path: root/README.md

# GLib

GLib is the low-level core library that forms the basis for projects such
as GTK and GNOME. It provides data structure handling for C, portability
wrappers, and interfaces for such runtime functionality as an event loop,
threads, dynamic loading, and an object system.

The official download locations are:
  <https://download.gnome.org/sources/glib>

The official web site is:
  <https://www.gtk.org/>

## Installation

See the file '[INSTALL.in](INSTALL.in)'

## How to report bugs

Bugs should be reported to the GNOME issue tracking system.
(<https://gitlab.gnome.org/GNOME/glib/issues/new>). You will need
to create an account for yourself.

In the bug report please include:

* Information about your system. For instance:
  * What operating system and version
  * For Linux, what version of the C library
  * And anything else you think is relevant.
* How to reproduce the bug.
  * If you can reproduce it with one of the test programs that are built
  in the tests/ subdirectory, that will be most convenient.  Otherwise,
  please include a short test program that exhibits the behavior.
  As a last resort, you can also provide a pointer to a larger piece
  of software that can be downloaded.
* If the bug was a crash, the exact text that was printed out
  when the crash occurred.
* Further information such as stack traces may be useful, but
  is not necessary.

## Patches

Patches should also be submitted as merge requests to gitlab.gnome.org. If the
patch fixes an existing issue, please refer to the issue in your commit message
with the following notation (for issue 123):
Closes: #123

Otherwise, create a new merge request that introduces the change, filing a
separate issue is not required.

## Notes

### Notes about GLib 2.48

* The system copy of PCRE is now used by default to implement GRegex.
  Configure with --with-pcre=internal if a system PCRE version
  is unavailable or undesired.

### Notes about GLib 2.46

* GTask no longer imposes a fixed limit on the number of tasks that
  can be run_in_thread() simultaneously, since doing this inevitably
  results in deadlocks in some use cases. Instead, it now has a base
  number of threads that can be used "for free", but will gradually
  add more threads to the pool if too much time passes without any
  tasks completing.

  The exact behavior may continue to change in the future, and it's
  possible that some future version of GLib may not do any
  rate-limiting at all. As a result, you should no longer assume that
  GTask will rate-limit tasks itself (or, by extension, that calls to
  certain async gio methods will automatically be rate-limited for
  you). If you have a very large number of tasks to run, and don't
  want them to all run at once, you should rate-limit them yourself.

### Notes about GLib 2.40

* g_test_run() no longer runs tests in exactly the order they are
  registered; instead, it groups them according to test suites (ie,
  path components) like the documentation always claimed it did. In
  some cases, this can result in a sub-optimal ordering of tests,
  relative to the old behavior. The fix is to change the test paths to
  properly group together the tests that should run together. (eg, if
  you want to run test_foo_simple(), test_bar_simple(), and
  test_foo_using_bar() in that order, they should have test paths like
  "/simple/foo", "/simple/bar", "/complex/foo-using-bar", not
  "/foo/simple", "/bar/simple", "/foo/using-bar" (which would result
  in test_foo_using_bar() running before test_bar_simple()).

  (The behavior actually changed in GLib 2.36, but it was not
  documented at the time, since we didn't realize it mattered.)

### Notes about GLib 2.36

* It is no longer necessary to call g_type_init().  If you are
  loading GLib as a dynamic module, you should be careful to avoid
  unloading it, then subsequently loading it again.  This never
  really worked before, but it is now explicitly undefined behavior.
  Note that if g_type_init() was the only explicit use of a GObject
  API and you are using linker flags such as --no-add-needed, then
  you may have to artificially use some GObject call to keep the
  linker from optimizing away -lgobject. We recommend to use
  g_type_ensure (G_TYPE_OBJECT) for this purpose.

* This release contains an incompatible change to the g_get_home_dir()
  function.  Previously, this function would effectively ignore the HOME
  environment variable and always return the value from /etc/password.
  As of this version, the HOME variable is used if it is set and the
  value from /etc/passwd is only used as a fallback.

* The 'flowinfo' and 'scope_id' fields of GInetSocketAddress
  (introduced in GLib 2.32) have been fixed to be in host byte order
  rather than network byte order. This is an incompatible change, but
  the previous behavior was clearly broken, so it seems unlikely that
  anyone was using it.

### Notes about GLib 2.34

* GIO now looks for thumbnails in XDG_CACHE_HOME, following a
  recent alignment of the thumbnail spec with the basedir spec.

* The default values for GThreadPools max_unused_threads and
  max_idle_time settings have been changed to 2 and 15*1000,
  respectively.

### Notes about GLib 2.32

* It is no longer necessary to use g_thread_init() or to link against
  libgthread.  libglib is now always thread-enabled. Custom thread
  system implementations are no longer supported (including errorcheck
  mutexes).

* The thread and synchronisation APIs have been updated.
  GMutex and GCond can be statically allocated without explicit
  initialisation, as can new types GRWLock and GRecMutex.  The
  GStatic_______ variants of these types have been deprecated.  GPrivate
  can also be statically allocated and has a nicer API (deprecating
  GStaticPrivate).  Finally, g_thread_create() has been replaced with a
  substantially simplified g_thread_new().

* The g_once_init_enter()/_leave() functions have been replaced with
  macros that allow for a pointer to any gsize-sized object, not just a
  gsize*.  The assertions to ensure that a pointer to a correctly-sized
  object is being used will not work with generic pointers (ie: (void*)
  and (gpointer) casts) which would have worked with the old version.

* It is now mandatory to include glib.h instead of individual headers.

* The -uninstalled variants of the pkg-config files have been dropped.

* For a long time, gobject-2.0.pc mistakenly declared a public
  dependency on gthread-2.0.pc (when the dependency should have been
  private).  This means that programs got away with calling
  g_thread_init() without explicitly listing gthread-2.0.pc among their
  dependencies.

  gthread has now been removed as a gobject dependency, which will cause
  such programs to break.

  The fix for this problem is either to declare an explicit dependency
  on gthread-2.0.pc (if you care about compatibility with older GLib
  versions) or to stop calling g_thread_init().

* g_debug() output is no longer enabled by default.  It can be enabled
  on a per-domain basis with the G_MESSAGES_DEBUG environment variable
  like
    G_MESSAGES_DEBUG=domain1,domain2
  or
    G_MESSAGES_DEBUG=all

### Notes about GLib 2.30

* GObject includes a generic marshaller, g_cclosure_marshal_generic.
  To use it, simply specify NULL as the marshaller in g_signal_new().
  The generic marshaller is implemented with libffi, and consequently
  GObject depends on libffi now.

### Notes about GLib 2.28

* The GApplication API has changed compared to the version that was
  included in the 2.25 development snapshots. Existing users will need
  adjustments.

### Notes about GLib 2.26

* Nothing noteworthy.

### Notes about GLib 2.24

* It is now allowed to call g_thread_init(NULL) multiple times, and
  to call glib functions before g_thread_init(NULL) is called
  (although the later is mainly a change in docs as this worked before
  too). See the GThread reference documentation for the details.

* GObject now links to GThread and threads are enabled automatically
  when g_type_init() is called.

* GObject no longer allows to call g_object_set() on construct-only properties
  while an object is being initialized. If this behavior is needed, setting a
  custom constructor that just chains up will re-enable this functionality.

* GMappedFile on an empty file now returns NULL for the contents instead of
  returning an empty string. The documentation specifically states that code
  may not rely on nul-termination here so any breakage caused by this change
  is a bug in application code.

### Notes about GLib 2.22

* Repeated calls to g_simple_async_result_set_op_res_gpointer used
  to leak the data. This has been fixed to always call the provided
  destroy notify.

### Notes about GLib 2.20

* The functions for launching applications (e.g. g_app_info_launch() +
  friends) now passes a FUSE file:// URI if possible (requires gvfs
  with the FUSE daemon to be running and operational). With gvfs 2.26,
  FUSE file:// URIs will be mapped back to gio URIs in the GFile
  constructors. The intent of this change is to better integrate
  POSIX-only applications, see bug #528670 for the rationale.  The
  only user-visible change is when an application needs to examine an
  URI passed to it (e.g. as a positional parameter). Instead of
  looking at the given URI, the application will now need to look at
  the result of g_file_get_uri() after having constructed a GFile
  object with the given URI.

### Notes about GLib 2.18

* The recommended way of using GLib has always been to only include the
  toplevel headers glib.h, glib-object.h and gio.h. GLib enforces this by
  generating an error when individual headers are directly included.
  To help with the transition, the enforcement is not turned on by
  default for GLib headers (it is turned on for GObject and GIO).
  To turn it on, define the preprocessor symbol G_DISABLE_SINGLE_INCLUDES.

### Notes about GLib 2.16

* GLib now includes GIO, which adds optional dependencies against libattr
  and libselinux for extended attribute and SELinux support. Use
  --disable-xattr and --disable-selinux to build without these.

### Notes about GLib 2.10

* The functions g_snprintf() and g_vsnprintf() have been removed from
  the gprintf.h header, since they are already declared in glib.h. This
  doesn't break documented use of gprintf.h, but people have been known
  to include gprintf.h without including glib.h.

* The Unicode support has been updated to Unicode 4.1. This adds several
  new members to the GUnicodeBreakType enumeration.

* The support for Solaris threads has been retired. Solaris has provided
  POSIX threads for long enough now to have them available on every
  Solaris platform.

* 'make check' has been changed to validate translations by calling
  msgfmt with the -c option. As a result, it may fail on systems with
  older gettext implementations (GNU gettext < 0.14.1, or Solaris gettext).
  'make check' will also fail on systems where the C compiler does not
  support ELF visibility attributes.

* The GMemChunk API has been deprecated in favour of a new 'slice
  allocator'. See the g_slice documentation for more details.

* A new type, GInitiallyUnowned, has been introduced, which is
  intended to serve as a common implementation of the 'floating reference'
  concept that is e.g. used by GtkObject. Note that changing the
  inheritance hierarchy of a type can cause problems for language
  bindings and other code which needs to work closely with the type
  system. Therefore, switching to GInitiallyUnowned should be done
  carefully. g_object_compat_control() has been added to GLib 2.8.5
  to help with the transition.

### Notes about GLib 2.6.0

* GLib 2.6 introduces the concept of 'GLib filename encoding', which is the
  on-disk encoding on Unix, but UTF-8 on Windows. All GLib functions
  returning or accepting pathnames have been changed to expect
  filenames in this encoding, and the common POSIX functions dealing
  with pathnames have been wrapped. These wrappers are declared in the
  header <glib/gstdio.h> which must be included explicitly; it is not
  included through <glib.h>.

  On current (NT-based) Windows versions, where the on-disk file names
  are Unicode, these wrappers use the wide-character API in the C
  library. Thus applications can handle file names containing any
  Unicode characters through GLib's own API and its POSIX wrappers,
  not just file names restricted to characters in the system codepage.

  To keep binary compatibility with applications compiled against
  older versions of GLib, the Windows DLL still provides entry points
  with the old semantics using the old names, and applications
  compiled against GLib 2.6 will actually use new names for the
  functions. This is transparent to the programmer.

  When compiling against GLib 2.6, applications intended to be
  portable to Windows must take the UTF-8 file name encoding into
  consideration, and use the gstdio wrappers to access files whose
  names have been constructed from strings returned from GLib.

* Likewise, g_get_user_name() and g_get_real_name() have been changed
  to return UTF-8 on Windows, while keeping the old semantics for
  applications compiled against older versions of GLib.

* The GLib uses an '_' prefix to indicate private symbols that
  must not be used by applications. On some platforms, symbols beginning
  with prefixes such as _g will be exported from the library, on others not.
  In no case can applications use these private symbols. In addition to that,
  GLib+ 2.6 makes several symbols private which were not in any installed
  header files and were never intended to be exported.

* To reduce code size and improve efficiency, GLib, when compiled
  with the GNU toolchain, has separate internal and external entry
  points for exported functions. The internal names, which begin with
  IA__, may be seen when debugging a GLib program.

* On Windows, GLib no longer opens a console window when printing
  warning messages if stdout or stderr are invalid, as they are in
  "Windows subsystem" (GUI) applications. Simply redirect stdout or
  stderr if you need to see them.

* The child watch functionality tends to reveal a bug in many
  thread implementations (in particular the older LinuxThreads
  implementation on Linux) where it's not possible to call waitpid()
  for a child created in a different thread. For this reason, for
  maximum portability, you should structure your code to fork all
  child processes that you want to wait for from the main thread.

* A problem was recently discovered with g_signal_connect_object();
  it doesn't actually disconnect the signal handler once the object being
  connected to dies, just disables it. See the API docs for the function
  for further details and the correct workaround that will continue to
  work with future versions of GLib.