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DateFri, 25 Aug 2000 13:10:54 +0200
FromAndries Brouwer <>
SubjectRe: [FIX] Make deadlock detection work for file locking
On Thu, Aug 24, 2000 at 11:38:02PM +0200, almesber@lrc.di.epfl.ch wrote:

> BTW, this is a little off-topic, I kind of wonder what the right semantics
> for deadlock detection are with threads. POSIX 1003.1 1996-07-12 says:
> 
>    ... If the system detects that sleeping until a
>    locked region is unlocked would cause a deadlock, the fcntl()
>    function shall fail with an [EDEADLK] error."
> 
> Okay, that's a little vague already. Now let's make it more interesting
> by adding threads:
> 
> Process	Thread	Action (executed in this order)
> A	1	grab lock X
> B	1	grab lock Y
> A	2	try to get lock Y
> B	2	try to get lock X
> 
> Solaris 2.5.1 thinks this is a deadlock. Linux 2.4.0-test1-ac16 thinks
> it isn't. I haven't found any definition of what "putting a process to
> sleep" means in POSIX.1.

I don't have POSIX in front of me, but I do not think
the system must detect deadlock. It is allowed to detect
deadlock, and in case it happens to do so EDEADLK is the
apprpriate error return.

Andries
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