* condition they signal the #GCond, and that causes the waiting
* threads to be woken up.
*
+ * Consider the following example of a shared variable. One or more
+ * threads can wait for data to be published to the variable and when
+ * another thread publishes the data, it can signal one of the waiting
+ * threads to wake up to collect the data.
+ *
* <example>
* <title>
* Using GCond to block a thread until a condition is satisfied
* </title>
* <programlisting>
- * GCond* data_cond = NULL; /<!-- -->* Must be initialized somewhere *<!-- -->/
- * GMutex* data_mutex = NULL; /<!-- -->* Must be initialized somewhere *<!-- -->/
* gpointer current_data = NULL;
+ * GMutex data_mutex;
+ * GCond data_cond;
*
* void
* push_data (gpointer data)
* {
- * g_mutex_lock (data_mutex);
+ * g_mutex_lock (&data_mutex);
* current_data = data;
- * g_cond_signal (data_cond);
- * g_mutex_unlock (data_mutex);
+ * g_cond_signal (&data_cond);
+ * g_mutex_unlock (&data_mutex);
* }
*
* gpointer
* {
* gpointer data;
*
- * g_mutex_lock (data_mutex);
+ * g_mutex_lock (&data_mutex);
* while (!current_data)
- * g_cond_wait (data_cond, data_mutex);
+ * g_cond_wait (&data_cond, &data_mutex);
* data = current_data;
* current_data = NULL;
- * g_mutex_unlock (data_mutex);
+ * g_mutex_unlock (&data_mutex);
*
* return data;
* }
* current_data is non-%NULL, i.e. until some other thread
* has called push_data().
*
- * <note><para>It is important to use the g_cond_wait() and
- * g_cond_timed_wait() functions only inside a loop which checks for the
- * condition to be true. It is not guaranteed that the waiting thread
- * will find the condition fulfilled after it wakes up, even if the
- * signaling thread left the condition in that state: another thread may
- * have altered the condition before the waiting thread got the chance
- * to be woken up, even if the condition itself is protected by a
- * #GMutex, like above.</para></note>
+ * The example shows that use of a condition variable must always be
+ * paired with a mutex. Without the use of a mutex, there would be a
+ * race between the check of <varname>current_data</varname> by the
+ * while loop in <function>pop_data</function> and waiting.
+ * Specifically, another thread could set <varname>pop_data</varname>
+ * after the check, and signal the cond (with nobody waiting on it)
+ * before the first thread goes to sleep. #GCond is specifically useful
+ * for its ability to release the mutex and go to sleep atomically.
+ *
+ * It is also important to use the g_cond_wait() and g_cond_wait_until()
+ * functions only inside a loop which checks for the condition to be
+ * true. See g_cond_wait() for an explanation of why the condition may
+ * not be true even after it returns.
*
* If a #GCond is allocated in static storage then it can be used
* without initialisation. Otherwise, you should call g_cond_init() on
* GThread:
*
* The #GThread struct represents a running thread. This struct
- * is returned by g_thread_new() or g_thread_new_full(). You can
- * obtain the #GThread struct representing the current thead by
- * calling g_thread_self().
+ * is returned by g_thread_new() or g_thread_try_new(). You can obtain
+ * the #GThread struct representing the current thead by calling
+ * g_thread_self().
*
* The structure is opaque -- none of its fields may be directly
* accessed.
* GThreadFunc:
* @data: data passed to the thread
*
- * Specifies the type of the @func functions passed to
- * g_thread_new() or g_thread_new_full().
- *
- * If the thread is joinable, the return value of this function
- * is returned by a g_thread_join() call waiting for the thread.
- * If the thread is not joinable, the return value is ignored.
+ * Specifies the type of the @func functions passed to g_thread_new() or
+ * g_thread_try_new().
*
* Returns: the return value of the thread
*/
/* GThread {{{1 -------------------------------------------------------- */
-static void
-g_thread_cleanup (gpointer data)
+GThread *
+g_thread_ref (GThread *thread)
{
- if (data)
- {
- GRealThread* thread = data;
+ GRealThread *real = (GRealThread *) thread;
- /* We only free the thread structure if it isn't joinable.
- * If it is, the structure is freed in g_thread_join()
- */
- if (!thread->thread.joinable)
- {
- if (thread->ours)
- g_system_thread_free (thread);
- else
- g_slice_free (GRealThread, thread);
- }
+ g_atomic_int_inc (&real->ref_count);
+
+ return thread;
+}
+
+void
+g_thread_unref (GThread *thread)
+{
+ GRealThread *real = (GRealThread *) thread;
+
+ if (g_atomic_int_dec_and_test (&real->ref_count))
+ {
+ if (real->ours)
+ g_system_thread_free (real);
+ else
+ g_slice_free (GRealThread, real);
}
}
+static void
+g_thread_cleanup (gpointer data)
+{
+ g_thread_unref (data);
+}
+
gpointer
g_thread_proxy (gpointer data)
{
* @name: a name for the new thread
* @func: a function to execute in the new thread
* @data: an argument to supply to the new thread
- * @joinable: should this thread be joinable?
* @error: return location for error
*
* This function creates a new thread. The new thread starts by invoking
* a debugger. Some systems restrict the length of @name to
* 16 bytes.
*
- * If @joinable is %TRUE, you can wait for this thread's termination
- * calling g_thread_join(). Resources for a joinable thread are not
- * fully released until g_thread_join() is called for that thread.
- * Otherwise the thread will just disappear when it terminates.
+ * If the thread can not be created the program aborts. See
+ * g_thread_try_new() if you want to attempt to deal with failures.
*
- * @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.
- *
- * Returns: the new #GThread, or %NULL if an error occurred
+ * Returns: the new #GThread
*
* Since: 2.32
*/
GThread *
-g_thread_new (const gchar *name,
- GThreadFunc func,
- gpointer data,
- gboolean joinable,
- GError **error)
+g_thread_new (const gchar *name,
+ GThreadFunc func,
+ gpointer data)
{
- return g_thread_new_internal (name, g_thread_proxy, func, data, joinable, 0, error);
+ GError *error = NULL;
+ GThread *thread;
+
+ thread = g_thread_new_internal (name, g_thread_proxy, func, data, 0, &error);
+
+ if G_UNLIKELY (thread == NULL)
+ g_error ("creating thread '%s': %s", name ? name : "", error->message);
+
+ return thread;
}
/**
- * g_thread_new_full:
+ * g_thread_try_new:
* @name: a name for the new thread
* @func: a function to execute in the new thread
* @data: an argument to supply to the new thread
- * @joinable: should this thread be joinable?
- * @stack_size: a stack size for the new thread
- * @error: return location for error
- *
- * This function creates a new thread. The new thread starts by
- * invoking @func with the argument data. The thread will run
- * until @func returns or until g_thread_exit() is called.
+ * @error: return location for error, or %NULL
*
- * The @name can be useful for discriminating threads in
- * a debugger. Some systems restrict the length of @name to
- * 16 bytes.
+ * This function is the same as g_thread_new() except that
+ * it allows for the possibility of failure.
*
- * If the underlying thread implementation supports it, the thread
- * gets a stack size of @stack_size or the default value for the
- * current platform, if @stack_size is 0. Note that you should only
- * use a non-zero @stack_size if you really can't use the default.
- * In most cases, using g_thread_new() (which doesn't take a
- * @stack_size) is better.
- *
- * If @joinable is %TRUE, you can wait for this thread's termination
- * calling g_thread_join(). Resources for a joinable thread are not
- * fully released until g_thread_join() is called for that thread.
- * Otherwise the thread will just disappear when it terminates.
- *
- * @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.
+ * If a thread can not be created (due to resource limits),
+ * @error is set and %NULL is returned.
*
* Returns: the new #GThread, or %NULL if an error occurred
*
* Since: 2.32
*/
GThread *
-g_thread_new_full (const gchar *name,
- GThreadFunc func,
- gpointer data,
- gboolean joinable,
- gsize stack_size,
- GError **error)
+g_thread_try_new (const gchar *name,
+ GThreadFunc func,
+ gpointer data,
+ GError **error)
{
- return g_thread_new_internal (name, g_thread_proxy, func, data, joinable, stack_size, error);
+ return g_thread_new_internal (name, g_thread_proxy, func, data, 0, error);
}
GThread *
GThreadFunc proxy,
GThreadFunc func,
gpointer data,
- gboolean joinable,
gsize stack_size,
GError **error)
{
thread = g_system_thread_new (proxy, stack_size, error);
if (thread)
{
+ thread->ref_count = 2;
thread->ours = TRUE;
- thread->thread.joinable = joinable;
+ thread->thread.joinable = TRUE;
thread->thread.func = func;
thread->thread.data = data;
thread->name = name;
*
* Terminates the current thread.
*
- * If another thread is waiting for that thread using g_thread_join()
- * and the current thread is joinable, the waiting thread will be woken
- * up and get @retval as the return value of g_thread_join(). If the
- * current thread is not joinable, @retval is ignored.
+ * If another thread is waiting for us using g_thread_join() then the
+ * waiting thread will be woken up and get @retval as the return value
+ * of g_thread_join().
*
* Calling <literal>g_thread_exit (retval)</literal> is equivalent to
* returning @retval from the function @func, as given to g_thread_new().
/**
* g_thread_join:
- * @thread: a joinable #GThread
+ * @thread: a #GThread
*
* Waits until @thread finishes, i.e. the function @func, as
* given to g_thread_new(), returns or g_thread_exit() is called.
* If @thread has already terminated, then g_thread_join()
- * returns immediately. @thread must be joinable.
+ * returns immediately.
*
- * Any thread can wait for any other (joinable) thread by calling
- * g_thread_join(), not just its 'creator'. Calling g_thread_join()
- * from multiple threads for the same @thread leads to undefined
- * behaviour.
+ * Any thread can wait for any other thread by calling g_thread_join(),
+ * not just its 'creator'. Calling g_thread_join() from multiple threads
+ * for the same @thread leads to undefined behaviour.
*
* The value returned by @func or given to g_thread_exit() is
* returned by this function.
gpointer retval;
g_return_val_if_fail (thread, NULL);
- g_return_val_if_fail (thread->joinable, NULL);
g_system_thread_wait (real);
/* Just to make sure, this isn't used any more */
thread->joinable = 0;
- /* the thread structure for non-joinable threads is freed upon
- * thread end. We free the memory here. This will leave a loose end,
- * if a joinable thread is not joined.
- */
- if (real->ours)
- g_system_thread_free (real);
- else
- g_slice_free (GRealThread, real);
+ g_thread_unref (thread);
return retval;
}
* g_thread_self:
*
* This functions returns the #GThread corresponding to the
- * current thread.
+ * current thread. Note that this function does not increase
+ * the reference count of the returned object.
*
* Returns: the #GThread representing the current thread
*/
* that are not created by GLib.
*/
thread = g_slice_new0 (GRealThread);
+ thread->ref_count = 1;
+
g_private_set (&g_thread_specific_private, thread);
}
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