7.4. Update Points

Update points are automatically inserted in points of execution in the original program that guarantee immediate updates. They are inserted in the beginning of each function (inside the function), and the beginning of each loop (inside the loop). The capability to update, if needed, at each iteration of a long-running loop makes it possible to dynamically update programs from one algorithm to another while taking advantage of the progress of the older algorithm.

A more aggressive transformation could insert update points in each basic block at the source-code level. However, there would be little benefit in this approach since function calls and loops are encountered sufficiently often to render update points in other basic blocks, like if-then-else and switch statements, unnecessary.

It is possible to have update points selectively activated or disabled. The application programmer can specify when requesting an update which update points should affect the update (e.g., all except points 250-259 and 262) and this information is stored in the dynamic updating runtime. This empowers the programmer to use the updating mechanism to enforce additional general safety. After an update is applied, all update points are disengaged. The current implementation is restricted to a coarse-grain activation of update points by using a single must_update flag, but we plan to support more fine-grain selective activation.