This article example describes how Python implements asynchronous IO via poll. Shared for your reference. Specific analysis is as follows:
Returns the polling object after using poll(), which supports the following methods:
(fd,[,eventmask]) The first argument is to register a new file descriptor, fd. fd is either an integer file descriptor or can be an object with a fileno() method that gets the file descriptor. eventmask is some per-position or marker that indicates the event to be processed.
POLLIN: for reading data
POLLPRI: for reading emergency data
POLLOUT: Prepare to write
POLLERR: Error condition
POLLHUP: Hold state
POLLNVAL: invalid request
Finally, polling for registered file descriptors is performed in a loop using (). Returns a one-dimensional ancestor (fd,event). Where fd is the file descriptor and event is a bitmask indicating the time. To the need to event and the corresponding time for & test can be.
Use poll to create a pair of multiplexed file copy programs with the following code:
#!/usr/bin/env python
import select
BLKSIZE=8192
def readwrite(fromfd,tofd):
readbuf = (BLKSIZE)
if readbuf:
(readbuf)
()
return len(readbuf)
def copyPoll(fromfd1,tofd1,fromfd2,tofd2):
# Define events to listen for
READ_ONLY = ( |
|
|
)
totalbytes=0
if not (fromfd1 or fromfd2 or tofd1 or tofd2) :
return 0
fd_dict = {():fromfd1,():fromfd2}
# Create poll object p
p=()
# Register the file descriptors to be monitored using the poll object p
(fromfd1,READ_ONLY)
(fromfd2,READ_ONLY)
while True:
# Polling registered file descriptors for readiness
result = ()
if len(result) != 0:
for fd,events in result:
if fd_dict[fd] is fromfd1:
if events & (|):
bytesread = readwrite(fromfd1,tofd1)
totalbytes+=bytesread
elif events & ():
(fd_dict[fd])
if fd_dict[fd] is fromfd2:
if events & (|):
bytesread = readwrite(fromfd2,tofd2)
totalbytes+=bytesread
elif events & ():
(fd_dict[fd])
if bytesread <= 0:
break
return totalbytes
def main():
fromfd1 = open("/etc/fstab","r")
fromfd2 = open("/root/VMwareTools-8.8.","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()
I hope that what I have described in this article will help you in your Python programming.