Building a lower-latency GC
Sounds like amazing work is happening here.For real time user applications such as games, newsfeeds, and mobile apps that have visual/audio feedback, I'm certain that the most important feature is the ability to have applications themselves control the process of collecting and the time constraints to operate within. It is possible to have a collector that is less efficient, but be entirely perceived to be more responsive as long as the wasteful or less efficient work is done at times when it does not matter - and this tradeoff would be gladly welcomed.So much of UI application time is idle. Even during fluid animations, the majority of the frame time goes wasted. But then something like Objective-C's ARC frees large trees of memory, or perhaps Java's GC collects, and causes your frame time to exceed 16ms. For UI applications, there are periods of time (during animations) where you must hit 16ms deadlines, and the difference between 1ms and 15ms is nothing, but the difference between 16ms and 17ms is everything. UI application animations are like train schedules. If you miss one train by only a microsecond, you still have to wait the entire time until the next train arrives. You don't get points for almost making the train. Furthermore, only the application can know the train schedule. It isn't something the language runtime can possibly know, so to do this right, the language must anticipate this and accept input from the application frameworks.Then there are other times when we are not performing an animation and we know that we could block a thread for as much as 50ms, without having any perceived delay experienced by the user. The latency constraints for starting a continuous interaction are larger than the constraints for continuing a continuous interaction. So in this case, our application still knows the train schedule, it's just a different train schedule that allows for more time to kill. If applications could tell the GC about this, it might decide that it's a good time to perform a major collection.I've found that many of what people consider to be performance problems in UI applications aren't problems of efficiency, they're problems of scheduling.