is it better to use sleep() or an infinite loop to wait for an event?

Question

I'm currently working on a client that talk with a SSH server. Everything works well, but, because the server is quite slow to answer, I have to wait for it to send data. I have two choices, and I'd like to have your advice about what is the most efficient way to wait for the server.

Choice #1 :

while (!(ssh_channel_poll(*sshChannel,0)))
 ;

Choice #2 :

while (!(ssh_channel_poll(*sshChannel,0)))
  sleep(1);

Answer 1

Both alternatives are undesirable. Normally, you would use a blocking read. I assume it looks something like this (since you say you are waiting for the server):

while (!ssh_channel_poll(...)) { ... }
ssh_channel_read(...);

In this case, the poll is unnecessary. Just make sure the SSH connection is a blocking connection, and the read function will wait until data is available if none is available when you call it.

// This is all you need.
ssh_channel_read(...);

Answer 2

You probably want to call the poll(2) system call (or the old select(2) one). Then you need to get the relevant file descriptor. Or use the ssh_channel_poll_timeout function or ssh_channel_select.

Look also into libssh poll functions.

Answer 3

I think use sleep instead of infinite loop because using infinite loop, you are wasting CPU Power and time. When using sleep, the CPU will be able to run other programs.

Answer 4

Clipping is not a good idea. With sleep(...) you don't use hardly your cpu like with empty while(...).