b02e29558f
As per https://gitlab.gnome.org/GNOME/glib/-/issues/3421#note_2206315: It seems like there’s agreement that glib_debug should be enabled for developers and disabled for distros; and it also seems like there’s no reliable way to figure this out magically (because not everyone ties things to `-Dbuildtype=*`). So, we’re left with forcing some group of people to manually set the value of `glib_debug`. There are more developers/contributors than there are distros, and distros are more likely to notice an accidentally-slow GLib package than developers are likely to notice an accidentally-not-asserting-hard-enough local build, so let’s say: The default should be `-Dglib_debug=enabled`, and distros should probably all override that to `-Dglib_debug=disabled`. Signed-off-by: Philip Withnall <pwithnall@gnome.org> Fixes: #3421
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GLib's configure options and corresponding macros
The following Meson configure options will result in certain macros or options being defined at build time:
--buildtype={plain,release,minsize,custom}
: No special macros or options
--buildtype={debug,debugoptimized} (debugoptimized is the default)
: -DG_ENABLE_DEBUG -g
-Dglib_debug=disabled
: Omits G_ENABLE_DEBUG when implied by --buildtype/-Ddebug
-Dglib_debug=enabled
: Defines G_ENABLE_DEBUG regardless of --buildtype/-Ddebug
-Dglib_asserts=false
: -DG_DISABLE_ASSERT
-Dglib_checks=false
: -DG_DISABLE_CHECKS
Besides these, there are some local feature specific options, but the main focus here is to concentrate on macros that affect overall GLib behaviour and/or third party code.
GLib's internal and global macros
G_DISABLE_ASSERT
The g_assert() and g_assert_not_reached() macros become non-functional
with this define. The motivation is to speed up end-user apps by
avoiding expensive checks.
This macro can affect third-party code. Defining it when building GLib
will only disable the assertion macros for GLib itself, but third-party code
that passes -DG_DISABLE_ASSERT to the compiler in its own build
will end up with the non-functional variants after including glib.h
as well.
Note: Code inside the assertion macros should not have side effects that affect the operation of the program, as they may get compiled out.
G_DISABLE_CHECKS
This macro is similar to G_DISABLE_ASSERT, it affects third-party
code as mentioned above and the note about G_DISABLE_ASSERT applies
too.
The macros that become non-functional here are g_return_if_fail(),
g_return_val_if_fail(), g_return_if_reached() and
g_return_val_if_reached().
This macro also switches off certain checks in the GSignal code.
G_ENABLE_DEBUG
Quite a bit of additional debugging code is compiled into GLib when this
macro is defined, and since it is a globally visible define, third-party code
may be affected by it similarly to G_DISABLE_ASSERT.
Some of these checks can be relatively expensive at runtime, as they affect
every GObject type cast. Distributions are recommended to disable
G_ENABLE_DEBUG in stable release builds.
The additional code executed/compiled for this macro currently includes the following, but this is not an exhaustive list:
- extra validity checks for
GDate - breakpoint abortion for fatal log levels in
gmessages.cinstead of plainabort()to allow debuggers trapping and overriding them - added verbosity of
gscanner.cto catch deprecated code paths - added verbosity of
gutils.cto catch deprecated code paths - object and type bookkeeping in
gobject.c - extra validity checks in
gsignal.c - support for tracking still-alive
GTasks