Struct
GLibStaticRWLock
deprecated: 2.32
Description
struct GStaticRWLock {
/* No available fields */
}
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:
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.
Deprecated since: 2.32
Use a GRWLock instead.
Instance methods
g_static_rw_lock_init
A GStaticRWLock must be initialized with this function before it
can be used. Alternatively you can initialize it with
G_STATIC_RW_LOCK_INIT.
deprecated: 2.32
g_static_rw_lock_reader_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().
deprecated: 2.32
g_static_rw_lock_reader_trylock
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().
deprecated: 2.32
g_static_rw_lock_reader_unlock
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.
deprecated: 2.32
g_static_rw_lock_writer_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().
deprecated: 2.32
g_static_rw_lock_writer_trylock
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().
deprecated: 2.32
g_static_rw_lock_writer_unlock
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.
deprecated: 2.32