Description 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, GStaticMutex, G_LOCK_DEFINE, GStaticRecMutex and GStaticRWLock). 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, GStaticPrivate). Last but definitely not least there are primitives to portably create and manage threads (GThread). The threading system is initialized with g_thread_init(), which takes an optional custom thread implementation or NULL for the default implementation. If you want to call g_thread_init() with a non-NULL argument this must be done before executing any other GLib functions (except g_mem_set_vtable()). This is a requirement even if no threads are in fact ever created by the process. Calling g_thread_init() with a NULL argument is somewhat more relaxed. You may call any other glib functions in the main thread before g_thread_init() as long as g_thread_init() is not called from a glib callback, or with any locks held. However, many libraries above glib does not support late initialization of threads, so doing this should be avoided if possible. Please note that since version 2.24 the GObject initialization function g_type_init() initializes threads (with a NULL argument), so most applications, including those using Gtk+ will run with threads enabled. If you want a special thread implementation, make sure you call g_thread_init() before g_type_init() is called. After calling g_thread_init(), GLib is completely thread safe (all global data is automatically locked), but individual data structure instances are not automatically locked for performance reasons. So, 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 threadsafe and need no further application-level locking to be accessed from multiple threads. To help debugging problems in multithreaded applications, GLib supports error-checking mutexes that will give you helpful error messages on common problems. To use error-checking mutexes, define the symbol G_ERRORCHECK_MUTEXES when compiling the application.