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[PATCH v2 00/24] python: introduce Asynchronous QMP package
[PATCH v2 00/24] python: introduce Asynchronous QMP package
Fri, 16 Jul 2021 20:32:29 -0400
This patch series adds an Asynchronous QMP package to the Python
library. It offers a few improvements over the previous library:
- out-of-band support
- true asynchronous event support
- avoids undocumented interfaces abusing non-blocking sockets
- unit tests!
This library serves as the basis for a new qmp-shell program that will
offer improved reconnection support, true asynchronous display of
events, VM and job status update notifiers, and so on.
My intent is to eventually publish this library directly to PyPI as a
standalone package. I would like to phase out our usage of the old QMP
library over time; eventually replacing it entirely with this one.
This series looks big by line count, but it's *mostly*
This package has *no* external dependencies whatsoever.
Notes & Design
Here are some notes on the design of how the library works, to serve as
a primer for review; however I also **highly recommend** browsing the
generated Sphinx documentation for this series.
Here's that link again:
The core machinery is split between the AsyncProtocol and QMP
classes. AsyncProtocol provides the generic machinery, while QMP
provides the QMP-specific details.
The design uses two independent coroutines that act as the "bottom
half", a writer task and a reader task. These tasks run for the duration
of the connection and independently send and receive messages,
A third task, disconnect, is scheduled asynchronously whenever an
unrecoverable error occurs and facilitates coalescing of the other two
This diagram for how execute() operates may be helpful for understanding
how AsyncProtocol is laid out. The arrows indicate the direction of a
QMP message; the long horizontal dash indicates the separation between
the upper and lower half of the event loop. The queue mechanisms between
both dashes serve as the intermediaries between the upper and lower
| caller |
+---------------> |execute()| -----------+
| +---------+ |
+----+------+ +----------------+ +------+-------+
| ExecQueue | | EventListeners | |Outbound Queue|
+----+------+ +----+-----------+ +------+-------+
^ ^ |
| | |
| | |
| | v
| Reader Task/Coroutine | | Writer Task/Coroutine |
The caller will invoke execute(), which in turn will deposit a message
in the outbound send queue. This will wake up the writer task, which
well send the message over the wire.
The execute() method will then yield to wait for a reply delivered to an
execution queue created solely for that execute statement.
When a message arrives, the Reader task will unblock and route the
message either to the EventListener subsystem, or place it in the
appropriate pending execution queue.
Once a message is placed in the pending execution queue, execute() will
unblock and the execution will conclude, returning the result of the RPC
call to the caller.
Patches 1-4 add tiny pre-requisites, utilities, etc.
Patches 5-12 add a generic async message-based protocol class,
AsyncProtocol. They are split fairly small and should
be reasonably self-contained.
Patches 13-15 check in more QMP-centric components.
Patches 16-21 add qmp_client.py, with a new 'QMPClient()' class.
They're split into reasonably tiny pieces here.
Patches 22-23 add a few finishing touches, they are small patches.
Patch 24 adds unit tests. They're maybe a little messy yet, but
they've been quite helpful to me so far. Coverage of
protocol.py is at about 86%.
These items are in progress:
- A synchronous QMP wrapper that allows this library to be easily used
from non-async code; this will also allow me to prove it works well by
demoing its replacement throughout iotests. I have all of iotests
passing locally, but I am still seeing some failures on gitlab CI I
need to diagnose, possibly a race condition somewhere.
- A QMP server class; to facilitate writing of unit tests. It's done,
but needs some polish and tests.
- More unit tests for qmp_client.py, qmp_server.py and other modules.
- Renamed qmp_protocol.py to qmp_client.py
- Renamed 'QMP' class to 'QMPClient'
- Renamed _begin_new_session() to _establish_session()
- Split _establish_connection() out from _new_session().
- Removed _results() method
- Suppress duplicate Exceptions when attempting to drain the
- Delay initialization of asyncio.Queue and asyncio.Event variables to
_new_session or later -- they must not be created outside of the loop,
even if they are not async functions.
- Rework runstate_changed events to guarantee visibility of events to
- Improve connect()/accept() cleanup to work with
- No-argument form of Message() now succeeds properly.
- flush utility will correctly yield when data is below the "high water
mark", giving the stream a chance to actually flush.
- Increase read buffer size to accommodate query-qmp-schema (Thanks
Ugly bits from V1 removed:
- Remove tertiary filtering from EventListener (for now), accompanying
documentation removed from events.py
- Use asyncio.wait() instead of custom wait_task_done()
- MultiException is removed in favor of just raising the first Exception
that occurs in the bottom half; other Exceptions if any are logged
- QMPClient now allows ID-less execution statements via the _raw()
- Add tests that grant ~86% coverage of protocol.py to the avocado test
- Removed 'force' parameter from _bh_disconnect; the disconnection
routine determines for itself if we are in the error pathway or not
instead now. This removes any chance of duplicate calls to
_schedule_disconnect accidentally dropping the 'force' setting.
- Add debug: bool parameter to asyncio_run utility wrapper
- Improve error messages for '@require' decorator
- Add debugging message for state change events
- Avoid flushing the StreamWriter if we don't have one (This
circumstance only arises in testing, but it's helpful.)
- Improved __repr__ method for AsyncProtocol, and removed __str__
method. enforcing eval(__repr__(x)) == x does not make sense for
- Misc logging message changes
- Add a suite of fancy Task debugging utilities.
- Most tracebacks now log at the DEBUG level instead of
CRITICAL/ERROR/WARNING; In those error cases, a one-line summary is
Misc. aesthetic changes:
- Misc docstring fixes, whitespace, etc.
- Reordered the definition of some methods to try and keep similar
methods near each other (Moved _cleanup near _bh_disconnect in
~ Shucks Howdy, Gee Golly!
John Snow (24):
python/aqmp: add asynchronous QMP (AQMP) subpackage
python/aqmp: add error classes
python/pylint: Add exception for TypeVar names ('T')
python/aqmp: add asyncio compatibility wrappers
python/aqmp: add generic async message-based protocol support
python/aqmp: add runstate state machine to AsyncProtocol
python/aqmp: Add logging utility helpers
python/aqmp: add logging to AsyncProtocol
python/aqmp: add AsyncProtocol.accept() method
python/aqmp: add configurable read buffer limit
python/aqmp: add _cb_inbound and _cb_inbound logging hooks
python/aqmp: add AsyncProtocol._readline() method
python/aqmp: add QMP Message format
python/aqmp: add well-known QMP object models
python/aqmp: add QMP event support
python/pylint: disable too-many-function-args
python/aqmp: add QMP protocol support
python/pylint: disable no-member check
python/aqmp: Add message routing to QMP protocol
python/aqmp: add execute() interfaces
python/aqmp: add _raw() execution interface
python/aqmp: add asyncio_run compatibility wrapper
python/aqmp: add scary message
python/aqmp: add AsyncProtocol unit tests
python/qemu/aqmp/__init__.py | 58 +++
python/qemu/aqmp/error.py | 50 ++
python/qemu/aqmp/events.py | 706 ++++++++++++++++++++++++++
python/qemu/aqmp/message.py | 209 ++++++++
python/qemu/aqmp/models.py | 133 +++++
python/qemu/aqmp/protocol.py | 882 +++++++++++++++++++++++++++++++++
python/qemu/aqmp/py.typed | 0
python/qemu/aqmp/qmp_client.py | 621 +++++++++++++++++++++++
python/qemu/aqmp/util.py | 207 ++++++++
python/setup.cfg | 5 +-
python/tests/null_proto.py | 67 +++
python/tests/protocol.py | 458 +++++++++++++++++
12 files changed, 3395 insertions(+), 1 deletion(-)
create mode 100644 python/qemu/aqmp/__init__.py
create mode 100644 python/qemu/aqmp/error.py
create mode 100644 python/qemu/aqmp/events.py
create mode 100644 python/qemu/aqmp/message.py
create mode 100644 python/qemu/aqmp/models.py
create mode 100644 python/qemu/aqmp/protocol.py
create mode 100644 python/qemu/aqmp/py.typed
create mode 100644 python/qemu/aqmp/qmp_client.py
create mode 100644 python/qemu/aqmp/util.py
create mode 100644 python/tests/null_proto.py
create mode 100644 python/tests/protocol.py
- [PATCH v2 00/24] python: introduce Asynchronous QMP package,
John Snow <=
- [PATCH v2 01/24] python/aqmp: add asynchronous QMP (AQMP) subpackage, John Snow, 2021/07/16
- [PATCH v2 02/24] python/aqmp: add error classes, John Snow, 2021/07/16
- [PATCH v2 04/24] python/aqmp: add asyncio compatibility wrappers, John Snow, 2021/07/16
- [PATCH v2 03/24] python/pylint: Add exception for TypeVar names ('T'), John Snow, 2021/07/16
- [PATCH v2 05/24] python/aqmp: add generic async message-based protocol support, John Snow, 2021/07/16
- [PATCH v2 06/24] python/aqmp: add runstate state machine to AsyncProtocol, John Snow, 2021/07/16
- [PATCH v2 07/24] python/aqmp: Add logging utility helpers, John Snow, 2021/07/16
- [PATCH v2 08/24] python/aqmp: add logging to AsyncProtocol, John Snow, 2021/07/16
- [PATCH v2 09/24] python/aqmp: add AsyncProtocol.accept() method, John Snow, 2021/07/16
- [PATCH v2 10/24] python/aqmp: add configurable read buffer limit, John Snow, 2021/07/16