1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
|
:mod:`selectors` -- High-level I/O multiplexing
===============================================
.. module:: selectors
:synopsis: High-level I/O multiplexing.
.. versionadded:: 3.4
Introduction
------------
This module allows high-level and efficient I/O multiplexing, built upon the
:mod:`select` module primitives. Users are encouraged to use this module
instead, unless they want precise control over the OS-level primitives used.
It defines a :class:`BaseSelector` abstract base class, along with several
concrete implementations (:class:`KqueueSelector`, :class:`EpollSelector`...),
that can be used to wait for I/O readiness notification on multiple file
objects. In the following, "file object" refers to any object with a
:meth:`fileno()` method, or a raw file descriptor. See :term:`file object`.
:class:`DefaultSelector` is an alias to the most efficient implementation
available on the current platform: this should be the default choice for most
users.
.. note::
The type of file objects supported depends on the platform: on Windows,
sockets are supported, but not pipes, whereas on Unix, both are supported
(some other types may be supported as well, such as fifos or special file
devices).
.. seealso::
:mod:`select`
Low-level I/O multiplexing module.
Classes
-------
Classes hierarchy::
BaseSelector
+-- SelectSelector
+-- PollSelector
+-- EpollSelector
+-- KqueueSelector
In the following, *events* is a bitwise mask indicating which I/O events should
be waited for on a given file object. It can be a combination of the constants
below:
+-----------------------+-----------------------------------------------+
| Constant | Meaning |
+=======================+===============================================+
| :const:`EVENT_READ` | Available for read |
+-----------------------+-----------------------------------------------+
| :const:`EVENT_WRITE` | Available for write |
+-----------------------+-----------------------------------------------+
.. class:: SelectorKey
A :class:`SelectorKey` is a :class:`~collections.namedtuple` used to
associate a file object to its underlying file decriptor, selected event
mask and attached data. It is returned by several :class:`BaseSelector`
methods.
.. attribute:: fileobj
File object registered.
.. attribute:: fd
Underlying file descriptor.
.. attribute:: events
Events that must be waited for this file object.
.. attribute:: data
Optional opaque data associated to this file object: for example, this
could be used to store per-client session.
.. class:: BaseSelector
A :class:`BaseSelector` is used to wait for I/O event readiness on multiple
file objects. It supports file stream registration, unregistration, and a
method to wait for I/O events on those streams, with an optional timeout.
It's an abstract base class, so cannot be instantiated. Use
:class:`DefaultSelector` instead, or one of :class:`SelectSelector`,
:class:`KqueueSelector` etc. if you want to specifically use an
implementation, and your platform supports it.
:class:`BaseSelector` and its concrete implementations support the
:term:`context manager` protocol.
.. method:: register(fileobj, events, data=None)
Register a file object for selection, monitoring it for I/O events.
*fileobj* is the file object to monitor.
*events* is a bitwise mask of events to monitor.
*data* is an opaque object.
This returns a new :class:`SelectorKey` instance, or raises a
:exc:`ValueError` in case of invalid event mask or file descriptor, or
:exc:`KeyError` if the file object is already registered.
.. method:: unregister(fileobj)
Unregister a file object from selection, removing it from monitoring. A
file object shall be unregistered prior to being closed.
*fileobj* must be a file object previously registered.
This returns the associated :class:`SelectorKey` instance, or raises a
:exc:`KeyError` if the file object is not registered.
.. method:: modify(fileobj, events, data=None)
Change a registered file object monitored events or attached data.
This is equivalent to :meth:`BaseSelector.unregister(fileobj)` followed
by :meth:`BaseSelector.register(fileobj, events, data)`, except that it
can be implemented more efficiently.
This returns a new :class:`SelectorKey` instance, or raises a
:exc:`ValueError` in case of invalid event mask or file descriptor, or
:exc:`KeyError` if the file object is not registered.
.. method:: select(timeout=None)
Wait until some registered file objects become ready, or the timeout
expires.
If ``timeout > 0``, this specifies the maximum wait time, in seconds.
If ``timeout <= 0``, the call won't block, and will report the currently
ready file objects.
If *timeout* is ``None``, the call will block until a monitored file object
becomes ready.
This returns a list of ``(key, events)`` tuple, one for each ready file
object.
*key* is the :class:`SelectorKey` instance corresponding to a ready file
object.
*events* is a bitmask of events ready on this file object.
.. method:: close()
Close the selector.
This must be called to make sure that any underlying resource is freed.
The selector shall not be used once it has been closed.
.. method:: get_key(fileobj)
Return the key associated to a registered file object.
This returns the :class:`SelectorKey` instance associated to this file
object, or raises :exc:`KeyError` if the file object is not registered.
.. class:: DefaultSelector()
The default selector class, using the most efficient implementation
available on the current platform. This should be the default choice for
most users.
.. class:: SelectSelector()
:func:`select.select`-based selector.
.. class:: PollSelector()
:func:`select.poll`-based selector.
.. class:: EpollSelector()
:func:`select.epoll`-based selector.
.. method:: fileno()
This returns the file descriptor used by the underlying
:func:`select.epoll` object.
.. class:: KqueueSelector()
:func:`select.kqueue`-based selector.
.. method:: fileno()
This returns the file descriptor used by the underlying
:func:`select.kqueue` object.
Examples of selector usage::
>>> import selectors
>>> import socket
>>>
>>> s = selectors.DefaultSelector()
>>> r, w = socket.socketpair()
>>>
>>> s.register(r, selectors.EVENT_READ)
SelectorKey(fileobj=<socket.socket fd=4, family=1, type=1, proto=0>, fd=4, events=1, data=None)
>>> s.register(w, selectors.EVENT_WRITE)
SelectorKey(fileobj=<socket.socket fd=5, family=1, type=1, proto=0>, fd=5, events=2, data=None)
>>>
>>> print(s.select())
[(SelectorKey(fileobj=<socket.socket fd=5, family=1, type=1, proto=0>, fd=5, events=2, data=None), 2)]
>>>
>>> for key, events in s.select():
... if events & selectors.EVENT_WRITE:
... key.fileobj.send(b'spam')
...
4
>>> for key, events in s.select():
... if events & selectors.EVENT_READ:
... print(key.fileobj.recv(1024))
...
b'spam'
>>> s.close()
|