[glib: 1/2] Fix initialization logic of GThreadPool if the first created pool is an exclusive one

[Philip Withnall <pwithnall src gnome org>]

commit 78bae85d215e3e1ce77c828c2075d216edbc36f6
Author: Sebastian Dröge <sebastian centricular com>
Date:   Sat Jan 25 11:08:22 2020 +0200

    Fix initialization logic of GThreadPool if the first created pool is an exclusive one
    
    Previously we would only ever run the initialization code once, but part
    of it only if a non-exclusive pool was created. This caused the shared
    state to be inconsistent if the first pool to be created was exclusive
    and the second non-exclusive.
    
    Fixes https://gitlab.gnome.org/GNOME/glib/issues/2012

 glib/gthreadpool.c | 67 +++++++++++++++++++++++++++---------------------------
 1 file changed, 33 insertions(+), 34 deletions(-)
---
diff --git a/glib/gthreadpool.c b/glib/gthreadpool.c
index dd6546be4..ed34fcd52 100644
--- a/glib/gthreadpool.c
+++ b/glib/gthreadpool.c
@@ -579,42 +579,41 @@ g_thread_pool_new (GFunc      func,
 
   G_LOCK (init);
   if (!unused_thread_queue)
-    {
       unused_thread_queue = g_async_queue_new ();
-      /* For the very first non-exclusive thread-pool we remember the thread
-       * scheduler settings of the thread creating the pool, if supported by
-       * the GThread implementation. This is then used for making sure that
-       * all threads created on the non-exclusive thread-pool have the same
-       * scheduler settings, and more importantly don't just inherit them
-       * from the thread that just happened to push a new task and caused
-       * a new thread to be created.
-       *
-       * Not doing so could cause real-time priority threads or otherwise
-       * threads with problematic scheduler settings to be part of the
-       * non-exclusive thread-pools.
-       *
-       * If this is not supported by the GThread implementation then we here
-       * start a thread that will inherit the scheduler settings from this
-       * very thread and whose only purpose is to spawn new threads with the
-       * same settings for use by the non-exclusive thread-pools.
-       *
-       *
-       * For non-exclusive thread-pools this is not required as all threads
-       * are created immediately below and are running forever, so they will
-       * automatically inherit the scheduler settings from this very thread.
-       */
-      if (!exclusive)
+
+  /* For the very first non-exclusive thread-pool we remember the thread
+   * scheduler settings of the thread creating the pool, if supported by
+   * the GThread implementation. This is then used for making sure that
+   * all threads created on the non-exclusive thread-pool have the same
+   * scheduler settings, and more importantly don't just inherit them
+   * from the thread that just happened to push a new task and caused
+   * a new thread to be created.
+   *
+   * Not doing so could cause real-time priority threads or otherwise
+   * threads with problematic scheduler settings to be part of the
+   * non-exclusive thread-pools.
+   *
+   * If this is not supported by the GThread implementation then we here
+   * start a thread that will inherit the scheduler settings from this
+   * very thread and whose only purpose is to spawn new threads with the
+   * same settings for use by the non-exclusive thread-pools.
+   *
+   *
+   * For non-exclusive thread-pools this is not required as all threads
+   * are created immediately below and are running forever, so they will
+   * automatically inherit the scheduler settings from this very thread.
+   */
+  if (!exclusive && !have_shared_thread_scheduler_settings && !spawn_thread_queue)
+    {
+      if (g_thread_get_scheduler_settings (&shared_thread_scheduler_settings))
         {
-          if (g_thread_get_scheduler_settings (&shared_thread_scheduler_settings))
-            {
-              have_shared_thread_scheduler_settings = TRUE;
-            }
-          else
-            {
-              spawn_thread_queue = g_async_queue_new ();
-              g_cond_init (&spawn_thread_cond);
-              g_thread_new ("pool-spawner", g_thread_pool_spawn_thread, NULL);
-            }
+          have_shared_thread_scheduler_settings = TRUE;
+        }
+      else
+        {
+          spawn_thread_queue = g_async_queue_new ();
+          g_cond_init (&spawn_thread_cond);
+          g_thread_new ("pool-spawner", g_thread_pool_spawn_thread, NULL);
         }
     }
   G_UNLOCK (init);