Hi Konstantin,
thank you for the very in-depth answer. Right now I am using the latest version of MIDAS (the head of the 
develop branch) and I have not noticed any bugs or problems in the MIDAS code, except the ones that I 
myself put in the part of the code that I am developing of course.
So I will do as you suggest and continue to use the head of the develop branch.
Thank you again for taking the time to answer all my questions!

PS other than the code peculiar to our experiment, I have made a little modification to the MIDAS install 
Makefile (I noticed that there is an "install" target but not an "uninstall" target so I wrote it).
If you are interested, I could make a merge request on BitBucket, just let me know.

Bests
Giorgio

> Hi, Giorgio - you are asking excellent questions. I will try to answer them, but as ever, there are no 
> easy answers.
> 
> In general, the top of the midas "develop" branch is "the best midas there is".
> 
> So for a new experiment, it is a reasonable place to start. Of course you can see
> that there is quite a bit of commit activity going on, however, most substantial
> changes are done on separate branches, where we try the new code, debug
> it and test it. Only when the new code is "ready", we commit it to the "develop"
> branch. Then, most often, we find some more last minute post-merge bugs,
> and fix them right then and there on the head of the "develop" branch. Eventually
> the dust settles and we have stable code that stays stable for a long time.
> 
> For example, right now we are waiting for the dust to settle on the change
> of the MIDAS URL scheme, which was necessitated by needs of several experiments
> that have more-complex-then-usual https proxy configurations. Unusual today,
> but more common as we move forward, I think.
> 
> So if the head of the "develop" branch does not work for you, we encourage
> that you file a bug report (here on this forum or on the bitbucket issue tracker).
> 
> While we try to sort out your problem, you can fall back to a previous version
> of midas:
> 
> a) go back to one of the older "midas-YYYY-MM-X" tags
> b) go back to one of the release candidate branches "feature/midas-YYYY-MM".
> 
> But if you have an already running system and you already have a working
> instance of MIDAS, you do not have to update it to the latest version
> unless you need some newest feature or you suffer from a bug
> that has been fixed in a newer version.
> 
> In general, I find that it is fairly safe to update a working instance of MIDAS to
> the latest code. But do keep your old working copy, if there is trouble, you can
> always go back to something that works.
> 
> Now to your questions:
> 
> > For a running experiment that needs software stability what branch of the MIDAS 
> > repository is better suited?
> 
> easy to answer. the most stable is the version you are using right now (doh!). each time
> you upgrade, there is a risk that something will go wrong.
> 
> if you start from scratch, use the head of the "develop" branch (the latest and greatest),
> if you run into trouble, report the trouble and update to a newer version with your
> trouble fixed, or go back in time to previous tags and release candidate branches (as I described 
> above).
> 
> > The master branch or the develop branch?
> 
> the "develop" branch.
> 
> > Moreover, what point in time do you think is more stable?
> 
> I find that it is impossible to have a stable-stable-stable version of midas
> because the rest of the world flows forward in time. Old versions of midas
> stop compiling because of OS and compiler changes; they stop running
> because of OS or web browser or hardware changes. Then somebody
> always asks for new features and new or old bugs surface constantly.
> 
> But we try to mark some "good" spots using git tags and release branches,
> however the more far you go back in time, the more likely the code will
> not even compile anymore.
> 
> 
> K.O.
> 
> 
> 
> > Hello!
> > My name is Giorgio Pintaudi and I am a Ph.D. student at Yokohama National 
> > University (Japan). I also happen to be a T2K collaborator.
> > I am currently developing the DAQ software for a T2K near detector called WAGASCI 
> > (different from ND280) and we recently decided to adopt MIDAS as a user 
> > interface.
> > Now I am using the "develop" branch of the MIDAS BitBucket repository: I merge 
> > the remote repository every now and then with my local copy and that is fine ... 
> > but on the 25th of April our experiment is officially starting and I was 
> > wondering which version of MIDAS should I use for "production".
> > So my question is:
> > For a running experiment that needs software stability what branch of the MIDAS 
> > repository is better suited? The master branch or the develop branch? Moreover, 
> > what point in time do you think is more stable?
> > Best regards
> > Giorgio

> > Hmm... for most experiments, we do not "install" midas. I should probably remove the "install" target from the Makefile.
> 
> 
> ... and change the documentation accordingly (Suzannah!?). Installing midas these days does not really make sense, since normally only one 
> users uses it on a given machine.
> 
> Stefan

I understand. Anyway, I preferred to install MIDAS in the /opt/midas folder to be consistent with the other programs (Pyrame and Calicoes from LLR) that we are using for our experiment (they are all installed in the /opt folder). Moreover, I am using Linux systemd to enable mhttpd on startup (and other handy features like auto-restart after a crash). And quite unfortunately CentOS doesn't support to start systemd units as a non-root user.
So in my particular case, perhaps it made some sense to install MIDAS in a folder other than the source code folder.

Giorgio

> > Hmm... for most experiments, we do not "install" midas. I should probably remove the "install" target from the Makefile.
> 
> 
> ... and change the documentation accordingly (Suzannah!?). Installing midas these days does not really make sense, since normally only one 
> users uses it on a given machine.
> 
> Stefan

I understand. Anyway, I preferred to install MIDAS in the /opt/midas folder to remain consistent with the other programs that we are using for 
our experiment (Pyrame and Calicoes from LLR). I am also using Linux systemd to enable mhttpd on startup (and other handy features like auto-
restart after a crash) and unfortunally CentOS doesn't support to enable systemd units as a non-root user.
So in my particular case, perhaps it made some sense to install MIDAS in a folder other than the source code folder
Giorgio

> I see. Would this work as well? Instead of "make install" do this:
> su - root
> cd /opt
> git pull midas
> cd midas
> make
> add /opt/midas/linux/bin to your PATH. (is it time to get rid of the "linux" part from the default build path?!?)

Got it. I will do that in the future.

> Can you post your systemd unit file to this elog, others may find it useful.

[Unit]
Description=MIDAS data acquisition system
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=3
User=neo
ExecStart=/opt/midas/bin/mhttpd -e WAGASCI --http 8081 --https 8444
Environment="MIDASSYS=/opt/midas" "MIDAS_EXPTAB=/home/neo/Code/WAGASCI/MIDAS/online/exptab" "MIDAS_EXPT_NAME=WAGASCI" 
"SVN_EDITOR=emacs -nw" "GIT_EDITOR=emacs -nw"
PassEnvironment=MIDASSYS MIDAS_EXPTAB MIDAS_EXPT_NAME SVN_EDITOR GIT_EDITOR

[Install]
WantedBy=multi-user.target

> Note: user name "neo" and home directory is hardwired into the unit file. Also
> it runs after "network.target", this may be too early, it should run after nis and autofs
> have started (and made home directories accessible). (not sure what systemd target
> that is).

Thank you very much for the comments!

My home directory is hardwired because it is not straightforward to add environment variables into 
systemd units. Actually, I install MIDAS through a bash shell script that automatically generates 
the unit file during installation. So, for another user who would use my script, the correct path 
in the unit file would be generated at installation time. Another option would be to create an 
environment file and then feed it to the unit file (EnvironmentFile directive) as explained here: 
https://coreos.com/os/docs/latest/using-environment-variables-in-systemd-units.html

For the autofs, thank you for the hint. I have modified the unit file accordingly.

As far as NIS is concerned, I am sorry but I don't know how it is used by MIDAS. Actually, I don't 
even have it installed on my machine. Anyway, I have modified the unit file accordingly (but I 
haven't tested with NIS installed).

The modified unit file is this:

[Unit]
Description=MIDAS data acquisition system
After=network.target rpcbind.target ypbind.target
StartLimitIntervalSec=0
RequiresMountsFor=%h

[Service]
Type=simple
Restart=always
RestartSec=3
User=neo
ExecStart=/opt/midas/bin/mhttpd -e <nameofyourexperiment> --http <yourhttpport> --https 
<yourhttpsport>
Environment="MIDASSYS=/opt/midas" "MIDAS_EXPTAB=<path/to/your/exptab>" "MIDAS_EXPT_NAME=
<nameofyourexperiment>" "SVN_EDITOR=emacs -nw" "GIT_EDITOR=emacs -nw"
PassEnvironment=MIDASSYS MIDAS_EXPTAB MIDAS_EXPT_NAME SVN_EDITOR GIT_EDITOR

[Install]
WantedBy=multi-user.target

Dear Konstantin,

even if I am still quite young and have only limited experience (but not null), I would like to give my two cents. I have reflected a bit about the C++ issue, also because I am developing a 
brand new MIDAS interface for the WAGASCI-T2K experiment, and I feel that the future of MIDAS could influence the future of our DAQ system, too. I'll start from the conclusions: I completely 
agree with you on a practical level, even if I kind of disagree on an "ethical" level.

What you propose in essence is to migrate the MIDAS core from pure C to a version of C with some fancy C++ features. Let's say a kind of C+ with only one plus. Theoretically speaking, even if 
on the surface C and C++ are very similar, they are completely different languages and require different mindsets (and I am sure that everyone is aware of it). This is the reason why even if I 
would have preferred to develop the MIDAS frontend for our experiment in C++, I have chosen to stick to pure C because I feel that MIDAS is still very C-like in its architecture (or from what 
I can see from the documentation). So I wanted to "keep on track" for better internal coherence. What I mean is that, if someone told me to port a C project of mine to C++, I would end up 
rewriting it almost completely, instead of just modifying it (I really don't know how much of the MIDAS core has been written with C++ in mind, so if a large part of it is already C++-like, 
please ignore my comment above).

Anyway, on a practical level, I completely agree with your approach, because I imagine that a complete rewrite of MIDAS is off the table but, at the same time, some new C++ features like 
better string and vector handling are very tempting to use. Moreover, in general, physicists are more familiar with the C syntax than with the C++ one (but thanks to ROOT that is changing). As 
for the use of MIDAS in embedded devices, I have no experience so I refrain from judging. So, in the particular case of MIDAS, what you propose is probably the best and only option.

As far as the C++ standard to adopt, I would say that the C++11 standard is the best fit for the T2K experiment since the official OS for T2K is CentOS7 and, out of the box, it supports C++11 
only. Anyway, I acknowledge that there are many other experiments and requirements. For the records, I do development on Ubuntu 18.04.

Best regards
Giorgio

• my_frontend.cpp
  
• driver/class/my_class_driver.cpp
  
• driver/device/my_device_driver.cpp
  

@@ -1141,7 +1141,13 @@ typedef struct eqpmnt {
+#ifdef __cplusplus
+extern "C" {
+#endif
 INT device_driver(DEVICE_DRIVER *device_driver, INT cmd, ...);
+#ifdef __cplusplus
+}
+#endif

Hello!
I am creating this thread to comment on an issue raised today during the MIDAS 
workshop.

It was said that ROOT doesn't play well with multithreading ... and it is 
definitely true. But since last year, many improvements have been done in ROOT 
multi-threading support and now even the ROOT fitter can be made thread-safe.

I know this because recently I had to completely rewrite the calibration 
software for the WAGASCI experiment and I wanted to use many ROOT analyzers in 
parallel.

Getting ROOT to work in a multi-thread environment is not painless. It took me 
many weeks to get to the end of it. But if using the latest ROOT version (from 
about ROOT 6.12.00 onwards), it should be possible. Basically, you have to 
compile ROOT with the Minuit2 minimizer support and then select it.

This is the thread on the ROOT forum where I have asked about and solved my 
issues (I am LastStarDust): https://root-forum.cern.ch/t/root-crashes-in-multi-
threaded-environment/35407

You can also refer to this bug report: https://sft.its.cern.ch/jira/browse/ROOT-
7173
and this documentation page: https://root.cern.ch/how/how-express-parallelism-
many-cores

Hope it may help.
Giorgio

    for (INT i = 0; i < hv_info->num_channels; i++) {
      char element[HKEY_STRING_LENGTH];
      snprintf(element, HKEY_STRING_LENGTH, "%s[%d]", path, i);
      if (db_find_key(hDB, hv_info->hKeyRoot, element, &hKey) == DB_SUCCESS) {
        if ((hv_info->driver[i]->flags & flag) == 0) 
          db_open_record(hDB, hKey, &array[i], sizeof(double), MODE_READ, callback, pequipment);
        else
          db_open_record(hDB, hKey, &array[i], sizeof(double), MODE_READ, NULL, NULL);
      } else {
        cm_msg(MERROR, __func__, "Key %s not found", element);
      }
    }

<html>
<head>
   <title>Test</title>
   <link rel="stylesheet" href="midas.css">
   <script src="controls.js"></script>
   <script src="midas.js"></script>
   <script src="mhttpd.js"></script>
</head>
<body class="mcss" onload="mhttpd_init('Test');">

<div id="mheader"></div>
<div id="msidenav"></div>

<div id="mmain">
  <div name="mhistory" data-group="Test" data-panel="Test" data-scale="1m" style="width:600px;border:1px solid black;"></div>
</div>
</body>
</html>

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

INT idle (EQUIPMENT * pequipment)

@@ -411,6 +411,17 @@ static INT register_equipment(void)
             ss_sleep(3000);
             return 0;
          }
+#ifdef WAGASCI_OPEN_ODB_HOTLINK
+         status = db_open_record(hDB, hKey, eq_info, sizeof(EQUIPMENT), MODE_READ,
+                                 nullptr, nullptr);
+         if (status != DB_SUCCESS) {
+            printf("ERROR: Cannot open hotlink with equipment record \"%s\", db_open_record() status %d\n",
+                   str, status);
+            cm_disconnect_experiment();
+            ss_sleep(3000);
+            return 0;
+         }
+#endif
       } else if (status == DB_STRUCT_MISMATCH) {
          cm_msg(MINFO, "register_equipment", "Correcting \"%s\", db_check_record() status %d", str, status);
          db_create_record(hDB, 0, str, EQUIPMENT_COMMON_STR);

• Every change to the equipment "/Equipment/<frontend name>/Common" is instantaneously applied (and might crash the frontend?)
  

INT idle (EQUIPMENT * pequipment)

About the boost library, that is exactly 
what I did for a project of mine (the 
calibration software for the WAGASCI 
experiment). It turned out not so easy to 
mantain because different Linux distros 
package different versions of boost.

The reason I went down the "c++11 plus 
boost" road is that the official T2K OS 
is CentOS7 as well.

Looking back I think that using c++17 and 
requiring a more recent version of the 
compiler is much easier to maintain than 
the combo c++11 + boost. In CentOS is 
just a matter of installing a recent 
devtool package ...

Another solution might be too repackage 
boost into MIDAS so you have full control 
of the environment.

> > After much discussion, and following 
the MIDAS workshop at TRIUMF, we made the 
decision to use C++11 in MIDAS.
> > 
> > There are many benefits, and only one 
drawback - no c++11 compilers in the 
default OS install on older computers 
(i.e. 
> > RHEL/SL/CentOS before el7). (the same 
applies to our use of cmake).
> >
> 
> It turns out that support for the c++11 
"regex" feature is missing on el7 
(CentOS-7, our most common platform at 
TRIUMF).
> 
> According to 
https://stackoverflow.com/questions/12530
406/is-gcc-4-8-or-earlier-buggy-about-
regular-expressions
> gcc 4.9.0 is the first one to implement 
c++11 regular expressions. el7 comes with 
gcc-4.8.5 and I confirm
> that examples of using 
std::regex_replace() do not compile. I 
was looking to use std::regex_replace to 
implement URL rewriting
> in the reverse proxy code in mhttpd.
> 
> I do not need this feature immediately, 
but I am surprised that such a thing can 
happen, thought others should know.
> 
> K.O.

• write a custom parser in C++ using the instructions contained in the Mhformat page;
  
• call the mhist program from within my application;
  
• call the mhdump program from within my application;