\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>.
\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?
\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.
If you don't, you really should use valgrind to debug your code, it's
almost magic.
-\subsubsection faq_trouble_vg_longjmp longjmp madness in valgrind
-
-This is when valgrind starts complaining about longjmp things, just like:
-
-\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
-
-This is the sign that you didn't used the exception mechanism 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??
-
\subsubsection faq_trouble_vg_libc Valgrind spits tons of errors about backtraces!
It may happen that valgrind, the memory debugger beloved by any decent C
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
