Python通过poll实现异步IO的方法

#!/usr/bin/env python
import select
BLKSIZE=8192
def readwrite(fromfd,tofd):
  readbuf = fromfd.read(BLKSIZE)
  if readbuf:
    tofd.write(readbuf)
    tofd.flush()
  return len(readbuf)
def copyPoll(fromfd1,tofd1,fromfd2,tofd2):
  #定义需要监听的事件
  READ_ONLY = (select.POLLIN |
       select.POLLPRI |
      select.POLLHUP |
      select.POLLERR )
  totalbytes=0
    if not (fromfd1 or fromfd2 or tofd1 or tofd2) :
    return 0
  fd_dict = {fromfd1.fileno():fromfd1,fromfd2.fileno():fromfd2}
  #创建poll对象p
  p=select.poll()
  #利用poll对象p对需要监视的文件描述符进行注册
  p.register(fromfd1,READ_ONLY)
  p.register(fromfd2,READ_ONLY)
  while True:
  #轮询已经注册的文件描述符是否已经准备好
    result = p.poll()
    if len(result) != 0:
      for fd,events in result:
        if fd_dict[fd] is fromfd1:
          if events & (select.POLLIN|select.POLLPRI):
            bytesread = readwrite(fromfd1,tofd1)
            totalbytes+=bytesread
          elif events & (select.POLLERR):
            p.unregister(fd_dict[fd])
        if fd_dict[fd] is fromfd2:
          if events & (select.POLLIN|select.POLLPRI):
            bytesread = readwrite(fromfd2,tofd2)
            totalbytes+=bytesread
          elif events & (select.POLLERR):
            p.unregister(fd_dict[fd])
    if bytesread <= 0:  
      break
  return totalbytes
def main():
  fromfd1 = open("/etc/fstab","r")
  fromfd2 = open("/root/VMwareTools-8.8.1-528969.tar.gz","r")
  tofd1 = open("/root/fstab","w+")
  tofd2 = open("/var/passwd","w+")
  totalbytes = copyPoll(fromfd1,tofd1,fromfd2,tofd2)
  print "Number of bytes copied %d\n" % totalbytes
  return 0
if __name__=="__main__":
  main()