[gimp/gimp-2-10] app: flush async-operations queue when setting async thread count to 0

[Ell <ell src gnome org>]

commit bc312531fbd2c4a1dc9294f4cce57dfc8e5a8fe8
Author: Ell <ell_se yahoo com>
Date:   Sun Jul 15 04:58:29 2018 -0400

    app: flush async-operations queue when setting async thread count to 0
    
    In gimp-parallel, always flush the async-operations queue (by
    executing all remaining operations on the caller thread) when
    setting the async-pool thread count to 0 (as happens when setting
    GEGL_THREADS=1, per the previous commit,) and not only when
    shutting GIMP down.  Otherwise, pending asynchronous operations
    can "get lost" when setting GEGL_THREADS to 1.
    
    Additionally, in gimp_gegl_init(), initialize gimp-parallel before
    before connecting to GimpGeglConfig's "notify::num-processors"
    signal, so that the number of async threads is set *before*
    GEGL_THREADS, in order to avoid setting GEGL_THREADS to 1 while
    async operations are still executing.
    
    Also, allow setting the number of gimp-parallel-distribute threads
    while a gimp-parallel-distribute function is running (which can
    happen if gimp-parallel-distribute is used in an async operation,
    as is the case for histogram calculation), by waiting for the
    parallel-distribute function to finish before setting the number of
    threads.
    
    (cherry picked from commit 432a8847159c33c2aca89a18b519fb5aab4c398f)

 app/core/gimp-parallel.cc | 34 +++++++++++++++++-----------------
 app/gegl/gimp-gegl.c      |  4 ++--
 2 files changed, 19 insertions(+), 19 deletions(-)
---
diff --git a/app/core/gimp-parallel.cc b/app/core/gimp-parallel.cc
index 5846dadb05..46bdfd5600 100644
--- a/app/core/gimp-parallel.cc
+++ b/app/core/gimp-parallel.cc
@@ -140,8 +140,6 @@ gimp_parallel_init (Gimp *gimp)
 void
 gimp_parallel_exit (Gimp *gimp)
 {
-  GimpParallelRunAsyncTask *task;
-
   g_return_if_fail (GIMP_IS_GIMP (gimp));
 
   g_signal_handlers_disconnect_by_func (gimp->config,
@@ -150,16 +148,6 @@ gimp_parallel_exit (Gimp *gimp)
 
   /* stop all threads */
   gimp_parallel_set_n_threads (0);
-
-  /* finish remaining tasks */
-  while ((task = (GimpParallelRunAsyncTask *)
-                   g_queue_pop_head (&gimp_parallel_run_async_queue)))
-    {
-      g_object_set_data (G_OBJECT (task->async),
-                         "gimp-parallel-run-async-link", NULL);
-
-      gimp_parallel_run_async_execute_task (task);
-    }
 }
 
 GimpAsync *
@@ -521,6 +509,21 @@ gimp_parallel_run_async_set_n_threads (gint n_threads)
     }
 
   gimp_parallel_run_async_n_threads = n_threads;
+
+  if (n_threads == 0)
+    {
+      GimpParallelRunAsyncTask *task;
+
+      /* finish remaining tasks */
+      while ((task = (GimpParallelRunAsyncTask *)
+                       g_queue_pop_head (&gimp_parallel_run_async_queue)))
+        {
+          g_object_set_data (G_OBJECT (task->async),
+                             "gimp-parallel-run-async-link", NULL);
+
+          gimp_parallel_run_async_execute_task (task);
+        }
+    }
 }
 
 static gpointer
@@ -613,11 +616,8 @@ gimp_parallel_distribute_set_n_threads (gint n_threads)
 {
   gint i;
 
-  if (! g_atomic_int_compare_and_exchange (&gimp_parallel_distribute_busy,
-                                           0, 1))
-    {
-      g_return_if_reached ();
-    }
+  while (! g_atomic_int_compare_and_exchange (&gimp_parallel_distribute_busy,
+                                              0, 1));
 
   n_threads = CLAMP (n_threads, 1, GIMP_PARALLEL_DISTRIBUTE_MAX_THREADS);
 
diff --git a/app/gegl/gimp-gegl.c b/app/gegl/gimp-gegl.c
index 1a67d42c9f..af0c28efca 100644
--- a/app/gegl/gimp-gegl.c
+++ b/app/gegl/gimp-gegl.c
@@ -57,6 +57,8 @@ gimp_gegl_init (Gimp *gimp)
                 "use-opencl",      config->use_opencl,
                 NULL);
 
+  gimp_parallel_init (gimp);
+
   g_signal_connect (config, "notify::tile-cache-size",
                     G_CALLBACK (gimp_gegl_notify_tile_cache_size),
                     NULL);
@@ -67,8 +69,6 @@ gimp_gegl_init (Gimp *gimp)
                     G_CALLBACK (gimp_gegl_notify_use_opencl),
                     NULL);
 
-  gimp_parallel_init (gimp);
-
   gimp_babl_init ();
 
   gimp_operations_init (gimp);