Re: select for UNIX sockets?

Chris Friesen
2003-06-08T04:02:21Z

David Schwartz wrote:

> You are doing something wrong. You are using 'select' along with blocking
> I/O operations. You can't make bricks without clay. If you don't want to
> block, you must use non-blocking socket operations. End of story.

That's funny, I was under the impression that the whole point of using select()
was to enable the use of blocking I/O. If you are on a uniprocessor system, in
a single thread, and select() says that a socket is writeable, then I had darn
well better be able to write to that socket!

Sure, this gets more complicated when multiprocessing or multithreading, but the
test program does neither of these.

> Just because 'select' indicates a write hit, you are not assured that some
> particular write at a later time will not block. Past performance does not
> guarantee future results.

Think about the whole reason for select()'s existance. If a single-threaded app
calls select() and is told a socket is writeable, then a write to that socket
should either immediately succeed or immediately fail (if the other socket
disappeared in between the calls, for instance).

Now granted I use non-blocking I/O out of paranoia, but even there if select()
says it is writeable and the send call returns EAGAIN then we get into a nice
little infinite loop.

select() should be reliable.

Chris

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