\section faq_simgrid I'm new to SimGrid. I have some questions. Where should I start?
-You are at the right place... Having a look to these
-<a href="http://www.loria.fr/~quinson/blog/2010/06/28/Tutorial_at_HPCS/">the slides of the HPCS'10 tutorial</a>
-(or to these <a href="http://graal.ens-lyon.fr/~alegrand/articles/slides_g5k_simul.pdf">ancient
-slides</a>, or to these
-<a href="http://graal.ens-lyon.fr/~alegrand/articles/Simgrid-Introduction.pdf">"obsolete" slides</a>)
-may give you some insights on what SimGrid can help you to do and what
-are its limitations. Then you definitely should read the \ref
-MSG_examples.
+You are at the right place... To understand what you can do or
+cannot do with SimGrid, you should read the
+<a href="http://simgrid.gforge.inria.fr/tutorials.php">tutorial
+slides</a> from the SimGrid's website. You may find more uptodate
+material on the
+<a href="http://people.irisa.fr/Martin.Quinson/blog/SimGrid/">blog of
+Martin Quinson</a>.
+
+Another great source of inspiration can be found in the \ref msg_examples.
If you are stuck at any point and if this FAQ cannot help you, please drop us a
mail to the user mailing list: <simgrid-user@lists.gforge.inria.fr>.
\subsection faq_C Argh! Do I really have to code in C?
-Currently bindings on top of MSG are supported for Java, Ruby and Lua. You can find a few
-documentation about them on the doc page. Note that bindings are released separately from the main dist
-and so have their own version numbers.
+We provide Java bindings of the MSG interface, which is the main
+SimGrid user API.
-Moreover If you use C++,
-you should be able to use the SimGrid library as a standard C library
-and everything should work fine (simply <i>link</i> against this
-library; recompiling SimGrid with a C++ compiler won't work and it
-wouldn't help if you could).
+Moreover If you use C++, you should be able to use the SimGrid library
+as a standard C library and everything should work fine (simply
+<i>link</i> against this library; recompiling SimGrid with a C++
+compiler won't work and it wouldn't help if you could).
-For now,
-we do not feel a real demand for any other language. But if you think there is one,
- please speak up!
+For now, we do not feel a real demand for any other language. But if
+you think there is one, please speak up!
\section faq_howto Feature related questions
\subsubsection faq_MIA_asynchronous I want to do asynchronous communications in MSG
-In the past (version <= 3.4), there was no function to perform asynchronous communications.
-It could easily be implemented by creating new process when needed though. Since version 3.5,
-we have introduced the following functions:
- - MSG_task_isend()
- - MSG_task_irecv()
- - MSG_comm_test()
- - MSG_comm_wait()
- - MSG_comm_waitall()
- - MSG_comm_waitany()
- - MSG_comm_destroy()
-
-We refer you to the description of these functions for more details on their usage as well
-as to the example section on \ref MSG_ex_asynchronous_communications.
-
-\subsubsection faq_MIA_thread_synchronization I need to synchronize my MSG processes
-
-You obviously cannot use pthread_mutexes of pthread_conds since we handle every
-scheduling related decision within SimGrid.
-
-In the past (version <=3.3.4) you could do it by playing with
-MSG_process_suspend() and MSG_process_resume() or with fake communications (using MSG_task_get(),
-MSG_task_put() and MSG_task_Iprobe()).
-
-Since version 3.4, you can use classical synchronization structures. See page \ref XBT_synchro or simply check in
-include/xbt/synchro_core.h.
+You are probably looking for the following functions:
+MSG_task_isend() and MSG_task_irecv();
+MSG_comm_test(), MSG_comm_wait(), MSG_comm_waitall() and MSG_comm_waitany();
+MSG_comm_destroy().
+
+There is even a specific example section on \ref msg_ex_async .
+
+\subsubsection faq_MIA_thread_synchronization How to synchronize my user processes?
+
+It depends on why you want to synchronize them. If you just want to
+have a shared state between your processes, then you probably don't
+need to do anything. User processes never get forcefully interrupted
+in SimGrid (unless you explicitly request the parallel execution of
+user processes -- see @ref options_virt_parallel).
+
+Even if several processes are executed at the exact same time within
+the simulation, they are linearized in reality by default: one process
+always run in an exclusive manner, atomic, uninterrupted until it does
+a simcall (until it ask a service from the simulation kernel). This is
+surprising at first, but things are much easier this way, both for the
+user (who don't have to protect her shared data) and for the kernel
+(that avoid many synchronization issues too). Processes are executed
+concurrently in the simulated realm, but you don't need to bother with
+this in the real realm.
+
+If you really need to synchronize your processes (because it's what
+you are studying or to create an atomic section that spans over
+several simcalls), you obviously cannot use regular synchronization
+mechanisms (pthread_mutexes in C or the synchronized keyword in Java).
+This is because the SimGrid kernel locks all processes and unlock them
+one after the other when they are supposed to run, until they give the
+control back in their simcall. If one of them gets locked by the OS
+before returning the control to the kernel, that's definitively a
+deadlock.
+
+Instead, you should use the synchronization mechanism provided by the
+simulation kernel. This could with a SimGrid mutex, a SimGrid
+condition variables or a SimGrid semaphore, as described in @ref
+msg_synchro (in Java, only semaphores are available). But actually,
+many synchronization patterns can be encoded with communication on
+mailboxes. Typically, if you need one process to notify another one,
+you could use a condition variable or a semphore, but sending a
+message to a specific mailbox does the trick in most cases.
\subsubsection faq_MIA_host_load Where is the get_host_load function hidden in MSG?
you could also get in real settings to not hinder the realism of your
simulation.
-\verbatim
+\code
double get_host_load() {
m_task_t task = MSG_task_create("test", 0.001, 0, NULL);
double date = MSG_get_clock();
MSG_task_destroy(task);
return (0.001/date);
}
-\endverbatim
+\endcode
Of course, it may not match your personal definition of "host load". In this
case, please detail what you mean on the mailing list, and we will extend
ready). However, getting the *real* communication time is not really
hard either. The following solution is a good starting point.
-\verbatim
+\code
int sender()
{
m_task_t task = MSG_task_create("Task", task_comp_size, task_comm_size,
MSG_task_destroy(task);
return 0;
}
-\endverbatim
+\endcode
\subsection faq_MIA_SimDag SimDag related questions
create 3 SD_tasks: t1, t2 and c and add dependencies in the following
way:
-\verbatim
+\code
SD_task_dependency_add(NULL, NULL, t1, c);
SD_task_dependency_add(NULL, NULL, c, t2);
-\endverbatim
+\endcode
This way task t2 cannot start before the termination of communication c
which in turn cannot start before t1 ends.
distributed. Here is an example of how you could do that. Assume T1
has to be done before T2.
-\verbatim
+\code
int your_agent(int argc, char *argv[] {
...
T1 = MSG_task_create(...);
}
}
}
-\endverbatim
+\endcode
If you decide that the distributed part is not that much important and that
DAG is really the level of abstraction you want to work with, then you should
file that highlights the most important changes) even before you
upgrade your copy of SimGrid, too.
-Backward compatibility is very important to us, as we want to provide
-a scientific tool allowing to evaluate the code you write in several
-years, too. That being said, we sometimes change the interface to make
-them more usable to the users. When we do so, we always keep the old
-interface as DEPRECATED. If you still want to use them, you want to
-define the SIMGRID_DEPRECATED preprocessor symbol before loading the
-SimGrid files:
-
-@verbatim
-#define SIMGRID_DEPRECATED
-#include <msg/msg.h>
-@endverbatim
+We do our best to maintain the backward compatibility, but we
+sometimes have to fix the things that are too broken. If we happen to
+kill a feature that you were using, we are sorry. We think that you
+should update to the new way of doing things, but if you can't afford
+it, that's ok. Just stick to the last version that were working for
+you, and have a pleasant day.
\subsection faq_trouble_lib_compil SimGrid compilation and installation problems
We know only one reason for the configure to fail:
- <b>You are using a broken build environment</b>\n
- If symptom is that the configury magic complains about gcc not being able to build
- executables, you are probably missing the libc6-dev package. Damn Ubuntu.
+ Try updating your cmake version. If symptom is that the configury
+ magic complains about gcc not being able to build executables, you
+ are probably missing the libc6-dev package. Damn Ubuntu.
If you experience other kind of issue, please get in touch with us. We are
always interested in improving our portability to new systems.
\subsubsection faq_trouble_err_logcat "gcc: _simgrid_this_log_category_does_not_exist__??? undeclared (first use in this function)"
-This is because you are using the log mecanism, but you didn't created
+This is because you are using the log mechanism, but you didn't created
any default category in this file. You should refer to \ref XBT_log
for all the details, but you simply forgot to call one of
XBT_LOG_NEW_DEFAULT_CATEGORY() or XBT_LOG_NEW_DEFAULT_SUBCATEGORY().
specify <tt>-lpthread</tt> on the linker command line. As usual, this should
come after <tt>-lsimgrid</tt> on this command line.
-\subsubsection faq_trouble_lib_msg_deprecated "gcc: undefined reference to MSG_*"
-
-Since version 3.7 all the m_channel_t mecanism is deprecated. So functions
-about this mecanism may get removed in future releases.
-
-List of functions:
-
-\li XBT_PUBLIC(int) MSG_get_host_number(void);
-
-\li XBT_PUBLIC(m_host_t *) MSG_get_host_table(void);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_get_errno(void);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_task_get(m_task_t * task, m_channel_t channel);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_task_get_with_timeout(m_task_t * task, m_channel_t channel, double max_duration);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_task_get_from_host(m_task_t * task, int channel, m_host_t host);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_task_get_ext(m_task_t * task, int channel, double max_duration, m_host_t host);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_task_put(m_task_t task, m_host_t dest, m_channel_t channel);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_task_put_bounded(m_task_t task, m_host_t dest, m_channel_t channel, double max_rate);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_task_put_with_timeout(m_task_t task, m_host_t dest, m_channel_t channel, double max_duration);
-
-\li XBT_PUBLIC(int) MSG_task_Iprobe(m_channel_t channel);
-
-\li XBT_PUBLIC(int) MSG_task_probe_from(m_channel_t channel);
-
-\li XBT_PUBLIC(int) MSG_task_probe_from_host(int channel, m_host_t host);
-
-\li XBT_PUBLIC(MSG_error_t) MSG_set_channel_number(int number);
-
-\li XBT_PUBLIC(int) MSG_get_channel_number(void);
-
-If you want them you have to compile Simgrid v3.7 with option "-Denable_msg_deprecated=ON".
-Using them should print warning to inform what new function you have to use.
-
\subsection faq_trouble_errors Runtime error messages
-\subsubsection faq_flexml_limit "surf_parse_lex: Assertion `next limit' failed."
-
-This is because your platform file is too big for the parser.
-
-Actually, the message comes directly from FleXML, the technology on top of
-which the parser is built. FleXML has the bad idea of fetching the whole
-document in memory before parsing it. And moreover, the memory buffer size
-must be determined at compilation time.
-
-We use a value which seems big enough for our need without bloating the
-simulators footprints. But of course your mileage may vary. In this case,
-just edit src/surf/surfxml.l modify the definition of
-FLEXML_BUFFERSTACKSIZE. E.g.
-
-\verbatim
-#define FLEXML_BUFFERSTACKSIZE 1000000000
-\endverbatim
-
-Then recompile and everything should be fine, provided that your version of
-Flex is recent enough (>= 2.5.31). If not the compilation process should
-warn you.
-
-A while ago, we worked on FleXML to reduce a bit its memory consumption, but
-these issues remain. There is two things we should do:
-
- - use a dynamic buffer instead of a static one so that the only limit
- becomes your memory, not a stupid constant fixed at compilation time
- (maybe not so difficult).
- - change the parser so that it does not need to get the whole file in
- memory before parsing
- (seems quite difficult, but I'm a complete newbe wrt flex stuff).
-
-These are changes to FleXML itself, not SimGrid. But since we kinda hijacked
-the development of FleXML, I can grant you that any patches would be really
-welcome and quickly integrated.
-
-<b>Update:</b> A new version of FleXML (1.7) was released. Most of the work
-was done by William Dowling, who use it in his own work. The good point is
-that it now use a dynamic buffer, and that the memory usage was greatly
-improved. The downside is that William also changed some things internally,
-and it breaks the hack we devised to bypass the parser, as explained in
-\ref pf_flexml_bypassing. Indeed, this is not a classical usage of the
-parser, and Will didn't imagine that we may have used (and even documented)
-such a crude usage of FleXML. So, we now have to repair the bypassing
-functionality to use the latest FleXML version and fix the memory usage in
-SimGrid.
-
\subsubsection faq_trouble_errors_big_fat_warning I'm told that my XML files are too old.
The format of the XML platform description files is sometimes
That is why the XML files are versionned using the 'version' attribute
of the root tag. Currently, it should read:
-\verbatim
- <platform version="2">
-\endverbatim
+@verbatim
+ <platform version="4">
+@endverbatim
If your files are too old, you can use the simgrid_update_xml.pl
script which can be found in the tools directory of the archive.
-\subsection faq_trouble_valgrind Valgrind-related and other debugger issues
+\subsection faq_trouble_debug Debugging SMPI applications
-If you don't, you really should use valgrind to debug your code, it's
-almost magic.
+In order to debug SMPI programs, you can use the following options:
-\subsubsection faq_trouble_vg_longjmp longjmp madness in valgrind
+- <b>-wrapper 'gdb --args'</b>: this option is used to use a wrapper
+ in order to call the SMPI process. Good candidates for this options
+ are "gdb --args", "valgrind", "rr record", "strace", etc;
-This is when valgrind starts complaining about longjmp things, just like:
+- <b>-foreground</b>: this options gives the debugger access to the terminal
+ which is needed in order to use an interactive debugger.
-\verbatim ==21434== Conditional jump or move depends on uninitialised value(s)
-==21434== at 0x420DBE5: longjmp (longjmp.c:33)
-==21434==
-==21434== Use of uninitialised value of size 4
-==21434== at 0x420DC3A: __longjmp (__longjmp.S:48)
-\endverbatim
+Both options are needed in order to run the SMPI process under GDB.
+
+\subsection faq_trouble_valgrind Valgrind-related and other debugger issues
-This is the sign that you didn't used the exception mecanism well. Most
-probably, you have a <tt>return;</tt> somewhere within a <tt>TRY{}</tt>
-block. This is <b>evil</b>, and you must not do this. Did you read the section
-about \ref XBT_ex??
+If you don't, you really should use valgrind to debug your code, it's
+almost magic.
\subsubsection faq_trouble_vg_libc Valgrind spits tons of errors about backtraces!
Unfortunately, we cannot debug every code written in SimGrid. We
furthermore believe that the framework provides ways enough
-information to debug such informations yourself. If the textual output
+information to debug such information yourself. If the textual output
is not enough, Make sure to check the \ref faq_visualization FAQ entry to see
how to get a graphical one.
on your side... We have plenty of FAQ entries to redact and new
features to implement for the impenitents! ;)
-Using
-
\subsection faq_surf_network_latency I get weird timings when I play with the latencies.
OK, first of all, remember that units should be Bytes, Flops and
\author Da SimGrid team <simgrid-devel@lists.gforge.inria.fr>
*/
-
-******************************************************************
-* OLD CRUFT NOT USED ANYMORE *
-******************************************************************
-
-
-subsection faq_crosscompile Cross-compiling a Windows DLL of SimGrid from linux
-
-At the moment, we do not distribute Windows pre-compiled version of SimGrid
-because the support for this platform is still experimental. We know that
-some parts of the GRAS environment do not work, and we think that the others
-environments (MSG and SD) have good chances to work, but we didn't test
-ourselves. This section explains how we generate the SimGrid DLL so that you
-can build it for yourself. First of all, you need to have a version more
-recent than 3.1 (ie, a SVN version as time of writting).
-
-In order to cross-compile the package to windows from linux, you need to
-install mingw32 (minimalist gnu win32). On Debian, you can do so by
-installing the packages mingw32 (compiler), mingw32-binutils (linker and
-so), mingw32-runtime.
-
-You can use the VPATH support of configure to compile at the same time for
-linux and windows without dupplicating the source nor cleaning the tree
-between each. Just run bootstrap (if you use the SVN) to run the autotools.
-Then, create a linux and a win directories. Then, type:
-\verbatim cd linux; ../configure --srcdir=.. <usual configure flags>; make; cd ..
-cd win; ../configure --srcdir=.. --host=i586-mingw32msvc <flags>; make; cd ..
-\endverbatim
-The trick to VPATH builds is to call configure from another directory,
-passing it an extra --srcdir argument to tell it where all the sources are.
-It will understand you want to use VPATH. Then, the trick to cross-compile
-is simply to add a --host argument specifying the target you want to build
-for. The i586-mingw32msvc string is what you have to pass to use the mingw32
-environment as distributed in Debian.
-
-After that, you can run all make targets from both directories, and test
-easily that what you change for one arch does not break the other one.
-
-It is possible that this VPATH build thing breaks from time to time in the
-SVN since it's quite fragile, but it's granted to work in any released
-version. If you experience problems, drop us a mail.
-
-Another possible source of issue is that at the moment, building the
-examples request to use the gras_stub_generator tool, which is a compiled
-program, not a script. In cross-compilation, you need to cross-execute with
-wine for example, which is not really pleasant. We are working on this, but
-in the meanwhile, simply don't build the examples in cross-compilation
-(<tt>cd src</tt> before running make).
-
-Program (cross-)compiled with mingw32 do request an extra DLL at run-time to be
-usable. For example, if you want to test your build with wine, you should do
-the following to put this library where wine looks for DLLs.
-\verbatim
-cp /usr/share/doc/mingw32-runtime/mingwm10.dll.gz ~/.wine/c/windows/system/
-gunzip ~/.wine/c/windows/system/mingwm10.dll.gz
-\endverbatim
-
-The DLL is built in src/.libs, and installed in the <i>prefix</i>/bin directory
-when you run make install.
-
-If you want to use it in a native project on windows, you need to use
-simgrid.dll and mingwm10.dll. For each DLL, you need to build .def file
-under linux (listing the defined symbols), and convert it into a .lib file
-under windows (specifying this in a way that windows compilers like). To
-generate the def files, run (under linux):
-\verbatim echo "LIBRARY libsimgrid-0.dll" > simgrid.def
-echo EXPORTS >> simgrid.def
-nm libsimgrid-0.dll | grep ' T _' | sed 's/.* T _//' >> simgrid.def
-nm libsimgrid-0.dll | grep ' D _' | sed 's/.* D _//' | sed 's/$/ DATA/' >> simgrid.def
-
-echo "LIBRARY mingwm10.dll" > mingwm10.def
-echo EXPORTS >> mingwm10.def
-nm mingwm10.dll | grep ' T _' | sed 's/.* T _//' >> mingwm10.def
-nm mingwm10.dll | grep ' D _' | sed 's/.* D _//' | sed 's/$/ DATA/' >> mingwm10.def
-\endverbatim
-
-To create the import .lib files, use the <tt>lib</tt> windows tool (from
-MSVC) the following way to produce simgrid.lib and mingwm10.lib
-\verbatim lib /def:simgrid.def
-lib /def:mingwm10.def
-\endverbatim
-
-If you happen to use Borland C Builder, the right command line is the
-following (note that you don't need any file.def to get this working).
-\verbatim implib simgrid.lib libsimgrid-0.dll
-implib mingwm10.lib mingwm10.dll
-\endverbatim
-
-Then, set the following parameters in Visual C++ 2005:
-Linker -> Input -> Additional dependencies = simgrid.lib mingwm10.lib
-
-Just in case you wonder how to generate a DLL from libtool in another
-project, we added -no-undefined to any lib*_la_LDFLAGS variables so that
-libtool accepts to generate a dynamic library under windows. Then, to make
-it true, we pass any dependencies (such as -lws2 under windows or -lpthread
-on need) on the linking line. Passing such deps is a good idea anyway so
-that they get noted in the library itself, avoiding the users to know about
-our dependencies and put them manually on their compilation line. Then we
-added the AC_LIBTOOL_WIN32_DLL macro just before AC_PROG_LIBTOOL in the
-configure.ac. It means that we exported any symbols which need to be.
-Nowadays, functions get automatically exported, so we don't need to load our
-header files with tons of __declspec(dllexport) cruft. We only need to do so
-for data, but there is no public data in SimGrid so we are good.
