IO Classification

IO Classification: Blocking IO, Non-Blocking IO, IO Multiplexing, Asynchronous IO, etc.

Blocking IO

1. Definition: Block if the execution condition is not satisfied when performing an IO operation.Blocking IO is the default form of IO.

2. Efficiency: Blocking IO is a very inefficient type of IO.But because of its simplicity, it is the default IO behavior.

3. Blockage:

• Function blocking caused by an unsatisfactory execution condition
  e.g. accept input recv

• Blocking state due to long IO processing time
  e.g. Network Transport, Large Files Read and Write

non-blocking IO

1. Definition: By modifying the IO property behavior, the originally blocked IO will become non-blocked.

Set socket to non-blocking IO

sockfd.setblocking(bool)

• Function: Set socket to non-blocking IO
• Parameters: The default is True, meaning socket IO is blocked; False makes socket IO non-blocked

Timeout detection: Set a maximum blocking time beyond which no blocking wait will occur.

sockfd.settimeout(sec)

• Function: Set timeout for sockets
• Parameter: Set time

IO Multiplex

1. Definition: Monitor multiple IO events simultaneously, when which IO event is ready to execute which IO event.This creates a behavior that can handle multiple IOs simultaneously, avoids one IO blocking causing other IOs to fail to execute, and improves the efficiency of IO execution.

2. Specific plan:

• select method: windows linux unix
• poll method: linux unix
• epoll method: linux

select method

rs, ws, xs=select(rlist, wlist, xlist[, timeout])

• Function: Monitor IO events, block waiting for IO to occur
• Parameters:
  • The rlist list holds focused IO events waiting to occur
  • The wlist list holds the IO events of interest to be proactively processed
  • The xlist list list holds IO to handle for focused exceptions
  • Timeout timeout
• Return value:
  • Ready IO in rs list rlist
  • Ready IO in ws list wlist
  • Ready IO in xs list xlist

select implements tcp service

1. Put IO of interest in the list of corresponding monitoring categories

2. Monitoring through the select function

3. Traverse through the list of returned select s to determine ready IO events

4. Handle IO events that occur

Be careful:

If there is an IO event in wlist, select immediately returns to ws

Do not have Dead Loop Occupying Server during IO Processing

IO multiplexing consumes less resources and is more efficient

 1 """
 2 Key Codes
 3 
 4 Idea analysis:
 5 1.Will Focus on IO Put in the list of corresponding monitoring categories
 6 2.adopt select Functions for monitoring
 7 3.ergodic select Return a list of values to make sure you're ready IO Event
 8 4.Handle Occurring IO Event
 9 """
10 
11 from socket import *
12 from select import select
13 
14 #　Create a listening socket as a concernＩＯ
15 s = socket()
16 s.setsockopt(SOL_SOCKET,SO_REUSEADDR,1)
17 s.bind(('0.0.0.0',8888))
18 s.listen(3)
19 
20 #　Set up a list of concerns
21 rlist = [s]
22 wlist = []
23 xlist = [s]
24 
25 #　Cycle MonitoringＩＯ
26 while True:
27   rs,ws,xs = select(rlist,wlist,xlist)
28   # Traverse through three return lists,HandleＩＯ
29   for r in rs:
30     # Based on traversal toＩＯDifferent usesｉｆCase-by-case processing
31     if r is s:
32       c,addr = r.accept()
33       print("Connect from",addr)
34       rlist.append(c) #　Add NewＩＯEvent
35     # else Client Socket Ready
36     else:
37       data = r.recv(1024)
38       # Client Exit
39       if not data:
40         rlist.remove(r) #　Remove from the list of concerns
41         r.close()
42         continue # Continue with other readinessＩＯ
43       print("Receive:",data.decode())
44       # r.send(b'OK')
45       #　We want to take the initiative in dealing with thisＩＯobject
46       wlist.append(r)
47 
48   for w in ws:
49     w.send(b'OK')
50     wlist.remove(w) #　Remove after Using
51 
52   for x in xs:
53     pass

select tcp service model