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How does epoll detect clients in Python?

Here is my server

"""Server using epoll method"""

import os
import select
import socket
import time

from oodict import OODict

addr = ('localhost', 8989)

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(addr)
s.listen(8)
s.setblocking(0) # Non blocking socket server
epoll = select.epoll()
epoll.register(s.fileno(), select.EPOLLIN) # Level triggerred

cs = {}
data = ''
while True:
    time.sleep(1)
    events = epoll.poll(1) # Timeout 1 second
    print 'Polling %d events' % len(events)
    for fileno, event in events:
        if fileno == s.fileno():
            sk, addr = s.accept()
            sk.setblocking(0)
            print addr
            cs[sk.fileno()] = sk
            epoll.register(sk.fileno(), select.EPOLLIN)

        elif event & select.EPOLLIN:
            data = cs[fileno].recv(4)
            print 'recv ', data
            epoll.modify(fileno, select.EPOLLOUT)
        elif event & select.EPOLLOUT:
            print 'send ', data
            cs[fileno].send(data)
            data = ''
            epoll.modify(fileno, select.EPOLLIN)

        elif event & select.EPOLLERR:
            print 'err'
            epoll.unregister(fileno)

client login

ideer@ideer:/home/chenz/source/ideerfs$ telnet localhost 8989
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
123456
123456
^]

telnet> q
Connection closed.

access to the server server

ideer@ideer:/chenz/source/ideerfs$ python epoll.py 
Polling 0 events
Polling 0 events
Polling 1 events
('127.0.0.1', 53975)
Polling 0 events
Polling 1 events
recv  1234
Polling 1 events
send  1234
Polling 1 events
recv  56

Polling 1 events
send  56

Polling 0 events
Polling 0 events
Polling 0 events
Polling 1 events
recv  
Polling 1 events
send  
Polling 1 events
recv  
Polling 1 events
send  
Polling 1 events
recv  
Polling 1 events
send  
Polling 1 events
recv  
^CTraceback (most recent call last):
  File "epoll.py", line 23, in <module>
    time.sleep(1)
KeyboardInterrupt

It is strange that after the client closed the connection, epoll can still poll recv and send events! Why will the EPOLLERR event never happen? this is the same if you are using EPOLLHUP.

I notice that the EPOLLERR event only occurs when trying to write a closed connection. Also, is there another way to tell if the connection was closed or not?

Is it right to consider a connection closed if you received nothing in the EPOLLIN event?

+3
source share
10 answers

EPOLLERR EPOLLHUP , , EPOLLIN EPOLLOUT ( ), if/then/else EPOLLIN EPOLLOUT.

, EPOLLHUP EPOLLERR, python epoll lowlevel IO, recv -1 errno EAGAIN, recv, python '' ( ) EOF.

telnet tcp-, recv , tcp, , .

, EPOLLIN recv, , , , , python ( epoll) , , , '', EOF .

+3

, / , epoll.poll -.

, , EPOLLIN, .

, EPOLLIN, , . "

, EPOLLHUP, .

.

elif event & select.EPOLLIN:
    data = cs[fileno].recv(4)

if not data:
    epoll.modify(fileno, 0)
    cs[fileno].shutdown(socket.SHUT_RDWR)
+2

ad-hoc

--- epoll_demo.py.orig  2009-04-28 18:11:32.000000000 +0800
+++ epoll_demo.py   2009-04-28 18:12:56.000000000 +0800
@@ -18,6 +18,7 @@
 epoll.register(s.fileno(), select.EPOLLIN) # Level triggerred

 cs = {}
+en = {}
 data = ''
 while True:
     time.sleep(1)
@@ -29,10 +30,18 @@
             sk.setblocking(0)
             print addr
             cs[sk.fileno()] = sk
+            en[sk.fileno()] = 0
             epoll.register(sk.fileno(), select.EPOLLIN)

         elif event & select.EPOLLIN:
             data = cs[fileno].recv(4)
+            if not data:
+                en[fileno] += 1
+                if en[fileno] >= 3:
+                    print 'closed'
+                    epoll.unregister(fileno)
+                continue
+            en[fileno] = 0
             print 'recv ', data
             epoll.modify(fileno, select.EPOLLOUT)
         elif event & select.EPOLLOUT:
+1

, EPOLLHUP EPOLLIN:


epoll.register(sk.fileno(), select.EPOLLIN | select.EPOLLHUP)

, , epoll, ...

0

, select.EPOLLHUP, select.EPOLLIN, hup - "telnet". , script, hup! ...

epoll_ctl

   EPOLLRDHUP (since Linux 2.6.17)
          Stream socket peer closed connection, or shut down writing half of connection.  (This flag is especially useful for writing simple code  to
          detect peer shutdown when using Edge Triggered monitoring.)

   EPOLLERR
          Error  condition  happened on the associated file descriptor.  epoll_wait(2) will always wait for this event; it is not necessary to set it
          in events.

   EPOLLHUP
          Hang up happened on the associated file descriptor.  epoll_wait(2) will always wait for this event; it  is  not  necessary  to  set  it  in
          events.

, EPOLLRDHUP, , python, ,

0

EPOLLRDHUP Python - . ​​Linux >= 2.6.17, epoll :

import select
if not "EPOLLRDHUP" in dir(select):
    select.EPOLLRDHUP = 0x2000
...
epoll.register(socket.fileno(), select.EPOLLIN | select.EPOLLRDHUP)

, (EPOLLRDHUP):

elif event & select.EPOLLRDHUP:
     print "Stream socket peer closed connection"
     # try shutdown on both side, then close the socket:
     socket.close()
     epoll.unregister(socket.fileno())

selectmodule.c python:

0

.

try:
    data = s.recv(4096)
except socket.error:
    if e[0] in (errno.EWOULDBLOCK, errno.EAGAIN): # since this is a non-blocking socket..
        return # no error
    else:
        # error
        socket.close()

if not data: #closed either
    socket.close()
0
if event & select.EPOLLHUP:
    epoll.unregister(fd)
0
elif event & (select.EPOLLERR | select.EPOLLHUP):
    epoll.unregister(fileno)
    cs[fileno].close()
    del cs[fileno]
0

, EPOLLHUP/EPOLLERR , , . ., epoll, 1, select.EPOLLIN(select.EPOLLIN == 1). , ( ) epoll 25, EPOLLIN + EPOLLERR + EPOLLHUP. , 25 ( ) , EPOLLERR , elif ( EPOLLOUT) 0, elif,

>>> from select import EPOLLIN,EPOLLOUT,EPOLLHUP,EPOLLERR
>>> event = 25
>>> event & EPOLLIN
1
>>> event & EPOLLERR
8
>>> event & EPOLLHUP
16
>>> event & EPOLLOUT
0

, 0? EPOLLERR/EPOLLHUP. , , (, 0 , ), , EPOLLIN, EPOLLHUP, EPOLLHUP, EPOLLERR as . , , , , - lol

, , :

import os
import select
import socket
import time

from oodict import OODict

addr = ('localhost', 8989)

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(addr)
s.listen(8)
s.setblocking(0) # Non blocking socket server
epoll = select.epoll()
read_only = select.EPOLLIN | select.EPOLLPRI | select.EPOLLHUP | select.EPOLLERR
read_write = read_only | select.EPOLLOUT
biterrs = [25,24,8,16,9,17,26,10,18] #Bitwise error numbers
epoll.register(s.fileno(),read_only)

cs = {}
data = ''
while True:
    time.sleep(1)
    events = epoll.poll(1) # Timeout 1 second
    print 'Polling %d events' % len(events)
    for fileno, event in events:
        if fileno == s.fileno():
            sk, addr = s.accept()
            sk.setblocking(0)
            print addr
            cs[sk.fileno()] = sk
            epoll.register(sk.fileno(),read_only)

        elif (event is select.EPOLLIN) or (event is select.EPOLLPRI):
            data = cs[fileno].recv(4)
            print 'recv ', data
            epoll.modify(fileno, read_write)
        elif event is select.EPOLLOUT:
            print 'send ', data
            cs[fileno].send(data)
            data = ''
            epoll.modify(fileno, read_only)

        elif event in biterrs:
            print 'err'
            epoll.unregister(fileno)
0

Source: https://habr.com/ru/post/1707189/

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