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();
+	
 	
 	
 	//==============//
@@ -142,14 +153,27 @@ public class GLBuffer implements AutoCloseable
 			return;
 		}
 		
-		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
-		// where the queued on render thread task runs before the ID is cleared
-		this.id = 0;
-		this.size = 0;
+		long writeStamp = 0;
+		try
+		{
+			// lock to prevent the render thread from accessing the buffer's ID
+			// while we are removing it
+			writeStamp = renderStampLock.writeLock();
 			
-		RenderThreadTaskHandler.INSTANCE.queueRunningOnRenderThread("GLBuffer destroyAsync", () -> { destroyBufferIdNow(idToDelete); });
+			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
+			// where the queued on render thread task runs before the ID is cleared
+			this.id = 0;
+			this.size = 0;
+			
+			RenderThreadTaskHandler.INSTANCE.queueRunningOnRenderThread("GLBuffer destroyAsync", () -> { destroyBufferIdNow(idToDelete); });
+		}
+		finally
+		{
+			renderStampLock.unlock(writeStamp);
+		}
 	}
 	private static void destroyBufferIdNow(int id)
 	{

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

@@ -341,33 +341,45 @@ public class GlDhTerrainShaderProgram extends GlShaderProgram implements IDhApiS
 						continue;
 					}
 					
-					// don't render empty sections
-					if (vbo.getVertexCount() == 0)
+					
+					// for lock information please view the lock's javadocs
+					long vboReadStamp = vbo.renderStampLock.readLock();
+					long iboReadStamp = vbo.getQuadIBO().renderStampLock.readLock();
+					try
 					{
-						continue;
-					}
+						// don't render empty sections
+						if (vbo.getVertexCount() == 0)
+						{
+							continue;
+						}
 						
-					// don't render deleted VBOs (this will crash the driver/game)
-					if (vbo.getId() == 0
-						|| vbo.getQuadIBO().getId() == 0)
+						// don't render deleted VBOs (this will crash the driver/game)
+						if (vbo.getId() == 0
+							|| vbo.getQuadIBO().getId() == 0)
+						{
+							continue;
+						}
+						
+						// 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);
+						
+						vbo.bind();
+						vbo.getQuadIBO().bind();
+						
+						GlDhMetaRenderer.INSTANCE.shaderProgramForThisFrame.bindVertexBuffer(vbo.getId());
+						GL32.glDrawElements(
+							GL32.GL_TRIANGLES,
+							indexCount,
+							vbo.getQuadIBO().getGlType(), 0);
+						
+						vbo.unbind();
+						vbo.getQuadIBO().unbind();
+					}
+					finally
 					{
-						continue;
+						vbo.renderStampLock.unlock(vboReadStamp);
+						vbo.getQuadIBO().renderStampLock.unlock(iboReadStamp);
 					}
-					
-					// 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);
-					
-					vbo.bind();
-					vbo.getQuadIBO().bind();
-					
-					GlDhMetaRenderer.INSTANCE.shaderProgramForThisFrame.bindVertexBuffer(vbo.getId());
-					GL32.glDrawElements(
-						GL32.GL_TRIANGLES,
-						indexCount,
-						vbo.getQuadIBO().getGlType(), 0);
-					
-					vbo.unbind();
-					vbo.getQuadIBO().unbind();
 				}
 			}
 		}