> it's probably better to run a multi-threaded setup, than individual frontends.

I recommend against using multiple threads if at all possible and unless absolutely required.

Only for one reason: multithreaded c++ programs are notoriously hard to debug.

In addition, one has to face several classes of bugs absent in single-threaded applications:

a) which thread "owns" which object
b) locking of all shared data
c) huge overheads from locking at high data rates (a performance bug)
d) correct locking order, dead locks, live locks
e) incomprehensible core dumps and stack traces
f) race conditions

To control 2 power supplies, run 2 frontend programs, 1 per power supply.

To control 64 frontend cards, run 1 frontend with many threads: 64 (per device) + 1 (main thread) + 1 (RPC handler) + 1 
(watchdog) + 1 (common event generator/data transmitter) + 1 (odb/web page status update). You *will* bump into each 
and every one of the problems (a) to (f) above.

K.O.

> thanks for your reply. I can confirm that your suggested workaround does indeed
> make the problem dissapear.
> I guess this issue hasn't been seen at T2K since we use MYSQL for the history.

I think you found the source of the problem, confused event id assignments. To confirm,
can you email me (or post here) the output of odbedit "ls -l /History/Events".

If that's the problem, you can avoid it completely by switching to a history storage method
that does not rely on magic mapping between equipment names and numeric event id's:
try the "FILE" method (set odb /Logger/History/FILE/Active to "y", restart the logger) or
the "MYSQL" method (you will need to setup a mysql database). You tell mhttpd and mhist which 
history data to read by setting ODB /History/LoggerHistoryChannel to one of the channel names 
from /logger/history/, restart mhttpd. (mhttpd and mhist used to print a message "reading history 
data from channel XXX", but somebody removed this message).

K.O.

Hi Konstantin,

thanks for your reply.

> > thanks for your reply. I can confirm that your suggested workaround does indeed
> > make the problem dissapear.
> > I guess this issue hasn't been seen at T2K since we use MYSQL for the history.
> 
> I think you found the source of the problem, confused event id assignments. To confirm,
> can you email me (or post here) the output of odbedit "ls -l /History/Events".

Sorry, do you want this for after I've applied the fix suggested by Ben or with the original code 
that I posted.

With the original code it only shows one fe even though both are running:

[local:e666:S]History>ls -l /History/Events
Key name                        Type    #Val  Size  Last Opn Mode Value
---------------------------------------------------------------------------
1                               STRING  1     10    2m   0   RWD  FeDummy02
0                               STRING  1     16    2m   0   RWD  Run transitions

[local:e666:S]History> scl
Name                Host
mhttpd              localhost           
fedummy01           localhost           
fedummy02           localhost           
ODBEdit             localhost           
Logger              localhost           
[local:e666:S]History>ls "/History/Display/Default/Dummy/
Timescale                       1h
Zero ylow                       n
Show run markers                y
Show values                     y
Sort Vars                       n
Log axis                        n
Minimum                         0
Maximum                         0
Variables
                                FeDummy01:Data
                                FeDummy02:Data
Label
                                
                                
Colour
                                #00AAFF
                                #FF9000
Factor
                                0
                                0
Offset
                                0
                                0
Buttons
                                10m
                                1h
                                3h
                                12h
                                24h
                                3d
                                7d
Formula
                                
                                
Show old vars                   n

> If that's the problem, you can avoid it completely by switching to a history storage method
> that does not rely on magic mapping between equipment names and numeric event id's:
> try the "FILE" method (set odb /Logger/History/FILE/Active to "y", restart the logger) or
> the "MYSQL" method (you will need to setup a mysql database). You tell mhttpd and mhist which 
> history data to read by setting ODB /History/LoggerHistoryChannel to one of the channel names 
> from /logger/history/, restart mhttpd. (mhttpd and mhist used to print a message "reading history 
> data from channel XXX", but somebody removed this message).

Using the orginal code I posted and switching from MIDAS history to FILE history did not seem to 
change the random behaviour in the history plots.

Regards,

Nick.

> [local:e666:S]History>ls -l /History/Events
> Key name                        Type    #Val  Size  Last Opn Mode Value
> ---------------------------------------------------------------------------
> 1                               STRING  1     10    2m   0   RWD  FeDummy02
> 0                               STRING  1     16    2m   0   RWD  Run transitions

Something is very broken. There should be more entries here, at least
there should be entries for "FeDummy01" and usually there is also an entry
for "FeDummy" because one invariably runs fedummy without "-i" at least once.

The fact that changing from "midas" storage to "file" storage makes no difference
also indicates that something is very broken.

I want to debug this.

Since you tried the "file" storage, can you send me the output of "ls -l mhf*.dat" in the directory
with the history files? (it should have the "*.hst" files from the "midas" storage and "mhf*.dat" files
from the "file" storage.

K.O.

I recently upgraded to MIDAS version midas-2019-06-b. I had to make a few changes 
to get our custom page running again, but am a little confused on starting and 
stopping runs. When I click on my "Start" button, it now redirects to a 
Transition page rather than reloading the status page. The standard MIDAS status 
page does the same. Could someone explain the reasoning for the current behavior?

Furthermore my "Stop" button is now broken with the following error:
Error: Invalid URL "CS/EngeRun&" or query "cmd=Stop&redir=EngeRun%26" or command 
"Stop"

I looked through the mhttpd.js code and managed to get the start button to load 
the status page, at least, but the stop button seems to be written differently. 
For example, start calls:
location.search = "cmd=Transition";
whereas stop does:
mhttpd_goto_page("Transition"); // DOES NOT RETURN

Can anyone offer any insights or advice? I can change the former to "cmd=Status", but 
the latter doesn't allow it.

> > [local:e666:S]History>ls -l /History/Events
> > Key name                        Type    #Val  Size  Last Opn Mode Value
> > ---------------------------------------------------------------------------
> > 1                               STRING  1     10    2m   0   RWD  FeDummy02
> > 0                               STRING  1     16    2m   0   RWD  Run transitions
> 
> Something is very broken. There should be more entries here, at least
> there should be entries for "FeDummy01" and usually there is also an entry
> for "FeDummy" because one invariably runs fedummy without "-i" at least once.
> 
> The fact that changing from "midas" storage to "file" storage makes no difference
> also indicates that something is very broken.
> 
> I want to debug this.
> 
> Since you tried the "file" storage, can you send me the output of "ls -l mhf*.dat" in the directory
> with the history files? (it should have the "*.hst" files from the "midas" storage and "mhf*.dat" files
> from the "file" storage.


> 
> K.O.

Hi Konstantin,

> > [local:e666:S]History>ls -l /History/Events
> > Key name                        Type    #Val  Size  Last Opn Mode Value
> > ---------------------------------------------------------------------------
> > 1                               STRING  1     10    2m   0   RWD  FeDummy02
> > 0                               STRING  1     16    2m   0   RWD  Run transitions
> 
> Something is very broken. There should be more entries here, at least
> there should be entries for "FeDummy01" and usually there is also an entry
> for "FeDummy" because one invariably runs fedummy without "-i" at least once.

This is a fresh experiment that I started just to test this this issue, that is why there are not many 
entries in /History/Events. I agree though that we should expect to see a FeDummy01 entry.
 
> The fact that changing from "midas" storage to "file" storage makes no difference
> also indicates that something is very broken.
> 
> I want to debug this.
> 
> Since you tried the "file" storage, can you send me the output of "ls -l mhf*.dat" in the directory
> with the history files? (it should have the "*.hst" files from the "midas" storage and "mhf*.dat" 
files
> from the "file" storage.

When I started this experiment yesterday(?) I disabled the Midas history when I enbled the file 
history. Jsut now I reenabled the Midas history, so they are currently both active.

% ls -l work/online/{*.hst,mhf*.dat}
-rw-r--r-- 1 hastings hastings  14996 Sep 17 10:21 work/online/190917.hst
-rw-r--r-- 1 hastings hastings   3292 Sep 18 16:29 work/online/190918.hst
-rw-r--r-- 1 hastings hastings 867288 Sep 18 16:29 work/online/mhf_1568683062_20190917_fedummy01.dat
-rw-r--r-- 1 hastings hastings 867288 Sep 18 16:29 work/online/mhf_1568683062_20190917_fedummy02.dat
-rw-r--r-- 1 hastings hastings    166 Sep 17 10:17 
work/online/mhf_1568683062_20190917_run_transitions.dat

And again, just as a sanity check:

% odbedit -c 'ls -l /History/Events'
Key name                        Type    #Val  Size  Last Opn Mode Value
---------------------------------------------------------------------------
1                               STRING  1     10    1m   0   RWD  FeDummy02
0                               STRING  1     16    1m   0   RWD  Run transitions

Regards,

Nick.

> I will try to use the db_watch function in the future.

Note that db_watch() and db_open_record() work exactly the same way, both only allow 
watching "whole" odb entries, you cannot watch individual array elements.

The db_watch() callback function gives you the array index of the array element that was 
changed and that fired the notification. 

*but*

If you change many array elements quickly you will not necessary receive notifications for 
all and each of of them (underlying transport is UDP allows notification packet loss).

If you are watching 1 array element change at a slow rate (1/sec), db_watch() will work well.

Otherwise, you can watch the whole array, in the db_watch() callback, read the new array 
contents, compare it with your saved copy of pervious array contents, identify which array 
elements have changed and dance from here. (this method does not work if you do not 
actually change the array element values: change from "1" to "1", this is an old weakness in 
the midas hot link mechanism).

If you are not sure how to use db_watch(), look inside midas/progs/odbedit.cxx search for 
db_watch() and search for the db_watch() callback function.

K.O.

We should fix this for midas-2019-10.

https://bitbucket.org/tmidas/midas/issues/193/confusion-in-history-event-ids

K.O.





> Hi Konstantin,
> 
> > > [local:e666:S]History>ls -l /History/Events
> > > Key name                        Type    #Val  Size  Last Opn Mode Value
> > > ---------------------------------------------------------------------------
> > > 1                               STRING  1     10    2m   0   RWD  FeDummy02
> > > 0                               STRING  1     16    2m   0   RWD  Run transitions
> > 
> > Something is very broken. There should be more entries here, at least
> > there should be entries for "FeDummy01" and usually there is also an entry
> > for "FeDummy" because one invariably runs fedummy without "-i" at least once.
> 
> This is a fresh experiment that I started just to test this this issue, that is why there are not many 
> entries in /History/Events. I agree though that we should expect to see a FeDummy01 entry.
>  
> > The fact that changing from "midas" storage to "file" storage makes no difference
> > also indicates that something is very broken.
> > 
> > I want to debug this.
> > 
> > Since you tried the "file" storage, can you send me the output of "ls -l mhf*.dat" in the directory
> > with the history files? (it should have the "*.hst" files from the "midas" storage and "mhf*.dat" 
> files
> > from the "file" storage.
> 
> When I started this experiment yesterday(?) I disabled the Midas history when I enbled the file 
> history. Jsut now I reenabled the Midas history, so they are currently both active.
> 
> % ls -l work/online/{*.hst,mhf*.dat}
> -rw-r--r-- 1 hastings hastings  14996 Sep 17 10:21 work/online/190917.hst
> -rw-r--r-- 1 hastings hastings   3292 Sep 18 16:29 work/online/190918.hst
> -rw-r--r-- 1 hastings hastings 867288 Sep 18 16:29 work/online/mhf_1568683062_20190917_fedummy01.dat
> -rw-r--r-- 1 hastings hastings 867288 Sep 18 16:29 work/online/mhf_1568683062_20190917_fedummy02.dat
> -rw-r--r-- 1 hastings hastings    166 Sep 17 10:17 
> work/online/mhf_1568683062_20190917_run_transitions.dat
> 
> And again, just as a sanity check:
> 
> % odbedit -c 'ls -l /History/Events'
> Key name                        Type    #Val  Size  Last Opn Mode Value
> ---------------------------------------------------------------------------
> 1                               STRING  1     10    1m   0   RWD  FeDummy02
> 0                               STRING  1     16    1m   0   RWD  Run transitions
> 
> Regards,
> 
> Nick.

> I recently upgraded to MIDAS version midas-2019-06-b. I had to make a few changes 
> to get our custom page running again, but am a little confused on starting and 
> stopping runs.

So far so good.

> When I click on my "Start" button, it now redirects to a 
> Transition page rather than reloading the status page.

Are you sure? The "start" button redirects to the "start" page (start.html) which redirects
to the "transition" page (transition.html), which does not redirect anywhere so you can see
the result of the transition.

> Could someone explain the reasoning for the current behavior?

It's been like this for years now. Stefan suggest that we implement the "start" page
and the "transition" page as overlays on top of the status page, but it did not happen yet.

> Furthermore my "Stop" button is now broken with the following error:
> Error: Invalid URL "CS/EngeRun&" or query "cmd=Stop&redir=EngeRun%26" or command  "Stop"

I grep for "EngeRun" and I do not see it anywhere in the midas sources. Can you grep for it
to see if it is coming from one of your pages?

If you want to start/stop runs from your custom page, look at start.html and transition.html - you will
need to make the run transition RPC calls (cut-and-paste the code to your page) and (obviously)
you will not have any redirects to some strange pages.

> For example, start calls:
> location.search = "cmd=Transition";
> whereas stop does:
> mhttpd_goto_page("Transition"); // DOES NOT RETURN

It's the same thing, look at mhttpd_goto_page().

> Can anyone offer any insights or advice? I can change the former to "cmd=Status", but 
> the latter doesn't allow it.

I am not sure what you are trying to do. If you need the "start" button on the status page
to do something different from what it does now, just hack status.html until it does so.
If you need some specific help with that, I am happy to help. I think I answered all questions
you asked so far.

K.O.

> online monitor would show (almost in real-time) the 
> gain, the dark noise, and the pedestal for all the channels, the 2D tracks 
> inside the detectors for each spill and so on.

Hmm... I now realize that the midas distribution does not include an example web page that 
integrates all these elements into one easy to understand html file.

I think an example page that would answer your questions and the questions from the other 
thread about starting/stopping runs, should include following elements:

- the general midas web page framework (the midas left-hand side menu, the top side 
status display, Stefan's new odb tags)
- buttons to start and stop runs (javascript code to call the run transition RPCs)
- embedded images for history display (old style gif and new style canvas)
- embedded images for ROOT histograms (via the ROOT http server and jsroot)
- code to live-update all these elements independantly from each other (to allow history 
plots and ROOT histograms to update at different frequencies).

As for the web page code for showing a mini-event-display, I think we do not know yet how 
to do - the event data lives inside the analyzer as C++ data structures, so somehow it 
needs to be encoded as json (this code is missing - but one can use the ROOT C++ to json 
encoder/streamer), needs to be transported to the web browser (we know how to do this) 
and at the end, plotting the json data on a canvas is the easy part.

I know some experiments have done all of this, and I think we should have such a pipeline 
available as part of the ROOTANA package. Maybe some day...

K.O.

Dear Thomas and Konstantin,

thank you very much for the feedback. I found the ROOTANA javascript display a good source of 
information and references.

As Thomas said, maybe the simplest thing would be to use the ROOT THttpServer. Honestly, I do 
not think that ROOT was ever meant to act as an online monitor due to its wacky memory 
management and abysmal multithread support. In other words, I think that by using ROOT we would 
inevitably lose some performance. 

Perhaps there are better ways of achieving the same goal. For example, I was leaning towards a 
plotly.js based approach where I would encode a series of vectors in base64 strings (for better 
transmission performance), send them to the client through the MJSONRPC mechanism, decode them 
and then feed them to plotly.js. But in this case, I should study many new libraries 
(plotly.js, the library for the base64 encoding, the Gaussian fitting, etc...) and I do not 
have the time to do that now: "beam is coming".

So ROOT it is. I will use the ROOTANA javascript display as a reference. Do you happen to know 
who wrote that part? 

In that example, you have some "static" histograms that you keep always in memory, while in our 
case the number of channels is so big that we have to dynamically generate the histograms only 
when needed (when the user select a single channel).

Best regards
Giorgio

> 
> As Thomas said, maybe the simplest thing would be to use the ROOT THttpServer. Honestly, I do 
> not think that ROOT was ever meant to act as an online monitor due to its wacky memory 
> management and abysmal multithread support. In other words, I think that by using ROOT we would 
> inevitably lose some performance.
>

Yes. The previous data analysis frameworks - PAW/PAW++/CERNlib (CERN), NOVA (TRIUMF) - certainly had
support for online monitoring. In CERNlib/PAW the histograms were stored in shared memory,
the analyzer running in the background was filling them, the PAW/PAW++ display was displaying
them "live". I was very surprised to find this function removed/not implemented in ROOT, given
that the same people were behind both projects (Rene Brun & co).

We tried to roll our own implementation of this in ROOTANA/ROODY, with mixed success.

I am glad the JSROOT project finally gained traction and web based "I can see the data" is now
available in ROOT.

> 
> Perhaps there are better ways of achieving the same goal. For example, I was leaning towards a 
> plotly.js based approach where 
>

There are many web/javascript graphics libraries out there, all have the weak spot - how do you
get your data into them?

Going forward, I see us standardizing on JSROOT: https://root.cern.ch/js/

>
> ... send them to the client through the MJSONRPC mechanism ...
>

I am not sure JSROOT have any support for interacting from the web page to the back-end analyzer. Perhaps
we can use the MIDAS MJSONRPC library for this. Hmm... (Note that the ROOT HTTP server is a derivative
of the mongoose web server library, which we use in mhttpd, so I already know how to work it)

>
> I would encode a series of vectors in base64 strings (for better transmission performance)
>

We looked into this when deciding on the data encoding for the midas history data. There is a tradeoff
between network use and cpu use - to save on the network, you try to reduce the data size by using
compressed binary data - to save on the CPU you try to minimize data encoding.

For history data, we gave up on binary json (extra decoding needed), gave up on text json (extra decoding 
needed), gave up on compression (extra cpu use for decompression) and use javascript native binary processing
("arraybuffer").

Our thinking is that network bandwidth is usually quite big and is getting bigger, but cpu resource is limited
and is expensive. (mobile devices seems to be stuck with ~2 GHz CPUs; cpu use means battery use and
battery capacity is limited, not improving quickly)

> 
> So ROOT it is. I will use the ROOTANA javascript display as a reference. Do you happen to know 
> who wrote that part? 
> 

Yes. See "Contact" at https://root.cern.ch/js/

>
> In that example, you have some "static" histograms that you keep always in memory, while in our 
> case the number of channels is so big that we have to dynamically generate the histograms only 
> when needed (when the user select a single channel).
> 

This requires interaction with the analyzer, requires some kind of RPC mechanism. I am now curious what jsroot 
have, also it would not be too hard to add the mjsonrpc library to rootana. Cooperation from ROOT multithreading
is not required: I can queue the RPC requests in a separate (thread safe, non-ROOT) buffer, then process
them in the ROOT main event loop (this is how the ROOTANA histogram server worked in the days when
ROOT had no multithread support at all).

K.O.

Hi,

I have been looking at the 2019 workshop slides, I am interested in the C++ future of MIDAS. 

I am quite interested in using the object oriented 


ALPHA will start data taking in 2021

I keep on getting messages like this:

16:25:35 [fecaen,ERROR] [odb.c:4567:db_get_data,ERROR] data for key
"/DAQ/params/VX1730/custom/Board 0/Channel 0/Input range" truncated

whenever I start my frontend. Input range is defined to be a BOOL and using
odbedit to read it shows:

Key name                        Type    #Val  Size  Last Opn Mode Value
---------------------------------------------------------------------------
Input range                     BOOL    1     4     75h  0   RWD  y

without any error message. The entry is read using

         size = sizeof(fInputRange);
         db_get_data(hDb, hSubKey, &fInputRange, &size, TID_BOOL);

where fInputRange is a bool.

Where does this message come from and how can I resolve this?

> I keep on getting messages like this:
> 16:25:35 [fecaen,ERROR] [odb.c:4567:db_get_data,ERROR] data for key
> "/DAQ/params/VX1730/custom/Board 0/Channel 0/Input range" truncated
>
>  [  bool fInputRange... ]
>          size = sizeof(fInputRange);
>          db_get_data(hDb, hSubKey, &fInputRange, &size, TID_BOOL);
>

The error is correct. size of TID_BOOL is 4 byte (uint32_t) and you give is sizeof(bool) instead which is probably not 4.

Note that sizeof(bool) is not well defined, sometimes it is 1 (you need 4), sometimes something else, see
https://stackoverflow.com/questions/4897844/is-sizeofbool-defined-in-the-c-language-standard

A good fix would be to change fInputRange from bool to uint32_t (which is always 4 byte size).

#include <stdint.h>
...
uint32_t fInputRange;

K.O.