Difference between revisions of "Auto start"

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== From https://midas.triumf.ca/elog/Midas/919 ==
 
== From https://midas.triumf.ca/elog/Midas/919 ==
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This information has been added to the documentation on page [[/Programs ODB tree]] (Auto start,Auto stop, Auto restart).
  
 
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Latest revision as of 17:00, 6 August 2015

Note on Programs auto start, auto stop, auto restart

From https://midas.triumf.ca/elog/Midas/919

This information has been added to the documentation on page /Programs ODB tree (Auto start,Auto stop, Auto restart).

MIDAS "programs" settings include: /programs/xxx/"auto start", "auto restart" and "auto stop". What do 
they do?

"auto start":

if set to "y", the program's "start command" will be unconditionally executed at the beginning of the run 
start transition.

Because there are no checks or tests, the "start command" will be executed even if the program is already 
running. It means that this function cannot be used to start frontend programs - a new copy will be 
started each time, and a previously running copy will be killed.

Also the timing of the program startup and run transition is wrong - in my tests, the program starts too 
late to see the run transition. If the program is a frontend, it will never see the begin-of-run transition.

1st conclusion: "auto start" should be "n" for frontend programs and for any other programs that are 
supposed to be continuously running (mlogger, lazylogger, etc).

2nd conclusion: "auto start" does the same thing as "/programs/execute on start run".

"auto stop":

if set to "y", the program will be stopped after the end of run. (using cm_shutdown).

"auto restart":

this has nothing to do with starting and stopping runs. Instead, it works in conjunction with the alarm 
system and the "program is not running" alarm.

The alarm system periodically calls al_check(). al_check() checks all programs defined under /Programs to 
see if they are running (using cm_exist()). If a program is not running and an alarm is defined, the alarm is 
raised ("program is not running" alarm). If there is a start command and "auto restart" is set to "y", the 
start command is executed.

When using these "auto start" and "auto restart" functions, one needs to be careful about the context 
where the start command will be executed: midas clients may be running from different directories, under 
different user names and on different computers.

In "auto start", the start command is executed from cm_transition. For remote clients, this will happen on 
the remote computer. (against the expectation that the program will be started on the main computer).

In "auto restart", the start command is executed by al_check() which always runs locally (for remote 
clients, it runs inside the mserver). So the started program will always run on the main computer, but 
maybe not in the same directory as when started from the mhttpd "programs -> start" button.

Conclusion:

"programs auto start" : works but has strange interactions and side effects, do not use it.
"programs auto stop" : works, can be used to stop programs at the end of run (but what for?)
"programs auto restart" : works, seems to work correctly, can be used to auto restart mlogger, frontends, 
etc.

K.O.

From https://midas.triumf.ca/elog/Midas/926


> "programs auto start" : works but has strange interactions and side effects, do not use it.
> "programs auto stop" : works, can be used to stop programs at the end of run (but what for?)
> "programs auto restart" : works, seems to work correctly, can be used to auto restart mlogger, frontends, 

auto start and auto stop have been requested by PAA loooong time ago. Maybe he remembers if/where this has been used at all. I never used it. So if 
this is the case for others, we can easily change it and won't break anything. Like auto start can be executed before the run transition happens, check 
for a previous version of the program, and only continue when the program is actually running. Should be only a few lines of code. Auto restart is used 
successfully here at PSI, for example for the lazy logger.

/Stefan