+XBT_PUBLIC_DATA(int) (*xbt_pid) ();
+int xbt_log_no_loc = 0; /* if set to true (with --log=no_loc), file localization will be omitted (for tesh tests) */
+
+/** \addtogroup XBT_log
+ *
+ * This section describes the API to the log functions used
+ * everywhere in this project.
+
+\section XBT_log_toc Table of contents
+
+ - \ref log_overview
+ - \ref log_cat
+ - \ref log_pri
+ - \ref log_app
+ - \ref log_hist
+ - \ref log_API
+ - \ref log_API_cat
+ - \ref log_API_pri
+ - \ref log_API_isenabled
+ - \ref log_API_subcat
+ - \ref log_API_easy
+ - \ref log_API_example
+ - \ref log_user
+ - \ref log_use_conf
+ - \ref log_use_conf_thres
+ - \ref log_use_conf_multi
+ - \ref log_use_conf_fmt
+ - \ref log_use_conf_app
+ - \ref log_use_conf_add
+ - \ref log_use_misc
+ - \ref log_internals
+ - \ref log_in_perf
+ - \ref log_in_app
+ - \ref XBT_log_cats
+
+\section log_overview 1. Introduction
+
+This module is in charge of handling the log messages of every SimGrid
+program. The main design goal are:
+
+ - <b>configurability</b>: the user can choose <i>at runtime</i> what messages to show and
+ what to hide, as well as how messages get displayed.
+ - <b>ease of use</b>: both to the programmer (using preprocessor macros black magic)
+ and to the user (with command line options)
+ - <b>performances</b>: logging shouldn't slow down the program when turned off, for example
+ - deal with <b>distributed settings</b>: SimGrid programs are [often] distributed ones,
+ and the logging mechanism allows to syndicate each and every log source into the same place.
+ At least, its design would allow to, once we write the last missing pieces
+
+There is three main concepts in SimGrid's logging mechanism: <i>category</i>,
+<i>priority</i> and <i>appender</i>. These three concepts work together to
+enable developers to log messages according to message type and priority, and
+to control at runtime how these messages are formatted and where they are
+reported.
+
+\subsection log_cat 1.1 Category hierarchy
+
+The first and foremost advantage of any logging API over plain printf()
+resides in its ability to disable certain log statements while allowing
+others to print unhindered. This capability assumes that the logging space,
+that is, the space of all possible logging statements, is categorized
+according to some developer-chosen criteria.
+
+This observation led to choosing category as the central concept of the
+system. In a certain sense, they can be considered as logging topics or
+channels.
+
+\subsection log_pri 1.2 Logging priorities
+
+The user can naturally declare interest into this or that logging category, but
+he also can specify the desired level of details for each of them. This is
+controlled by the <i>priority</i> concept (which should maybe be renamed to
+<i>severity</i>).
+
+Empirically, the user can specify that he wants to see every debugging message
+of GRAS while only being interested into the messages at level "error" or
+higher about the XBT internals.
+
+\subsection log_app 1.3 Message appenders
+
+The message appenders are the elements in charge of actually displaying the
+message to the user. For now, only two appenders exist: the default one prints
+stuff on stderr while it is possible to create appenders printing to a specific
+file.
+
+Other are planed (such as the one sending everything to a remote server,
+or the one using only a fixed amount of lines in a file, and rotating content on
+need). One day, for sure ;)
+
+\subsection log_lay 1.4 Message layouts
+
+The message layouts are the elements in charge of choosing how each message
+will look like. Their result is a string which is then passed to the appender
+attached to the category to be displayed.
+
+For now, there is two layouts: The simple one, which is good for most cases,
+and another one allowing users to specify the format they want.
+\ref log_use_conf provides more info on this.
+
+\subsection log_hist 1.5 History of this module
+
+Historically, this module is an adaptation of the log4c project, which is dead
+upstream, and which I was given the permission to fork under the LGPL licence
+by the log4c's authors. The log4c project itself was loosely based on the
+Apache project's Log4J, which also inspired Log4CC, Log4py and so on. Our work
+differs somehow from these projects anyway, because the C programming language
+is not object oriented.
+
+\section log_API 2. Programmer interface
+
+\subsection log_API_cat 2.1 Constructing the category hierarchy
+
+Every category is declared by providing a name and an optional
+parent. If no parent is explicitly named, the root category, LOG_ROOT_CAT is
+the category's parent.
+
+A category is created by a macro call at the top level of a file. A
+category can be created with any one of the following macros:
+
+ - \ref XBT_LOG_NEW_CATEGORY(MyCat,desc); Create a new root
+ - \ref XBT_LOG_NEW_SUBCATEGORY(MyCat, ParentCat,desc);
+ Create a new category being child of the category ParentCat
+ - \ref XBT_LOG_NEW_DEFAULT_CATEGORY(MyCat,desc);
+ Like XBT_LOG_NEW_CATEGORY, but the new category is the default one
+ in this file
+ - \ref XBT_LOG_NEW_DEFAULT_SUBCATEGORY(MyCat, ParentCat,desc);
+ Like XBT_LOG_NEW_SUBCATEGORY, but the new category is the default one
+ in this file
+
+The parent cat can be defined in the same file or in another file (in
+which case you want to use the \ref XBT_LOG_EXTERNAL_CATEGORY macro to make
+it visible in the current file), but each category may have only one
+definition. Likewise, you can use a category defined in another file as
+default one using \ref XBT_LOG_EXTERNAL_DEFAULT_CATEGORY
+
+Typically, there will be a Category for each module and sub-module, so you
+can independently control logging for each module.
+
+For a list of all existing categories, please refer to the \ref XBT_log_cats
+section. This file is generated automatically from the SimGrid source code, so
+it should be complete and accurate.
+
+\section log_API_pri 2.2 Declaring message priority
+
+A category may be assigned a threshold priority. The set of priorities are
+defined by the \ref e_xbt_log_priority_t enum. All logging request under
+this priority will be discarded.
+
+If a given category is not assigned a threshold priority, then it inherits
+one from its closest ancestor with an assigned threshold. To ensure that all
+categories can eventually inherit a threshold, the root category always has
+an assigned threshold priority.
+
+Logging requests are made by invoking a logging macro on a category. All of
+the macros have a printf-style format string followed by arguments. If you
+compile with the -Wall option, gcc will warn you for unmatched arguments, ie
+when you pass a pointer to a string where an integer was specified by the
+format. This is usually a good idea.
+
+Because some C compilers do not support vararg macros, there is a version of
+the macro for any number of arguments from 0 to 6. The macro name ends with
+the total number of arguments.
+
+Here is an example of the most basic type of macro. This is a logging
+request with priority <i>warning</i>.
+
+<code>CLOG5(MyCat, gras_log_priority_warning, "Values are: %d and '%s'", 5,
+"oops");</code>
+
+A logging request is said to be enabled if its priority is higher than or
+equal to the threshold priority of its category. Otherwise, the request is
+said to be disabled. A category without an assigned priority will inherit
+one from the hierarchy.
+
+It is possible to use any non-negative integer as a priority. If, as in the
+example, one of the standard priorities is used, then there is a convenience
+macro that is typically used instead. For example, the above example is
+equivalent to the shorter:
+
+<code>CWARN4(MyCat, "Values are: %d and '%s'", 5, "oops");</code>
+
+\section log_API_isenabled 2.3 Checking if a particular category/priority is enabled
+
+It is sometimes useful to check whether a particular category is
+enabled at a particular priority. One example is when you want to do
+some extra computation to prepare a nice debugging message. There is
+no use of doing so if the message won't be used afterward because
+debugging is turned off.
+
+Doing so is extremely easy, thanks to the XBT_LOG_ISENABLED(category, priority).
+
+\section log_API_subcat 2.4 Using a default category (the easy interface)
+
+If \ref XBT_LOG_NEW_DEFAULT_SUBCATEGORY(MyCat, Parent) or
+\ref XBT_LOG_NEW_DEFAULT_CATEGORY(MyCat) is used to create the
+category, then the even shorter form can be used:
+
+<code>WARN3("Values are: %s and '%d'", 5, "oops");</code>
+
+Only one default category can be created per file, though multiple
+non-defaults can be created and used.
+
+\section log_API_easy 2.5 Putting all together: the easy interface
+
+First of all, each module should register its own category into the categories
+tree using \ref XBT_LOG_NEW_DEFAULT_SUBCATEGORY.
+
+Then, logging should be done with the DEBUG<n>, VERB<n>, INFO<n>, WARN<n>,
+ERROR<n> or CRITICAL<n> macro families (such as #DEBUG10, #VERB10,
+#INFO10, #WARN10, #ERROR10 and #CRITICAL10). For each group, there is at
+least 11 different macros (like DEBUG0, DEBUG1, DEBUG2, DEBUG3, DEBUG4 and
+DEBUG5, DEBUG6, DEBUG7, DEBUG8, DEBUG9, DEBUG10), only differing in the number of arguments passed along the format.
+This is because we want SimGrid itself to keep compilable on ancient
+compiler not supporting variable number of arguments to macros. But we
+should provide a macro simpler to use for the users not interested in SP3
+machines (FIXME).
+
+Under GCC, these macro check there arguments the same way than printf does. So,
+if you compile with -Wall, the following code will issue a warning:
+<code>DEBUG2("Found %s (id %f)", some_string, a_double)</code>
+
+If you want to specify the category to log onto (for example because you
+have more than one category per file, add a C before the name of the log
+producing macro (ie, use #CDEBUG10, #CVERB10, #CINFO10, #CWARN10, #CERROR10 and
+#CCRITICAL10 and friends), and pass the category name as first argument.
+
+The TRACE priority is not used the same way than the other. You should use
+the #XBT_IN, XBT_IN<n> (up to #XBT_IN5), #XBT_OUT and #XBT_HERE macros
+instead.
+
+\section log_API_example 2.6 Example of use
+
+Here is a more complete example:
+
+\verbatim
+#include "xbt/log.h"
+
+/ * create a category and a default subcategory * /
+XBT_LOG_NEW_CATEGORY(VSS);
+XBT_LOG_NEW_DEFAULT_SUBCATEGORY(SA, VSS);
+
+int main() {
+ / * Now set the parent's priority. (the string would typcially be a runtime option) * /
+ xbt_log_control_set("SA.thresh:3");
+
+ / * This request is enabled, because WARNING >= INFO. * /
+ CWARN0(VSS, "Low fuel level.");
+
+ / * This request is disabled, because DEBUG < INFO. * /
+ CDEBUG0(VSS, "Starting search for nearest gas station.");
+
+ / * The default category SA inherits its priority from VSS. Thus,
+ the following request is enabled because INFO >= INFO. * /
+ INFO0("Located nearest gas station.");
+
+ / * This request is disabled, because DEBUG < INFO. * /
+ DEBUG0("Exiting gas station search");
+}
+\endverbatim
+
+Another example can be found in the relevant part of the GRAS tutorial:
+\ref GRAS_tut_tour_logs.
+
+\section log_user 3. User interface
+
+\section log_use_conf 3.1 Configuration
+
+Although rarely done, it is possible to configure the logs during
+program initialization by invoking the xbt_log_control_set() method
+manually. A more conventional way is to use the --log command line
+argument. xbt_init() (called by MSG_init(), gras_init() and friends)
+checks and deals properly with such arguments.
+
+The following command line arguments exist, but are deprecated and
+may disappear in the future: --xbt-log, --gras-log, --msg-log and
+--surf-log.
+
+\subsection log_use_conf_thres 3.1.1 Threshold configuration
+
+The most common setting is to control which logging event will get
+displayed by setting a threshold to each category through the
+<tt>thres</tt> keyword.
+
+For example, \verbatim --log=root.thres:debug\endverbatim will make
+SimGrid <b>extremely</b> verbose while \verbatim
+--log=root.thres:critical\endverbatim should shut it almost
+completely off.
+
+\subsection log_use_conf_multi 3.1.2 Passing several settings
+
+You can provide several of those arguments to change the setting of several
+categories, they will be applied from left to right. So,
+\verbatim --log="root.thres:debug root.thres:critical"\endverbatim should
+disable almost any logging.
+
+Note that the quotes on above line are mandatory because there is a space in
+the argument, so we are protecting ourselves from the shell, not from SimGrid.
+We could also reach the same effect with this:
+\verbatim --log=root.thres:debug --log=root.thres:critical\endverbatim
+
+\subsection log_use_conf_fmt 3.1.3 Format configuration
+
+As with SimGrid 3.3, it is possible to control the format of log
+messages. This is done through the <tt>fmt</tt> keyword. For example,
+\verbatim --log=root.fmt:%m\endverbatim reduces the output to the
+user-message only, removing any decoration such as the date, or the
+process ID, everything.
+
+Here are the existing format directives:
+
+ - %%: the % char
+ - %%n: platform-dependent line separator (LOG4J compatible)
+ - %%e: plain old space (SimGrid extension)
+
+ - %%m: user-provided message
+
+ - %%c: Category name (LOG4J compatible)
+ - %%p: Priority name (LOG4J compatible)
+
+ - %%h: Hostname (SimGrid extension)
+ - %%P: Process name (SimGrid extension)
+ - %%t: Thread "name" (LOG4J compatible -- actually the address of the thread in memory)
+ - %%i: Process PID (SimGrid extension -- this is a 'i' as in 'i'dea)
+
+ - %%F: file name where the log event was raised (LOG4J compatible)
+ - %%l: location where the log event was raised (LOG4J compatible, like '%%F:%%L' -- this is a l as in 'l'etter)
+ - %%L: line number where the log event was raised (LOG4J compatible)
+ - %%M: function name (LOG4J compatible -- called method name here of course).
+ Defined only when using gcc because there is no __FUNCTION__ elsewhere.
+
+ - %%b: full backtrace (Called %%throwable in LOG4J).
+ Defined only under windows or when using the GNU libc because backtrace() is not defined
+ elsewhere, and we only have a fallback for windows boxes, not mac ones for example.
+ - %%B: short backtrace (only the first line of the %%b).
+ Called %%throwable{short} in LOG4J; defined where %%b is.
+
+ - %%d: date (UNIX-like epoch)
+ - %%r: application age (time elapsed since the beginning of the application)
+
+
+If you want to mimic the simple layout with the format one, you would use this
+format: '[%%h:%%i:(%%i) %%r] %%l: [%%c/%%p] %%m%%n'. This is not completely correct
+because the simple layout do not display the message location for messages at
+priority INFO (thus, the fmt is '[%%h:%%i:(%%i) %%r] [%%c/%%p] %%m%%n' in this
+case). Moreover, if there is no process name (ie, messages coming from the
+library itself, or test programs doing strange things) do not display the
+process identity (thus, fmt is '[%%r] %%l: [%%c/%%p] %%m%%n' in that case, and '[%%r]
+[%%c/%%p] %%m%%n' if they are at priority INFO).
+
+For now, there is only two format modifiers: the precision and the
+width fields. You can for example specify %.4r to get the application
+age with 4 numbers after the radix, or %15p to get the process name
+on 15 columns. Finally, you can specify %10.6r to get the time on at
+most 10 columns, with 6 numbers after the radix.
+
+Note that when specifying the width, it is filled with spaces. That
+is to say that for example %5r in your format is converted to "% 5f"
+for printf (note the extra space); there is no way to fill the empty
+columns with 0 (ie, pass "%05f" to printf). Another limitation is
+that you cannot set specific layouts to the several priorities.
+
+\subsection log_use_conf_app 3.1.4 Category appender
+
+As with SimGrid 3.3, it is possible to control the appender of log
+messages. This is done through the <tt>app</tt> keyword. For example,
+\verbatim --log=root.app:file:mylogfile\endverbatim redirects the output
+to the file mylogfile.
+
+Any appender setup this way have its own layout format (simple one by default),
+so you may have to change it too afterward. Moreover, the additivity of the log category
+is also set to false to prevent log event displayed by this appender to "leak" to any other
+appender higher in the hierarchy. If it is not what you wanted, you can naturally change it
+manually.
+
+\subsection log_use_conf_add 3.1.5 Category additivity
+
+The <tt>add</tt> keyword allows to specify the additivity of a
+category (see \ref log_in_app). '0', '1', 'no', 'yes', 'on'
+and 'off' are all valid values, with 'yes' as default.
+
+The following example resets the additivity of the xbt category to true (which is its default value).
+\verbatim --log=xbt.add:yes\endverbatim
+
+\section log_use_misc 3.2 Misc and Caveats
+
+ - Do not use any of the macros that start with '_'.
+ - Log4J has a 'rolling file appender' which you can select with a run-time
+ option and specify the max file size. This would be a nice default for
+ non-kernel applications.
+ - Careful, category names are global variables.
+
+\section log_internals 4. Internal considerations
+
+This module is a mess of macro black magic, and when it goes wrong,
+SimGrid studently loose its ability to explain its problems. When
+messing around this module, I often find useful to define
+XBT_LOG_MAYDAY (which turns it back to good old printf) for the time
+of finding what's going wrong. But things are quite verbose when
+everything is enabled...
+
+\section log_in_perf 4.1 Performance
+
+Except for the first invocation of a given category, a disabled logging request
+requires an a single comparison of a static variable to a constant.
+
+There is also compile time constant, \ref XBT_LOG_STATIC_THRESHOLD, which
+causes all logging requests with a lower priority to be optimized to 0 cost
+by the compiler. By setting it to gras_log_priority_infinite, all logging
+requests are statically disabled at compile time and cost nothing. Released executables
+<i>might</i> be compiled with (note that it will prevent users to debug their problems)
+\verbatim-DXBT_LOG_STATIC_THRESHOLD=gras_log_priority_infinite\endverbatim
+
+Compiling with the \verbatim-DNLOG\endverbatim option disables all logging
+requests at compilation time while the \verbatim-DNDEBUG\endverbatim disables
+the requests of priority below INFO.
+
+\todo Logging performance *may* be improved further by improving the message
+propagation from appender to appender in the category tree.
+
+\section log_in_app 4.2 Appenders
+
+Each category has an optional appender. An appender is a pointer to a
+structure which starts with a pointer to a do_append() function. do_append()
+prints a message to a log.
+
+When a category is passed a message by one of the logging macros, the
+category performs the following actions:
+
+ - if the category has an appender, the message is passed to the
+ appender's do_append() function,
+ - if additivity is true for the category, the message is passed to
+ the category's parent. Additivity is true by default, and can be
+ controlled by xbt_log_additivity_set() or something like --log=root.add:1 (see \ref log_use_conf_add).
+ Also, when you add an appender to a category, its additivity is automatically turned to off.
+ Turn it back on afterward if it is not what you wanted.
+
+By default, only the root category have an appender, and any other category has
+its additivity set to true. This causes all messages to be logged by the root
+category's appender.
+
+The default appender function currently prints to stderr, and the only other
+existing one writes to the specified file. More would be needed, like the one
+able to send the logs to a remote dedicated server.
+This is on our TODO list for quite a while now, but your help would be
+welcome here, too.
+
+
+ *//*' */
+
+
+xbt_log_appender_t xbt_log_default_appender = NULL; /* set in log_init */
+xbt_log_layout_t xbt_log_default_layout = NULL; /* set in log_init */
+