Will read() ever block after select()?

Question

I\'m reading a stream of data through TCP/IP socket. The stream load is very uneven. Sometimes large bulks of data arrive every second, sometimes no data come for an hour. I

Answer 1

A blocking file descriptor will block on read() until there is something to read - could be one byte or your entire request. A non-blocking descriptor won't block on read() if there is nothing to read. Select() is not read(). It basically puts the process to sleep and monitors the file descriptor(s), including non-blocking descriptors. When there is activity on one of the descriptors (or the timeout period expires) select returns and you can read your data, or do something else in the case of the timeout.

So you have two separate issues. (1) You want to "take some actions" when there is no data. That's the select timeout. (2) Once you have data (notified by select) you don't want to block on a read. That's the non-blocking mode. When you get EAGAIN on the non-blocking read you loop back to the select and/or "take some actions" and loop back to select.