Hi,

I've written a python script that reads some data from a file and generates a
.png image. I want to have a button on my MIDAS status page that:

- executes the script and waits for it to finish,
- then displays the image

How can I do that? I tried using the sequencer to just execute the script every
30 seconds, but I can't get it to work, and it would be better to only execute
the script on demand anyway. 

I also am having trouble getting image display to work. I have the ODB keys set:

[local:oven1:S]/Custom>ls
Temperature Map&                /home/deap/ovendaq/online/index.html
Images

[local:oven1:S]/Custom>ls Images/temps.png/           
Background                      /home/deap/ovendaq/online/temps.png

And the HTML file is just this:
<img src="temps.png">

But the image won't display. It shows a "broken" picture, and when I try to view
it directly it says: Invalid custom page: Page not found in ODB.

Any help would be appreciated...

Thanks
Shaun

Hi, I'm having some trouble getting ss_thread_kill() to work properly. It seems 
to kill the entire program instead 
of just the thread. Here is a test program to show the error:

_________________________________
#include <stdio.h>
#include <stdlib.h>
#include "midas.h"
#include "msystem.h"

INT f(void *param)
{
  for (int x = 0; x < 100; x++)
    sleep(1);
  return 0;
}

int main()
{
  printf("creating thread\n");
  midas_thread_t thr = ss_thread_create(f, NULL);
  sleep(2);
  printf("killing thread\n");
  ss_thread_kill(thr);
  printf("success\n");
  return 0;
}
_________________________________

Makefile:
_________________________________
FLAGS=-g -Wall -DLINUX -DOS_LINUX -I/home/deap/packages/midas/include 
LIBS=-L/home/deap/packages/midas/linux-m64/lib -lmidas -lpthread -lrt -lutil

main.exe: main.cpp 
	g++ $(FLAGS) -o $@ $^ $(LIBS)

_________________________________

Output when run:

_________________________________

[deap@deap04 multithread]$ ./main.exe 
creating thread
killing thread
Killed
[deap@deap04 multithread]$ 
_________________________________

The last "Killed" indicated the whole program got killed, when it should 
actually just kill the thread and then 
print "success".

I noticed the function in system.c uses pthread_kill(). Some google searches 
show me that it may be better to use 
pthread_cancel() (ie http://stackoverflow.com/questions/3438536/when-to-use-
pthread-cancel-and-not-pthread-kill ).


Shaun

> > Hi, I'm having some trouble getting ss_thread_kill() to work properly. It seems 
> > to kill the entire program instead of just the thread.
> 
> You cannot kill a thread. It's not a well defined operation. Most OSes do have the 
> technical possibility to kill threads, but if you use them, you will not like the 
> results. For a taste of small trouble, if a thread is holding a lock and you kill 
> it, who's job is it to release the lock?
> 
> The best you can do is to ask the thread to gracefully shutdown itself. (I.e. by 
> using global variable flags).
> 
> P.S. I did not implement the ss_thread stuff, I do not know what ss_thread_kill() 
> does, but I recommend that you do not use it.
> 
> P.P.S. Programming using threads is complicated, I recommend that you read at least 
> some literature on the topic before using threads. At the least you must understand 
> the common pitfalls and mistakes. At the least, you must know about deadlocks, 
> livelocks, race conditions and semaphore priority inversions.
> 
> K.O.

Yes, but unfortunately what I was attempting to do was use a library function that I
can't alter. It sometimes gets stuck and I wanted a way to kill it. Anyway I ended up
not doing this at all in c++; I was able to do what I needed in python.

Shaun

 Hi,
I was trying to update the checkout of Midas, but it looks like something is not
working - maybe a component of the Savannah system:
[sergio@daq-pc midas-SVN]$ svn update
svn@savannah.psi.ch's password: svn
unix dgram connect: Connection refused at /bin/cvssh.pl line 32
no connection to syslog available at /bin/cvssh.pl line 32
svn: Connection closed unexpectedly

my .svn/entries says (amongst the rest)
 url="svn+ssh://svn@savannah.psi.ch/afs/psi.ch/project/meg/svn/midas/trunk"
and yes, it used to work well... 

Cheers,
  Sergio

> I just tried now and it seemed to work fine. Do you still have the problem?
> 
> - Stefan

 The problem was still there this morning, shortly after seeing your mail, but seems
to be fixed now.
 BTW, which is the best way to submit patches ? I have a version of khyt1331 for Linux
kernel 2.6 (we are running Scientific Linux 4.1), and a few smaller things, mostly in
the examples. 

 Thanks, Sergio

I have a possibly simple feature request for the MIDAS sequencer.  It would be
helpful to be able to save an ODB key's value to a variable, for later use, and
would be the analogue of the ODBSET command.  I had in mind an application where
a user wants to temporarily change some settings in the ODB, then restore the
ODB to its original values.  Maybe something like on ODBRead command:

<ODBRead path="/Path/ODBkey">varname</ODBRead>
<ODBSet path="/Path/ODBkey">0</ODBRead> 
<Wait for="events">3000</Wait>
<ODBSet path="/Path/ODBkey">$varname</ODBRead> 

(In which the key's value is saved to variable varname, then later written back
to the ODB.)

I'm open to other suggestions for simple ways to do this through the sequencer.

Thanks! 

Thanks, this seems very helpful, and we'll give it a try.

> > I have a possibly simple feature request for the MIDAS sequencer.  It would be
> > helpful to be able to save an ODB key's value to a variable, for later use, and
> > would be the analogue of the ODBSET command.  I had in mind an application where
> > a user wants to temporarily change some settings in the ODB, then restore the
> > ODB to its original values.  Maybe something like on ODBRead command:
> 
> I implemented your request, committed the changed to GIT and updated the documentation. Now you can run 
> things like:
> 
> ODBSET /System/tmp/test 1234 
> ODBGET /System/tmp/test v 
> MESSAGE $v 
> 
> (first you must create the key in the ODB manually).
> 
> Best regards,
> Stefan

> I guess the simplest way to do that without breaking with existing code is to change the 
> second number to a float. So a
> 
> WAIT SECONDS, 1
> 
> will still work, and you can then write
> 
> WAIT SECONDS, 0.01
> 
> to get a 10 ms wait. Would that work for you?

This would work fine in principle, but isn't implemented in the current MIDAS sequencer as we understand it.  (We tried!) Is your proposal to rewrite the sequencer 
to allow fractional waits?  Right now the code seems to store the start_time as a DWORD and uses atoi to parse the wait time, and uses ss_time (which seems only get
the time to the nearest second) to fetch the time.

> > This would work fine in principle, but isn't implemented in the current MIDAS sequencer as we understand it.  (We tried!) Is your proposal to rewrite the sequencer 
> > to allow fractional waits?  Right now the code seems to store the start_time as a DWORD and uses atoi to parse the wait time, and uses ss_time (which seems only get
> > the time to the nearest second) to fetch the time.
> 
> No it's not implemented, was just my idea. If it would work for you, I can implement it in the next couple of days.
> 
> Stefan

Yes, please!  Something like WAIT seconds, 0.01 would be perfect.

> While I will do it, i'm not sure if this is what you want. If I understand correctly, some process gets triggered and then writes some values to the ODB, then the sequencer 
> should continue. Putting a wait there is dangerous. Maybe your process always takes like 10-20 ms, so you put a wait of let's say 100ms, and things are fine with you. Your 
> script runs many days, but then once in a while your machine is on heavy load because someone starts a web browser, and your process takes 110ms, and you script crashes.
> 
> I would rather go following path: put a "done" flag in the ODB, which is the last one which gets set by your process. Then the sequencer does a 
> 
> WAIT ODBvalue, /path/value, =, 1
> 
> which will work always, independend of the delay of your process.
> 
> Stefan

Our use case is pretty simple and I don't think is affected by the scenario you envision.  We want to turn on a setting in our equipment, and turn it off again some 0.2 s later.  We don't need msec timing.  So something like:

ODBSET /somekey 1   # this will cause a front-end to flip a bit in our hardware     
WAIT seconds, 0.2
ODBSET /somekey 0   # this will cause a front-end to reset a bit in our hardware 

It is true that if the load is high there could be a little delay, and the time that the bit is set will not be 0.2 seconds, but on average it should work, 
and it should be good enough we think.

Yes, we could also check an ODB key to see that something is done, but we'd still need the ability to wait for time intervals less than 1 second, which
right now doesn't exist.

> Ok, I implemented the float second wait function. Internally it works in ms, so the maximum resolution is 0.001 s.
> 
> Best,
> Stefan

Thank you, we will test this soon and let you know if we see any issues (but we're not expecting any).

We often use the MIDAS sequencer to temporarily control detector settings, such as:

* <change some setting>
* WAIT 60 seconds
* <revert setting to original value>

The question arises of what happens if the sequencer scripts gets aborted during that wait, preventing the value from being reset.  Depending on the setting, this could be undesirable or even damage something if left uncorrected for too long.

Is there any way to have a "safe abort" from the sequencer so that the "Stop immediately" button will call some cleanup script to leave things in a safe state?  Or what about if the sequencer process itself gets killed in the middle of a script?

How have other experiments using MIDAS protected themselves from unplanned terminations of sequencer scripts?

> This request came more than once in the past. One thing I could implement is a "atexit" function similarly to the C funciton atexit().
> 
> Then we would have a function in the script which gets called whenever one does "stop immediately". This function can then restore
> some ODB values or do whatever is necessary. 
> 
> If the sequencer gets killed in the middle, it can safely be restarted since the complete sequencer state is kept in the ODB under
> /Sequencer/State. After the restart, the sequencer continues exactly where it has been killed before.
> 
> Would that solve your problem?
> 
> Stefan

Yes, an "atexit" functionality within the Midas Sequencer Language would be useful for us with this issue.  Is this easy for you to implement?

Thanks,
Scott Oser

I think I've found a bug in MIDAS ...

Description: If you have an ODB subtree that contains only an array of BOOLs, you cannot edit them from the ODB webpage, although you can change them using odbedit (and probably from code as well). See for example: https://scdms-zeus.triumf.ca/midas/?cmd=ODB&odb_path=%2FScottBugTest

(If you use the dropdown menu to change any value from No to Yes, it just flips back to No immediately.)

But if you create a new key in that directory (doesn't seem to matter what), then you can edit the BOOLs from webpage. Delete that key, and once again you can't edit the BOOLs.

On February 13, 2007, gcc 4.1.2 was released.
I checked this version, and it compiles midas successfully,

GCC 3                    - OK
GCC 4.0                  - OK
GCC 4.1.0 and 4.1.1      - Bad
GCC 4.1.2                - OK
GCC 4.2                  - This is not released. Development version of GCC 4.2 is OK