What does poll() do with a timeout of 0?
Solution 1
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
, thepoll
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 isINFTIM (-1)
,poll()
will block indefinitely until a condition is found.
, as of OpenBSD 3.8
Solution 2
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,
Paul Holden
Updated on October 05, 2022Comments
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Paul Holden over 1 year
I'm looking at the
poll()
man page, and it tells me the behavior ofpoll()
when positive and negative values are passed in for the timeout parameter. It doesn't doesn't tell me what happens if timeout is0
. Any ideas?Looking at the
epoll_wait()
man page, it tells me that with a timeout value of0
, it will return right away, even if there are no events available. Is it safe to assume thatpoll()
would behave the same way?