g_thread_init ()

void
g_thread_init (gpointer vtable);

If you use GLib from more than one thread, you must initialize the thread system by calling g_thread_init().

Since version 2.24, calling g_thread_init() multiple times is allowed, but nothing happens except for the first call.

Since version 2.32, GLib does not support custom thread implementations anymore and the vtable parameter is ignored and you should pass NULL.

<note><para>g_thread_init() must not be called directly or indirectly in a callback from GLib. Also no mutexes may be currently locked while calling g_thread_init().</para></note>

<note><para>To use g_thread_init() in your program, you have to link with the libraries that the command <command>pkg-config --libs gthread-2.0</command> outputs. This is not the case for all the other thread-related functions of GLib. Those can be used without having to link with the thread libraries.</para></note>

g_thread_supported ()

gboolean
g_thread_supported ();

This macro returns TRUE if the thread system is initialized, and FALSE if it is not.

For language bindings, g_thread_get_initialized() provides the same functionality as a function.

g_thread_get_initialized ()

gboolean
g_thread_get_initialized (void);

Indicates if g_thread_init() has been called.

Since 2.20

g_thread_create ()

GThread *
g_thread_create (GThreadFunc func,
                 gpointer data,
                 gboolean joinable,
                 GError **error);

This function creates a new thread.

The new thread executes the function func with the argument data . If the thread was created successfully, it is returned.

error can be NULL to ignore errors, or non-NULL to report errors. The error is set, if and only if the function returns NULL.

This function returns a reference to the created thread only if joinable is TRUE. In that case, you must free this reference by calling g_thread_unref() or g_thread_join(). If joinable is FALSE then you should probably not touch the return value.

g_thread_create_full ()

GThread *
g_thread_create_full (GThreadFunc func,
                      gpointer data,
                      gulong stack_size,
                      gboolean joinable,
                      gboolean bound,
                      GThreadPriority priority,
                      GError **error);

This function creates a new thread.

g_thread_set_priority ()

void
g_thread_set_priority (GThread *thread,
                       GThreadPriority priority);

This function does nothing.

g_thread_foreach ()

void
g_thread_foreach (GFunc thread_func,
                  gpointer user_data);

Call thread_func on all GThreads that have been created with g_thread_create().

Note that threads may decide to exit while thread_func is running, so without intimate knowledge about the lifetime of foreign threads, thread_func shouldn't access the GThread* pointer passed in as first argument. However, thread_func will not be called for threads which are known to have exited already.

Due to thread lifetime checks, this function has an execution complexity which is quadratic in the number of existing threads.

Since 2.10

g_mutex_new ()

GMutex *
g_mutex_new ();

Allocates and initializes a new GMutex.

g_mutex_free ()

void
g_mutex_free (GMutex *mutex);

Destroys a mutex that has been created with g_mutex_new().

Calling g_mutex_free() on a locked mutex may result in undefined behaviour.

g_cond_new ()

GCond*
g_cond_new ();

Allocates and initializes a new GCond.

g_cond_free ()

void
g_cond_free (GCond *cond);

Destroys a GCond that has been created with g_cond_new().

Calling g_cond_free() for a GCond on which threads are blocking leads to undefined behaviour.

g_private_new ()

GPrivate *
g_private_new (GDestroyNotify notify);

Creates a new GPrivate.

g_static_mutex_init ()

void
g_static_mutex_init (GStaticMutex *mutex);

Initializes mutex . Alternatively you can initialize it with G_STATIC_MUTEX_INIT.

g_static_mutex_lock ()

void
g_static_mutex_lock (GStaticMutex *mutex);

Works like g_mutex_lock(), but for a GStaticMutex.

g_static_mutex_trylock ()

gboolean
g_static_mutex_trylock (GStaticMutex *mutex);

Works like g_mutex_trylock(), but for a GStaticMutex.

g_static_mutex_unlock ()

void
g_static_mutex_unlock (GStaticMutex *mutex);

Works like g_mutex_unlock(), but for a GStaticMutex.

g_static_mutex_get_mutex ()

GMutex *
g_static_mutex_get_mutex (GStaticMutex *mutex);

For some operations (like g_cond_wait()) you must have a GMutex instead of a GStaticMutex. This function will return the corresponding GMutex for mutex .

g_static_mutex_free ()

void
g_static_mutex_free (GStaticMutex *mutex);

Releases all resources allocated to mutex .

You don't have to call this functions for a GStaticMutex with an unbounded lifetime, i.e. objects declared 'static', but if you have a GStaticMutex as a member of a structure and the structure is freed, you should also free the GStaticMutex.

Calling g_static_mutex_free() on a locked mutex may result in undefined behaviour.

g_static_rec_mutex_init ()

void
g_static_rec_mutex_init (GStaticRecMutex *mutex);

A GStaticRecMutex must be initialized with this function before it can be used. Alternatively you can initialize it with G_STATIC_REC_MUTEX_INIT.

g_static_rec_mutex_lock ()

void
g_static_rec_mutex_lock (GStaticRecMutex *mutex);

Locks mutex . If mutex is already locked by another thread, the current thread will block until mutex is unlocked by the other thread. If mutex is already locked by the calling thread, this functions increases the depth of mutex and returns immediately.

g_static_rec_mutex_trylock ()

gboolean
g_static_rec_mutex_trylock (GStaticRecMutex *mutex);

Tries to lock mutex . If mutex is already locked by another thread, it immediately returns FALSE. Otherwise it locks mutex and returns TRUE. If mutex is already locked by the calling thread, this functions increases the depth of mutex and immediately returns TRUE.

g_static_rec_mutex_unlock ()

void
g_static_rec_mutex_unlock (GStaticRecMutex *mutex);

Unlocks mutex . Another thread will be allowed to lock mutex only when it has been unlocked as many times as it had been locked before. If mutex is completely unlocked and another thread is blocked in a g_static_rec_mutex_lock() call for mutex , it will be woken and can lock mutex itself.

g_static_rec_mutex_lock_full ()

void
g_static_rec_mutex_lock_full (GStaticRecMutex *mutex,
                              guint depth);

Works like calling g_static_rec_mutex_lock() for mutex depth times.

g_static_rec_mutex_unlock_full ()

guint
g_static_rec_mutex_unlock_full (GStaticRecMutex *mutex);

Completely unlocks mutex . If another thread is blocked in a g_static_rec_mutex_lock() call for mutex , it will be woken and can lock mutex itself. This function returns the number of times that mutex has been locked by the current thread. To restore the state before the call to g_static_rec_mutex_unlock_full() you can call g_static_rec_mutex_lock_full() with the depth returned by this function.

g_static_rec_mutex_free ()

void
g_static_rec_mutex_free (GStaticRecMutex *mutex);

Releases all resources allocated to a GStaticRecMutex.

You don't have to call this functions for a GStaticRecMutex with an unbounded lifetime, i.e. objects declared 'static', but if you have a GStaticRecMutex as a member of a structure and the structure is freed, you should also free the GStaticRecMutex.

g_static_rw_lock_init ()

void
g_static_rw_lock_init (GStaticRWLock *lock);

A GStaticRWLock must be initialized with this function before it can be used. Alternatively you can initialize it with G_STATIC_RW_LOCK_INIT.

g_static_rw_lock_reader_lock ()

void
g_static_rw_lock_reader_lock (GStaticRWLock *lock);

Locks lock for reading. There may be unlimited concurrent locks for reading of a GStaticRWLock at the same time. If lock is already locked for writing by another thread or if another thread is already waiting to lock lock for writing, this function will block until lock is unlocked by the other writing thread and no other writing threads want to lock lock . This lock has to be unlocked by g_static_rw_lock_reader_unlock().

GStaticRWLock is not recursive. It might seem to be possible to recursively lock for reading, but that can result in a deadlock, due to writer preference.

g_static_rw_lock_reader_trylock ()

gboolean
g_static_rw_lock_reader_trylock (GStaticRWLock *lock);

Tries to lock lock for reading. If lock is already locked for writing by another thread or if another thread is already waiting to lock lock for writing, immediately returns FALSE. Otherwise locks lock for reading and returns TRUE. This lock has to be unlocked by g_static_rw_lock_reader_unlock().

g_static_rw_lock_reader_unlock ()

void
g_static_rw_lock_reader_unlock (GStaticRWLock *lock);

Unlocks lock . If a thread waits to lock lock for writing and all locks for reading have been unlocked, the waiting thread is woken up and can lock lock for writing.

Deprectated: 2.32: Use g_rw_lock_reader_unlock() instead

g_static_rw_lock_writer_lock ()

void
g_static_rw_lock_writer_lock (GStaticRWLock *lock);

Locks lock for writing. If lock is already locked for writing or reading by other threads, this function will block until lock is completely unlocked and then lock lock for writing. While this functions waits to lock lock , no other thread can lock lock for reading. When lock is locked for writing, no other thread can lock lock (neither for reading nor writing). This lock has to be unlocked by g_static_rw_lock_writer_unlock().

Deprectated: 2.32: Use g_rw_lock_writer_lock() instead

g_static_rw_lock_writer_trylock ()

gboolean
g_static_rw_lock_writer_trylock (GStaticRWLock *lock);

Tries to lock lock for writing. If lock is already locked (for either reading or writing) by another thread, it immediately returns FALSE. Otherwise it locks lock for writing and returns TRUE. This lock has to be unlocked by g_static_rw_lock_writer_unlock().

g_static_rw_lock_writer_unlock ()

void
g_static_rw_lock_writer_unlock (GStaticRWLock *lock);

Unlocks lock . If a thread is waiting to lock lock for writing and all locks for reading have been unlocked, the waiting thread is woken up and can lock lock for writing. If no thread is waiting to lock lock for writing, and some thread or threads are waiting to lock lock for reading, the waiting threads are woken up and can lock lock for reading.

Deprectated: 2.32: Use g_rw_lock_writer_unlock() instead

g_static_rw_lock_free ()

void
g_static_rw_lock_free (GStaticRWLock *lock);

Releases all resources allocated to lock .

You don't have to call this functions for a GStaticRWLock with an unbounded lifetime, i.e. objects declared 'static', but if you have a GStaticRWLock as a member of a structure, and the structure is freed, you should also free the GStaticRWLock.

g_static_private_init ()

void
g_static_private_init (GStaticPrivate *private_key);

Initializes private_key . Alternatively you can initialize it with G_STATIC_PRIVATE_INIT.

g_static_private_get ()

gpointer
g_static_private_get (GStaticPrivate *private_key);

Works like g_private_get() only for a GStaticPrivate.

This function works even if g_thread_init() has not yet been called.

g_static_private_set ()

void
g_static_private_set (GStaticPrivate *private_key,
                      gpointer data,
                      GDestroyNotify notify);

Sets the pointer keyed to private_key for the current thread and the function notify to be called with that pointer (NULL or non-NULL), whenever the pointer is set again or whenever the current thread ends.

This function works even if g_thread_init() has not yet been called. If g_thread_init() is called later, the data keyed to private_key will be inherited only by the main thread, i.e. the one that called g_thread_init().

notify is used quite differently from destructor in g_private_new().

g_static_private_free ()

void
g_static_private_free (GStaticPrivate *private_key);

Releases all resources allocated to private_key .

You don't have to call this functions for a GStaticPrivate with an unbounded lifetime, i.e. objects declared 'static', but if you have a GStaticPrivate as a member of a structure and the structure is freed, you should also free the GStaticPrivate.

G_THREADS_IMPL_POSIX

#define G_THREADS_IMPL_POSIX

This macro is defined if POSIX style threads are used.

G_THREADS_IMPL_WIN32

#define G_THREADS_IMPL_NONE

This macro is defined if Windows style threads are used.

enum GThreadPriority

GStaticMutex

typedef struct _GStaticMutex GStaticMutex;

A GStaticMutex works like a GMutex.

Prior to GLib 2.32, GStaticMutex had the significant advantage that it doesn't need to be created at run-time, but can be defined at compile-time. Since 2.32, GMutex can be statically allocated as well, and GStaticMutex has been deprecated.

Here is a version of our give_me_next_number() example using a GStaticMutex:

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int
give_me_next_number (void)
{
  static int current_number = 0;
  int ret_val;
  static GStaticMutex mutex = G_STATIC_MUTEX_INIT;

  g_static_mutex_lock (&mutex);
  ret_val = current_number = calc_next_number (current_number);
  g_static_mutex_unlock (&mutex);

  return ret_val;
}

Sometimes you would like to dynamically create a mutex. If you don't want to require prior calling to g_thread_init(), because your code should also be usable in non-threaded programs, you are not able to use g_mutex_new() and thus GMutex, as that requires a prior call to g_thread_init(). In theses cases you can also use a GStaticMutex. It must be initialized with g_static_mutex_init() before using it and freed with with g_static_mutex_free() when not needed anymore to free up any allocated resources.

Even though GStaticMutex is not opaque, it should only be used with the following functions, as it is defined differently on different platforms.

All of the g_static_mutex_* functions apart from g_static_mutex_get_mutex() can also be used even if g_thread_init() has not yet been called. Then they do nothing, apart from g_static_mutex_trylock() which does nothing but returning TRUE.

All of the g_static_mutex_* functions are actually macros. Apart from taking their addresses, you can however use them as if they were functions.

G_STATIC_MUTEX_INIT

#define G_STATIC_MUTEX_INIT

A GStaticMutex must be initialized with this macro, before it can be used. This macro can used be to initialize a variable, but it cannot be assigned to a variable. In that case you have to use g_static_mutex_init().

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GStaticMutex my_mutex = G_STATIC_MUTEX_INIT;

struct GStaticRecMutex

struct GStaticRecMutex {
};

A GStaticRecMutex works like a GStaticMutex, but it can be locked multiple times by one thread. If you enter it n times, you have to unlock it n times again to let other threads lock it. An exception is the function g_static_rec_mutex_unlock_full(): that allows you to unlock a GStaticRecMutex completely returning the depth, (i.e. the number of times this mutex was locked). The depth can later be used to restore the state of the GStaticRecMutex by calling g_static_rec_mutex_lock_full(). In GLib 2.32, GStaticRecMutex has been deprecated in favor of GRecMutex.

Even though GStaticRecMutex is not opaque, it should only be used with the following functions.

All of the g_static_rec_mutex_* functions can be used even if g_thread_init() has not been called. Then they do nothing, apart from g_static_rec_mutex_trylock(), which does nothing but returning TRUE.

G_STATIC_REC_MUTEX_INIT

#define G_STATIC_REC_MUTEX_INIT { G_STATIC_MUTEX_INIT }

A GStaticRecMutex must be initialized with this macro before it can be used. This macro can used be to initialize a variable, but it cannot be assigned to a variable. In that case you have to use g_static_rec_mutex_init().

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GStaticRecMutex my_mutex = G_STATIC_REC_MUTEX_INIT;

struct GStaticRWLock

struct GStaticRWLock {
};

The GStaticRWLock struct represents a read-write lock. A read-write lock can be used for protecting data that some portions of code only read from, while others also write. In such situations it is desirable that several readers can read at once, whereas of course only one writer may write at a time.

Take a look at the following example:

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GStaticRWLock rwlock = G_STATIC_RW_LOCK_INIT;
GPtrArray *array;

gpointer
my_array_get (guint index)
{
  gpointer retval = NULL;

  if (!array)
    return NULL;

  g_static_rw_lock_reader_lock (&rwlock);
  if (index < array->len)
    retval = g_ptr_array_index (array, index);
  g_static_rw_lock_reader_unlock (&rwlock);

  return retval;
}

void
my_array_set (guint index, gpointer data)
{
  g_static_rw_lock_writer_lock (&rwlock);

  if (!array)
    array = g_ptr_array_new ();

  if (index >= array->len)
    g_ptr_array_set_size (array, index + 1);
  g_ptr_array_index (array, index) = data;

  g_static_rw_lock_writer_unlock (&rwlock);
}

This example shows an array which can be accessed by many readers (the my_array_get() function) simultaneously, whereas the writers (the my_array_set() function) will only be allowed once at a time and only if no readers currently access the array. This is because of the potentially dangerous resizing of the array. Using these functions is fully multi-thread safe now.

Most of the time, writers should have precedence over readers. That means, for this implementation, that as soon as a writer wants to lock the data, no other reader is allowed to lock the data, whereas, of course, the readers that already have locked the data are allowed to finish their operation. As soon as the last reader unlocks the data, the writer will lock it.

Even though GStaticRWLock is not opaque, it should only be used with the following functions.

All of the g_static_rw_lock_* functions can be used even if g_thread_init() has not been called. Then they do nothing, apart from g_static_rw_lock_*_trylock, which does nothing but returning TRUE.

A read-write lock has a higher overhead than a mutex. For example, both g_static_rw_lock_reader_lock() and g_static_rw_lock_reader_unlock() have to lock and unlock a GStaticMutex, so it takes at least twice the time to lock and unlock a GStaticRWLock that it does to lock and unlock a GStaticMutex. So only data structures that are accessed by multiple readers, and which keep the lock for a considerable time justify a GStaticRWLock. The above example most probably would fare better with a GStaticMutex.

G_STATIC_RW_LOCK_INIT

#define G_STATIC_RW_LOCK_INIT { G_STATIC_MUTEX_INIT, NULL, NULL, 0, FALSE, 0, 0 }

A GStaticRWLock must be initialized with this macro before it can be used. This macro can used be to initialize a variable, but it cannot be assigned to a variable. In that case you have to use g_static_rw_lock_init().

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GStaticRWLock my_lock = G_STATIC_RW_LOCK_INIT;

struct GStaticPrivate

struct GStaticPrivate {
};

A GStaticPrivate works almost like a GPrivate, but it has one significant advantage. It doesn't need to be created at run-time like a GPrivate, but can be defined at compile-time. This is similar to the difference between GMutex and GStaticMutex.

Now look at our give_me_next_number() example with GStaticPrivate:

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int
give_me_next_number ()
{
  static GStaticPrivate current_number_key = G_STATIC_PRIVATE_INIT;
  int *current_number = g_static_private_get (&current_number_key);

  if (!current_number)
    {
      current_number = g_new (int, 1);
      *current_number = 0;
      g_static_private_set (&current_number_key, current_number, g_free);
    }

  *current_number = calc_next_number (*current_number);

  return *current_number;
}

G_STATIC_PRIVATE_INIT

#define G_STATIC_PRIVATE_INIT 

Every GStaticPrivate must be initialized with this macro, before it can be used.

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GStaticPrivate my_private = G_STATIC_PRIVATE_INIT;