Re: Multithread select() bug
From: Andre Ben Hamou
Date: Mon May 10 2004 - 17:15:17 EST
Eric Dumazet wrote:
Your program is racy and have undefined behavior.
A thread should not close a handle 'used by another thread blocked in a
The race is : if a thread does a close(fd), then the fd value may be
reused by another thread during an open()/socket()/dup()... syscall, and
the first thread could issue the select() syscall (or
read()/write()/...) on the bad file.
Apologies, but I don't follow this.
It was my understanding that the (potentially) many threads of a single
process all share a canonical file descriptor table. Hence as long as
the various calls you mention are issued in a guaranteed order,
maintaining state as you go (which is what the 1 second sleep in the
test code was a very quick and dirty way to almost do), I don't see how
a race condition arises.
If I were to replace the sleep (1) with, say a global semaphore or
something similar, would your explanation still hold?
Andre Ben Hamou
Imperial College London
...and, on the seventh day, God switched off his Mac.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/