Fix double send measurements

[gpad]

I found that the measurements are sent 2 times with the same timestamp. To find this bug I configured some predefined measurements, I sent it via statsd subscriber and I set the level of logger to debug. In this way I found that the measurements are sent 2 times on the same seconds (I set the interval to 5 seconds):

2018-02-14 19:04:40.626 [debug] <0.1462.0>@exometer_report_statsd:exometer_report:68 Report metric [<<"rezolve~core_1@elixir-node_1~local_dev">>,".","erlang",".","memory",".","total"] = 75257336
2018-02-14 19:04:40.629 [debug] <0.1462.0>@exometer_report_statsd:exometer_report:68 Report metric [<<"rezolve~core_1@elixir-node_1~local_dev">>,".","erlang",".","memory",".","total"] = 75248920

2018-02-14 19:04:45.631 [debug] <0.1462.0>@exometer_report_statsd:exometer_report:68 Report metric [<<"rezolve~core_1@elixir-node_1~local_dev">>,".","erlang",".","memory",".","total"] = 75306448
2018-02-14 19:04:45.636 [debug] <0.1462.0>@exometer_report_statsd:exometer_report:68 Report metric [<<"rezolve~core_1@elixir-node_1~local_dev">>,".","erlang",".","memory",".","total"] = 75328744

2018-02-14 19:04:50.637 [debug] <0.1462.0>@exometer_report_statsd:exometer_report:68 Report metric [<<"rezolve~core_1@elixir-node_1~local_dev">>,".","erlang",".","memory",".","total"] = 75451056
2018-02-14 19:04:50.639 [debug] <0.1462.0>@exometer_report_statsd:exometer_report:68 Report metric [<<"rezolve~core_1@elixir-node_1~local_dev">>,".","erlang",".","memory",".","total"] = 75481512

Debugging the code I fix this problem in this way. I would also rewrite the function in this way that is (for me) more clear but in the PR I change the minimum required.

adjust_interval(Interval, T0) ->
    Now = os:timestamp(),
    case tdiff(Now, T0) of
        Elapsed when Elapsed > Interval; Elapsed < 0 ->
            %% Most likely due to clock adjustment
            {Interval, Now};
        Elapsed ->
            {Interval - Elapsed, T0}
    end.

[uwiger]

Ah, I was just looking at that myself, and created my own PR. I could have saved some time by checking my email first. :)

[uwiger]

Actually, hut handles the logging (possibly with lager) in exometer_core.

[uwiger]

Since my PR is identical, except for the change in rebar.config, I'll just go ahead and merge that instead. Thanks for the contribution, though!

[gpad]

I need to add lager because using this branch directly in a elixir project doesn't compile the exometer package (I don't known why?!?) so I need to add it. I also open the issue #107. When do you plan to release a new version on hex.pm? thanks

[uwiger]

You can find the discussion leading up to the removal of lager from exometer_core here:
#57

[gpad]

@uwiger I check the discussion and you are right it's not necessary add lager on exometer_core. In my app I need exometer_report_statsd that is in exometer and in exometer master there is a reference to exometer_collectd tag, "1.0.1" that still use lager. Forcing to use the master also for exometer_collectd everything work.