Python套接字导致挂起

Question

Occasionally my python App hangs when there is a burst of send/receive on the socket. What am I missing here: seems basic:

skt.send(packet)

and

skt.recv_into(pkt)

If a put a sleep(0.2) after the call, then it works fine.

Should I change to the select() way of talking to socket? I have tried 2.7 to 3.3 which seems to be better, but still that hang occurs.

The socket is setup as:

skt = socket(AF_INET, SOCK_STREAM)

skt.connect((ipAddress, nwPort))

Answer 1

There is far too little information to tell. I don't think there's a hang, but a sleep pending data (which you could disable with MSG_DONTWAIT or setblocking , or another check such as select) when you read, because data isn't present yet. If you know it has been sent, it's possible it's in various network delays, particularly Nagle's algorithm which you can disable with TCP_NODELAY. You should generally use select or poll if you want your program to be responsive - note that for a stream protocol like TCP, you'll need to combine it with nonblocking behaviour if you don't know the exact sizes arriving ahead of time.

Answer 2

Documentation of socket.recv_into(buffer[, nbytes[, flags]]) specifies that:

Receive up to nbytes bytes from the socket, storing the data into a buffer rather than creating a new bytestring. If nbytes is not specified (or 0), receive up to the size available in the given buffer.

Try to be more specific in how many bytes for data you're actually receiving from the socket by setting nbytes to a number of bytes. Typically, messages are either delimited (eg by CRLF ) so even if you allow fewer bytes on recv function you can just wait for the delimiter to arrive; or they are fixed-length, in which case you just set to that byte-length (or slightly over it).