When to use the POLLOUT event of the poll C function?

Question

I wrote a small TCP servers with socket() + POLLIN poll() + recv() + send(), but I don\'t know when to use <

Answer 1

Working on a Raspberry PI 3, Debian, using c++ 98 with gcc . . .

In an implementation of the Acceptor / Connector pattern and Reactor / Proactor / ACT pattern I regulary use POLLOUT in the following sequence:

1. Open a socket using the socket function.
2. Set the socket file descriptor to non blocking mode with fcntl.
3. Call connect and check return code.

In most cases connect returns a -1. Because of the non blocking file descriptor this is very likely. Then I check the result code.

If it is EINPROGRESS, I register an event handler in the reactor (which uses ppoll or epoll) with POLLOUT. When the connection is finally done, poll returns with POLLOUT set.

Then I create a new TcpConnection class and communicate.