erlang time handling (in calendar.erl and erlang.erl)

Ulf Wiger (AL/EAB) ulf.wiger@REDACTED
Mon Jan 31 13:46:11 CET 2005

On January 31 2005 11:28, Matthias Lang wrote:
> Rant Mode On.
> This clock fudging is my #2 pet peeve about Erlang.

What's #1?

> In Erlang, now() tries to solve all timing problems---it promises to
> track real time while still preserving intervals. For good measure, it
> also promises to return "continuously increasing" values (more
> commonly called "strictly increasing").
> The result is that nothing behaves when the user makes a dramatic
> adjustment to the time (1). Timeouts and intervals are off by 1% (2)
> and timestamps can be off by an arbitrarily large amount for an
> arbitrarily long time (3).
> Solutions? It's probably too late to fix now() since there's a lot of
> code out there depending on various, mutually incompatible aspects of
> its behaviour.

One thing that could be done, AFAIKT, is to fix the obvious dilemma 
that erlang:now() is the _only_ time function available that offers 
sub-second precision. I don't think presenting time down to millisecond
level creates any portability problems.

After that, I'm not aware of any good reasons to use erlang:now(),
perhaps apart from the nice feature that it is guaranteed to 
produce increasing values. OTOH, this guarantee is offered by 
ets:update_counter() as well.

> (2) This is particularly annoying when your system enters "Spinal
> Tap Emulation Mode" during a customer's stress testing, e.g.
> claiming that the load on a signalling link is 101%

So you mean that without this 1% adjustment made by erlang:now(),
you could measure the load on a signalling link with a margin of
error of less than 1%?

> Rant Mode Off.


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