CODEWITHSUNDEEP
csocketstcpnetwork-programming
wlformyd
wlformyd

Reputation: 237

Socket being busy causes delays in poll()

I'm using a TCP socket to send data from a client. The data is prepared, in advance, so I always have more data to send. Moreover, I can't change the size of the writes, otherwise the server will complain. I do the following:

while (1) {
    poll(for POLLOUT condition);
    write(to TCP socket);
    if (no more data)
        break;
}

The problem is that the POLL takes a very long time. I assume this is the time that the socket is actually being written to (or responded to). Is there anyway that I can reduce the amount of time spent in the poll? It is currently a major bottleneck.

Upvotes: 0

Views: 1122

Answers (2)

user207421
user207421

Reputation: 311054

Socket being busy causes delays in poll()

Of course it does. That's what poll() is for. To delay until a socket becomes readable or writable.

Your writer is faster than your reader. Look for a solution at the reading end. Your writing end is behaving correctly.

However calling it every time at the head of that loop is pointless. Only call it when you need to know the socket has become writable. It is normally writable all the time, except when your socket send buffer is full, so calling it every time is a waste of time.

Just keep writing until you get EAGAIN/EWOULDBLOCK. Then is the time to call poll(), to tell you when there is space in the socket send buffer. Then just resume writing again as before.

Upvotes: 3

Davide Berra
Davide Berra

Reputation: 6568

Poll will raise a POLLOUT event when there's enough buffer space to enqueue further data. (Look at this link - Man (7) socket )

If it doesn't, it means write buffer is full and it means you're writing faster than the read capabilities of the other peer. Or simply the network is slower than you expect.

Upvotes: 3

Related Questions