I can confirm part of the problem - the new inline-edit function - after you finish editing - shows you what you 
have typed, not what's actually in ODB - at the very end it should do an ODBGet() to load the actual ODB 
contents and show *that* to the user.

The truncation to 32 characters - most likely it is a failure to resize the ODB string - is probably in mhttpd and 
I can take a quick look into it.

There is a 3rd problem - the mhttpd ODB editor "create" function does not ask for the string length to create.

Actually, in ODB, "create" and "set string size" are two separate functions - db_create_key(TID_STRING) creates 
a string of length zero, then db_set_data() creates an empty string of desired length.

In the new AJAX interface these two functions are separate (ODBCreate just calls db_create_key()).

In the present ODBSet() function the two are mixed together - and the ODB inline edit function uses ODBSet().

K.O.



> I find that new mhttpd has strange behaviour for ODB strings.
> 
> - I create a new STRING variable in ODB through mhttpd.  It defaults to size 32.
> 
> - I then edit the STRING variable through mhttpd, writing a new string larger
> than 32 characters.
> 
> - Initially everything looks fine; it seems as if the new string value has been
> accepted.
> 
> - But if you reload the page, or navigate back to the page, you realize that
> mhttpd has silently truncated the string back to 32 characters.
> 
> You can reproduce this problem on a test page here:
> 
> http://midptf01.triumf.ca:8081/AnnMessage
> 
> Older versions of mhttpd (I'm testing one from 2 years ago) don't have this
> 'feature'.  For older mhttpd the string variable would get resized when a larger
> string was inputted.  That definitely seems like the right behavior to me.
> 
> I am using fresh copy of midas from bitbucket as of this morning. (How do I get
> a particular tag/hash of the version of midas that I am using?)

I would like to share with you a silly problem with mktime() and daylight savings time (Summer 
time/Winter time) that I have run into while working on the mhttpd history query page.

I am implementing 1 hour granularity for the queries (was 1 day granularity) and somehow all my queries 
were off by 1 hour.

It turns out that the mktime() and localtime() functions for converting between time_t and normal time 
units (days, hours) are not exact inverses of each other.

Daylight savings time (DST) is to blame.

While localtime() always applies the current DST,  mktime() will return the wrong answer unless tm_isdst is 
set correctly.

For tm_isdst, the default value 0 is wrong 50% of the time in most locations as it means "DST off" (whether 
that's Summer time or Winter time depends on your location).

Today in Vancouver, BC, DST is in effect, and localtime(mktime()) is off by 1 hour.

If I were doing this in January, I would not see this problem.

"man mktime" talks about "tm_isdst" special value "-1" that is supposed to fix this. But the wording of 
"man mktime" on Linux and on MacOS is different (I am amused by the talk about "attempting to divine 
the DST setting"). Wording at http://pubs.opengroup.org/onlinepubs/007908799/xsh/mktime.html is 
different again. MS Windows (Visual Studio) documentation says different things for different versions.

So for mhttpd I use the following code. First mktime() gets the approximate time, a call to localtime() 
returns the DST setting in effect for that date, a second mktime() with the correct DST setting returns the 
correct time. (By "correct" I mean that localtime(mktime(t)) == t).

time_t mktime_with_dst(const struct tm* ptms)
{
   // this silly stuff is required to correctly handle daylight savings time (Summer time/Winter time)
   // when we fill "struct tm" from user input, we cannot know if daylight savings time is in effect
   // and we do not know how to initialize the value of tms->tm_isdst.
   // This can cause the output of mktime() to be off by one hour.
   // (Rules for daylight savings time are set by national and local govt and in some locations, changes 
yearly)
   // (There are no locations with 2 hour or half-hour daylight savings that I know of)
   // (Yes, "man mktime" talks about using "tms->tm_isdst = -1")
   //
   // We assume the user is using local time and we convert in two steps:
   //
   // first we convert "struct tm" to "time_t" using mktime() with unknown tm_isdst
   // second we convert "time_t" back to "struct tm" using localtime_r()
   // this fills "tm_isdst" with correct value from the system time zone database
   // then we reset all the time fields (except for sub-minute fields not affected by daylight savings)
   // and call mktime() again, now with the correct value of "tm_isdst".
   // K.O. 2013-09-14

   struct tm tms = *ptms;
   struct tm tms2;
   time_t t1 = mktime(&tms);
   localtime_r(&t1, &tms2);
   tms2.tm_year = ptms->tm_year;
   tms2.tm_mon  = ptms->tm_mon;
   tms2.tm_mday = ptms->tm_mday;
   tms2.tm_hour = ptms->tm_hour;
   tms2.tm_min  = ptms->tm_min;
   time_t t2 = mktime(&tms2);
   //printf("t1 %.0f, t2 %.0f, diff %d\n", (double)t1, (double)t2, (int)(t1-t2));
   return t2;
}

K.O.

I confirm the second part of the problem.

Inline edit uses ODBSet(), which uses the "jset" AJAX call to mhttpd which does not extend string variables.

This is the jset code. The best I can tell it truncates string variables to the existing size in ODB:

db_find_key(hDB, 0, str, &hkey)
db_get_key(hDB, hkey, &key);
memset(data, 0, sizeof(data));
size = sizeof(data);
db_sscanf(getparam("value"), data, &size, 0, key.type);
db_set_data_index(hDB, hkey, data, key.item_size, index, key.type);

These original jset/jget functions are a little bit too complicated and there is no documentation (what exists is done by me trying to read the existing code).

We now have a jcopy/ODBMCopy() as a sane replacement for jget, but nothing comparable for jset, yet.

I think this quirk of inline edit cannot be fixed in javascript - the mhttpd code for "jset" has to change.

K.O.


> 
> I can confirm part of the problem - the new inline-edit function - after you finish editing - shows you what you 
> have typed, not what's actually in ODB - at the very end it should do an ODBGet() to load the actual ODB 
> contents and show *that* to the user.
> 
> The truncation to 32 characters - most likely it is a failure to resize the ODB string - is probably in mhttpd and 
> I can take a quick look into it.
> 
> There is a 3rd problem - the mhttpd ODB editor "create" function does not ask for the string length to create.
> 
> Actually, in ODB, "create" and "set string size" are two separate functions - db_create_key(TID_STRING) creates 
> a string of length zero, then db_set_data() creates an empty string of desired length.
> 
> In the new AJAX interface these two functions are separate (ODBCreate just calls db_create_key()).
> 
> In the present ODBSet() function the two are mixed together - and the ODB inline edit function uses ODBSet().
> 
> K.O.
> 
> 
> 
> > I find that new mhttpd has strange behaviour for ODB strings.
> > 
> > - I create a new STRING variable in ODB through mhttpd.  It defaults to size 32.
> > 
> > - I then edit the STRING variable through mhttpd, writing a new string larger
> > than 32 characters.
> > 
> > - Initially everything looks fine; it seems as if the new string value has been
> > accepted.
> > 
> > - But if you reload the page, or navigate back to the page, you realize that
> > mhttpd has silently truncated the string back to 32 characters.
> > 
> > You can reproduce this problem on a test page here:
> > 
> > http://midptf01.triumf.ca:8081/AnnMessage
> > 
> > Older versions of mhttpd (I'm testing one from 2 years ago) don't have this
> > 'feature'.  For older mhttpd the string variable would get resized when a larger
> > string was inputted.  That definitely seems like the right behavior to me.
> > 
> > I am using fresh copy of midas from bitbucket as of this morning. (How do I get
> > a particular tag/hash of the version of midas that I am using?)

Due to popular request, I implemented a custom header for mhttpd. This allows to inject some HTML code 
to be shown on top of the menu bar on all mhttpd pages. One possible application is to bring back the old 
status line with the name of the current experiment, the actual time and the refresh interval. 

To use this feature, one can put a new entry into the ODB under

/Custom/Header

which can be either a string (to show some short HTML code directly) or the name of a file containing some 
HTML code. If /Custom/Path is present, that path is used to locate the header file. A simple header file to 
recreate the GOT look (good-old-times) is here:

<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 c =	document.cookie.split('midas_refr=');
r.innerHTML = now.toString() + '&nbsp;&nbsp;&nbsp;' + 'Refr:' + c.pop().split(';').shift();
</script>

The JavaScript code is used to retrieve the midas_refr cookie which stores the refresh interval and displays 
it together with the current time.

Another application of this feature might be to check certain values in the ODB (via the ODBGet function) 
and some some important status or error condition.

/Stefan

I vaguely remember that I had a similar problem with ELOG. The solution was to call tzset() at the beginning of the program. The man page says that 
this function is called automatically by programs using time zones, but apparently it is not. Can you try that? There is also the TZ environment 
variable and /etc/localtime. I never understood the details, but playing with these things can influence mktime() and localtime().

/Stefan

Actually this was no bug, but a missing feature. Strings were never meant to be extended via the web interface. 
Now I added that feature to the current version. Please check it.

/Stefan

> I vaguely remember that I had a similar problem with ELOG. The solution was to call tzset() at the beginning of the program. The man page says that 
> this function is called automatically by programs using time zones, but apparently it is not. Can you try that? There is also the TZ environment 
> variable and /etc/localtime. I never understood the details, but playing with these things can influence mktime() and localtime().

I confirm that the timezone is set correctly - I do get the correct time eventually - so there is no missing call to tzet().

K.O.

> > I vaguely remember that I had a similar problem with ELOG. The solution was to call tzset() at the beginning of the program. The man page says that 
> > this function is called automatically by programs using time zones, but apparently it is not. Can you try that? There is also the TZ environment 
> > variable and /etc/localtime. I never understood the details, but playing with these things can influence mktime() and localtime().
> 
> I confirm that the timezone is set correctly - I do get the correct time eventually - so there is no missing call to tzet().
> 
> K.O.

tzset() not only sets the time zone, but also DST.

> > > I vaguely remember that I had a similar problem with ELOG. The solution was to call tzset() at the beginning of the program. The man page says that 
> > > this function is called automatically by programs using time zones, but apparently it is not. Can you try that? There is also the TZ environment 
> > > variable and /etc/localtime. I never understood the details, but playing with these things can influence mktime() and localtime().
> > 
> > I confirm that the timezone is set correctly - I do get the correct time eventually - so there is no missing call to tzet().
> > 
> > K.O.
> 
> tzset() not only sets the time zone, but also DST.

I found following code in elogd.c, maybe it helps:

/* workaround for wong timezone under MAX OSX */
long my_timezone()
{
#if defined(OS_MACOSX) || defined(__FreeBSD__) || defined(__OpenBSD__)
   time_t tp;
   time(&tp);
   return -localtime(&tp)->tm_gmtoff;
#else
   return timezone;
#endif
}



void get_rfc2822_date(char *date, int size, time_t ltime)
{
   time_t now;
   char buf[256];
   int offset;
   struct tm *ts;

   /* switch locale temporarily back to english to comply with RFC2822 date format */
   setlocale(LC_ALL, "C");

   if (ltime == 0)
      time(&now);
   else
      now = ltime;
   ts = localtime(&now);
   assert(ts);
   strftime(buf, sizeof(buf), "%a, %d %b %Y %H:%M:%S", ts);
   offset = (-(int) my_timezone());
   if (ts->tm_isdst)
      offset += 3600;
   snprintf(date, size - 1, "%s %+03d%02d", buf, (int) (offset / 3600),
            (int) ((abs((int) offset) / 60) % 60));
}

> This is the jset code. The best I can tell it truncates string variables to the existing size in ODB:
> 
> db_find_key(hDB, 0, str, &hkey)
> db_get_key(hDB, hkey, &key);
> memset(data, 0, sizeof(data));
> size = sizeof(data);
> db_sscanf(getparam("value"), data, &size, 0, key.type);
> db_set_data_index(hDB, hkey, data, key.item_size, index, key.type);


Correct. So I added some code which extends strings if necessary (NOT string arrays, they are more complicated to handle).

> > The bulk of the MIDAS AJAX and Javascript functions is now documented on the MIDAS Wiki:
> > 
> > https://midas.triumf.ca/MidasWiki/index.php/Mhttpd.js
> > https://midas.triumf.ca/MidasWiki/index.php/AJAX
> > 
> 
> The documentation was updated again.
> 

Newly documented are the additional Javascript and AJAX functions present in the GIT branch "feature/ajax":

ODBMCreate(paths, types);
ODBMCreate(paths, types, arraylengths, stringlengths, callback);  
ODBMResize(paths, arraylengths, stringlengths, callback);  
ODBMRename(paths, names, callback);  
ODBMLink(paths, links, callback);  
ODBMReorder(paths, indices, callback);
ODBMKey(paths, callback);
ODBMDelete(paths, callback);

All these functions permit asynchronous use (with callback on completion) and the underlying AJAX functions permit JSON-P encoding.

ODBSetUrl("http://mhttpd.somewhere.com:8080") : this new function removes the restriction that custom scripts had to be loaded from the same mhttpd that they will 
access. Together with the newly added CORS support in mhttpd, allows loading custom scripts from any web server, including local file, and having then access any one (or 
any several) mhttpd data sources.

I think these new functions are now stable (I still had to make some changes to ODBMCreate() recently) and after some more testing this branch will be merged into 
"develop".

To use this branch, do either:
a) git clone midas; git pull; git checkout feature/ajax
b) git clone midas; git checkout develop; git pull; git checkout -b ajaxtest; git merge feature/ajax;

(Option (b) creates a local branch with the latest "develop" and "feature/ajax" merged together).

K.O.

> odbedit can now save ODB in JSON-formatted files.
> 
> JSON encoding implementation follows specifications at:
> http://json.org/
> 
> The result passes validation by:
> http://jsonlint.com/
> 

A bug was reported in my JSON ODB encoder: NaN values are not encoded correctly. A quick review found this:

1) the authors of JSON smoked some bad mushrooms and specifically disallowed NaN and Inf values for floating point numbers: 
http://tools.ietf.org/html/rfc4627
2) most JSON encoders and decoders do reasonable and unreasonable things with NaN and Inf values. The worst ones encode them as zero. More bad 
mushrooms.

There is a quick survey at: http://lavag.org/topic/16217-cr-json-labview/?p=99058

<pre>
Some Javascript engines allow it since it is valid Javascript but not valid Json however there is no concensus.
cmj-JSON4Lua: raw tostring() output (invalid JSON).
dkjson: 'null' (like in the original JSON-implementation).
Fleece: NaN is 0.0000, freezes on +/-Inf.
jf-JSON: NaN is 'null', Inf is 1e+9999 (the encode_pretty function still outputs raw tostring()).
Lua-Yajl: NaN is -0, Inf is 1e+666.
mp-CJSON: raises invalid JSON error by default, but runtime configurable ('null' or Nan/Inf).
nm-luajsonlib: 'null' (like in the original JSON-implementation).
sb-Json: raw tostring() output (invalid JSON).
th-LuaJSON: JavaScript? constants: NaN is 'NaN', Inf is 'Infinity' (this is valid JavaScript?, but invalid JSON).
</pre>

For the MIDAS JSON encoder (and decoder) I have several choices:
a) encode NaN and Inf using the printf("%f") encoding (as strings, making it valid JSON)
b) encode NaN and Inf as strings using the Javascript special values: "NaN", "Infinity" and "-Infinity", see 
http://www.w3schools.com/jsref/jsref_positive_infinity.asp

I note that the Python JSON encoder does (b), see section 18.2.3.3 at http://docs.python.org/2/library/json.html

In either case, behaviour of the JSON decoder on the Javascript side needs to be tested. (Silent conversion to value of zero is not acceptable).

If anybody has an suggestion on this, please let me know.



P.S. If you do not know all about NaN, Inf, "-0" and other floating point funnies, please read:  https://www.ualberta.ca/~kbeach/phys420_580_2010/docs/ACM-Goldberg.pdf

P.P.S. If you ever used the type "float" or "double", used the "/" operator or the function "sqrt()" you also should read that reference.

K.O.

The following code found in mhttpd does not work on MacOS (BSD UNIX).

On Linux, the do-loop will finish after 2 seconds as expected. On MacOS (and other BSD systems), it will 
loop forever.

The cause is the MIDAS watchdog alarm() signal that fires every 1 second and always interrupts the 2 
second sleep of select(). The Linux select() updates it's timeout argument to reflect time already slept, so 
eventually we finish. The MacOS (BSD) select() does not update the timeout argument and select goes back 
to sleep for another 2 seconds (to be again interrupted half-way through).

The POSIX standard (specification for select() & co) permits either behaviour. Compare "man select" on 
MacOS and on Linux.

If the select() timeout were not 2 seconds, but 0.9 seconds; or if the MIDAS watchdog alarm fired every 
2.1 seconds, this problem would also not exist.

I think there are several places in MIDAS with code like this. An audit is required.

{
                  FD_ZERO(&readfds);
                  FD_SET(_sock, &readfds);

                  timeout.tv_sec = 2;
                  timeout.tv_usec = 0;

                  do {
                     status = select(FD_SETSIZE, &readfds, NULL, NULL, &timeout);
                     /* if an alarm signal was cought, restart with reduced timeout */
                  } while (status == -1 && errno == EINTR);
}

K.O.

> > odbedit can now save ODB in JSON-formatted files.
> A bug was reported in my JSON ODB encoder: NaN values are not encoded correctly.

Tested the browser-builtin JSON.stringify() function in google-chrome, firefox, safari, opera:
everybody encodes numeric values NaN and Inf as JSON value [null].

To me, this clearly demonstrates a severe defect in the JSON standard and in it's Javascript implementation:
a) NaN, Inf and -Inf are valid, useful and commonly used numeric values defined by the IEEE754/854 standard (as opposed to the special value "-0", which is also defined by the standard, but is not nearly as useful)
b) they are all distinct numeric values, encoding them all into the same JSON value [null] is the same as encoding all even numbers into the JSON value [42].
c) on the decoding end, JSON value [null] is decoded into Javascript value [null], which works as 0 for numeric computation, so effectively NaN, Inf and -Inf are made equal to zero. A neat trick.

Note that (c) - NaN, Inf is same as 0 - eventually produces incorrect numerical results by breaking the IEEE754/854 standard specification that number+NaN->NaN, number+infinity->infinity, etc.

In MIDAS we have a requirement that results be numerically correct: if an ODB value is "infinity", the corresponding web page should not show "0".

In addition we have a requirement that JSON encoding should be lossess: i.e. ODB contents encoded by JSON should decode back into the same ODB contents.

To satisfy both requirements, I now encode NaN, Inf and -Inf as JSON string values "NaN", "Infinity" and "-Infinity". (Corresponding to the respective Javascript values).

Notes:
1) this is valid JSON
2) it survives decode/encode in the browser (ODBMCopy()/JSON.parse/modify some values/JSON.stringify/ODBMPaste() does not destroy these special values)
3) it is numerically correct for "NaN" values (Javascript [1+"NaN"] -> NaN)
4) it fails in an obvious way for Inf and -Inf values (Javascript [1+"Infinity"] is NaN instead of Infinity).

https://bitbucket.org/tmidas/midas/commits/82dd203cc95dacb6ec9c0a24bc97ffd45bb58427
K.O.

MIDAS "programs" settings include: /programs/xxx/"auto start", "auto restart" and "auto stop". What do 
they do?

"auto start":

if set to "y", the program's "start command" will be unconditionally executed at the beginning of the run 
start transition.

Because there are no checks or tests, the "start command" will be executed even if the program is already 
running. It means that this function cannot be used to start frontend programs - a new copy will be 
started each time, and a previously running copy will be killed.

Also the timing of the program startup and run transition is wrong - in my tests, the program starts too 
late to see the run transition. If the program is a frontend, it will never see the begin-of-run transition.

1st conclusion: "auto start" should be "n" for frontend programs and for any other programs that are 
supposed to be continuously running (mlogger, lazylogger, etc).

2nd conclusion: "auto start" does the same thing as "/programs/execute on start run".

"auto stop":

if set to "y", the program will be stopped after the end of run. (using cm_shutdown).

"auto restart":

this has nothing to do with starting and stopping runs. Instead, it works in conjunction with the alarm 
system and the "program is not running" alarm.

The alarm system periodically calls al_check(). al_check() checks all programs defined under /Programs to 
see if they are running (using cm_exist()). If a program is not running and an alarm is defined, the alarm is 
raised ("program is not running" alarm). If there is a start command and "auto restart" is set to "y", the 
start command is executed.

When using these "auto start" and "auto restart" functions, one needs to be careful about the context 
where the start command will be executed: midas clients may be running from different directories, under 
different user names and on different computers.

In "auto start", the start command is executed from cm_transition. For remote clients, this will happen on 
the remote computer. (against the expectation that the program will be started on the main computer).

In "auto restart", the start command is executed by al_check() which always runs locally (for remote 
clients, it runs inside the mserver). So the started program will always run on the main computer, but 
maybe not in the same directory as when started from the mhttpd "programs -> start" button.

Conclusion:

"programs auto start" : works but has strange interactions and side effects, do not use it.
"programs auto stop" : works, can be used to stop programs at the end of run (but what for?)
"programs auto restart" : works, seems to work correctly, can be used to auto restart mlogger, frontends, 
etc.

K.O.

Record-oriented ODB functions db_create_record(), db_get_record(), db_check_record() and 
db_set_record() require special attention to the consistency between their "C struct"s (usually defined in 
midas.h), their initialization strings (usually defined in midas.h) and the contents of ODB.

When these 3 items become inconsistent, the corresponding midas functions tend to break.

Unlike ODB internal structures and event buffer internal structures, these record-oriented functions are 
not part of the midas binary-compatibility abi and they are not protected by db_validate_sizes().

From time to time, new items are added to some of these data structures. Usually this does not cause 
problems, but recently we had some difficulty with the runinfo and equipment structures, prompting this 
audit.

db_check_record: note: (C) means that this record is created there

alarm.c: alarm_odb_str(C)
mana.c: skipped
mfe.c: equipment_common_str, equipment_statistics_str(C), event_descrip(C), bank_list(C)
mhttpd.cxx: cgif_label_str(C), cgif_bar_str(C), runinfo_str(C), equipment_common_str(C)
mlogger.cxx: ch_settings_str(C)
sequencer.cxx: sequencer_str(C)

db_create_record:

alarm.c: alarm_odb_str, alarm_periodic_str, alarm_class_str
fal.c: skipped
mfe.c: equipment_common_str
midas.c: program_info_str (maybe)
odb.c: (maybe)
lazylogger.cxx: lazy_settings, lazy_statistics
mhttpd.cxx: runinfo_str
mlogger.cxx: chn_settings_str

db_get_record: (hard to do with grep, will have to check every db_get_record by hand)

alarm.c: alarm, class, program_info
fal.c: skipped
mana.c: skipped
midas.c: program_info
odb.c: (maybe)
lazylogger.cxx: lazyst
mhttpd.cxx: runinfo, equipment, ?hkeytemp?, chn_settings, chn_stats, ?label?, ?bar?
mlogger.cxx: ?, ?, chn_stats, chn, settings
sequencer.cxx: hkeyseq

db_set_record:

alarm.c: hkeyalarm, hkeyclass, ???, program_info
fal.c: skipped
mana.c: skipped
mfe.c: equipment_info, ?event structure?
odb.c: (maybe)
lazelogger.cxx: lazyst
mlogger.cxx: chn_stat
sequencer.cxx: seq

db_open_record: note: (W) means MODE_WRITE

fal.c: skipped
mana.c: skipped
mfe.c: equipment_info, equipment_stats(W)
midas.c: requested_transition
odbedit.c: key_update - generic test of hotlink
lazylogger.cxx: runstate, lazyst(W), lazy?
mlogger.cxx: history, chn_statistics, chn_settings
sequencer.cxx: seq

K.O.

A problem existed in midas for some time: when recording long data sets of time (or event) limited runs 
with logger run auto restart set to "yes", the runs will automatically stop and restart as expected, but 
sometimes the run will stop and never restart and beam will be lost until the experiment operator on shift 
wakes up and restarts the run manually.

I have now traced this problem to a race condition inside the mlogger - when a run is being stopped from 
the mlogger, the mlogger run transition handler (tr_stop) triggers an immediate attempt to start the next 
run, without waiting for the run-stop transition to actually complete. If the run-stop transition does not 
finish quickly enough, a safety check in start_the_run() will cause the run restart attempt to silently fail 
without any error message.

This race condition is pretty rare but somehow I managed to replicate it while debugging the 
multithreaded transitions. It is fixed by making mlogger wait until the run-stop transition completes.

https://bitbucket.org/tmidas/midas/commits/b2631fbed5f7b1ec80e8a6c8781ada0baed7702b

K.O.

> The following code found in mhttpd does not work on MacOS (BSD UNIX). ...

Because of this problem, on MacOS, run transitions can get stuck forever - most timeouts do not work. (Specifically, recv_string() never times out)

K.O.

> A problem existed in midas for some time: when recording long data sets of time (or event) limited runs 
> with logger run auto restart set to "yes", the runs will automatically stop and restart as expected, but 
> sometimes the run will stop and never restart and beam will be lost until the experiment operator on shift 
> wakes up and restarts the run manually.
> 
> I have now traced this problem to a race condition inside the mlogger - when a run is being stopped from 
> the mlogger, the mlogger run transition handler (tr_stop) triggers an immediate attempt to start the next 
> run, without waiting for the run-stop transition to actually complete. If the run-stop transition does not 
> finish quickly enough, a safety check in start_the_run() will cause the run restart attempt to silently fail 
> without any error message.
> 
> This race condition is pretty rare but somehow I managed to replicate it while debugging the 
> multithreaded transitions. It is fixed by making mlogger wait until the run-stop transition completes.
> 
> https://bitbucket.org/tmidas/midas/commits/b2631fbed5f7b1ec80e8a6c8781ada0baed7702b
> 
> K.O.

More generally I kind of consider the mlogger auto restart facility as deprecated. It works in the background and the operator does not have a clue 
what is going on. We use now the sequencer to achieve exactly the same functionality. It just requires a few lines of sequencer code:

LOOP INFINITE 
  TRANSITION start 
  WAIT events, 5000 
  TRANSITION stop 
ENDLOOP 

So the run start is only executed after the runs has been successfully stopped. You can do things in the sequencer like "stop run and sequence 
immediately" or "stop after current run has finished" which are a bit hard to do with the old method. So people should move to the sequencer.

/Stefan

> 
> More generally I kind of consider the mlogger auto restart facility as deprecated. It works in the background and the operator does not have a clue 
> what is going on. We use now the sequencer to achieve exactly the same functionality.
>

Before subruns were available, most experiments at TRIUMF have used the "auto restart" function. Now, I think most of them use subruns,
with the notable exception of PIENU where the analysis framework could not handle subruns. (PIENU is now shutdown and disassembled).

>
> It just requires a few lines of sequencer code:
> 
> LOOP INFINITE 
>   TRANSITION start 
>   WAIT events, 5000 
>   TRANSITION stop 
> ENDLOOP 
> 

Mouse click "auto restart" to "yes" is a little bit simpler than setting up a sequencer file, and it survives a crash of mhttpd.

Does the sequencer survive a crash or a restart of mhttpd?

K.O.