potential nvidia null VBO pointer crash fix

common/src/main/java/com/seibel/distanthorizons/common/render/openGl/glObject/buffer/GLBuffer.java

@@ -69,6 +69,17 @@ public class GLBuffer implements AutoCloseable
 	protected boolean bufferStorage;
 	protected boolean isMapped = false;
 	
+	/**
+	 * Locking on the render thread isn't great, but is needed due to an inconsistent
+	 * race condition where VBOs can be marked as deleted outside the render thread. <br><br>
+	 * 
+	 * But, due to being a read-write lock the chance of freezing
+	 * the render thread is very low
+	 * and since this is a stamped lock, the optimistic read time is basically zero.
+	 * (The optimistic lock time doesn't even appear in the profiler).
+	 */
+	public final StampedLock renderStampLock = new StampedLock();
+	
 	
 	
 	//==============//
@@ -142,6 +153,14 @@ public class GLBuffer implements AutoCloseable
 			return;
 		}
 		
+		
+		long writeStamp = 0;
+		try
+		{
+			// lock to prevent the render thread from accessing the buffer's ID
+			// while we are removing it
+			writeStamp = renderStampLock.writeLock();
+			
 			final int idToDelete = this.id; // saving the ID to a separate variable is necessary so it can be captured by the lambda
 			
 			// mark the old data is invalid before deleting to prevent a rare race condition
@@ -151,6 +170,11 @@ public class GLBuffer implements AutoCloseable
 			
 			RenderThreadTaskHandler.INSTANCE.queueRunningOnRenderThread("GLBuffer destroyAsync", () -> { destroyBufferIdNow(idToDelete); });
 		}
+		finally
+		{
+			renderStampLock.unlock(writeStamp);
+		}
+	}
 	private static void destroyBufferIdNow(int id)
 	{
 		// only delete valid buffers

common/src/main/java/com/seibel/distanthorizons/common/render/openGl/terrain/GlDhTerrainShaderProgram.java

@@ -341,6 +341,12 @@ public class GlDhTerrainShaderProgram extends GlShaderProgram implements IDhApiS
 						continue;
 					}
 					
+					
+					// for lock information please view the lock's javadocs
+					long vboReadStamp = vbo.renderStampLock.readLock();
+					long iboReadStamp = vbo.getQuadIBO().renderStampLock.readLock();
+					try
+					{
 						// don't render empty sections
 						if (vbo.getVertexCount() == 0)
 						{
@@ -355,7 +361,7 @@ public class GlDhTerrainShaderProgram extends GlShaderProgram implements IDhApiS
 						}
 						
 						// 4 vertices per face, but 6 indices (IE 2 triangles) per face, aka need to multiply by 1.5
-					int indexCount = (int)(vbo.getVertexCount() * 1.5);
+						int indexCount = (int) (vbo.getVertexCount() * 1.5);
 						
 						vbo.bind();
 						vbo.getQuadIBO().bind();
@@ -369,6 +375,12 @@ public class GlDhTerrainShaderProgram extends GlShaderProgram implements IDhApiS
 						vbo.unbind();
 						vbo.getQuadIBO().unbind();
 					}
+					finally
+					{
+						vbo.renderStampLock.unlock(vboReadStamp);
+						vbo.getQuadIBO().renderStampLock.unlock(iboReadStamp);
+					}
+				}
 			}
 		}