Messages in this thread | | | Date | Wed, 05 Aug 1998 19:41:46 -0700 | From | Tristan Savatier <> | Subject | can select with infinite timeout return 0 |
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Hi,
We recently spent 2 days tracking a bug in our multithreaded MPEG player and eventually found that it was caused by a behavior of select that we think may be a bug.
I use 2.0.27 but our problem was also seen on Red-Hat 5.0 systems (x86).
We observed that select sometimes returns 0 even though a NULL pointer is passed for the timeout.
According to the man page and all our books, select returns 0 only if no fd is ready when the timeout expires. Consequently if should never return 0 if a NULL pointer is passed for the timeout (infinite timeout).
My understanding is that with a NULL timeout, select should never return 0. It should only return n > 0 (or -1 in case of error or EINTR).
Is my understanding correct ? If so, is that a bug in the kernel ?
Note: This situation only occurs in a multithreaded environment, with at least two threads running. One of the select fd's was a pipe with the NON_BLOCKING flag set.
Another thing bothers me: when select returns 0, one of the fd showed data ready (i.e. FD_ISSET(fd) was TRUE), even though no data was immediately available on that fd. Is that legal ? IMHO, when select returns 0, FD_ISSET(fd) should be 0 on all the fd in the set.
Could someone comment on that ?
Please Cc any answer directly to me.
Thanks.
-- Regards, -- Tristan Savatier
MpegTV: http://www.mpegtv.com
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