docs: changelog concision / additions

Author: dw

docs/changelog.rst

@@ -24,19 +24,44 @@ To avail of fixes in an unreleased version, please download a ZIP file
 Enhancements
 ^^^^^^^^^^^^
 
-* `#587 <https://github.com/dw/mitogen/issues/587>`_: partial support for
-  Ansible 2.8 is available. This implementation does not yet support the new
-  `become plugins
-  <https://docs.ansible.com/ansible/latest/plugins/become.html>`_
-  functionality, which will be addressed in a future release.
+* `#587 <https://github.com/dw/mitogen/issues/587>`_: Ansible 2.8 is partially
+  supported. `Become plugins
+  <https://docs.ansible.com/ansible/latest/plugins/become.html>`_ and
+  `interpreter discovery
+  <https://docs.ansible.com/ansible/latest/reference_appendices/interpreter_discovery.html>`_
+  are not yet handled.
+
+* The ``MITOGEN_CPU_COUNT`` environment variable shards the connection
+  multiplexer into per-CPU worker processes. This improves throughput for large
+  runs especially involving file transfer, and is a prerequisite to future
+  in-process SSH support. To match the behaviour of older releases, only one
+  multiplexer is started by default.
+
+* `#419 <https://github.com/dw/mitogen/issues/419>`_,
+  `#470 <https://github.com/dw/mitogen/issues/470>`_, file descriptor usage
+  during large runs is halved, as it is no longer necessary to manage read and
+  write sides distinctly in order to work around a design limitation.
+
+* `#419 <https://github.com/dw/mitogen/issues/419>`_: almost all connection
+  setup happens on one thread, reducing GIL contention and context switching
+  early in a run.
+
+* `#419 <https://github.com/dw/mitogen/issues/419>`_: 2 network round-trips
+  were removed from early connection setup.
+
+* `? <https://github.com/dw/mitogen/commit/7ae926b3>`_,
+  `? <https://github.com/dw/mitogen/commit/7ae926b3>`_,
+  `? <https://github.com/dw/mitogen/commit/7ae926b3>`_,
+  `? <https://github.com/dw/mitogen/commit/7ae926b3>`_: locking is avoided in
+  some hot paths, and locks that must be taken are held for less time.
 
 
 Fixes
 ^^^^^
 
-* `#363 <https://github.com/dw/mitogen/issues/363>`_: fix a rare race matching
-  *Permission denied* errors from some versions of ``su`` running on heavily
-  loaded machines.
+* `#363 <https://github.com/dw/mitogen/issues/363>`_: fix an obscure race
+  matching *Permission denied* errors from some versions of ``su`` running on
+  heavily loaded machines.
 
 * `#578 <https://github.com/dw/mitogen/issues/578>`_: the extension could crash
   while rendering an error message, due to an incorrect format string.
@@ -61,61 +86,56 @@ Fixes
   ``lineinfile`` module began leaking writable temporary file descriptors since
   Ansible 2.7.0. When ``lineinfile`` was used to create or modify a script, and
   that script was later executed, the execution could fail with "*text file
-  busy*" due to the open descriptor. Temporary descriptors are now tracked and
-  cleaned up on module exit.
+  busy*" due to the leaked descriptor. Temporary descriptors are now tracked
+  and cleaned up on exit for all modules.
 
 
 Core Library
 ~~~~~~~~~~~~
 
 * Logs are more readable, and many :func:`repr` strings are more descriptive.
-  The old pseudo-function-call format is slowly being migrated to
-  human-readable output where appropriate. For example,
-  *"Stream(ssh:123).connect()"* could become *"connecting to ssh:123"*.
+  The old pseudo-function-call format is slowly migrating to human-readable
+  output where possible. For example, *"Stream(ssh:123).connect()"* might
+  be written *"connecting to ssh:123"*.
 
 * :func:`bytearray` was removed from the list of supported serialization types.
-  It has never been portable, and does not appear to have been used.
+  It was never portable between Python versions, unused, and never made much
+  sense to support as a wire type.
 
-* `#170 <https://github.com/dw/mitogen/issues/170>`_: to better support child
-  process management and a future asynchronous connect implementation, a
-  :class:`mitogen.parent.TimerList` API is available.
+* `#170 <https://github.com/dw/mitogen/issues/170>`_: to improve subprocess
+  management and asynchronous connect, a :class:`mitogen.parent.TimerList`
+  interface is available, accessible as :attr:`Broker.timers` in an
+  asynchronous context.
 
 * `#419 <https://github.com/dw/mitogen/issues/419>`_: the internal
   :class:`mitogen.core.Stream` has been refactored into 7 new classes,
   modularizing protocol behaviour, output buffering, line-oriented input
-  parsing, options handling and connection management. Connection setup is
+  parsing, option handling and connection management. Connection setup is
   internally asynchronous, laying almost all the groundwork needed for fully
   asynchronous connect, proxied Ansible become plug-ins, and integrating
   `libssh <https://www.libssh.org/>`_.
 
-* `#419 <https://github.com/dw/mitogen/issues/419>`_: zombie process reaping
-  has vastly improved, by using the timer API to efficiently poll for a slow
-  child to finish exiting. Polling avoids the need to install a process-global
-  `SIGCHLD` handler, or rely on the process-global 'signal file descriptor'
-  functionality only available in newer Python releases.
+* `#169 <https://github.com/dw/mitogen/issues/169>`_,
+  `#419 <https://github.com/dw/mitogen/issues/419>`_: zombie child reaping has
+  vastly improved, by using timers to efficiently poll for a slow child to
+  finish exiting. Polling avoids relying on process-global configuration such
+  as a `SIGCHLD` handler, or :func:`signal.set_wakeup_fd` available in modern
+  Python.
 
-* `#419 <https://github.com/dw/mitogen/issues/419>`_: most uses of
-  :func:`os.dup` have been removed, along with almost all cases of manual file
-  descriptor management. Descriptors are trapped in :func:`os.fdopen` objects
-  as soon as they are opened, ensuring a leaked object will close itself, and
-  ensuring every descriptor is fused to a `closed` flag, preventing historical
-  bugs where a double close could destroy descriptors belonging to an unrelated
-  stream.
+* `#256 <https://github.com/dw/mitogen/issues/256>`_,
 
-* `#419 <https://github.com/dw/mitogen/issues/419>`_,
-  `#549 <https://github.com/dw/mitogen/issues/549>`_, file descriptor usage
-  during large runs has approximately halved, as it is no longer necessary to
-  manage every read and write side distinctly, in order to avoid double-close
-  bugs. Avoiding double-close is instead handled by Python's built-in file
-  object.
+`#419 <https://github.com/dw/mitogen/issues/419>`_: most :func:`os.dup` was
+  eliminated, along with almost all manual file descriptor management.
+  Descriptors are trapped in :func:`os.fdopen` objects when they are created,
+  ensuring a leaked object will close itself, and ensuring every descriptor is
+  fused to a `closed` flag, preventing historical bugs where a double close
+  could destroy descriptors belonging to unrelated streams.
 
 * `a5536c35 <https://github.com/dw/mitogen/commit/a5536c35>`_: avoid quadratic
   buffer management when logging lines received from a child's redirected
   standard IO.
 
 
-
-
 Thanks!
 ~~~~~~~