Thanks for your advice. We now have Midas installed on both our machines (remote machine-Rpi &
hostmachine-Centos). 

=========================================================================================================
One the host machine:
[hh19285@it038146 bin]$ uname -a
Linux it038146.users.bris.ac.uk 3.10.0-957.21.2.el7.x86_64 #1 SMP Wed Jun 5 14:26:44 UTC 2019 x86_64 x86_64
x86_64 GNU/Linux
[hh19285@it038146 bin]$ uname -a
Linux it038146.users.bris.ac.uk 3.10.0-957.21.2.el7.x86_64 #1 SMP Wed Jun 5 14:26:44 UTC 2019 x86_64 x86_64
x86_64 GNU/Linux
[hh19285@it038146 bin]$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.5/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin --enable-initfini-array
--disable-libgcj --with-isl=/builddir/build/BUILD/gcc-4.8.5-20150702/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.5-20150702/obj-x86_64-redhat-linux/cloog-install
--enable-gnu-indirect-function --with-tune=generic --with-arch_32=x86-64 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.8.5 20150623 (Red Hat 4.8.5-36) (GCC) 
[hh19285@it038146 bin]$ lsb_release -a
LSB Version:	:core-4.1-amd64:core-4.1-noarch
Distributor ID:	CentOS
Description:	CentOS Linux release 7.6.1810 (Core) 
Release:	7.6.1810
Codename:	Core

===========================================================================================================
On remote machine:
pi@raspberrypi:~/packages/midas/bin $ uname -a
Linux raspberrypi 4.19.42-v7+ #1219 SMP Tue May 14 21:20:58 BST 2019 armv7l GNU/Linux
pi@raspberrypi:~/packages/midas/bin $ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-linux-gnueabihf/6/lto-wrapper
Target: arm-linux-gnueabihf
Configured with: ../src/configure -v --with-pkgversion='Raspbian 6.3.0-18+rpi1+deb9u1'
--with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-6
--program-prefix=arm-linux-gnueabihf- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/
--enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-libitm --disable-libquadmath --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-armhf/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-armhf
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-armhf --with-arch-directory=arm
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-sjlj-exceptions --with-arch=armv6 --with-fpu=vfp --with-float=hard
--enable-checking=release --build=arm-linux-gnueabihf --host=arm-linux-gnueabihf --target=arm-linux-gnueabihf
Thread model: posix
gcc version 6.3.0 20170516 (Raspbian 6.3.0-18+rpi1+deb9u1) 
pi@raspberrypi:~/packages/midas/bin $ lsb_release -a
No LSB modules are available.
Distributor ID:	Raspbian
Description:	Raspbian GNU/Linux 9.9 (stretch)
Release:	9.9
Codename:	stretch







> Yikes, the error is in the CRC library. The assembly-optimized crc32c function fails to build, and the 
> error does not look familiar to me. I do not see this error here. What is your host system ("uname -
> a") and what is your gcc ("gcc -v")?
> 
> BTW, "make linux32" will build an Intel 32-bit version (see "-m32" in "man gcc"). For ARM 32-bit 
> you need a different switch, I think, also depending how you are cross-compiling it.
> 
> For straight cross-compilation, look at the Makefile target "make linuxarm" (you will need to change 
> the location of your ARM gcc cross-compiler).
> 
> For running MIDAS frontend on the Raspberry Pi 3, I build MIDAS on the Pi3 itself, the machine is big 
> enough to run CentOS7 linux and gcc to build the full MIDAS.
> 
> But if you have a different cross-compilation scheme, I am happy to help you and to add your 
> scheme to the MIDAS Makefile. We can start by looking at "uname -a" and "gcc -v" and "lsb_release 
> -a" (if you have it).
> 
> K.O.
> 
> 
> > Hi, we are part of the Mu3e research based at University of Bristol. We have a 
> > remote 32 bit frontend (raspberry pi) connected to a 64 bit Data Acquisition 
> > system.we are following the instructions at installation/quickstart linux/Build 
> > 32-bit MIDAS libraries. when we execute the commands: 
> > [mhostpc] cd /home/packages/midas
> > [mhostpc] make linux32             
> > 
> > we get an error:
> > 
> > make NO_ROOT=1 NO_MYSQL=1 NO_ODBC=1 NO_SQLITE=1 OS_DIR=linux-m32 USERFLAGS=-
> m32
> > make[1]: Entering directory `/home/hh19285/packages/midas'
> > g++ -m32 -c -g -O2 -Wall -Wno-strict-aliasing -Wuninitialized -Iinclude -
> > Idrivers -Imxml -Imscb/include -DHAVE_FTPLIB -D_LARGEFILE64_SOURCE -DHAVE_ZLIB -
> > DHAVE_MSCB -DHAVE_MONGOOSE6 -DMG_ENABLE_THREADS -DMG_DISABLE_CGI -
> DMG_ENABLE_SSL 
> > -DOS_LINUX -fPIC -Wno-unused-function -o lib/crc32c.o src/crc32c.cxx
> > src/crc32c.cxx: In function ‘uint32_t crc32c_hw(uint32_t, const void*, size_t)’:
> > src/crc32c.cxx:283:66: error: ‘asm’ operand has impossible constraints
> >                      : "r"(next), "0"(crc0), "1"(crc1), "2"(crc2));
> >                                                                   ^
> > src/crc32c.cxx:303:66: error: ‘asm’ operand has impossible constraints
> >                      : "r"(next), "0"(crc0), "1"(crc1), "2"(crc2));
> >                                                                   ^
> > src/crc32c.cxx: In function ‘uint32_t crc32c(uint32_t, const void*, size_t)’:
> > src/crc32c.cxx:348:34: error: PIC register clobbered by ‘%ebx’ in ‘asm’
> >                  : "%ebx", "%edx"); \
> >                                   ^
> > src/crc32c.cxx:362:5: note: in expansion of macro ‘SSE42’
> >      SSE42(sse42);
> >      ^
> > make[1]: *** [lib/crc32c.o] Error 1
> > make[1]: Leaving directory `/home/hh19285/packages/midas'
> > make: *** [linux32] Error 2
> > 
> > Could you please help with getting past this? otherwise we may need to change 
> > our whole experimental setup.
> > 
> > Thank you in advance

I'm still trying to upgrade my MIDAS system to midas-2019-09-i. Most frontends work fine with the modifications already discussed.
However, I ran into some trouble with the epics frontend. Even with the modifications it throws a lot of warnings and errors (see attached log file). I can reduce the errors with -fpermissive, but the following two errors are persistent:

/home/ays/packages/midas/drivers/device/epics_ca.cxx:167:38: error: ‘ca_create_channel’ was not declared in this scope
            , &(info->caid[i].chan_id))

/home/ays/packages/midas/drivers/device/epics_ca.cxx:178:37: error: ‘ca_create_subscription’ was not declared in this scope
            , &(info->caid[i].evt_id))

This is strange because the functions seem to be declared in base/include/cadef.h along with similar functions that don't throw an error.
I don't know what's going on. The frontend which is almost identical to the example in the midas distribution compiles without warnings or errors under the Midas2017 version. 

> I'm still trying to upgrade my MIDAS system to midas-2019-09-i. Most frontends work fine with the modifications already discussed.
> However, I ran into some trouble with the epics frontend. Even with the modifications it throws a lot of warnings and errors (see attached log file). I can reduce the errors with -fpermissive, but the following two errors are persistent:
> 
> /home/ays/packages/midas/drivers/device/epics_ca.cxx:167:38: error: ‘ca_create_channel’ was not declared in this scope
>             , &(info->caid[i].chan_id))
> 
> /home/ays/packages/midas/drivers/device/epics_ca.cxx:178:37: error: ‘ca_create_subscription’ was not declared in this scope
>             , &(info->caid[i].evt_id))
> 
> This is strange because the functions seem to be declared in base/include/cadef.h along with similar functions that don't throw an error.
> I don't know what's going on. The frontend which is almost identical to the example in the midas distribution compiles without warnings or errors under the Midas2017 version. 

Hi, Peter - it looks like epics_ca.cxx needs to be updated to proper C++ (char* warnings, etc).

As for the "function not declared" errors, it's the C++ way to say "you are calling a function with wrong arguments",
again, something I should be able to fix without too much trouble.

Thank you for reporting this, the midas version of epics_ca.cxx definitely needs fixing.

K.O.

I fixed the compiler errors in epics_ca.cxx, can you try again? (see https://bitbucket.org/tmidas/midas/commits/)

But, I do not see errors with ca_create_channel() and ca_create_subscription().

Maybe I am using the wrong epics. If you still see these errors, let me know what epics you have, I will try the same one.

This is what I do (and I get epics 7.0).

mkdir -p $HOME/git
cd $HOME/git
git clone https://git.launchpad.net/epics-base
cd epics-base
make
ls -l include/cadef.h
ls -l lib/darwin-x86/libca.a # also linux-x86/libca.a

K.O.

> > I'm still trying to upgrade my MIDAS system to midas-2019-09-i. Most frontends work fine with the modifications already discussed.
> > However, I ran into some trouble with the epics frontend. Even with the modifications it throws a lot of warnings and errors (see attached log file). I can reduce the errors with -fpermissive, but the following two errors are persistent:
> > 
> > /home/ays/packages/midas/drivers/device/epics_ca.cxx:167:38: error: ‘ca_create_channel’ was not declared in this scope
> >             , &(info->caid[i].chan_id))
> > 
> > /home/ays/packages/midas/drivers/device/epics_ca.cxx:178:37: error: ‘ca_create_subscription’ was not declared in this scope
> >             , &(info->caid[i].evt_id))
> > 
> > This is strange because the functions seem to be declared in base/include/cadef.h along with similar functions that don't throw an error.
> > I don't know what's going on. The frontend which is almost identical to the example in the midas distribution compiles without warnings or errors under the Midas2017 version. 
> 
> Hi, Peter - it looks like epics_ca.cxx needs to be updated to proper C++ (char* warnings, etc).
> 
> As for the "function not declared" errors, it's the C++ way to say "you are calling a function with wrong arguments",
> again, something I should be able to fix without too much trouble.
> 
> Thank you for reporting this, the midas version of epics_ca.cxx definitely needs fixing.
> 
> K.O.

Hi Konstantin,
I have EPICS Base Release 3.14.8.2 and got your example running with it, though I had to make one change.
For some reason it wouldn't find libca.so, but when I linked the static library libca.a instead, it worked.
Also my midas frontend works now with the updated epics_ca.xx. There was a problem with an old local version of cadef.h
(probably a leftover from some previous testing). After removing it everything compiled well.

Thanks,
Peter


> I fixed the compiler errors in epics_ca.cxx, can you try again? (see https://bitbucket.org/tmidas/midas/commits/)
> 
> But, I do not see errors with ca_create_channel() and ca_create_subscription().
> 
> Maybe I am using the wrong epics. If you still see these errors, let me know what epics you have, I will try the same one.
> 
> This is what I do (and I get epics 7.0).
> 
> mkdir -p $HOME/git
> cd $HOME/git
> git clone https://git.launchpad.net/epics-base
> cd epics-base
> make
> ls -l include/cadef.h
> ls -l lib/darwin-x86/libca.a # also linux-x86/libca.a
> 
> K.O.
> 
> > > I'm still trying to upgrade my MIDAS system to midas-2019-09-i. Most frontends work fine with the modifications already discussed.
> > > However, I ran into some trouble with the epics frontend. Even with the modifications it throws a lot of warnings and errors (see attached log file). I can reduce the errors with -fpermissive, but the following two errors are persistent:
> > > 
> > > /home/ays/packages/midas/drivers/device/epics_ca.cxx:167:38: error: ‘ca_create_channel’ was not declared in this scope
> > >             , &(info->caid[i].chan_id))
> > > 
> > > /home/ays/packages/midas/drivers/device/epics_ca.cxx:178:37: error: ‘ca_create_subscription’ was not declared in this scope
> > >             , &(info->caid[i].evt_id))
> > > 
> > > This is strange because the functions seem to be declared in base/include/cadef.h along with similar functions that don't throw an error.
> > > I don't know what's going on. The frontend which is almost identical to the example in the midas distribution compiles without warnings or errors under the Midas2017 version. 
> > 
> > Hi, Peter - it looks like epics_ca.cxx needs to be updated to proper C++ (char* warnings, etc).
> > 
> > As for the "function not declared" errors, it's the C++ way to say "you are calling a function with wrong arguments",
> > again, something I should be able to fix without too much trouble.
> > 
> > Thank you for reporting this, the midas version of epics_ca.cxx definitely needs fixing.
> > 
> > K.O.

> I have EPICS Base Release 3.14.8.2 and got your example running with it...

Ok, good.

> I had to make one change.
> For some reason it wouldn't find libca.so, but when I linked the static library libca.a instead, it worked.

Yes, libca.a is what I see in my epics, too. I recommend static linking (libxxx.a instead of libxxx.so) as it eliminates
all possible problems with "cannot find the shared library" and "found the wrong shared library" and "found
a shared library from a different version of epics".

> Also my midas frontend works now with the updated epics_ca.xx. There was a problem with an old local version of cadef.h
> (probably a leftover from some previous testing). After removing it everything compiled well.

Ok. good. I also see some old epics header files in the midas repository. I guess I should remove them.

K.O.


> 
> Thanks,
> Peter
> 
> 
> > I fixed the compiler errors in epics_ca.cxx, can you try again? (see https://bitbucket.org/tmidas/midas/commits/)
> > 
> > But, I do not see errors with ca_create_channel() and ca_create_subscription().
> > 
> > Maybe I am using the wrong epics. If you still see these errors, let me know what epics you have, I will try the same one.
> > 
> > This is what I do (and I get epics 7.0).
> > 
> > mkdir -p $HOME/git
> > cd $HOME/git
> > git clone https://git.launchpad.net/epics-base
> > cd epics-base
> > make
> > ls -l include/cadef.h
> > ls -l lib/darwin-x86/libca.a # also linux-x86/libca.a
> > 
> > K.O.
> > 
> > > > I'm still trying to upgrade my MIDAS system to midas-2019-09-i. Most frontends work fine with the modifications already discussed.
> > > > However, I ran into some trouble with the epics frontend. Even with the modifications it throws a lot of warnings and errors (see attached log file). I can reduce the errors with -fpermissive, but the following two errors are persistent:
> > > > 
> > > > /home/ays/packages/midas/drivers/device/epics_ca.cxx:167:38: error: ‘ca_create_channel’ was not declared in this scope
> > > >             , &(info->caid[i].chan_id))
> > > > 
> > > > /home/ays/packages/midas/drivers/device/epics_ca.cxx:178:37: error: ‘ca_create_subscription’ was not declared in this scope
> > > >             , &(info->caid[i].evt_id))
> > > > 
> > > > This is strange because the functions seem to be declared in base/include/cadef.h along with similar functions that don't throw an error.
> > > > I don't know what's going on. The frontend which is almost identical to the example in the midas distribution compiles without warnings or errors under the Midas2017 version. 
> > > 
> > > Hi, Peter - it looks like epics_ca.cxx needs to be updated to proper C++ (char* warnings, etc).
> > > 
> > > As for the "function not declared" errors, it's the C++ way to say "you are calling a function with wrong arguments",
> > > again, something I should be able to fix without too much trouble.
> > > 
> > > Thank you for reporting this, the midas version of epics_ca.cxx definitely needs fixing.
> > > 
> > > K.O.

>
> > I have EPICS Base Release 3.14.8.2 ...
>

For the record, according to https://epics.anl.gov/

the 3.14 branch is "Closed, please upgrade!"
the 3.15 branch seems to be the current "stable" branch, and
the 7.0 branch is the "current release"

I forget which version of EPICS is currently recommended by the TRIUMF controls group. I will have to go and ask them.

K.O.

The documentation fro the Elog ODB tree here:
https://midas.triumf.ca/MidasWiki/index.php//Elog_ODB_tree#Url

says:

The Built-in elog will ignore this key.

If using an Built-in Elog, this key must NOT be present.

I assume this is an artifact from amending the documentation, but it's unclear if 
the key has to be removed or not. I.e. if the key exists and is empty, will the 
built-in elog work? In what way will it break?

Hi,

We have recently been changing the code in mhttpd that maps custom web pages and resources to 
particular files on the server file system.  Ie, changing the code that uses the ODB keys in /Custom to 
map a web address like 

http://myhost:8081/CS/MyCustomPage 

to some file like

/home/user/resource/mypage.html

This mapping gets complicated when you use the /Custom/Path key to specify a location for web 
resources like images.  We have tried to summarize how the current system works on the wiki

https://midas.triumf.ca/MidasWiki/index.php//Custom_ODB_tree

Please provide any suggestions on how either the documentation or the actual algorithm can be 
improved.

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

Enjoy,
K.O.

> 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.

All functions and AJAX methods except jset, jget, jrpc (ODBGet, ODBSet, ODBRpc) and inline edit are now fully 
documented. AJAX methods jset/jget and their javascript wrappers ODBSet/ODBGet/ODBMGet/ODBGetRecord() are 
partially documented. Inline edit will have to be documented by Stefan.

When using these functions please read the "BUG" sections carefully.

When using the Javascript functions (ODBGet, ODBSet, ODBMCopy, etc) please pay special attention to the rules for URI-
encoding function arguments - some functions require that some arguments be pre-encoded by 
"encodeURIComponent()", some functions require some arguments to NOT be pre-encoded. The examples in 
examples/javascript1/example.html are mostly correct.

Special confusion is created by special handling in mhttpd of URI-encoding of parameters named "format".

Special confusion is created by ODBSet(path, value), where "path" should be pre-encoded, while "value" is now encoded 
internally, which is a recent change introduced with the inline edit function. Older versions of mhttpd.js still require that 
"value" be URI-encoded.

Going forward, I hope to resolve most of the confusion by providing a cleaner interface for reading ODB
- ODBMCopy() already looks good with full async JSON/JSONP support (already implemented)
- ODBMKey() to read just the keys, with async JSON/JSONP support (to be added)
- ODBMCreate() to create ODB keys (RPC for db_create()) (to be added)
- ODBMSet() to write into ODB. (to be added)

K.O.

> > 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.

The general Midas documentation has been rejuvenated by Suzannah Daviel through 
a proof reading and with a collection of custom perl scripts to improve the 
Doxygen capabilities for the document itself. In particular, a contents list and 
alphabetical index of the documentation is generated automatically.

The new content is based on the previous version but with more cross-references, 
examples and descriptive images where necessary. Many of the previously 
undocumented features are now included.

The layout and organization is slightly different and requires getting used to, 
but hopefully will be an improvement.
Some of the changes are:
- The main topics are maintained, but we try to regroup all the aspects
  related to a particular topic in the same section.
- The Yellow icons provide navigation within the index section.
- The Blue icons provide navigation within the section content.

The full documentation is included under the midas/doc/src directory in the 
Midas distribution (SVN) and can be generated with the Doxygen tool.
The midasdoc-images.tar.gz from either https://midas.psi.ch/download/ or 
http://ladd00.triumf.ca/~daqweb/ftp/ needs to be extracted to the midas 
directory under doc/images for complete local web pages generation.

There are a few "ToDo" items which hopefully will be ironed out soon.
Feel free to contact us for pointing out omissions or improvements.

We hope this online documentation will serve as a better tool for your 
understanding of the Midas capabilities.

I found where we tickle the race condition in db_create_record().

1) in mhttpd.c,  every time we show the status page, we call
db_create_record(hDB, 0, "/Runinfo", strcomb(runinfo_str));
2) internally db_create_record() deletes /RunInfo
3) other programs read "/runinfo/run number" while it is deleted do not
check for the db_get_value() error code and happily get a zero run number.

Stephan fixed the race condition, and now I commited an mhttpd.c change that
only calls db_create_record(hDB, 0, "/Runinfo", strcomb(runinfo_str)); if
/runinfo does not exist. This seems to be redundant with a similar call in
cm_connect_experiment1(), called each time a new client starts up.

Files changed:
src/mhttpd.c

K.O.

> I found where we tickle the race condition in db_create_record().
> 
> 1) in mhttpd.c,  every time we show the status page, we call
> db_create_record(hDB, 0, "/Runinfo", strcomb(runinfo_str));
> 2) internally db_create_record() deletes /RunInfo
> 3) other programs read "/runinfo/run number" while it is deleted do not
> check for the db_get_value() error code and happily get a zero run number.
> 
> Stephan fixed the race condition, and now I commited an mhttpd.c change that
> only calls db_create_record(hDB, 0, "/Runinfo", strcomb(runinfo_str)); if
> /runinfo does not exist. This seems to be redundant with a similar call in
> cm_connect_experiment1(), called each time a new client starts up.

The reason for the db_create_record() is the following: Assume that we change 
the /runinfo structure, by adding an additional variable in the future. If we 
run a "new" mhttpd on an "old" experiment, the "runinfo" C structure does not 
match the ODB contents. The db_create_record() ensures that the ODB structure 
exactly matches the C structure. I agree with you that this can cause 
potential problems. But most of them should be fixed by the additional lock() 
I added recently. So other programs cannot read the run number while it is 
deleted.

One could think of checking the record size, and re-creating the runinfo if 
the ODB record size does not match the C record size. But this does not 
prevent the potential error that some variable are reversed in order. They 
are then mapped wrongly to the C runinfo structure.

I see that you work very hard now on all possible checks for the run number. 
But I would not commit that and make it part of the distribution, since all 
experiments at PSI for example do not have this run number problem. Run it 
locally, determine the cause of your problem (the discovery of the race 
condition was already very good, I'm glad that your found it, should make the 
system much more stable), and we'll fix it. Puttin ASSERT's is a good idea, I 
should have done it from the very beginning. But if you start now, please put 
it in all other 100000 places (;-)

I would not add a db_get_value_cannot_possibly_fail() into the standard 
distribution, because it probably cannot correct the initial problem and then 
just will go into an infinite loop. We should tackle problems always at their 
source. 

If you cannot resolve your zero run number problem, do the following: There 
is a cm_msg(MDEBUG, ...) which only puts a message into the shared memory, 
but not in midas.log. This can be used for real time debugging. Add those 
message temporarily in db_get_value() etc. to see what is going on. As soon 
as the run number goes to zero, stop all processes immediately (for example 
by locking the database with db_lock_database), and the look backwards in the 
sysmsg buffer to see what happened *before* the run number went to zero.

- Stefan

> > I found where we tickle the race condition in db_create_record().
> The reason for the db_create_record() is the following: Assume that we change 
> the /runinfo structure...

I think there is a deep fundamental problem with changing data structures "on the
fly". Calling db_create_record("/runinfo") at every show_status_page() does not
fix it.

If I change the runinfo structure, rebuild, relink and restart "mhttpd", the
db_create_record("/runinfo") from cm_connect_experiment() will update the runinfo
structure in ODB. In this case, the call from show_status_page() is redundant. As
a side effect, when we do this, we break every running ODB client- they still
have the old runinfo layout. Not good...

If I change the runinfo structure, rebuild, relink and restart all applications,
*except* for mhttpd, "/runinfo" in ODB will be updated when the first updated
client connects to ODB via the db_create_record("/runinfo") from
cm_connect_experiment(). Then, the old mhttpd will restore the old layout via the 
db_create_record("/runinfo") in show_status_page(), breaking everything. Not good...

If I change the runinfo structure, rebuild, relink and restart everything,
"/runinfo" in ODB will be updated when the first client connects to ODB via the
db_create_record("/runinfo") from cm_connect_experiment(). In this case, the call
from show_status_page() is redundant. This is the only corruption-free scenario.

This lack of integrity enforcement vs version skew in binary data structures is,
I think, an ODB design error. Perhaps, ODB applications should be prohibited from
 direct access to ODB "C" data structures: we cannot ensure that the data layout
in the application and in ODB are the same.

> One could think of checking the record size, and re-creating the runinfo if 
> the ODB record size does not match the C record size. But this does not 
> prevent the potential error that some variable are reversed in order. They 
> are then mapped wrongly to the C runinfo structure.

Exacto.

> I see that you work very hard now on all possible checks for the run number. 
> But I would not commit that and make it part of the distribution...

This is a philosophical issue.

My checks are in line with the "design by contract" school of programming. In a
nutshell, this ideology requires that before I do anything, I should enforce the
validity of my inputs and after I am done, I should enforce the validity of my
outputs. In practice, this translates into liberal use of assert()'s *in
production code*.

To ensure that old bugs stay fixed, and that new bugs are promptly discovered, it
is essential that the "contract checks" stay in the production code forever.

But let better writers argue programming philosophy in the literature.

Personally, when hunting down bugs in unstable code, I find this technique to be
vastly superior to the more common appoach of "This program has no bugs. Error
checking and assert()s are wasteful. Let's close our eyes and hope no bad things
happen to us (again)".

> But if you start now, please put [asserts] in all other 100000 places (;-)

I know that no good deed goes unpunished, but pewleeze!!!

> If you cannot resolve your zero run number problem, do the following: ...
> [lock ODB, freeze the experiment, look at log files]

This technique is obsolete. Today, we instrument the code with sanity checks
and validity tests. Then all the bugs find themselves with minimal manual
intervention.

K.O.

The default C indentation style in xemacs uses "tab" characters, violating
the MIDAS coding convention. To disable this misfeature in xemacs (emacs
too?), put this incantation in your .xemacs/custom.el file:

(custom-set-variables
 '(indent-tabs-mode nil))

K.O.

Dear all,

we are trying to build Midas events on FPGAs and send them directly to the midas
ring buffer via copy_n. According to the wiki
https://midas.triumf.ca/MidasWiki/index.php/Event_Structure Event Data Size is:
"The event data size contains the size of the event in bytes excluding the
header." and All Bank Size is: "Size in bytes of the following data plus the
size of the bank header". So are they actually the same or what header is the
header in the first sentence also the bank header?

Cheers,
Marius