Re: fcntl and flock wakeups not FIFO?

[Chris Friesen <cfriesen@nortelnetworks.com>]

Matthew Wilcox wrote:
> On Tue, Feb 18, 2003 at 09:44:19AM -0500, Chris Friesen wrote:


>>It appears that if this function is called with a wait value of zero,
>>all of the waiting processes will be woken up before the scheduler gets
>>called.  This means that the scheduler ends up picking which process
>>runs rather than the locking code.

> Right.  That's why I asked whether you were doing something clever with
> scheduling ;-)

Ah, okay.

>>Looking through the file, there is no call chain on an unlock or on
>>closing the last locked fd which can give a nonzero wait value, meaning
>>that we will always end up with the scheduler making the decision in
>>these cases.

> I'm impressed that you chased it through ;-)

I was bored and it was bothering me.... :)



>>Am I missing something?

> Nope, it's true.  But the tasks get marked as runnable in the right order,
> so the scheduler should be doing the right thing -- if any tasks really
> have a better reason to run first (whether it's through RT scheduling
> or through standard Unix priority scheduling) then they'll get the lock
> first.  Otherwise, I'd've thought it should be first-runnable, first-run.

Apparently not always.  I guess it's probably good enough for my 
purposes the way it is, it just surprised me a bit.

Is 2.5 the same way?  (Haven't looked at it yet.)

Chris



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