Emanuel Berg <[email protected]> writes: > "Devrin Talen" <[email protected]> writes: > >> To block on accesses to a file until it actually has >> data for you try reading up on the `select` call: >> >> % man 2 select > > That would be great because that is exactly what I > need. However I didn't get it to work. I always get > "No data." for the below code, but it doesn't wait for > the timeout, it is just no data instantly on every > iteration. Does select(2) really block until there is > data, or does it block until it is possible to read > the fd?
It will block until there is a non-zero amount of data to read. It's always possible to read the file descriptor; it just sounds like in your case there's usually nothing to get out of it. The way you're calling select(2) right now: > retval = select(fd + 1, &rfds, NULL, NULL, &tv); Will use the timeout value stored in tv, which you have set to rate * 1000, which is in microseconds. I'm not sure what command line you're using so I'm not sure how quickly it's timing out for you. I would suggest finding out two things: 1. What happens if you pass in NULL instead of &tv? This will block indefinitely until there is data ready. 2. Have you ever gotten valid data out of the file handle when not using the select call? If not, I would solve that issue first. I've used the select call before and found it a bit tricky (but it does work!), but you've already gotten past my pitfall, which was that I passed in `1` instead of `fd+1` and nothing worked until I fixed that. -- Devrin Talen <[email protected]> -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: https://lists.debian.org/[email protected]
