Current File : //snap/core/current/usr/lib/python3/dist-packages/pyudev/__pycache__/monitor.cpython-35.pyc
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pyudev.monitor
==============
Monitor implementation.
.. moduleauthor:: Sebastian Wiesner <lunaryorn@gmail.com>
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A synchronous device event monitor.
A :class:`Monitor` objects connects to the udev daemon and listens for
changes to the device list. A monitor is created by connecting to the
kernel daemon through netlink (see :meth:`from_netlink`):
>>> from pyudev import Context, Monitor
>>> context = Context()
>>> monitor = Monitor.from_netlink(context)
Once the monitor is created, you can add a filter using :meth:`filter_by()`
or :meth:`filter_by_tag()` to drop incoming events in subsystems, which are
not of interest to the application:
>>> monitor.filter_by('input')
When the monitor is eventually set up, you can either poll for events
synchronously:
>>> device = monitor.poll(timeout=3)
>>> if device:
... print('{0.action}: {0}'.format(device))
...
Or you can monitor events asynchronously with :class:`MonitorObserver`.
To integrate into various event processing frameworks, the monitor provides
a :func:`selectable <select.select>` file description by :meth:`fileno()`.
However, do *not* read or write directly on this file descriptor.
Instances of this class can directly be given as ``udev_monitor *`` to
functions wrapped through :mod:`ctypes`.
.. versionchanged:: 0.16
Remove :meth:`from_socket()` which is deprecated, and even removed in
recent udev versions.
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Create a monitor by connecting to the kernel daemon through netlink.
``context`` is the :class:`Context` to use. ``source`` is a string,
describing the event source. Two sources are available:
``'udev'`` (the default)
Events emitted after udev as registered and configured the device.
This is the absolutely recommended source for applications.
``'kernel'``
Events emitted directly after the kernel has seen the device. The
device has not yet been configured by udev and might not be usable
at all. **Never** use this, unless you know what you are doing.
Return a new :class:`Monitor` object, which is connected to the
given source. Raise :exc:`~exceptions.ValueError`, if an invalid
source has been specified. Raise
:exc:`~exceptions.EnvironmentError`, if the creation of the monitor
failed.
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``True``, if this monitor was started, ``False`` otherwise. Readonly.
.. seealso:: :meth:`start()`
.. versionadded:: 0.16
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Return the file description associated with this monitor as integer.
This is really a real file descriptor ;), which can be watched and
:func:`select.select`\ ed.
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Filter incoming events.
``subsystem`` is a byte or unicode string with the name of a
subsystem (e.g. ``'input'``). Only events originating from the
given subsystem pass the filter and are handed to the caller.
If given, ``device_type`` is a byte or unicode string specifying the
device type. Only devices with the given device type are propagated
to the caller. If ``device_type`` is not given, no additional
filter for a specific device type is installed.
These filters are executed inside the kernel, and client processes
will usually not be woken up for device, that do not match these
filters.
.. versionchanged:: 0.15
This method can also be after :meth:`start()` now.
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Filter incoming events by the given ``tag``.
``tag`` is a byte or unicode string with the name of a tag. Only
events for devices which have this tag attached pass the filter and are
handed to the caller.
Like with :meth:`filter_by` this filter is also executed inside the
kernel, so that client processes are usually not woken up for devices
without the given ``tag``.
.. udevversion:: 154
.. versionadded:: 0.9
.. versionchanged:: 0.15
This method can also be after :meth:`start()` now.
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Remove any filters installed with :meth:`filter_by()` or
:meth:`filter_by_tag()` from this monitor.
.. warning::
Up to udev 181 (and possibly even later versions) the underlying
``udev_monitor_filter_remove()`` seems to be broken. If used with
affected versions this method always raises
:exc:`~exceptions.ValueError`.
Raise :exc:`~exceptions.EnvironmentError` if removal of installed
filters failed.
.. versionadded:: 0.15
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Switch the monitor into listing mode.
Connect to the event source and receive incoming events. Only after
calling this method, the monitor listens for incoming events.
.. note::
This method is implicitly called by :meth:`__iter__`. You don't
need to call it explicitly, if you are iterating over the
monitor.
.. deprecated:: 0.16
Will be removed in 1.0. Use :meth:`start()` instead.
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Start this monitor.
The monitor will not receive events until this method is called. This
method does nothing if called on an already started :class:`Monitor`.
.. note::
Typically you don't need to call this method. It is implicitly
called by :meth:`poll()` and :meth:`__iter__()`.
.. seealso:: :attr:`started`
.. versionchanged:: 0.16
This method does nothing if the :class:`Monitor` was already
started.
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Set the receive buffer ``size``.
``size`` is the requested buffer size in bytes, as integer.
.. note::
The CAP_NET_ADMIN capability must be contained in the effective
capability set of the caller for this method to succeed. Otherwise
:exc:`~exceptions.EnvironmentError` will be raised, with ``errno``
set to :data:`~errno.EPERM`. Unprivileged processes typically lack
this capability. You can check the capabilities of the current
process with the python-prctl_ module:
>>> import prctl
>>> prctl.cap_effective.net_admin
Raise :exc:`~exceptions.EnvironmentError`, if the buffer size could not
bet set.
.. versionadded:: 0.13
.. _python-prctl: http://packages.python.org/python-prctl
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Receive a single device from the monitor.
Return the received :class:`Device`. Raise
:exc:`~exceptions.EnvironmentError`, if no device could be read.
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Poll for a device event.
You can use this method together with :func:`iter()` to synchronously
monitor events in the current thread::
for device in iter(monitor.poll, None):
print('{0.action} on {0.device_path}'.format(device))
Since this method will never return ``None`` if no ``timeout`` is
specified, this is effectively an endless loop. With
:func:`functools.partial()` you can also create a loop that only waits
for a specified time::
for device in iter(partial(monitor.poll, 3), None):
print('{0.action} on {0.device_path}'.format(device))
This loop will only wait three seconds for a new device event. If no
device event occurred after three seconds, the loop will exit.
``timeout`` is a floating point number that specifies a time-out in
seconds. If omitted or ``None``, this method blocks until a device
event is available. If ``0``, this method just polls and will never
block.
.. note::
This method implicitly calls :meth:`start()`.
Return the received :class:`Device`, or ``None`` if a timeout
occurred. Raise :exc:`~exceptions.EnvironmentError` if event retrieval
failed.
.. seealso::
:attr:`Device.action`
The action that created this event.
:attr:`Device.sequence_number`
The sequence number of this event.
.. versionadded:: 0.16
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Receive a single device from the monitor.
.. warning::
You *must* call :meth:`start()` before calling this method.
The caller must make sure, that there are events available in the
event queue. The call blocks, until a device is available.
If a device was available, return ``(action, device)``. ``device``
is the :class:`Device` object describing the device. ``action`` is
a string describing the action. Usual actions are:
``'add'``
A device has been added (e.g. a USB device was plugged in)
``'remove'``
A device has been removed (e.g. a USB device was unplugged)
``'change'``
Something about the device changed (e.g. a device property)
``'online'``
The device is online now
``'offline'``
The device is offline now
Raise :exc:`~exceptions.EnvironmentError`, if no device could be
read.
.. deprecated:: 0.16
Will be removed in 1.0. Use :meth:`Monitor.poll()` instead.
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Wait for incoming events and receive them upon arrival.
This methods implicitly calls :meth:`start()`, and starts polling the
:meth:`fileno` of this monitor. If a event comes in, it receives the
corresponding device and yields it to the caller.
The returned iterator is endless, and continues receiving devices
without ever stopping.
Yields ``(action, device)`` (see :meth:`receive_device` for a
description).
.. deprecated:: 0.16
Will be removed in 1.0. Use an explicit loop over :meth:`poll()`
instead, or monitor asynchronously with :class:`MonitorObserver`.
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An asynchronous observer for device events.
This class subclasses :class:`~threading.Thread` class to asynchronously
observe a :class:`Monitor` in a background thread:
>>> from pyudev import Context, Monitor, MonitorObserver
>>> context = Context()
>>> monitor = Monitor.from_netlink(context)
>>> monitor.filter_by(subsystem='input')
>>> def print_device_event(device):
... print('background event {0.action}: {0.device_path}'.format(device))
>>> observer = MonitorObserver(monitor, callback=print_device_event, name='monitor-observer')
>>> observer.daemon
True
>>> observer.start()
In the above example, input device events will be printed in background,
until :meth:`stop()` is called on ``observer``.
.. note::
Instances of this class are always created as daemon thread. If you do
not want to use daemon threads for monitoring, you need explicitly set
:attr:`~threading.Thread.daemon` to ``False`` before invoking
:meth:`~threading.Thread.start()`.
.. seealso::
:attr:`Device.action`
The action that created this event.
:attr:`Device.sequence_number`
The sequence number of this event.
.. versionadded:: 0.14
.. versionchanged:: 0.15
:meth:`Monitor.start()` is implicitly called when the thread is started.
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Create a new observer for the given ``monitor``.
``monitor`` is the :class:`Monitor` to observe. ``callback`` is the
callable to invoke on events, with the signature ``callback(device)``
where ``device`` is the :class:`Device` that caused the event.
.. warning::
``callback`` is invoked in the observer thread, hence the observer
is blocked while callback executes.
``args`` and ``kwargs`` are passed unchanged to the constructor of
:class:`~threading.Thread`.
.. deprecated:: 0.16
The ``event_handler`` argument will be removed in 1.0. Use
the ``callback`` argument instead.
.. versionchanged:: 0.16
Add ``callback`` argument.
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Send a stop signal to the background thread.
The background thread will eventually exit, but it may still be running
when this method returns. This method is essentially the asynchronous
equivalent to :meth:`stop()`.
.. note::
The underlying :attr:`monitor` is *not* stopped.
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Synchronously stop the background thread.
.. note::
This method can safely be called from the observer thread. In this
case it is equivalent to :meth:`send_stop()`.
Send a stop signal to the backgroud (see :meth:`send_stop`), and waits
for the background thread to exit (see :meth:`~threading.Thread.join`)
if the current thread is *not* the observer thread.
After this method returns in a thread *that is not the observer
thread*, the ``callback`` is guaranteed to not be invoked again
anymore.
.. note::
The underlying :attr:`monitor` is *not* stopped.
.. versionchanged:: 0.16
This method can be called from the observer thread.
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