IPC-->PIPO

Programing python 4th page 228

 1 """
 2 IPC
 3 http://www.cnblogs.com/BoyXiao/archive/2011/01/01/1923828.html
 4 """
 5 import os,time
 6 import threading
 7 
 8 def child(pipeout):
 9     zzz = 0
10     while True:
11         time.sleep(zzz)                                             # make parent wait
12         msg=('spam %03d \n' % zzz).encode()                         # pipes are binary bytes
13         os.write(pipeout,msg)                                       # send to parent
14         zzz = (zzz+1)%5
15         
16 def parent(pipein):
17     while True:
18         line = os.read(pipein,32)                                   # blocks until data sent
19         print('parent %d got [%s]  at [%s]'%(os.getpid(),line,time.ctime()))
20     
21 pipein,pipeout = os.pipe()
22 threading.Thread(target = child,args=(pipeout,)).start()
23 parent(pipein)

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2.Bidirectional IPC

 1 """
 2 location: programing python 4td page 229
 3 spawn a child process/program,connect my stdin/stdput to child process's stdout/stdin 
 4 my reads and writes map to output and input streams of the spawn program;much like typing
 5  together streams with subprocess module
 6 """
 7 import  os,sys
 8 def spawn(prog,*args):
 9     stdinFd = sys.stdin.fileno()            #pass progname,cmdline args
10     stdoutFd =sys.stdin.fileno()            # get desciptors for streams,normally stdin =0,stdout =1
11     
12     parentStdin,childStdout = os.pipe()     # make two IPC pipe changels
13     childStdin,parentStdout = os.pipe()     # pipe returns(inputfd,outputfd)
14     pid = os.fork()                         #make a copy of this process
15     if pid:
16         os.close(childStdout)               # in parent process after fork
17         os.close(childStdin)                # close child ends in parent
18         os.dump2(parentStdin,stdinFd)       # my sys.stdin copy = pipe1[0]
19         os.dump2(parentStdout,stdoutFd)     # my sys.stdout copy = pipe2[1]
20     else:
21         os.close(parentStdin)               # in child process afte fork:
22         os.close(parentStdout)              # close parent ends in child
23         os.dump2(childStdin,stdinFd)        # my sys.stdin copy = pipe2[0]
24         os.dump2(childStdout,stdoutFd)      # my sysout copu = pipe1[1]
25         args = (prog,)+args
26         os.execvo(prog,args)                # new program in this process
27         assert False,'execvp failed'        # os.exec call never returns here
28     
29 if __name__=='__main__':
30     mypid = os.getpid()
31     spawn('python','pipes-testchild.py','spawm') # fork child program
32     
33     print('hello  1 from parent',mypid)      # to child's stdin
34     
35     sys.stdout.flush()                       # subvert stdio buffering
36     reply = input()                          # from child's stdout
37     sys.stderr.write('parent got: "%s"\n' % reply) # stderr not tied to pipe
38     
39     print('hello 2 from parent',mypid)
40     sys.stdout.flush()
41     reply = sys.stdin.readline()
42     sys.stderr.write('parent got:"%s"\n' % reply[:-1])
43     

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 3.Named Pipes（Fifos）pages 234

Create a long-lived pipe that exists as a real named file in the filesystem. such files are called named pipes(or sometime,fifos). 

雖然其是任意程序以外的，可是和計算機中真實文件有關，不依賴被其餘任務所共享的內存。所以能夠用於線程，進程和獨立程序的IPC機制。一旦命名管道文件建立，客戶端能夠經過名字打開並使用正常的文件操做進行讀寫。其是單向流。典型的操做是，服務器程序從fifos讀數據，客戶端程序寫數據。另外，2個fifos集能夠用於實現雙向通訊，和匿名通訊所作的同樣。fifos不支持遠程網絡鏈接。

 1 """
 2 name pipes;os.mkfifo is not available on windown
 3 thare is no reason to fork here ,since fifo file ipes
 4 are external to proceses--shared fds in parent/child processes
 5 are irrelevent;
 6 """
 7 import os,time,sys
 8 fifoname ='/tmp/pipefifo'
 9 def child():
10     pipeout = os.open(filename,os.O_WRONLY)                 # open fifo pipe as fd
11     zzz = 0
12     while True:
13         time.sleep(zzz)
14         msg =('spam %03d\n' %zzz).encode()
15         os.write(pipeout,msg)
16         zzz =(zzz+1)%5
17 def parent():
18     pipein = open(fifoname,'r')                                             # open file as text file object
19     while True:
20         line = pipein.readline()[:-1]                                       #block until data sent
21         print('parent %d got "%s" at %s' % (os.getpid(),line,time.ctime()))
22 
23 if __name__ =='__main__':
24     if not os.path.exits(filename):
25         os.mkfifo(fifename)                                                 #create a named pipe file
26     if len(sys.argv) == 1:
27         parent()                                                            # run as parent if no args
28     else:
29         child()                                                             # else run as child process

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