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-8.8.1-5269.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
" % totalbytes
 return 0
if __name__=="__main__":
 main()