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<refentry id="glib-running">
<refmeta>
<refentrytitle>Running GLib Applications</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>GLib Library</refmiscinfo>
</refmeta>

<refnamediv>
<refname>Running GLib Applications</refname>
<refpurpose>
How to run and debug your GLib application
</refpurpose>
</refnamediv>

<refsect1>
<title>Running and debugging GLib Applications</title>

<refsect2>
<title>Environment variables</title>

<para>
  The runtime behaviour of GLib applications can be influenced by a
  number of environment variables.
</para>

<formalpara>
  <title>Standard variables</title>

  <para>
    GLib reads standard environment variables like <envar>LANG</envar>,
    <envar>PATH</envar>, <envar>HOME</envar>, <envar>TMPDIR</envar>,
    <envar>TZ</envar> and <envar>LOGNAME</envar>.
  </para>
</formalpara>

<formalpara>
  <title>XDG directories</title>

  <para>
    GLib consults the environment variables <envar>XDG_DATA_HOME</envar>,
    <envar>XDG_DATA_DIRS</envar>, <envar>XDG_CONFIG_HOME</envar>,
    <envar>XDG_CONFIG_DIRS</envar>, <envar>XDG_CACHE_HOME</envar> and
    <envar>XDG_RUNTIME_DIR</envar> for the various XDG directories.
    For more information, see the <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG basedir spec</ulink>.
  </para>
</formalpara>

<formalpara id="G_FILENAME_ENCODING">
  <title><envar>G_FILENAME_ENCODING</envar></title>

  <para>
    This environment variable can be set to a comma-separated list of character
    set names. GLib assumes that filenames are encoded in the first character
    set from that list rather than in UTF-8. The special token "@locale" can be
    used to specify the character set for the current locale.
  </para>
</formalpara>

<formalpara id="G_BROKEN_FILENAMES">
  <title><envar>G_BROKEN_FILENAMES</envar></title>

  <para>
    If this environment variable is set, GLib assumes that filenames are in
    the locale encoding rather than in UTF-8. G_FILENAME_ENCODING takes
    priority over G_BROKEN_FILENAMES.
  </para>
</formalpara>

<formalpara id="G_MESSAGES_PREFIXED">
  <title><envar>G_MESSAGES_PREFIXED</envar></title>

  <para>
    A list of log levels for which messages should be prefixed by the
    program name and PID of the application. The default is to prefix
    everything except <literal>G_LOG_LEVEL_MESSAGE</literal> and
    <literal>G_LOG_LEVEL_INFO</literal>.
    The possible values are
    <literal>error</literal>,
    <literal>warning</literal>,
    <literal>critical</literal>,
    <literal>message</literal>,
    <literal>info</literal> and
    <literal>debug</literal>.
    You can also use the special values
    <literal>all</literal> and
    <literal>help</literal>.
  </para>
  <para>
    This environment variable only affects the default log handler,
    g_log_default_handler().
  </para>
</formalpara>

<formalpara id="G_MESSAGES_DEBUG">
  <title><envar>G_MESSAGES_DEBUG</envar></title>

  <para>
    A space-separated list of log domains for which informational
    and debug messages should be printed. By default, these
    messages are not printed.
  </para>
  <para>
    You can also use the special value <literal>all</literal>.
  </para>
  <para>
    This environment variable only affects the default log handler,
    g_log_default_handler().
  </para>
</formalpara>

<formalpara id="G-DEBUG:CAPS">
  <title><envar>G_DEBUG</envar></title>

  <para>
    This environment variable can be set to a list of debug options,
    which cause GLib to print out different types of debugging information.
    <variablelist>
      <varlistentry>
        <term>fatal-warnings</term>
        <listitem><para>Causes GLib to abort the program at the first call
           to g_warning() or g_critical().</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>fatal-criticals</term>
        <listitem><para>Causes GLib to abort the program at the first call
           to g_critical().</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>gc-friendly</term>
        <listitem><para>Newly allocated memory that isn't directly initialized,
          as well as memory being freed will be reset to 0. The point here is
          to allow memory checkers and similar programs that use Boehm GC alike
          algorithms to produce more accurate results.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>resident-modules</term>
        <listitem><para>All modules loaded by GModule will be made resident.
          This can be useful for tracking memory leaks in modules which are
          later unloaded; but it can also hide bugs where code is accessed
          after the module would have normally been unloaded.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>bind-now-modules</term>
        <listitem><para>All modules loaded by GModule will bind their symbols
          at load time, even when the code uses %G_MODULE_BIND_LAZY.</para>
        </listitem>
      </varlistentry>
    </variablelist>
    The special value all can be used to turn on all debug options.
    The special value help can be used to print all available options.
  </para>
</formalpara>

<formalpara id="G_SLICE">
  <title><envar>G_SLICE</envar></title>

  <para>
    This environment variable allows reconfiguration of the GSlice
    memory allocator.
    <variablelist>
      <varlistentry>
        <term>always-malloc</term>
        <listitem><para>This will cause all slices allocated through
          g_slice_alloc() and released by g_slice_free1() to be actually
          allocated via direct calls to g_malloc() and g_free().
          This is most useful for memory checkers and similar programs that
          use Boehm GC alike algorithms to produce more accurate results.
          It can also be in conjunction with debugging features of the system's
          malloc() implementation such as glibc's MALLOC_CHECK_=2 to debug
          erroneous slice allocation code, although
          <literal>debug-blocks</literal> is usually a better suited debugging
          tool.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>debug-blocks</term>
        <listitem><para>Using this option (present since GLib 2.13) engages
          extra code which performs sanity checks on the released memory
          slices. Invalid slice adresses or slice sizes will be reported and
          lead to a program halt. This option is for debugging scenarios.
          In particular, client packages sporting their own test suite should
          <emphasis>always enable this option when running tests</emphasis>.
          Global slice validation is ensured by storing size and address
          information for each allocated chunk, and maintaining a global
          hash table of that data. That way, multi-thread scalability is
          given up, and memory consumption is increased. However, the
          resulting code usually performs acceptably well, possibly better
          than with comparable memory checking carried out using external
          tools.</para>
          <para>An example of a memory corruption scenario that cannot be
          reproduced with <literal>G_SLICE=always-malloc</literal>, but will
          be caught by <literal>G_SLICE=debug-blocks</literal> is as follows:
          <programlisting>
            void *slist = g_slist_alloc (); /* void* gives up type-safety */
            g_list_free (slist);            /* corruption: sizeof (GSList) != sizeof (GList) */
          </programlisting></para>
        </listitem>
      </varlistentry>
    </variablelist>
    The special value all can be used to turn on all options.
    The special value help can be used to print all available options.
  </para>
</formalpara>

<formalpara id="G_RANDOM_VERSION">
  <title><envar>G_RANDOM_VERSION</envar></title>

  <para>
    If this environment variable is set to '2.0', the outdated
    pseudo-random number seeding and generation algorithms from
    GLib 2.0 are used instead of the newer, better ones. You should
    only set this variable if you have sequences of numbers that were
    generated with Glib 2.0 that you need to reproduce exactly.
  </para>
</formalpara>

<formalpara id="LIBCHARSET_ALIAS_DIR">
  <title><envar>LIBCHARSET_ALIAS_DIR</envar></title>

  <para>
    Allows to specify a nonstandard location for the
    <filename>charset.aliases</filename> file that is used by the
    character set conversion routines. The default location is the
    <replaceable>libdir</replaceable> specified at compilation time.
  </para>
</formalpara>

<formalpara id="TZDIR">
  <title><envar>TZDIR</envar></title>

  <para>
    Allows to specify a nonstandard location for the timezone data files
    that are used by the #GDateTime API. The default location is under
    <filename>/usr/share/zoneinfo</filename>. For more information,
    also look at the <command>tzset</command> manual page.
  </para>
</formalpara>

</refsect2>

<refsect2 id="setlocale">
<title>Locale</title>

<para>
A number of interfaces in GLib depend on the current locale in which
an application is running. Therefore, most GLib-using applications should
call <function>setlocale (LC_ALL, "")</function> to set up the current
locale.
</para>

<para>
On Windows, in a C program there are several locale concepts
that not necessarily are synchronized. On one hand, there is the
system default ANSI code-page, which determines what encoding is used
for file names handled by the C library's functions and the Win32
API. (We are talking about the "narrow" functions here that take
character pointers, not the "wide" ones.)
</para>

<para>
On the other hand, there is the C library's current locale. The
character set (code-page) used by that is not necessarily the same as
the system default ANSI code-page. Strings in this character set are
returned by functions like <function>strftime()</function>.
</para>

</refsect2>

<refsect2>
<title>Traps and traces</title>

<para>
<indexterm><primary>g_trap_free_size</primary></indexterm>
<indexterm><primary>g_trap_realloc_size</primary></indexterm>
<indexterm><primary>g_trap_malloc_size</primary></indexterm>
Some code portions contain trap variables that can be set during debugging
time if GLib has been configured with <option>--enable-debug=yes</option>.
Such traps lead to immediate code halts to examine the current program state
and backtrace.
</para>

<para>
Currently, the following trap variables exist:
<programlisting>
static volatile gulong g_trap_free_size;
static volatile gulong g_trap_realloc_size;
static volatile gulong g_trap_malloc_size;
</programlisting>
If set to a size > 0, <link linkend="g-free">g_free</link>(),
<link linkend="g-realloc">g_realloc</link>() and
<link linkend="g-malloc">g_malloc</link>() will be intercepted if the size
matches the size of the corresponding memory block. This will only work with
<literal>g_mem_set_vtable (glib_mem_profiler_table)</literal> upon startup
though, because memory profiling is required to match on the memory block sizes.
</para>
<para>
Note that many modern debuggers support conditional breakpoints, which achieve
pretty much the same. E.g. in gdb, you can do
<programlisting>
break g_malloc
condition 1 n_bytes == 20
</programlisting>
to break only on g_malloc() calls where the size of the allocated memory block
is 20.
</para>
</refsect2>

<refsect2>
<title>Gdb debugging macros</title>

<para>
glib ships with a set of python macros for the gdb debugger. These includes pretty
printers for lists, hashtables and gobject types. It also has a backtrace filter
that makes backtraces with signal emissions easier to read.
</para>

<para>
To use this you need a recent enough gdb that supports python scripting. Gdb 7.0
should be recent enough, but branches of the "archer" gdb tree as used in Fedora 11
and Fedora 12 should work too. You then need to install glib in the same prefix as
gdb so that the python gdb autoloaded files get installed in the right place for
gdb to pick up.
</para>

<para>
General pretty printing should just happen without having to do anything special.
To get the signal emission filtered backtrace you must use the "new-backtrace" command
instead of the standard one.
</para>

<para>
There is also a new command called gforeach that can be used to apply a command
on each item in a list. E.g. you can do
<programlisting>
gforeach i in some_list_variable: print *(GtkWidget *)l
</programlisting>
Which would print the contents of each widget in a list of widgets.
</para>

</refsect2>

<refsect2>
<title>SystemTap</title>

<para>
<ulink url="http://sourceware.org/systemtap/">SystemTap</ulink> is a dynamic whole-system
analysis toolkit.  GLib ships with a file <filename>glib.stp</filename> which defines a
set of probe points, which you can hook into with custom SystemTap scripts.
See the files <filename>glib.stp</filename> and <filename>gobject.stp</filename> which
are in your shared SystemTap scripts directory.
</para>

</refsect2>

<refsect2>
<title>Memory statistics</title>

<para>
g_mem_profile() will output a summary g_malloc() memory usage, if memory
profiling has been enabled by calling
<literal>g_mem_set_vtable (glib_mem_profiler_table)</literal> upon startup.
</para>

<para>
If GLib has been configured with <option>--enable-debug=yes</option>,
then g_slice_debug_tree_statistics() can be called in a debugger to
output details about the memory usage of the slice allocator.
</para>

</refsect2>
</refsect1>
</refentry>
