Gunnar Holm, "After upgrading from 2.8.3 to 3.0.1 we experienced a lock in the Mutex

functionality when using Terrain::setVerticalScale. This was caused by
the following call sequence resulting in a lockup:

void Terrain::setVerticalScale(float scale)
  CALLS    dirtyRegisteredTiles();


void Terrain::dirtyRegisteredTiles(int dirtyMask)
 SETS LOCK    OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_mutex);
 and CALLS (on every tile)   setDirtyMask(dirtyMask);


void TerrainTile::setDirtyMask(int dirtyMask)
 CALLS _terrain->updateTerrainTileOnNextFrame(this);


void Terrain::updateTerrainTileOnNextFrame(TerrainTile* terrainTile)
 SETS LOCK   OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_mutex);
******* PROBLEM - since lock has already been set! ********


The suggested fix submitted changes from using Mutex to ReentrantMutex.
"

include/osgTerrain/Terrain

@@ -15,6 +15,7 @@
 #define OSGTerrain 1
 
 #include <osg/CoordinateSystemNode>
+#include <OpenThreads/ReentrantMutex>
 
 #include <osgTerrain/TerrainTile>
 
@@ -109,7 +110,7 @@ class OSGTERRAIN_EXPORT Terrain : public osg::CoordinateSystemNode
         TerrainTile::BlendingPolicy         _blendingPolicy;
         bool                                _equalizeBoundaries;
 
-        mutable OpenThreads::Mutex          _mutex;
+        mutable OpenThreads::ReentrantMutex _mutex;
         TerrainTileSet                      _terrainTileSet;
         TerrainTileMap                      _terrainTileMap;
         TerrainTileSet                      _updateTerrainTileSet;