Transitional Permissions

To complete our three-part series on permissions, which began with Race-Safe Strategies, let’s talk about the transitional nature of reference permissions. When are permissions transitional? When we can safely create a copy of a reference which has a different permission than the reference it copied from. There are several ways in which this can happen, which this diagram summarizes (and the following sections explain): The following sections describe the nature of several one-way transitions that flow downward in the diagram.

Race-Safe Strategies

I recently made the observation that many people seem unaware of the full collection of constraint mechanisms available for protecting race safety. Someone sensibly asked for a link to an article that provides a modern, comprehensive review. It turns out that the pickings are very slim; the best I could find is this Wikipedia article on thread safety. It’s accurate, but incomplete. To close that gap, let me take a stab here at more comprehensive treatment.

The IR Tree: The INode Interface

Having spoken about the compiler’s IR tree in general terms, let’s focus in on an important detail: how to represent a node that could be any arbitary type. Cone’s IR makes use of dozens of different types of nodes, each defined using a different struct. However, sometimes the compiler needs to point to a node without restricting which type of node it must be. For example, consider an assignment node.

Gradual Memory Management

Realtime, quality 3D is punishing on hardware and software alike. At least every 17 milliseconds, the scene needs to be updated and redrawn. Managing memory efficiently across the many large and small data structures that make up an interesting 3D scene is a well-known and important part of that challenge.