我想编写一个客户端可以连接并接收定期更新的服务器,而不需要轮询。我在使用asyncore时遇到的问题是,如果在调用dispatcher.writable()时没有返回true,则必须等到asyncore.loop超时之后(默认为30s)。
我试图解决这个问题的两种方法是: 1)将超时时间减少到一个较低的值;2)查询连接的下次更新时间并生成足够的超时值。但是,如果您在‘man2select_tut’中引用'Select Law‘,它会声明,“您应该始终尝试使用select()而不超时。”
有没有更好的方法来做这件事?也许是扭曲的?我想试着避免额外的线程。我将在这里包含变量超时示例:
#!/usr/bin/python
import time
import socket
import asyncore
# in seconds
UPDATE_PERIOD = 4.0
class Channel(asyncore.dispatcher):
def __init__(self, sock, sck_map):
asyncore.dispatcher.__init__(self, sock=sock, map=sck_map)
self.last_update = 0.0 # should update immediately
self.send_buf = ''
self.recv_buf = ''
def writable(self):
return len(self.send_buf) > 0
def handle_write(self):
nbytes = self.send(self.send_buf)
self.send_buf = self.send_buf[nbytes:]
def handle_read(self):
print 'read'
print 'recv:', self.recv(4096)
def handle_close(self):
print 'close'
self.close()
# added for variable timeout
def update(self):
if time.time() >= self.next_update():
self.send_buf += 'hello %f\n'%(time.time())
self.last_update = time.time()
def next_update(self):
return self.last_update + UPDATE_PERIOD
class Server(asyncore.dispatcher):
def __init__(self, port, sck_map):
asyncore.dispatcher.__init__(self, map=sck_map)
self.port = port
self.sck_map = sck_map
self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
self.bind( ("", port))
self.listen(16)
print "listening on port", self.port
def handle_accept(self):
(conn, addr) = self.accept()
Channel(sock=conn, sck_map=self.sck_map)
# added for variable timeout
def update(self):
pass
def next_update(self):
return None
sck_map = {}
server = Server(9090, sck_map)
while True:
next_update = time.time() + 30.0
for c in sck_map.values():
c.update() # <-- fill write buffers
n = c.next_update()
#print 'n:',n
if n is not None:
next_update = min(next_update, n)
_timeout = max(0.1, next_update - time.time())
asyncore.loop(timeout=_timeout, count=1, map=sck_map)发布于 2009-06-24 07:10:19
"select法则“不适用于您的情况,因为您不仅有客户端触发的(纯服务器)活动,而且还有时间触发的活动-这正是select超时的原因。法律真正应该说的是“如果你指定了一个超时,确保当超时到来时,你实际上必须做一些有用的事情”。该法律旨在防止繁忙等待;您的代码不会繁忙等待。
我不会将_timeout设置为最大值0.1和下一次更新时间,而是设置为最大值0.0和下一次超时。如果在你进行更新时更新周期已经过期,你应该立即进行特定的更新。
您可以将所有通道存储在优先级队列中(按下一次更新时间排序),然后只对最早的通道运行更新(直到找到更新时间尚未到达的通道),而不是每次都询问每个通道是否要更新。为此,您可以使用heapq模块。
您还可以节省一些系统调用,方法是不让每个通道都询问当前时间,而是只轮询当前时间一次,并将其传递给.update。
发布于 2010-04-24 15:56:52
也许你可以用sched.scheduler这样做,就像这样(注意:未测试):
import sched, asyncore, time
# Create a scheduler with a delay function that calls asyncore.loop
scheduler = sched.scheduler(time.time, lambda t: _poll_loop(t, time.time()) )
# Add the update timeouts with scheduler.enter
# ...
def _poll_loop(timeout, start_time):
asyncore.loop(timeout, count=1)
finish_time = time.time()
timeleft = finish_time - start_time
if timeleft > timeout: # there was a message and the timeout delay is not finished
_poll_loop(timeleft, finish_time) # so wait some more polling the socket
def main_loop():
while True:
if scheduler.empty():
asyncore.loop(30.0, count=1) # just default timeout, use what suits you
# add other work that might create scheduled events here
else:
scheduler.run()发布于 2011-02-10 20:08:58
这基本上是demiurgus的解决方案,粗糙的边缘是圆形的。它保留了他的基本思想,但防止了RuntimeErrors和繁忙循环,并进行了测试。编辑:解决了在_delay期间修改调度程序的问题
class asynschedcore(sched.scheduler):
"""Combine sched.scheduler and asyncore.loop."""
# On receiving a signal asyncore kindly restarts select. However the signal
# handler might change the scheduler instance. This tunable determines the
# maximum time in seconds to spend in asycore.loop before reexamining the
# scheduler.
maxloop = 30
def __init__(self, map=None):
sched.scheduler.__init__(self, time.time, self._delay)
if map is None:
self._asynmap = asyncore.socket_map
else:
self._asynmap = map
self._abort_delay = False
def _maybe_abort_delay(self):
if not self._abort_delay:
return False
# Returning from this function causes the next event to be executed, so
# it might be executed too early. This can be avoided by modifying the
# head of the queue. Also note that enterabs sets _abort_delay to True.
self.enterabs(0, 0, lambda:None, ())
self._abort_delay = False
return True
def _delay(self, timeout):
if self._maybe_abort_delay():
return
if 0 == timeout:
# Should we support this hack, too?
# asyncore.loop(0, map=self._asynmap, count=1)
return
now = time.time()
finish = now + timeout
while now < finish and self._asynmap:
asyncore.loop(min(finish - now, self.maxloop), map=self._asynmap,
count=1)
if self._maybe_abort_delay():
return
now = time.time()
if now < finish:
time.sleep(finish - now)
def enterabs(self, abstime, priority, action, argument):
# We might insert an event before the currently next event.
self._abort_delay = True
return sched.scheduler.enterabs(self, abstime, priority, action,
argument)
# Overwriting enter is not necessary, because it is implemented using enter.
def cancel(self, event):
# We might cancel the next event.
self._abort_delay = True
return sched.scheduler.cancel(self, event)
def run(self):
"""Runs as long as either an event is scheduled or there are
sockets in the map."""
while True:
if not self.empty():
sched.scheduler.run(self)
elif self._asynmap:
asyncore.loop(self.maxloop, map=self._asynmap, count=1)
else:
breakhttps://stackoverflow.com/questions/1036646
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