[zeromq-dev] zloop_timer() does not fire if added after zloop_start()...

[Pieter Hintjens]

Andy,

You can trace this quite simply; print the tickless timer value before
each zmq_poll in zloop. It should change when you add your new timer.

-Pieter

On Thu, Dec 27, 2012 at 5:01 PM, Andy Ballingall TF
<ballingall at thefoundry.co.uk> wrote:
> Hi Pieter,
>
> On 27 December 2012 13:55, Pieter Hintjens <ph at imatix.com> wrote:
>> On Thu, Dec 27, 2012 at 2:53 PM, Andy Ballingall TF
>> <ballingall at thefoundry.co.uk> wrote:
>>
>>> Note how my timer registration succeeds, but the polling seems to
>>> ignore it?
>>
>> Then it's because the tickless timer is being miscalculated; it should
>> be re-calculated each time you add or remove a timer handler. If not,
>> there's a bug.
>
> I agree with Apostolis below that the zloop code seems correct, with
> respect to the calculation of the next timer expiry. Replicating my
> scenario with test code would be quite a bit of work, so I took
> another look at the zloop implementation again, and I think I can see
> what's happening.
>
> Firstly, my timer mutations were occurring within a message handler,
> and the mutation consisted of:
> a) Remove existing timer
> b) Create a new one.
>
> The old removed timer and the new timer both have the same 'arg' (in
> my case this is an instance of my communications class).
>
> The reactor loop (in function zloop_start() ) first processes any poll
> handlers, then at the end, checks if the zombies list has any timers
> to clear.
>
> By the time the zloop_start() function gets to line 420 (where it
> checks for zombies), then the state is:
>
> Zombies: 1 (arg='this')
>
> Timers: 2
> 1 = old timer (arg='this', expiry=<old time>)
> 2 = new timer (arg = 'this', expiry = <new time>)
>
> The loop at line 423 will blow away all the timers - including the one
> I just added - as it matches the zombie arg.
>
> That explains why my newly added timer wasn't firing, and why the poll
> timeout was set to 1 hour: It's because my newly added timer had been
> removed almost immediately!
>
> If the timer deletion used a reference to the timer object rather than
> 'arg' to reference it, then it would ensure that I could call
> zloop_timer_end() and subsequently zloop_timer() from within a
> handler, without the zloop_start() function removing that newly added
> timer...
>
> In the end, this isn't a problem for me because I've changed my
> implementation to use a heartbeat timer which never gets removed and
> replaced, but I can see scenarios in the future where it would be good
> to reset an existing timer, or delete and add a number of timers
> inside a handler...
>
> Anyway, thanks for your help.
>
> Andy
>
>
>
>
>
>
>
>
>
>>
>> -Pieter
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>
>
>
> --
> Andy Ballingall
> Senior Software Engineer
>
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