[Bf-blender-cvs] [754630cee4f] blender-v2.79a-release: Fix T52823: New Depsgraph - Shrinkwrap crashes blender

[Sergey Sharybin]

Commit: 754630cee4fec23fc407876b5199c40ea892e8c3
Author: Sergey Sharybin
Date:   Tue Sep 19 16:09:35 2017 +0500
Branches: blender-v2.79a-release
https://developer.blender.org/rB754630cee4fec23fc407876b5199c40ea892e8c3

Fix T52823: New Depsgraph - Shrinkwrap crashes blender

The issue was caused by threading conflict around looptris: it was possible
that DM will return non-NULL but non-initialized array of looptris.

Thanks Campbell for second pair of eyes!

===================================================================

M       source/blender/blenkernel/intern/DerivedMesh.c

===================================================================

diff --git a/source/blender/blenkernel/intern/DerivedMesh.c 
b/source/blender/blenkernel/intern/DerivedMesh.c
index 58ce00f2fdb..ace79f4125b 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.c
+++ b/source/blender/blenkernel/intern/DerivedMesh.c
@@ -94,7 +94,7 @@ static DerivedMesh 
*navmesh_dm_createNavMeshForVisualization(DerivedMesh *dm);
 #endif
 
 
-static ThreadMutex loops_cache_lock = BLI_MUTEX_INITIALIZER;
+static ThreadRWMutex loops_cache_lock = PTHREAD_RWLOCK_INITIALIZER;
 
 
 static void add_shapekey_layers(DerivedMesh *dm, Mesh *me, Object *ob);
@@ -241,19 +241,26 @@ static int dm_getNumLoopTri(DerivedMesh *dm)
 
 static const MLoopTri *dm_getLoopTriArray(DerivedMesh *dm)
 {
-       if (dm->looptris.array) {
+       MLoopTri *looptri;
+
+       BLI_rw_mutex_lock(&loops_cache_lock, THREAD_LOCK_READ);
+       looptri = dm->looptris.array;
+       BLI_rw_mutex_unlock(&loops_cache_lock);
+
+       if (looptri != NULL) {
                BLI_assert(dm->getNumLoopTri(dm) == dm->looptris.num);
        }
        else {
-               BLI_mutex_lock(&loops_cache_lock);
+               BLI_rw_mutex_lock(&loops_cache_lock, THREAD_LOCK_WRITE);
                /* We need to ensure array is still NULL inside mutex-protected 
code, some other thread might have already
                 * recomputed those looptris. */
                if (dm->looptris.array == NULL) {
                        dm->recalcLoopTri(dm);
                }
-               BLI_mutex_unlock(&loops_cache_lock);
+               looptri = dm->looptris.array;
+               BLI_rw_mutex_unlock(&loops_cache_lock);
        }
-       return dm->looptris.array;
+       return looptri;
 }
 
 static CustomData *dm_getVertCData(DerivedMesh *dm)

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