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Entry  27 Sep 2019, Konstantin Olchanski, Bug Fix, improvement for midas web page resource use 
    Reply  27 Sep 2019, Konstantin Olchanski, Bug Fix, improvement for midas web page resource use (alarm sound) 
       Reply  28 Nov 2019, Konstantin Olchanski, Bug Fix, improvement for midas web page resource use (alarm sound and fit_message) 
          Reply  28 Nov 2019, Konstantin Olchanski, Bug Fix, improvement for midas web page resource use (alarm sound and fit_message) 
Message ID: 1705     Entry time: 27 Sep 2019     In reply to: 1704     Reply to this: 1744
Author: Konstantin Olchanski 
Topic: Bug Fix 
Subject: improvement for midas web page resource use (alarm sound) 
> I noticed that midas web pages consume unexpectedly large amount of resources, as observed by the chrome browser 
> "task manager" and by other tools.
> 
> For example, size of the "status" page was observe to reach 200, 600 and even 900 Mbytes.
> [this was fixed by using set_if_changed(e, v);
> 
> Also I observed the midas web pages consume an unusual amount of CPU - 5-10-15% - all in inactive tabs in minimized 
> windows.
> 

The case of high CPU use turned out to be quite nasty.

The symptoms:
- the "programs" page in an inactive tab in a minimized window sits "doing nothing" for a day or two.
- uses about 0 to 0.1 to 1% CPU and 40-50-60 Mbytes of RAM (after the previous improvements)
- suddenly I see it use 10-15-20% CPU, continuously, non stop
- I open this tab
- suddenly, CPU use goes to 100%, memory use quickly grows from 40-50-60 Mbytes to 100-200 Mbytes.
- after a few seconds everything settles down, CPU use is back to 0-0.1-1%, but memory use does not go down.
- WTH?!?

The culprit turned out to be the playing of the alarm sound. (I have all tabs "muted" by default, also speakers usually powered down).

If I comment-out the playing of the alarm sound, this problem goes away completely. Pretty conclusive, I think.

After adding lots of debug console.log() calls, I think I identified the problem: audio objects were being created,
but they were not starting to play their sound files. When I opened the tab, all of them (about 400) at the same time
loaded the mp3 file (resulting in memory use going from 50 Mbytes to 190 Mbytes, typical) and started playing
(as seen on the audio event activity in the cpu profile traces from the google-chrome "performance" tool).

I think I am looking at an unexpected interaction between audio objects and google-chrome throttling of inactive tabs.

To muddy the waters some more, google-chrome periodically fails audio.play() with an exception to the effect of
"we will not play audio because user is not interacting with this page enough". See
https://bitbucket.org/tmidas/midas/issues/191/exception-on-audioplay

Now I think I have this sort of fixed. I have to handle the audio.play() failure (which is not a normal exception,
but a rejected promise, the handler is quite different), and I do not allow creating new audio objects if previous
audio object did not finish playing.

(note the "normal" timing: periodic update every 1 sec, playing of alarm sound event 60 seconds, length of alarm sound file is 3 sec,
two sound files should never overlap. now a console.log message is printed if overlap is detected)

This leaves us with the problem of alarm sound not playing "because the user didn't interact with the document first",
and I think there is nothing I can do about that.

K.O.

P.S. Another quirk is I discovered: go to the "config" page and press the new buttons "play test sound" and "speak test message". In muted
tabs, the test sound will not sound, but the test message will be shouted out loudly. This seems inconsistent to me. Unwanted audio/video ads
are blocked but loud shouting of "shave with burma-shave" is permitted. I also wonder if speaking is subject to this
"user did not interact" business. If not, we could replace the playing of our relaxing alarm beep with the yelling of "alarm! alarm! alarm!".

K.O.
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