We have seen several times a problem with stuck data buffers. The symptoms are very confusing - 
frontends cannot start, instead hang forever in a state very hard to kill. Also "mdump -s -d -z 
BUF03" for the affected data buffers is stuck.

We have identified the source of this problem - the semaphore for the buffer is locked and nobody 
will ever unlock it - MIDAS relies on a feature of SYSV semaphores where they are automatically 
unlocked by the OS and cannot ever be stuck ever. (see man semop, SEM_UNDO function).

I think this SEM_UNDO function is broken in recent Linux kernels and sometimes the semaphore 
remains locked after the process that locked it has died. MIDAS is not programmed to deal with this 
situation and the stuck semaphore has to be cleared manually.

Here, "BUF3" is used as example, but we have seen "SYSTEM" and ODB with stuck semaphores, too.

Steps:
a) confirm that we are using SYSV semaphores: "ipcs" should show many semaphores
b) identify the stuck semaphore: "strace mdump -s -d -z BUF03".
c) here will be a large printout, but ultimately you will see repeated entries of 
"semtimedop(9633800, {{0, -1, SEM_UNDO}}, 1, {1, 0}^C <unfinished ...>"
d) erase the stuck semaphore "ipcrm -s 9633800", where the number comes from semtimedop() in 
the strace output.
e) try again: "mdump -s -d -z BUF03" should work now.

Ultimately, I think we should switch to POSIX semaphores - they are easier to manage (the strace 
and ipcrm dance becomes "rm /dev/shm/deap_BUF03.sem" - but they do not have the SEM_UNDO 
function, so detection of locked and stuck semaphores will have to be done by MIDAS. (Unless we 
can find some library of semaphore functions that already provides such advanced functionality).

K.O.

I was looking at something in the mserver and noticed that for remote frontends, for every periodic event, 
there are about 3 RPC calls to bm_flush_cache().

Sure enough, in mfe.c::send_event(), for every event sent, there are 2 calls to bm_flush_cache() (once for 
the buffer we used, second for all buffers). Then, for a good measure, the mfe idle loop calls 
bm_flush_cache() for all buffers about once per second (even if no events were generated).

So what is going on here? To allow good performance when processing many small events,
the MIDAS event buffer code (bm_send_event()) buffers small events internally, and only after this internal
buffer is full, the accumulated events are flushed into the shared memory event buffer,
where they become visible to the mlogger, mdump and other consumers.

Because of this internal buffering, infrequent small size periodic events can become
stuck for quite a long time, confusing the user: "my frontend is sending events, how come I do not
see them in mdump?"

To avoid this, mfe.c manually flushes these internal event buffers by calling bm_flush_buffer().

And I think that works just fine for frontends directly connected to the shared memory, one call to 
bm_flush_buffer() should be sufficient.

But for remote fronends connected through the mserver, it turns out there is a race condition between 
sending the event data on one tcp connection and sending the bm_flush_cache() rpc request on another 
tcp connection.

I see that the mserver always reads the rpc connection before the event connection, so bm_flush_cache() 
is done *before* the event is written into the buffer by bm_send_event(). So the newly
send event is stuck in the buffer until bm_flush_cache() for the *next* event shows up:

mfe.c: send_event1 -> flush -> ... wait until next event ... -> send_event2 -> flush
mserver: flush -> receive_event1 -> ... wait ... -> flush -> receive_event2 -> ... wait ...
mdump -> ... nothing ... -> ... nothing ... -> event1 -> ... nothing ...

Enter the 2nd call to bm_flush_cache in mfe.c (flush all buffers) - now because mserver seems to be 
alternating between reading the rpc connection and the event connection, the race condition looks like 
this:

mfe.c: send_event -> flush -> flush
mserver: flush -> receive_event -> flush
mdump: ... -> event -> ...

So in this configuration, everything works correctly, the data is not stuck anywhere - but by accident, and 
at the price of an extra rpc call.

But what about the periodic 1/second bm_flush_cache() on all buffers? I think it does not quite work
either because the race condition is still there: we send an event, and the first flush may race it and only 
the 2nd flush gets the job done, so the delay between sending the event and seeing it in mdump would be 
around 1-2 seconds. (no more than 2 seconds, I think). Since users expect their events to show up "right
away", a 2 second delay is probably not very good.

Because periodic events are usually not high rate, the current situation (4 network transactions to send 1 
event - 1x send event, 3x flush buffer) is probably acceptable. But this definitely sets a limit on the 
maximum rate to 3x (2x?) the mserver rpc latency - without the rpc calls to bm_flush_buffer() there
would be no limit - the events themselves are sent through a pipelined tcp connection without 
handshaking.

One solution to this would be to implement periodic bm_flush_buffer() in the mserver, making all calls to 
bm_flush_buffer() in mfe.c unnecessary (unless it's a direct connection to shared memory).

Another solution could be to send events with a special flag telling the mserver to "flush the buffer right 
away".

P.S. Look ma!!! A race condition with no threads!!!

K.O.

In one of the experiments, we hit a long time bug in mdump - there was an array of 32 equipments and if 
there were more than 32 entries under /equipment, it would overrun and corrupt memory. Somehow this 
only showed up after mdump was switched to c++. The solution was to use std::vector instead of fixed 
size array.

Just in case, I checked other midas programs for fixed size arrays (other than fixed size strings) and found 
none. (in midas.c, there is a fixed size array of TR_FIFO[10], but code inspection shows that it cannot 
overrun).

I used this script. It can be modified to also identify any strange sized string arrays.

K.O.

#!/usr/bin/perl -w

while (1) {
  my $in = <STDIN>;
  last unless $in;
  #print $in;

  $in =~ s/^\s+//;

  next if $in =~ /^char/;
  next if $in =~ /^static char/;

  my $a = $in =~ /(.*)[(\d+)\]/;

  next unless $a;

  my $a1 = $1;
  my $a2 = $2;

  next if $a2 == 0;
  next if $a2 == 1;
  next if $a2 == 2;
  next if $a2 == 3;

  #print "[$a] [$a1] [$a2]\n";
  print "-> $a1[$a2]\n";
}

# end

I added MIDAS Makefile rules for building ARM binaries: "make linuxarm" and "make cleanarm" will create 
(and clean) object files, libraries and executables under "linux-arm" using the TI Sitara ARM SDK or the 
Yocto SDK ARM cross-compilers (GCC 4.7.x and 4.8.x respectively). (Makefile rules for building PPC 
binaries have existed for years).

The hardware we have at TRIUMF are "ARMv7" machines - TI Sitara 335x CPUs (google mityarm) and Altera 
Cyclone 5 FPGA ARM (google sockit). (as opposed to the ARMv5 CPU on the RaspberryPi). The software 
binary API standard settled by Fedora Linux is "hard float" (as opposed to "soft float" used by older SDKs).

So "ARMv7 hard float" is what we intend to use at TRIUMF, but ARMv5 and soft-float should also work ok, 
so please report successes and/or problems to this forum.

K.O.

A few months ago, definitions of SYNC and ASYNC in midas.h have been changed away from "0" and "1", 
and this caused problems with some event buffer management functions bm_xxx().

For example, when event buffers are getting full, bm_send_event(SYNC) unexpectedly started returning 
BM_ASYNC_RETURN instead of waiting for free space, causing unexpected crashes of frontend programs.

Part of the problem was confusion between SYNC/ASYNC used by buffer management (bm_xxx) and by run 
transition (cm_transition()) functions. Adding to confusion, documentation of bm_send_event() & co used 
FALSE/TRUE while most actual calls used SYNC/ASYNC.

To sort this out, an executive decision was made to abolish the SYNC/ASYNC defines:

For buffer management calls bm_send_event(), bm_receive_event(), etc, please use:
SYNC -> BM_WAIT
ASYNC -> BM_NO_WAIT

For run transitions, please use:
SYNC -> TR_SYNC
ASYNC -> TR_ASYNC
MTHREAD -> TR_MTHREAD
DETACH -> TR_DETACH

K.O.

If you follow the MIDAS documentation for setting up password protection, you will get strange messages:

ladd00:midas$ ./linux/bin/odbedit
[local:testexpt:S]/>passwd                <---- setup a password
Password: 
Retype password: 
[local:testexpt:S]/> exit

ladd00:midas$ odbedit
Password:    <---- enter correct password here
ss_semaphore_wait_for: semop/semtimedop(21135376) returned -1, errno 22 (Invalid argument)
ss_semaphore_release: semop/semtimedop(21135376) returned -1, errno 22 (Invalid argument)
[local:testexpt:S]/>ss_semaphore_wait_for: semop/semtimedop(21037069) returned -1, errno 43 (Identifier removed)

The same messages will appear from all other programs - mhttpd, etc. They will be printed about every 1 second.

So what do they mean? They mean what they say - the semaphore is not there, it is easy to check using "ipcs" that semaphores with 
those ids do not exist. In fact all the semaphores are missing (the ODB semaphore is eventually recreated, so at least ODB works 
correctly).

In this situation, MIDAS will not work correctly.

What is happening?

- cm_connect_experiment1() creates all the semaphores and remembers them in cm_set_experiment_semaphore()
- calls cm_set_client_info()
- cm_set_client_info() finds ODB /expt/sec/password, and returns CM_WRONG_PASSWORD
- before returning, it calls db_close_all_databases() and bm_close_all_buffers(), which delete all semaphores (put a print statement in 
ss_semaphore_delete() to see this).
- (values saved by cm_set_experiment_semaphore() are stale now).
- (if by luck you have other midas programs still running, the semaphores will not be deleted)
- we are back to cm_connect_experiment1() which will ask for the password, call cm_set_client_info() again and continue as usual
- it will reopen ODB, recreating the ODB semaphore
- (but all the other semaphores are still deleted and values saved by cm_set_experiment_semaphore() are stale)

I through to improve this by fixing a bug in cm_msg_log() (where the messages are coming from) - it tries to lock the "MSG" 
semaphore, but even if it could not lock it, it continues as usual and even calls an unlock at the end. (very bad). For catastrophic 
locking failures like this (semaphore is deleted), we usually abort. But if I abort here, I get completely locked out from odb - odbedit 
crashes right away and there is no way to do any corrective action other than delete odb and reload it from an xml file.

I know that some experiments use this password protection - why/how does it work there?

I think they are okey because they put critical programs like odbedit, mserver, mlogger and mhttpd into "/expt/sec/allowed 
programs". In this case the pass the password check in cm_set_client_info() and the semaphores are not deleted. If any subsequent 
program asks for the password, the semaphores survive because mlogger or mhttpd is already running and keeps semaphores from 
being deleted.

What a mess.

K.O.

The MIDAS Web password function is broken - with the web password enabled, I am not prompted for a 
password when editing ODB. The password still partially works - I am prompted for the web password 
when starting a run. K.O.

P.S. https://midas.triumf.ca/MidasWiki/index.php/Security says "web password" needed for "write access", 
but does not specify if this includes editing odb. (I would think so, and I think I remember that it used to).

> I through to improve this by fixing a bug in cm_msg_log() (where the messages are coming from)

The periodic messages about broken semaphore actually come from al_check(). I put some whining there, too.

K.O.

In some experiments (i.e. DEAP), we see spurious symlinks to midas.log scattered just about everywhere. I 
now traced this to an uninitialized variable in cm_msg_log() and it should be fixed now. K.O.

I made some tests of MIDAS support for "international characters" and we seem to be in a reasonable 
shape.

The standard standard is UTF-8 encoding of Unicode and the MIDAS core is believed to be UTF-8 clean - 
one can use "international characters" in ODB names, in ODB values, in filenames, etc.

The web interface had some problems with percent-encoding of ODB URLs, but as of current git version, 
everything seems to work okey, as long as the web browser is in the UTF-8 encoding mode. The default 
mode is "Western ISO-8859-1" and javascript encodeURIComponent() is mangling some stuff making the 
ODB editor not work. Switching to UTF-8 mode seems to fix that.

Perhaps we should make the UTF-8 encoding the default for mhttpd-generated web pages. This should be 
okey for TRIUMF - we use English language almost exclusively, but need to check with other labs before 
making such a change. I especially worry about PSI because I am not sure if and how they any of the special 
German-language characters.

On the minus side, odbedit does not seem to accept non-English characters at all. Maybe it is easy to fix.

K.O.

The capability to generate doxygen documentation of MIDAS was restored.

Use "make dox" and "make cleandox",
find generated documentation in ./html,
look at it via "firefox html/index.html".

The documentation is not generated by default - it takes quite a long time to build all the call graphs.

And the call graphs is what makes this documentation useful - without some visual graphical 
representation it is quite difficult to understand some parts of MIDAS. Both caller and callee graphs are 
generated.

Note that doxygen documentation for the javascript functions in mhttpd.js is also generated, making a 
handy reference in addition to the full documentation on the MIDAS Wiki.

K.O.

> Since several projects at PSI need MSCB but not MIDAS, I decided to separate the two repositories. So if you 
> need MIDAS with MSCB support inside mhttpd, you have to clone MIDAS, MXML and MSCB from bitbucket 
> (or the local clone at TRIUMF) as described in
> 
> https://midas.triumf.ca/MidasWiki/index.php/Main_Page#Download
> 
> I tried to fix all Makefiles to link to the new locations, but I'm not sure if I got all. So if something does not 
> compile please let me know.
> 
> -Stefan

After this split, Makefiles used to build experiment frontends need to be modified for the new location of the mscb tree:

replace
$(MIDASSYS)/mscb
with
$(MIDASSYS)/../mscb

K.O.

I am not sure what to do with the javascript snippet - I understand it should be somehow connected to /Custom/Header, but if I create the /Custom/Header string, I cannot put this snippet 
into this string using odbedit - if I try to cut&paste it into odbedit, it is truncated to the first line - nor using the mhttpd odb editor - when I cut&paste it into the odb editor text entry box, it 
is truncated to the first 519 bytes (must be a hard limit somewhere). K.O.

> As reported in the bug tracker, the proposed header does not work if no specific (= different from the default 60 sec.) update period is specified, 
> since then no cookie is present. Here is the updated code which works for all cases:
> 
> 
> 
> <div id="footerDiv" class="footerDiv">
> <div style="display:inline; float:left;">MIDAS experiment "Test"</div>
> <div id="refr" style="display:inline; float:right;"></div>
> </div>
> <script type="text/javascript">
> var r = document.getElementById('refr');
> var now = new Date();
> var refr;
> if (document.cookie.search('midas_refr') == -1)
>    refr = 60;
> else {
>    var c = document.cookie.split('midas_refr=');
>    refr = c.pop().split(';').shift();
> }
> r.innerHTML = now.toString() + '&nbsp;&nbsp;&nbsp;' + 'Refr:' + refr;
> </script>
> 
> 
> 
> /Stefan

> I'm looking into using MIDAS for an experiment that creates one large event
> (20MB or more) every second.

Hi, there - 20 Mbyte event at 1/sec is not so large these days. (Well, depending on your hardware).

Using typical 1-2 year old PC hardware, 20 M/sec to local disk should work right away. Sending data from a 
remote front end (through the mserver), or writing to a remote disk (NFS, etc) - will of course requre a GigE 
network connection.

By default, MIDAS is configured for using about 1-2 Mbyte events, so for your case, you will need to:

- increase the event size limits in your frontend,
- increase /Experiment/MAX_EVENT_SIZE in ODB
- increase the size of the SYSTEM event buffer (/Experiment/Buffer sizes/SYSTEM in ODB)

I generally recommend sizing the SYSTEM event buffer to hold a few seconds worth of data (ot 
accommodate any delays in writing to local disk - competing  reads, internal delays of the disks, etc).

So for 20 M/s, the SYSTEM buffer size should be about 40-60 Mbytes.

For your case, you also want to buffer 3-5-10 events, so the SYSTEM buffer size would be between 100 and 
200 MBytes.

Assuming you have between 8-16-32 GBytes of RAM, this should not be a problem.

One the other hand, if you are running on a low-power ("green") ARM system with 1 Gbyte of RAM and a 
1GHz CPU, you should be able to handle the data rate of 20 Mbytes/sec, as long as your network and 
storage can handle it - I see GigE ethernet running at about 30-40 Mbytes/sec, so you should be okey,
but local storage to SD flash is only about 10 Mbytes/sec - too slow. You can try USB-attached HDD or SSD, 
this should run at up to 30-40 Mbytes/sec. I would expect no problems with this rate from MIDAS, as long 
as you can fit into your 1 GByte of RAM - obviously your SYSTEM buffer will have to be a little smaller than 
on a full-featured PC.

More information on MIDAS event size limits is here (as already reported by Stefan)
https://midas.triumf.ca/MidasWiki/index.php/Event_Buffer

Let us know how it works out for you.

K.O.

> > The capability to generate doxygen documentation of MIDAS was restored.
> > 
> > Use "make dox" and "make cleandox",
> > find generated documentation in ./html,
> > look at it via "firefox html/index.html".
> > 
> 
> To generate the files, you need doxygen installed which not everybody has.

On most Linux systems, doxygen is easy to install. Red Hat instructions are here: 
http://www.triumf.info/wiki/DAQwiki/index.php/SLinstall#Install_packages_needed_for_QUARTUS.2C_ROOT.2C_EPICS_and_MIDAS_DAQ

On MacOS, doxygen is easy to install via macports: sudo port install doxygen

> Is there a web site where one can see the generated graphs?

http://ladd00.triumf.ca/~olchansk/midas/index.html

there is no cron job to update this, but I may update it infrequently.

K.O.

I made a few minor modifications to the ODB JSON encoder and implemented a javascript "ls" function to 
report full ODB directory information as available from odbedit "ls -l" and the mhttpd odb editor page.

Using the new ODBMLs(), the existing ODBMCreate(), ODBMDelete() & etc a complete ODB editor can be 
written in Javascript (or in any other AJAX-capable language).

While implementing this function, I found some problems in the ODB JSON encoder when handling 
symlinks, also some problems with handling symlinks in odbedit and in the mhttpd ODB editor - these are 
now fixed.

Changes to the ODB JSON encoder:
- added the missing information to the ODB KEY (access_mode, notify_count)
- added symlink target information ("link")
- changed encoding of simple variable (i.e. jcopy of /experiment/name) - when possible (i.e. ODB KEY 
information is omitted), they are encoded as bare values (before, they were always encoded as structures 
with variable names, etc). This change makes it possible to implement ODBGet() and ODBMGet() using the 
AJAX jcopy method with JSON data encoding. Bare value encoding in ODBMCopy()/AJAX jcopy is enabled by 
using the "json-nokeys-nolastwritten" encoding option.

All these changes are supposed to be backward compatible (encoding used by ODBMCopy() for simple 
values and "-nokeys-nolastwritten" was previously not documented).

Documentation was updated:
https://midas.triumf.ca/MidasWiki/index.php/Mhttpd.js

K.O.

> If I am not mistaken, the mhttpd.css is hard coded (path/name) into the mhttpd.

mhttpd.css is served from $MIDASSYS/resources/mhttpd.css. The actual path is reported on the mhttpd 
"help" page.

(I think the internal mhttpd.css and mhttpd.js should be removed as no longer useful - nothing will work 
right if the real mhttpd.js and mhttpd.css cannot be served).

> Especially the look and feel of the runlog is unsatisfactorily from my point of view.

persons in charge of implementing the CSS stuff failed to convert quite a few pages, for example, the elog 
and the history editor pages were left completely broken. (mostly fixed now).

so thank you for reporting the runlog breakage, I hope Stefan & co can fix it quickly. (I cannot do - I have 
have no runlog pages on any of my test experiments).

> the old style was much more readable.

I think the new style is not too bad, except for a few visual artefacts here and there, the general comment 
that CSS is too complicated and hard to debug and the fact that over-subtle colouring yields inconsistent 
visuals between different monitors and ambient lighting conditions. (persons who select the colours always 
respond that "but to me, it looks just fine on my laptop", making it hard to resolve any issues).

> I could recover the old style look and feel by slightly changing the mhttpd.cxx

If you post the patches that fix it for you, I can commit them to midas. (git diff | mail olchansk@triumf.ca).

K.O.

> 
> I don't know if this actually fits the Bug Report category. I've been trying to install Midas on my Mac OS 
> Mavericks and I keep getting errors like "conflicting types for '___builtin____strlcpy_chk' ..." and similarly for 
> strlcat. I googled a bit and I think the problem might be that in Mavericks strlcat and strlcpy are already 
> defined in string.h, and so there might be a redundant definition somewhere. I'm not sure what the best 
> way to fix this would be though. Any help would be appreciated.
> 

We have run into this problem - MacOS 10.9 plays funny games with definitions of strlcpy() & co - and it has been fixed since last Summer.

For the record, current MIDAS builds just fine on MacOS 10.9.2.

For a pure test, try the instructions posted at midas.triumf.ca:

cd $HOME
mkdir packages
cd packages
git clone https://bitbucket.org/tmidas/midas
git clone https://bitbucket.org/tmidas/mscb
git clone https://bitbucket.org/tmidas/mxml
cd midas
make

K.O.

The midas wiki at https://midas.triumf.ca was updated to mediawiki 1.22.4 - the latest production version. 
If you see any problems, please report them to this elog. K.O.

> In the old SVN midas world it was typically such that the Windows dll's and
> exe's were ready to be used when checking out.

The Windows executables are no longer included in the midas git repository. Old versions are still available in 
the git repository - they got pulled in during conversion from svn.

One reason for removing them is that neither myself, nor Pierre, nor Stefan have ready access to a Windows 
development environment and we cannot keep Windows binaries up to date. Theoretically we can setup a 
Windows machine just for compiling MIDAS, but then there is a question of which Windows we should use and 
how much priority we should put into it. I do not think there is any demand for MIDAS on Windows at TRIUMF.

(Personally, I think Windows is no longer a viable platform for any business use - with Microsoft focusing on 
"experiences", "tiles", touch screens, portable devices, and other gimmicks - rather than on providing a solid OS 
to get work done)

> I am not so sure this is the case
> for the current version, since when I use the packed dll's  and exe's (e.g.
> odbedit.exe) I get the warning that this is running midas 2.0.0 but the current
> version (on the linux server) is 2.1. What does this mean?

You can ignore this message. Stefan incremented the MIDAS version when we migrated to git, but
there are no changes to the MIDAS RPC mechanism and we are still fully compatible with old versions,
at least in the MIDAS RPC and in the mserver.

So tools like odbedit.exe should still work okey when connecting from Windows to MIDAS running on Linux or 
MacOS.

But old frontend programs may cause some trouble because the ODB layout changed somewhat with new things 
added to /eq/xxx/common. Simplest is to try, if it works, it works.

> 1) A little bug in the packed windows part, but up-to-date dll's and exe's?
> 2) The dll's and exe's are not bundled any more to up-to-date version?

Case (2) is the case. Personally I do not have any capability to build Windows binaries. Same for Pierre and I think 
for Stefan.

> If 2) is the case, I would like to get a hint how to build midas under Windows
> (Windows 7), since we still have some few Windows clients.  

I do not think pre-built executables will ever return - the new way of things is to "cut-and-paste" the "git clone" 
command from a web page, type "make", and be done with it. If your OS does not have "git", "make" & etc, you 
should switch to a real OS.

On the MIDAS software side, we have no problem with supporting Windows - same as on any other platform, 
please try to build and run it, report any problems, fixes, patches and improvements - we will commit them into 
the midas repository.

K.O.