IPC-->PIPO

Programing python 4th page 228

 """
 IPC
 http://www.cnblogs.com/BoyXiao/archive/2011/01/01/1923828.html
 """
 import os,time
 import threading

 def child(pipeout):
     zzz = 0
     while True:
         time.sleep(zzz)                                             # make parent wait
         msg=('spam %03d \n' % zzz).encode()                         # pipes are binary bytes
         os.write(pipeout,msg)                                       # send to parent
         zzz = (zzz+1)%5

 def parent(pipein):
     while True:
         line = os.read(pipein,32)                                   # blocks until data sent
         print('parent %d got [%s]  at [%s]'%(os.getpid(),line,time.ctime()))

 pipein,pipeout = os.pipe()
 threading.Thread(target = child,args=(pipeout,)).start()
 parent(pipein)

2.Bidirectional IPC

 """
 location: programing python 4td page 229
 spawn a child process/program,connect my stdin/stdput to child process's stdout/stdin
 my reads and writes map to output and input streams of the spawn program;much like typing
  together streams with subprocess module
 """
 import  os,sys
 def spawn(prog,*args):
     stdinFd = sys.stdin.fileno()            #pass progname,cmdline args
     stdoutFd =sys.stdin.fileno()            # get desciptors for streams,normally stdin =0,stdout =1

     parentStdin,childStdout = os.pipe()     # make two IPC pipe changels
     childStdin,parentStdout = os.pipe()     # pipe returns(inputfd,outputfd)
     pid = os.fork()                         #make a copy of this process
     if pid:
         os.close(childStdout)               # in parent process after fork
         os.close(childStdin)                # close child ends in parent
         os.dump2(parentStdin,stdinFd)       # my sys.stdin copy = pipe1[0]
         os.dump2(parentStdout,stdoutFd)     # my sys.stdout copy = pipe2[1]
     else:
         os.close(parentStdin)               # in child process afte fork:
         os.close(parentStdout)              # close parent ends in child
         os.dump2(childStdin,stdinFd)        # my sys.stdin copy = pipe2[0]
         os.dump2(childStdout,stdoutFd)      # my sysout copu = pipe1[1]
         args = (prog,)+args
         os.execvo(prog,args)                # new program in this process
         assert False,'execvp failed'        # os.exec call never returns here

 if __name__=='__main__':
     mypid = os.getpid()
     spawn('python','pipes-testchild.py','spawm') # fork child program

     print('hello  1 from parent',mypid)      # to child's stdin

     sys.stdout.flush()                       # subvert stdio buffering
     reply = input()                          # from child's stdout
     sys.stderr.write('parent got: "%s"\n' % reply) # stderr not tied to pipe

     print('hello 2 from parent',mypid)
     sys.stdout.flush()
     reply = sys.stdin.readline()
     sys.stderr.write('parent got:"%s"\n' % reply[:-1])
     

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).

虽然其是任意程序之外的，但是和计算机中真实文件有关，不依赖被其他任务所共享的内存。因此可以用于线程，进程和独立程序的IPC机制。一旦命名管道文件创建，客户端可以通过名字打开并使用正常的文件操作进行读写。其是单向流。典型的操作是，服务器程序从fifos读数据，客户端程序写数据。另外，2个fifos集可以用于实现双向通信，和匿名通信所做的一样。fifos不支持远程网络连接。

 """
 name pipes;os.mkfifo is not available on windown
 thare is no reason to fork here ,since fifo file ipes
 are external to proceses--shared fds in parent/child processes
 are irrelevent;
 """
 import os,time,sys
 fifoname ='/tmp/pipefifo'
 def child():
     pipeout = os.open(filename,os.O_WRONLY)                 # open fifo pipe as fd
     zzz = 0
     while True:
         time.sleep(zzz)
         msg =('spam %03d\n' %zzz).encode()
         os.write(pipeout,msg)
         zzz =(zzz+1)%5
 def parent():
     pipein = open(fifoname,'r')                                             # open file as text file object
     while True:
         line = pipein.readline()[:-1]                                       #block until data sent
         print('parent %d got "%s" at %s' % (os.getpid(),line,time.ctime()))

 if __name__ =='__main__':
     if not os.path.exits(filename):
         os.mkfifo(fifename)                                                 #create a named pipe file
     if len(sys.argv) == 1:
         parent()                                                            # run as parent if no args
     else:
         child()                                                             # else run as child process