libuv on Linux (e.g., pip's --no-binary option).
      • Timers (such as gevent.sleep and gevent.Timeout) only support a resolution of 1ms (in practice, it's closer to 1.5ms). Attempting to use something smaller will automatically increase it to 1ms and issue a warning. Because libuv only supports millisecond resolution by rounding a higher-precision clock to an integer number of milliseconds, timers apparently suffer from more jitter.
      • Using negative timeouts may behave differently from libev.
      • libuv blocks delivery of all signals, so signals are handled using an (arbitrary) 0.3 second timer. This means that signal handling will be delayed by up to that amount, and that the longest the event loop can sleep in the operating system's poll call is that amount. Note that this is what gevent does for libev on Windows too.
      • libuv only supports one io watcher per file descriptor, whereas libev and gevent have always supported many watchers using different settings. The libev behaviour is emulated at the Python level, but that adds overhead.
      • Looping multiple times and expecting events for the same file descriptor to be raised each time without any data being read or written (as works with libev) does not appear to work correctly on Linux when using or a monkey-patched selectors.PollSelector.
      • The build system does not support using a system libuv; the embedded copy must be used. Using setuptools to compile libuv was the most portable method found.
      • If anything unexpected happens, libuv likes to abort() the entire process instead of reporting an error. For example, closing a file descriptor it is using in a watcher may cause the entire process to be exited.
      • There may be occasional otherwise unexplained and hard to duplicate crashes. If you can duplicate a crash, please submit an issue.
      • This is the only backend that PyPy can use on Windows. As of this alpha, there are many known issues with non-blocking sockets (e.g., as used by :mod:asyncore; see and sometimes sockets not getting closed in a timely fashion (apparently; see and communicating with subprocesses (it always hangs). Help tracking those down would be appreciated. Only PyPy2 is tested.

    Feedback and pull requests are welcome, especially to address the issues mentioned above.

    Other differences include:

    • The order in which timers and other callbacks are invoked may be different than in libev. In particular, timers and IO callbacks happen in a different order, and timers may easily be off by up to half of the supposed 1ms resolution. See :issue:1057.

    • Starting a timer watcher does not update the loop's time by default. This is because, unlike libev, a timer callback can cause other timer callbacks to be run if they expire because the loop's time updated, without cycling the event loop. See :issue:1057.

      libev has also been changed to follow this behaviour.

      Also see :issue:1072.

    • Timers of zero duration do not necessarily cause the event loop to cycle, as they do in libev. Instead, they may be called immediately. If zero duration timers are added from other zero duration timer callbacks, this can lead the loop to appear to hang, as no IO will actually be done.

      To mitigate this issue, loop.timer() detects attempts to use zero duration timers and turns them into a check watcher. check watchers do not support the again method.

    • All watchers (e.g., and the Timeout class have a close method that should be called when code is done using the object (they also function as context managers and a with statement will automatically close them). gevent does this internally for sockets, file objects and internal timeouts. Neglecting to close an object may result in leaking native resources. To debug this, set the environment variables GEVENT_DEBUG=debug and PYTHONTRACEMALLOC=n before starting the process.

      The traditional cython-based libev backend will not leak if close is not called and will not produce warnings. The CFFI-based libev backend will not currently leak but will produce warnings. The CFFI-based libuv backend may leak and will produce warnings.

    Again, this is extremely experimental and all of it is subject to change.

    See :issue:790 for history and more in-depth discussion.


    • ⚑️ The C extension has been updated to use more modern Cython idioms and generate less code for simplicity, faster compilation and better cache usage. See :pr:1077.

      • Watcher objects may be slightly larger. On a 64-bit platform, a typical watcher may be 16 bytes (2 pointers) larger. This is offset by slight performance gains.
      • Cython is no longer preprocessed. Certain attributes that were previously only defined in certain compilation modes (notably LIBEV_EMBED) are now always defined, but will raise AttributeError or have a negative value when not available. In general these attributes are not portable or documented and are not implemented by libuv or the CFFI backend. See :issue:1076.
      • Certain private helper functions (gevent_handle_error, and part of gevent_call) are now implemented in Cython instead of C. This reduces our reliance on internal undocumented implementation details of Cython and Python that could change. See :pr:1080.