What does poll() do with a timeout of 0?

As I see it, waiting for a timeout means "having" a timeout. This way I would expect that poll() actually checks the file descriptors, and then waits if no one is ready to a timeout of 0 milliseconds (no wait at all). But the case is that it will just signal if a fd is available.

I also checked linux source code and to my knowledge, this is the way it works: first calculates the "future" waiting point, then checks the file descriptors, then if none available, waits for the timeout specified time.

Regards,

It will return immediately:

If timeout is greater than zero, it specifies a maximum interval (in milliseconds) to wait for any file descriptor to become ready. If timeout is zero, then poll() will return without blocking. If the value of timeout is -1, the poll blocks indefinitely.

, as of Mac OS X 10.5;

Maximum interval to wait for the poll to complete, in milliseconds. If this value is 0, poll() will return immediately. If this value is INFTIM (-1), poll() will block indefinitely until a condition is found.

, as of OpenBSD 3.8