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
|
"""Contains a queue based channel implementation"""
from Queue import (
Empty,
Full
)
from util import (
AsyncQueue,
SyncQueue,
ReadOnly
)
from time import time
import sys
#{ Classes
class Channel(object):
"""A channel is similar to a file like object. It has a write end as well as one or
more read ends. If Data is in the channel, it can be read, if not the read operation
will block until data becomes available.
If the channel is closed, any read operation will result in an exception
This base class is not instantiated directly, but instead serves as constructor
for RWChannel pairs.
Create a new channel """
__slots__ = tuple()
class WChannel(Channel):
"""The write end of a channel - it is thread-safe"""
__slots__ = ('_queue')
# The queue to use to store the actual data
QueueCls = AsyncQueue
def __init__(self):
"""initialize this instance, able to hold max_items at once
Write calls will block if the channel is full, until someone reads from it"""
self._queue = self.QueueCls()
#{ Interface
def write(self, item, block=True, timeout=None):
"""Send an item into the channel, it can be read from the read end of the
channel accordingly
:param item: Item to send
:param block: If True, the call will block until there is free space in the
channel
:param timeout: timeout in seconds for blocking calls.
:raise ReadOnly: when writing into closed channel"""
# let the queue handle the 'closed' attribute, we write much more often
# to an open channel than to a closed one, saving a few cycles
self._queue.put(item, block, timeout)
def size(self):
""":return: approximate number of items that could be read from the read-ends
of this channel"""
return self._queue.qsize()
def close(self):
"""Close the channel. Multiple close calls on a closed channel are no
an error"""
self._queue.set_writable(False)
def closed(self):
""":return: True if the channel was closed"""
return not self._queue.writable()
#} END interface
class SerialWChannel(WChannel):
"""A slightly faster version of a WChannel, which sacrificed thead-safety for
performance"""
QueueCls = SyncQueue
class RChannel(Channel):
"""The read-end of a corresponding write channel"""
__slots__ = '_wc'
def __init__(self, wchannel):
"""Initialize this instance from its parent write channel"""
self._wc = wchannel
#{ Interface
def read(self, count=0, block=True, timeout=None):
"""read a list of items read from the channel. The list, as a sequence
of items, is similar to the string of characters returned when reading from
file like objects.
:param count: given amount of items to read. If < 1, all items will be read
:param block: if True, the call will block until an item is available
:param timeout: if positive and block is True, it will block only for the
given amount of seconds, returning the items it received so far.
The timeout is applied to each read item, not for the whole operation.
:return: single item in a list if count is 1, or a list of count items.
If the channel was empty and count was 1, an empty list will be returned.
If count was greater 1, a list with less than count items will be
returned.
If count was < 1, a list with all items that could be read will be
returned."""
# if the channel is closed for writing, we never block
# NOTE: is handled by the queue
# We don't check for a closed state here has it costs time - most of
# the time, it will not be closed, and will bail out automatically once
# it gets closed
# in non-blocking mode, its all not a problem
out = list()
queue = self._wc._queue
if not block:
# be as fast as possible in non-blocking mode, hence
# its a bit 'unrolled'
try:
if count == 1:
out.append(queue.get(False))
elif count < 1:
while True:
out.append(queue.get(False))
# END for each item
else:
for i in xrange(count):
out.append(queue.get(False))
# END for each item
# END handle count
except Empty:
pass
# END handle exceptions
else:
# to get everything into one loop, we set the count accordingly
if count == 0:
count = sys.maxint
# END handle count
i = 0
while i < count:
try:
out.append(queue.get(block, timeout))
i += 1
except Empty:
# here we are only if
# someone woke us up to inform us about the queue that changed
# its writable state
# The following branch checks for closed channels, and pulls
# as many items as we need and as possible, before
# leaving the loop.
if not queue.writable():
try:
while i < count:
out.append(queue.get(False, None))
i += 1
# END count loop
except Empty:
break # out of count loop
# END handle absolutely empty queue
# END handle closed channel
# if we are here, we woke up and the channel is not closed
# Either the queue became writable again, which currently shouldn't
# be able to happen in the channel, or someone read with a timeout
# that actually timed out.
# As it timed out, which is the only reason we are here,
# we have to abort
break
# END ignore empty
# END for each item
# END handle blocking
return out
#} END interface
#} END classes
#{ Constructors
def mkchannel(wctype = WChannel, rctype = RChannel):
"""Create a channel, which consists of one write end and one read end
:return: tuple(write_channel, read_channel)
:param wctype: The type of the write channel to instantiate
:param rctype: The type of the read channel to instantiate"""
wc = wctype()
rc = rctype(wc)
return wc, rc
#} END constructors
|
