Problem with socketpair , AF_UNIX and select call - can anybody through any light on this!
Andy Green
andy at warmcat.com
Fri Oct 12 11:02:41 UTC 2007
Somebody in the thread at some point said:
> Andy Green wrote,
>> Why don't you try removing the O_NONBLOCK since you test with
>> select...
>
> Never, ever, do that ... select only returns a hint that an IO operation
> might succeed, not a guarantee (google for "spurious wakeup"), hence a
> subsequent read/write might block if the descriptor isn't set to
> O_NONBLOCK, and that's almost always not what's wanted or expected.
Wah, man select says it too
Under Linux, select() may report a socket file descriptor
as "ready for reading", while nevertheless a subsequent read
blocks. This could for example happen when data has arrived but
upon examination has wrong checksum and is discarded. There
may be other circumstances in which a file descriptor is
spuriously reported as ready. Thus it may be safer to use O_NON-
BLOCK on sockets that should not block.
Pretty freakish, thanks for the tip.
-Andy
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