Date: Thu, 3 Jul 2014 21:15:22 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: arch@FreeBSD.org Subject: callout(9) really this complicated? Message-ID: <20140704041521.GW45513@funkthat.com>
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So, I was going to look at using callout(9) for some time delayed
actions... But upon reading the docs, a) the docs are inconsistent,
and b) the docs only talk about requirements in other section...
Is there a better interface? If so, can we mark callout(9) deprecated?
If not, I have some questions...
If you want callout_drain to work properly, you have to add extra code
to both your callout, and around the usage of it...
callout_drain does not drain the callout:
However, the callout subsystem does guarantee that the callout will be
fully stopped before callout_drain() returns.
Yet other parse of the docs say that you can depend upon the callout
being fully stopped.. I've sent email to Ian (iedowse) about why he
added this statement...
Second, the amount of work you have to do to make sure you drain
seems pretty crazy as documented in Avoiding Race Conditions...
It seems like if I have created a callout w/ callout_init_mtx,
that I shouldn't have to do extra work to make it work correctly...
When calling _callout_stop_safe as callout_drain, there is no assert
that the lock is held, though it is documented as requiring it by:
The function callout_drain() is identical to callout_stop() except that
it will wait for the callout to be completed if it is already in
progress.
Maybe we need to add an additional statement here? and assert that it
isn't locked?
Also, I have tried to follow the code, but it's complicated, so I'm
hoping that I can get some help here.
Thanks.
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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