[gimp] Bug 795385 - Segmentation fault when using gradient tool

[Michael Natterer <mitch src gnome org>]

commit e4f327eca838380868adc11a93d97b8d5bdf5d38
Author: Michael Natterer <mitch gimp org>
Date:   Fri Apr 20 12:31:04 2018 +0200

    Bug 795385 - Segmentation fault when using gradient tool
    
    We don't currently use GimpOperationGradient multi-threaded, but
    protect cache initialization in process() with a mutex anyway in cae
    we ever do.

 app/operations/gimpoperationgradient.c |    6 ++++++
 app/operations/gimpoperationgradient.h |    1 +
 2 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/app/operations/gimpoperationgradient.c b/app/operations/gimpoperationgradient.c
index f14f030..84e641a 100644
--- a/app/operations/gimpoperationgradient.c
+++ b/app/operations/gimpoperationgradient.c
@@ -315,6 +315,7 @@ gimp_operation_gradient_class_init (GimpOperationGradientClass *klass)
 static void
 gimp_operation_gradient_init (GimpOperationGradient *self)
 {
+  g_mutex_init (&self->gradient_cache_mutex);
 }
 
 static void
@@ -325,6 +326,7 @@ gimp_operation_gradient_dispose (GObject *object)
   g_clear_object (&self->gradient);
   g_clear_object (&self->context);
   g_clear_pointer (&self->gradient_cache, g_free);
+  g_mutex_clear (&self->gradient_cache_mutex);
 
   G_OBJECT_CLASS (parent_class)->dispose (object);
 }
@@ -995,6 +997,8 @@ gimp_operation_gradient_process (GeglOperation       *operation,
   if (! self->gradient)
     return TRUE;
 
+  g_mutex_lock (&self->gradient_cache_mutex);
+
   if (! self->gradient_cache_valid)
     {
       GimpGradientSegment *last_seg = NULL;
@@ -1029,6 +1033,8 @@ gimp_operation_gradient_process (GeglOperation       *operation,
       self->gradient_cache_valid = TRUE;
     }
 
+  g_mutex_unlock (&self->gradient_cache_mutex);
+
   rbd.gradient            = self->gradient;
   rbd.gradient_cache      = self->gradient_cache;
   rbd.gradient_cache_size = self->gradient_cache_size;
diff --git a/app/operations/gimpoperationgradient.h b/app/operations/gimpoperationgradient.h
index 5f29464..65a1288 100644
--- a/app/operations/gimpoperationgradient.h
+++ b/app/operations/gimpoperationgradient.h
@@ -59,6 +59,7 @@ struct _GimpOperationGradient
   GimpRGB                      *gradient_cache;
   gint                          gradient_cache_size;
   gboolean                      gradient_cache_valid;
+  GMutex                        gradient_cache_mutex;
 };
 
 struct _GimpOperationGradientClass