Sets our main struct and passes it to the parent class
Frees the resources allocated to a mutex with g_mutex_init(). This function should not be used with a GMutex that has been statically allocated. Calling g_mutex_clear() on a locked mutex leads to undefined behaviour. Sine: 2.32
the main Gtk struct as a void*
Initializes a GMutex so that it can be used. This function is useful to initialize a mutex that has been allocated on the stack, or as part of a larger structure. It is not necessary to initialize a mutex that has been statically allocated. To undo the effect of g_mutex_init() when a mutex is no longer needed, use g_mutex_clear(). Calling g_mutex_init() on an already initialized GMutex leads to undefined behaviour. Since 2.32
Locks mutex. If mutex is already locked by another thread, the current thread will block until mutex is unlocked by the other thread. Note GMutex is neither guaranteed to be recursive nor to be non-recursive. As such, calling g_mutex_lock() on a GMutex that has already been locked by the same thread results in undefined behaviour (including but not limited to deadlocks).
Tries to lock mutex. If mutex is already locked by another thread, it immediately returns FALSE. Otherwise it locks mutex and returns TRUE. Note GMutex is neither guaranteed to be recursive nor to be non-recursive. As such, calling g_mutex_lock() on a GMutex that has already been locked by the same thread results in undefined behaviour (including but not limited to deadlocks or arbitrary return values).
Unlocks mutex. If another thread is blocked in a g_mutex_lock() call for mutex, it will become unblocked and can lock mutex itself. Calling g_mutex_unlock() on a mutex that is not locked by the current thread leads to undefined behaviour.
the main Gtk struct
Threads act almost like processes, but unlike processes all threads of one process share the same memory. This is good, as it provides easy communication between the involved threads via this shared memory, and it is bad, because strange things (so called "Heisenbugs") might happen if the program is not carefully designed. In particular, due to the concurrent nature of threads, no assumptions on the order of execution of code running in different threads can be made, unless order is explicitly forced by the programmer through synchronization primitives.
The aim of the thread-related functions in GLib is to provide a portable means for writing multi-threaded software. There are primitives for mutexes to protect the access to portions of memory (GMutex, GRecMutex and GRWLock). There is a facility to use individual bits for locks (g_bit_lock()). There are primitives for condition variables to allow synchronization of threads (GCond). There are primitives for thread-private data - data that every thread has a private instance of (GPrivate). There are facilities for one-time initialization (GOnce, g_once_init_enter()). Finally, there are primitives to create and manage threads (GThread).
The GLib threading system used to be initialized with g_thread_init(). This is no longer necessary. Since version 2.32, the GLib threading system is automatically initialized at the start of your program, and all thread-creation functions and synchronization primitives are available right away.
Note that it is not safe to assume that your program has no threads even if you don't call g_thread_new() yourself. GLib and GIO can and will create threads for their own purposes in some cases, such as when using g_unix_signal_source_new() or when using GDBus.
Originally, UNIX did not have threads, and therefore some traditional UNIX APIs are problematic in threaded programs. Some notable examples are
C library functions that return data in statically allocated buffers, such as strtok() or strerror(). For many of these, there are thread-safe variants with a _r suffix, or you can look at corresponding GLib APIs (like g_strsplit() or g_strerror()).
setenv() and unsetenv() manipulate the process environment in a not thread-safe way, and may interfere with getenv() calls in other threads. Note that getenv() calls may be “hidden” behind other APIs. For example, GNU gettext() calls getenv() under the covers. In general, it is best to treat the environment as readonly. If you absolutely have to modify the environment, do it early in main(), when no other threads are around yet.
setlocale() changes the locale for the entire process, affecting all threads. Temporary changes to the locale are often made to change the behavior of string scanning or formatting functions like scanf() or printf(). GLib offers a number of string APIs (like g_ascii_formatd() or g_ascii_strtod()) that can often be used as an alternative. Or you can use the uselocale() function to change the locale only for the current thread.
fork() only takes the calling thread into the child's copy of the process image. If other threads were executing in critical sections they could have left mutexes locked which could easily cause deadlocks in the new child. For this reason, you should call exit() or exec() as soon as possible in the child and only make signal-safe library calls before that.
daemon() uses fork() in a way contrary to what is described above. It should not be used with GLib programs.
GLib itself is internally completely thread-safe (all global data is automatically locked), but individual data structure instances are not automatically locked for performance reasons. For example, you must coordinate accesses to the same GHashTable from multiple threads. The two notable exceptions from this rule are GMainLoop and GAsyncQueue, which are thread-safe and need no further application-level locking to be accessed from multiple threads. Most refcounting functions such as g_object_ref() are also thread-safe.