<!-- ##### FUNCTION g_static_mutex_lock ##### -->
<para>
-works like g_mutex_lock(), but for a #GStaticMutex.
+Works like g_mutex_lock(), but for a #GStaticMutex.
</para>
@mutex: a #GStaticMutex
<!-- ##### FUNCTION g_static_mutex_trylock ##### -->
<para>
-works like g_mutex_trylock(), but for a #GStaticMutex.
+Works like g_mutex_trylock(), but for a #GStaticMutex.
</para>
@mutex: a #GStaticMutex
<!-- ##### FUNCTION g_static_mutex_unlock ##### -->
<para>
-works like g_mutex_unlock(), but for a #GStaticMutex.
+Works like g_mutex_unlock(), but for a #GStaticMutex.
</para>
@mutex: a #GStaticMutex
<!-- ##### MACRO G_LOCK ##### -->
<para>
-works like g_mutex_lock(), but for a lock defined with #G_LOCK_DEFINE.
+Works like g_mutex_lock(), but for a lock defined with #G_LOCK_DEFINE.
</para>
@name: the name of the lock
<!-- ##### MACRO G_TRYLOCK ##### -->
<para>
-works like g_mutex_trylock(), but for a lock defined with #G_LOCK_DEFINE.
+Works like g_mutex_trylock(), but for a lock defined with #G_LOCK_DEFINE.
</para>
@name: the name of the lock
<!-- ##### MACRO G_UNLOCK ##### -->
<para>
-works like g_mutex_unlock(), but for a lock defined with #G_LOCK_DEFINE.
+Works like g_mutex_unlock(), but for a lock defined with #G_LOCK_DEFINE.
</para>
@name: the name of the lock
<!-- ##### STRUCT GStaticRWLock ##### -->
<para>
+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 followin
+example:
+<example>
+<title>An array with access functions</title>
+<programlisting>
+ 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);
+ }
+</programlisting>
+</example>
+</para>
+
+<para>
+This example shows an array, which can be accessed by many readers
+(the my_array_get function) simultaniously, whereas the writers (the
+my_array_set function) only will be allowed once a time and only if no
+readers currently access the array. This is because of the potentially
+dangerous resizing of the array. Using that functions is fully
+multithread safe now.
+</para>
+
+</para>
+Most of the time the writers should have precedence of 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.
+</para>
+
+<para>
+Even though #GStaticRWLoc is not opaque, it should only be used with
+the following functions.
</para>
+<para>
+All of the g_static_rw_lock_* functions can also be used, if
+g_thread_init() has not been called.
+</para>
+
+<note>
+<para>
+A read-write lock has a higher overhead as a mutex. For example both
+g_static_rw_lock_reader_lock() and g_static_rw_lock_reader_unlock()
+has to lock and unlock a #GStaticMutex, so it takes at least twice the
+time to lock and unlock a #GStaticRWLock than to lock and unlock a
+#GStaticMutex. So only data structures, that are accessed by multiple
+readers, which keep the lock for a considerable time justify a
+#GStaticRWLock. The above example most probably would fare better with
+a #GStaticMutex.
+</para>
+</note>
+
@mutex:
@read_cond:
@write_cond:
<!-- ##### MACRO G_STATIC_RW_LOCK_INIT ##### -->
<para>
+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().
+</para>
+<para>
+<informalexample>
+<programlisting>
+GStaticRWLock my_lock = G_STATIC_RW_LOCK_INIT;
+</programlisting>
+</informalexample>
</para>
<!-- ##### FUNCTION g_static_rw_lock_init ##### -->
<para>
-
+A #GStaticRWLock must be initialized with this function, before it can
+be used. Alternatively you can initialize it with
+#G_STATIC_RW_LOCK_INIT.
</para>
-@lock:
+@lock: a #GStaticRWLock to be initialized
<!-- ##### FUNCTION g_static_rw_lock_reader_lock ##### -->
<para>
+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().
+</para>
+<para>
+#GStaticRWLock in general is not recursive, but as there may be
+unlimited concurrent locks for reading, it effectively is for
+recursive for reading, but for reading only. Locking for writing after
+locking for reading will deadlock, the same holds true for the
+opposite order.
</para>
-@lock:
+@lock: a #GStaticRWLock to lock for reading
<!-- ##### FUNCTION g_static_rw_lock_reader_trylock ##### -->
<para>
-
+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, it immediately returns #FALSE. Otherwise it
+locks @lock for reading and returns TRUE. This lock has to be unlocked
+by g_static_rw_lock_reader_unlock().
</para>
-@lock:
-@Returns:
+@lock: a #GStaticRWLock to lock for reading
+@Returns: TRUE, if @lock could be locked for reading
<!-- ##### FUNCTION g_static_rw_lock_reader_unlock ##### -->
<para>
-
+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.
</para>
-@lock:
+@lock: a #GStaticRWLock to unlock after reading
<!-- ##### FUNCTION g_static_rw_lock_writer_lock ##### -->
<para>
-
+Locks @lock for writing. If @lock is already locked for writing or
+reading by other threads, this function will block until @lock is
+completly 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().
</para>
-@lock:
+@lock: a #GStaticRWLock to lock for writing
<!-- ##### FUNCTION g_static_rw_lock_writer_trylock ##### -->
<para>
-
+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().
</para>
-@lock:
-@Returns:
+@lock: a #GStaticRWLock to lock for writing
+@Returns: TRUE, if @lock could be locked for writing
<!-- ##### FUNCTION g_static_rw_lock_writer_unlock ##### -->
<para>
-
+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. If no thread waits to lock @lock for
+writing and threads wait to lock @lock for reading, the waiting
+threads are woken up and can lock @lock for reading.
</para>
-@lock:
+@lock: a #GStaticRWLock to unlock after writing
<!-- ##### FUNCTION g_static_rw_lock_free ##### -->
<para>
+Releases all resources allocated to @lock.
+</para>
+<para>
+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.
</para>
-@lock:
+@lock: a #GStaticRWLock to be freed
<!-- ##### STRUCT GCond ##### -->
projects / platform / upstream / glib.git / commitdiff