Fix race conditions caused by Array <-> GLBufferObject interactions (Bug #3580)

The first part of the fix is to assign VBO/EBO's upon loading the array in the Nif reader. This avoids triggering the 'addVertexBufferObjectIfRequired' code path in osg::Geometry which has the race condition when two threads add the same Array at the same time. Essentially, we want the Arrays to be 'const' when they come out of the Nif reader.

The second part of the fix is to make sure not to create empty arrays in the Nif reader (importantly, not assigning a VBO to the empty array). This empty array would be deleted when the NIFFile is cleaned up, and the detachment of the VBO assigned to it (which is still in use by other arrays) would cause threading issues.

This rare crash bug was first introduced with commit a7c5beb7c5. When using OSG dev version 3.5 the crashes were a little more prevalent, because 'addVertexBufferObjectIfRequired' in osg::Geometry is now used even when VBO's are disabled (as part of the VAO support changes).

components/nif/data.cpp

@@ -40,32 +40,45 @@ void ShapeData::read(NIFStream *nif)
 {
     int verts = nif->getUShort();
 
-    vertices = new osg::Vec3Array;
-    if(nif->getInt())
+    // Assign a VBO right off the bat to avoid race conditions later, in case two threads load this data into a Geometry at the same time
+    osg::ref_ptr<osg::VertexBufferObject> vbo = new osg::VertexBufferObject;
+
+    if(nif->getInt() && verts)
+    {
+        vertices = new osg::Vec3Array;
         nif->getVector3s(vertices, verts);
+        vertices->setVertexBufferObject(vbo);
+    }
 
-    normals = new osg::Vec3Array(osg::Array::BIND_PER_VERTEX);
-    if(nif->getInt())
+    if(nif->getInt() && verts)
+    {
+        normals = new osg::Vec3Array(osg::Array::BIND_PER_VERTEX);
         nif->getVector3s(normals, verts);
+        normals->setVertexBufferObject(vbo);
+    }
 
     center = nif->getVector3();
     radius = nif->getFloat();
 
-    colors = new osg::Vec4Array(osg::Array::BIND_PER_VERTEX);
-    if(nif->getInt())
+    if(nif->getInt() && verts)
+    {
+        colors = new osg::Vec4Array(osg::Array::BIND_PER_VERTEX);
         nif->getVector4s(colors, verts);
+        colors->setVertexBufferObject(vbo);
+    }
 
     // Only the first 6 bits are used as a count. I think the rest are
     // flags of some sort.
     int uvs = nif->getUShort();
     uvs &= 0x3f;
 
-    if(nif->getInt())
+    if(nif->getInt() && verts)
     {
         uvlist.resize(uvs);
         for(int i = 0;i < uvs;i++)
         {
             osg::Vec2Array* list = uvlist[i] = new osg::Vec2Array(osg::Array::BIND_PER_VERTEX);
+            list->setVertexBufferObject(vbo);
             nif->getVector2s(list, verts);
 
             // flip the texture coordinates to convert them to the OpenGL convention of bottom-left image origin
@@ -86,8 +99,14 @@ void NiTriShapeData::read(NIFStream *nif)
     // We have three times as many vertices as triangles, so this
     // is always equal to tris*3.
     int cnt = nif->getInt();
-    triangles = new osg::DrawElementsUShort(osg::PrimitiveSet::TRIANGLES);
-    nif->getUShorts(triangles, cnt);
+    if (cnt)
+    {
+        triangles = new osg::DrawElementsUShort(osg::PrimitiveSet::TRIANGLES);
+        nif->getUShorts(triangles, cnt);
+
+        // Assign an EBO right off the bat to avoid race conditions later, in case two threads load this data into a Geometry at the same time
+        triangles->setElementBufferObject(new osg::ElementBufferObject);
+    }
 
     // Read the match list, which lists the vertices that are equal to
     // vertices. We don't actually need need this for anything, so

components/nifbullet/bulletnifloader.cpp

@@ -268,7 +268,9 @@ void BulletNifLoader::handleNiTriShape(const Nif::NiTriShape *shape, int flags,
 
     if (shape->data.empty())
         return;
-    if (shape->data->triangles->empty())
+
+    const Nif::NiTriShapeData *data = shape->data.getPtr();
+    if (!data->triangles || !data->vertices)
         return;
 
     if (isAnimated)
@@ -278,8 +280,6 @@ void BulletNifLoader::handleNiTriShape(const Nif::NiTriShape *shape, int flags,
 
         btTriangleMesh* childMesh = new btTriangleMesh();
 
-        const Nif::NiTriShapeData *data = shape->data.getPtr();
-
         childMesh->preallocateVertices(data->vertices->size());
         childMesh->preallocateIndices(data->triangles->size());
 
@@ -320,7 +320,6 @@ void BulletNifLoader::handleNiTriShape(const Nif::NiTriShape *shape, int flags,
             mStaticMesh = new btTriangleMesh(false);
 
         // Static shape, just transform all vertices into position
-        const Nif::NiTriShapeData *data = shape->data.getPtr();
         const osg::Vec3Array& vertices = *data->vertices;
         const osg::DrawElementsUShort& triangles = *data->triangles;
 

components/nifosg/nifloader.cpp

@@ -894,6 +894,10 @@ namespace NifOsg
 
             osg::BoundingBox box;
 
+            osg::Vec3Array* verts = particledata->vertices;
+            if (!verts)
+                return;
+
             int i=0;
             for (std::vector<Nif::NiParticleSystemController::Particle>::const_iterator it = partctrl->particles.begin();
                  i<particledata->activeCount && it != partctrl->particles.end(); ++it, ++i)
@@ -908,11 +912,11 @@ namespace NifOsg
                 // Note this position and velocity is not correct for a particle system with absolute reference frame,
                 // which can not be done in this loader since we are not attached to the scene yet. Will be fixed up post-load in the SceneManager.
                 created->setVelocity(particle.velocity);
-                const osg::Vec3f& position = particledata->vertices->at(particle.vertex);
+                const osg::Vec3f& position = verts->at(particle.vertex);
                 created->setPosition(position);
 
                 osg::Vec4f partcolor (1.f,1.f,1.f,1.f);
-                if (particle.vertex < int(particledata->colors->size()))
+                if (particledata->colors.valid() && particle.vertex < int(particledata->colors->size()))
                     partcolor = particledata->colors->at(particle.vertex);
 
                 float size = particledata->sizes.at(particle.vertex) * partctrl->size;
@@ -1074,7 +1078,7 @@ namespace NifOsg
 
             geometry->setVertexArray(data->vertices);
 
-            if (!data->normals->empty())
+            if (data->normals)
                 geometry->setNormalArray(data->normals);
 
             int textureStage = 0;
@@ -1092,10 +1096,10 @@ namespace NifOsg
                 geometry->setTexCoordArray(textureStage, data->uvlist[uvSet]);
             }
 
-            if (!data->colors->empty())
+            if (data->colors)
                 geometry->setColorArray(data->colors);
 
-            if (!data->triangles->empty())
+            if (data->triangles)
                 geometry->addPrimitiveSet(data->triangles);
 
             // osg::Material properties are handled here for two reasons:
@@ -1104,7 +1108,7 @@ namespace NifOsg
             //   above the actual renderable would be tedious.
             std::vector<const Nif::Property*> drawableProps;
             collectDrawableProperties(triShape, drawableProps);
-            applyDrawableProperties(parentNode, drawableProps, composite, !data->colors->empty(), animflags, false);
+            applyDrawableProperties(parentNode, drawableProps, composite, data->colors.valid(), animflags, false);
         }
 
         void handleTriShape(const Nif::NiTriShape* triShape, osg::Group* parentNode, SceneUtil::CompositeStateSetUpdater* composite, const std::vector<int>& boundTextures, int animflags)