That should be read as "five usecs later, there's a high probability that it can still be read without blocking".
The easiest way to get into trouble is if you have some other thread or process that reads the data before you get to it. But I wouldn't want to bet that's the only way to get into trouble.
I'm pretty sure it can hapoen with accept() and write(). Not as sure about read(). But I'd prefer a simple rule "don't use callbacks on blocking sockets" to the hairier rule "don't use write or accept callbacks on blocking sockets, but read callbacks are fine, most of the time on most systems".
/ Niels Möller ()
Previous text:
2003-03-19 13:49: Subject: I/O callbacks in blocking mode
The defenition of select is that the bit in the FD-set is set when read() can be called _without_blocking_ according to the manpage.
/ Per Hedbor ()