coroutine-gthread.c: Avoid threading APIs deprecated in GLib 2.31

The GLib threading APIs were revamped in GLib 2.31 and a number
of the old interfaces were deprecated, which means they provoke
compilation warnings (errors if -Werror) now. Add support for the
new interfaces while retaining the old ones so we can still compile
on older versions of GLib too.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

coroutine-gthread.c

@@ -26,13 +26,93 @@ typedef struct {
     Coroutine base;
     GThread *thread;
     bool runnable;
+    bool free_on_thread_exit;
     CoroutineAction action;
 } CoroutineGThread;
 
-static GCond *coroutine_cond;
 static GStaticMutex coroutine_lock = G_STATIC_MUTEX_INIT;
+
+/* GLib 2.31 and beyond deprecated various parts of the thread API,
+ * but the new interfaces are not available in older GLib versions
+ * so we have to cope with both.
+ */
+#if GLIB_CHECK_VERSION(2, 31, 0)
+/* Default zero-initialisation is sufficient for 2.31+ GCond */
+static GCond the_coroutine_cond;
+static GCond *coroutine_cond = &the_coroutine_cond;
+static inline void init_coroutine_cond(void)
+{
+}
+
+/* Awkwardly, the GPrivate API doesn't provide a way to update the
+ * GDestroyNotify handler for the coroutine key dynamically. So instead
+ * we track whether or not the CoroutineGThread should be freed on
+ * thread exit / coroutine key update using the free_on_thread_exit
+ * field.
+ */
+static void coroutine_destroy_notify(gpointer data)
+{
+    CoroutineGThread *co = data;
+    if (co && co->free_on_thread_exit) {
+        g_free(co);
+    }
+}
+
+static GPrivate coroutine_key = G_PRIVATE_INIT(coroutine_destroy_notify);
+
+static inline CoroutineGThread *get_coroutine_key(void)
+{
+    return g_private_get(&coroutine_key);
+}
+
+static inline void set_coroutine_key(CoroutineGThread *co,
+                                     bool free_on_thread_exit)
+{
+    /* Unlike g_static_private_set() this does not call the GDestroyNotify
+     * if the previous value of the key was NULL. Fortunately we only need
+     * the GDestroyNotify in the non-NULL key case.
+     */
+    co->free_on_thread_exit = free_on_thread_exit;
+    g_private_replace(&coroutine_key, co);
+}
+
+static inline GThread *create_thread(GThreadFunc func, gpointer data)
+{
+    return g_thread_new("coroutine", func, data);
+}
+
+#else
+
+/* Handle older GLib versions */
+static GCond *coroutine_cond;
+static inline void init_coroutine_cond(void)
+{
+    coroutine_cond = g_cond_new();
+}
+
 static GStaticPrivate coroutine_key = G_STATIC_PRIVATE_INIT;
 
+static inline CoroutineGThread *get_coroutine_key(void)
+{
+    return g_static_private_get(&coroutine_key);
+}
+
+static inline void set_coroutine_key(CoroutineGThread *co,
+                                     bool free_on_thread_exit)
+{
+    g_static_private_set(&coroutine_key, co,
+                         free_on_thread_exit ? (GDestroyNotify)g_free : NULL);
+}
+
+static inline GThread *create_thread(GThreadFunc func, gpointer data)
+{
+    return g_thread_create_full(func, data, 0, TRUE, TRUE,
+                                G_THREAD_PRIORITY_NORMAL, NULL);
+}
+
+#endif
+
+
 static void __attribute__((constructor)) coroutine_init(void)
 {
     if (!g_thread_supported()) {
@@ -44,7 +124,7 @@ static void __attribute__((constructor)) coroutine_init(void)
 #endif
     }
 
-    coroutine_cond = g_cond_new();
+    init_coroutine_cond();
 }
 
 static void coroutine_wait_runnable_locked(CoroutineGThread *co)
@@ -65,7 +145,7 @@ static gpointer coroutine_thread(gpointer opaque)
 {
     CoroutineGThread *co = opaque;
 
-    g_static_private_set(&coroutine_key, co, NULL);
+    set_coroutine_key(co, false);
     coroutine_wait_runnable(co);
     co->base.entry(co->base.entry_arg);
     qemu_coroutine_switch(&co->base, co->base.caller, COROUTINE_TERMINATE);
@@ -77,8 +157,7 @@ Coroutine *qemu_coroutine_new(void)
     CoroutineGThread *co;
 
     co = g_malloc0(sizeof(*co));
-    co->thread = g_thread_create_full(coroutine_thread, co, 0, TRUE, TRUE,
+    co->thread = create_thread(coroutine_thread, co);
-                                      G_THREAD_PRIORITY_NORMAL, NULL);
     if (!co->thread) {
         g_free(co);
         return NULL;
@@ -117,12 +196,11 @@ CoroutineAction qemu_coroutine_switch(Coroutine *from_,
 
 Coroutine *qemu_coroutine_self(void)
 {
-    CoroutineGThread *co = g_static_private_get(&coroutine_key);
+    CoroutineGThread *co = get_coroutine_key();
-
     if (!co) {
         co = g_malloc0(sizeof(*co));
         co->runnable = true;
-        g_static_private_set(&coroutine_key, co, (GDestroyNotify)g_free);
+        set_coroutine_key(co, true);
     }
 
     return &co->base;
@@ -130,7 +208,7 @@ Coroutine *qemu_coroutine_self(void)
 
 bool qemu_in_coroutine(void)
 {
-    CoroutineGThread *co = g_static_private_get(&coroutine_key);
+    CoroutineGThread *co = get_coroutine_key();
 
     return co && co->base.caller;
 }