[haiku-development] Re: select_sync reference counting
- From: Hamish Morrison <hamishm53@xxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Thu, 11 Jun 2015 14:22:33 +0100
Hi Ingo,
On 11/06/2015 09:58, Ingo Weinhold wrote:
E.g. have a look at deselect_select_infos() [1] -- which is called when
the FD slot is vacated -- and deselect_fd() [2] -- which is called by
the select() and friends.
Thanks for the explanation. I see it now -- the deselection is done
outwith the io_mutex, so the notification from the file close can race
with the deselection at the end of the select/poll/wait_for_objects
call. Ports and semaphores do everything under the lock for that port or
semaphore, so they can avoid this.
As a bit of background, I was looking into implementing a 'stateful
poll' -- like epoll or kqueue -- where an fd is registered with an event
queue, and events are retrieved later. This race makes deregistration of
an fd problematic; the event can't be deleted right after deselection,
and it would be preferable not to make the individual events reference
counted.
I'm sure I'll figure something out though.
Cheers
Hamish
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