[core libraries] Improved TimerManager API

[Kazu Yamamoto (=?iso-2022-jp?B?GyRCOzNLXE9CSScbKEI=?=)]

Hello,

If I remember correctly, the current algorithm of TimerManager was
proposed by me. That is, TimerManager is waken up only when the
internal PSQ is changed. (See abda03be6794ffd9bbc2c4f77d7f9d534a202b21)

I would like to understand what failure (or success) means. Does it
include BOTH TimerManager is not waken up AND poll() system call
returns -1?

I guess that this change is a little bit harder than people expect.

--Kazu

> Andrew has done a lot of work with the Event Manager. Perhaps he has a more
> nuanced opinion on this, but I don't see any reason why not. So I am +1.
> 
> Out of curiosity, what are you doing with the event manager?
> 
> On Sat, May 30, 2020, 10:38 PM George Wilson <george at wils.online> wrote:
> 
>> Admittedly I'm not familiar with that module, but this change seems
>> easy to make.
>> It seems as though these functions don't exactly "fail"; rather they
>> don't bother updating the queue if the change would be redundant. Is
>> that correct? Could you explain why you want to detect this?
>>
>> Cheers,
>> George
>>
>> On Wed, 13 May 2020 at 09:59, Mitchell Rosen <mitchellwrosen at gmail.com>
>> wrote:
>> >
>> > Hi all,
>> >
>> > I'd like to propose we modify GHC.Event.updateTimeout and
>> GHC.Event.unregisterTimeout to each return a Bool, indicating whether the
>> update/unregister was successful.
>> >
>> > Thanks,
>> > Mitchell
>> >
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