The answer is in the error message: „Object went out of scope“. When your frontent_init() exits, the odb objects are destroyed. When you get a callback, it‘s linked to the
destroyed object. This is like if you have a local string and pass a reference to that string in the return of the function.

Use a global object (bad) or use „new“ (potential memory leak). I would use a global structure which holds all odb objects.

Stefan
 
> 
> last week I was running MIDAS with the commit 3ad98c5. Today I updated MIDAS and now all my watch functions are crashing. Attached I have a minimal example frontend of the problem.
> 
> In our software we have two functions one which sets up the ODB values of the frontend and another one which sets up all watch functions. So overall we connect two time to the ODB during fronend_init one time to create the values and one time to create the watch. In the example code a simple version of this setup is shown:
> 
> INT frontend_init() {
> 
>   cm_msg(MINFO, "frontend_init() setup", "Test FE");
> 
>   odb settings = {
>     {"Test", 123},
>     {"sub", {}}
>   };
>   settings.connect_and_fix_structure("/Equipment/Test FE/Settings");
>   // settings.watch(watch); <-- this works without segmentation fault
> 
>   odb new_settings("/Equipment/Test FE/Settings");
>   new_settings.watch(watch); // <-- here I am getting a segmentation fault
> 
>   return CM_SUCCESS;
> }
> 
> When I directly set the watch everything runs fine however, when I create a new ODB object and use this one to set a watch I am getting the following segmentation fault:
> 
> Process 18474 stopped
> * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x34)
>     frame #0: 0x000000010004fa38 test_fe`midas::odb::watch_callback(hDB=<unavailable>, hKey=<unavailable>, index=0, info=0x00006000002001c0) at odbxx.cxx:96:25 [opt]
>    93  	      if (po->m_data == nullptr)
>    94  	         mthrow("Callback received for a midas::odb object which went out of scope");
>    95  	      midas::odb *poh = search_hkey(po, hKey);
> -> 96  	      poh->m_last_index = index;
>    97  	      po->m_watch_callback(*poh);
>    98  	      poh->m_last_index = -1;
>    99  	   }
> 
> Best,
> Marius

Well, the object *went* out of scope. For my code it‘s hard to realize this, so the error reporting is poor. Also the first object should have the same
problem. Just by accident that it does not crash.

Stefan 

> This is not the case here. Note that the error message: "Callback received for a midas::odb object which went out of scope" is not called! The segmentation fault happens later line 96.
> 
> > The answer is in the error message: „Object went out of scope“. When your frontent_init() exits, the odb objects are destroyed. When you get a callback, it‘s linked to the
> > destroyed object. This is like if you have a local string and pass a reference to that string in the return of the function.
> > 
> > Use a global object (bad) or use „new“ (potential memory leak). I would use a global structure which holds all odb objects.
> > 
> > Stefan
> >  
> > > 
> > > last week I was running MIDAS with the commit 3ad98c5. Today I updated MIDAS and now all my watch functions are crashing. Attached I have a minimal example frontend of the problem.
> > > 
> > > In our software we have two functions one which sets up the ODB values of the frontend and another one which sets up all watch functions. So overall we connect two time to the ODB during fronend_init one time to create the values and one time to create the watch. In the example code a simple version of this setup is shown:
> > > 
> > > INT frontend_init() {
> > > 
> > >   cm_msg(MINFO, "frontend_init() setup", "Test FE");
> > > 
> > >   odb settings = {
> > >     {"Test", 123},
> > >     {"sub", {}}
> > >   };
> > >   settings.connect_and_fix_structure("/Equipment/Test FE/Settings");
> > >   // settings.watch(watch); <-- this works without segmentation fault
> > > 
> > >   odb new_settings("/Equipment/Test FE/Settings");
> > >   new_settings.watch(watch); // <-- here I am getting a segmentation fault
> > > 
> > >   return CM_SUCCESS;
> > > }
> > > 
> > > When I directly set the watch everything runs fine however, when I create a new ODB object and use this one to set a watch I am getting the following segmentation fault:
> > > 
> > > Process 18474 stopped
> > > * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x34)
> > >     frame #0: 0x000000010004fa38 test_fe`midas::odb::watch_callback(hDB=<unavailable>, hKey=<unavailable>, index=0, info=0x00006000002001c0) at odbxx.cxx:96:25 [opt]
> > >    93  	      if (po->m_data == nullptr)
> > >    94  	         mthrow("Callback received for a midas::odb object which went out of scope");
> > >    95  	      midas::odb *poh = search_hkey(po, hKey);
> > > -> 96  	      poh->m_last_index = index;
> > >    97  	      po->m_watch_callback(*poh);
> > >    98  	      poh->m_last_index = -1;
> > >    99  	   }
> > > 
> > > Best,
> > > Marius

The problem has been fixed in the current version. Here is my analysis:

- the midas::odb object *can* go out of scope in the function, since the odb::watch() function creates a deep copy of the object. 
This does not cause a memory leak if one call odb::unwatch_all() at the end of a program.

- The creation from XML had a flaw where the ODB key handle ("hKey") is not initialized since it is not passed by the db_copy_xml() function.
I added code to db_copy_xml() to also fetch the key handle in the XML file, which now fixes the issue. Please note that you have to
update both the server and client side of midas to get this functionality if you are using it by a remote client.

- I saw the flag MK added on his pull request to the constructor of odb::odb(). This is a way to fight the symptoms (by creating an
object the "old" way if not otherwise needed, but how we have the cause cured. Nevertheless I added that parameter, but set to to true by default:

   odb::odb(const std::string &str, bool init_via_xml = true);

since this should be fully working now and should always be faster than the old method. I only keep it for debugging should we observe
another flaw in odb_from_xml(). 

Best regards,
Stefan

> I like the look of std::format, looks cleaner than string streams

I fully agree. String streams is a pain if you want to do zero-leading hex output mixed with decimal output. Yes it's easier to read if you don't know printf syntax,
but 10-20 times more chars to write and not necessarily cleaner.

Proble is that we would have to convert about a few thousand of sprintf's() in midas.

Stefan

> Where is the example of error handling?

#include "mscbxx.h"
#include "mexcept.h"

...
   try {
   
      // connect to node 10 at submaster mscb123
      midas::mscb m("mscb123", 10);

      // print a variable
      std::cout << m["Input0"] << std::endl;
   
   } catch (mexception e) {
      std::cout << e << std::endl; // simply print exception
   }
...

Hello!

My name is Soichiro Kuribayashi and I am a Ph.D. student at Kyoto University. 
I'm a T2K collaborator and working for Super FGD which is new detector in ND280.

I'm a beginner of MIDAS and I've just started to develop the DAQ software with 
MIDAS for Super FGD.
For the DAQ of Super FGD, we will run remotely front end part of MIDAS on ZYNQ 
which is system on chip.

For this remote control of front end part with mserver, we have to mount home 
directory of DAQ PC(Cent OS8) on that of Linux on ZYNQ.
So I wonder if we should use NFS(Network file system) + NIS(Network information 
service) + autofs for the mounting. Is it correct?

If you have any information or any suggestion for the remote control on chip, 
please let me know.

Best regards,
Soichiro 

Dear Konstantin,

Thank you very much for your reply and detailed information.
I would appreciate if you could help us.

> I can also suggest that on your frontend SOC/FPGA machine, you boot linux
> using the "nfs-root" method. This way, the local flash memory only
> contains a boot loader (and maybe the linux kernel image, depending on
> bootloader limitations). The rest of the linux rootfs can be on your
> central development machine. This way management of flash cards,
> confusion with different contents of local flash and need to make backups
> of frontend machines is much reduced.

As you said, we can run complete Linux (Ubuntu 16) on ZYNQ and I'm using common NFS 
system now. However, I didn't know "nfs-root" method which you mentioned and this method 
seems to be reasonable way to just share linux rootfs.
First of all, I will try this method for simpler system.

> If you use a fast SSD and ZFS with deduplication, you will also have good
> performance gain (NFS over 1gige network to server with fast SSD works
> so much better compared to the very slow SD/MMC/NAND flash).
>
> I can point you to some of my documentation how we do this.

I'm concerned about such performance and I have checked the performance with common NFS 
over gige network and my DAQ PC roughly(data transfer rate ~ O(10) MByte/sec). However, I 
didn't know the ZFS and also how we can have performance gain with a fast SSD and ZFS.
Please let me know your documentation how to do it if possible.

> I would say you are on a good track. For early development on just one board,
> pretty much any way you do it will work, but once you start scaling up
> beyound 3-4-5 frontends, you will start seeing benefits from common NFS-mounted
> home directories, NFS-root booted linux, etc.

I'm developing with just one board and common NFS-mounted now. I'm looking forward to 
seeing such benefits when I will use multiple frontends.
 
> And of course you may want to study the existing ND280/FGD DAQ. I hope you
> have access to the running system at Jparc. If not, I have a copy of
> pretty much everything (except for running hardware, it is stored in the basement, 
> dead) and I can give you access.

I don't have access to the system at Jparc, but Nick has told us where FGD DAQ code is.
Is bellow URL everything of code of FGD DAQ?
https://git.t2k.org/hastings/fgddaq/-/tree/master

Best regards,
Soichiro

Dear Stefan,

Thank you very much for your help.

I have already contacted someone who has used ZYNQ in that order and It's working fine for now.
But, I'll let you know if something goes wrong.

Best regards,
Soichiro 

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!