Future Protections in Managed Languages and Runtimes

Question

In the future, will managed runtimes provide additional protections against subtle data corruption issues?

Managed runtimes such as Java and the .NET CLR reduce or eliminate the possibility of many memory corruption bugs common in native languages like C#. Nonetheless, they are surprisingly not immune from all memory corruption problems. One intuitively expects that a method that validates its input, has no bugs, and robustly handles exceptions will always transform its object from one valid state to another, but this is not the case. (It is more accurate to say that it is not the case using prevailing programming conventions--object implementors need to go out of their way to avoid the problems I describe.)

Consider the following scenarios:

1. Threading. The caller might share the object with other threads and make concurrent calls on it. If the object does not implement locking, the fields might be corrupted. (Perhaps--unless notified that the object is thread-safe--runtimes should use an interlock on every method call to throw an exception if any method on the same object executing concurrently on another thread. This would be a protection feature and, just like other well-accepted safety features of managed runtimes, it has some cost.)

2. Re-entrancy. The method makes a callout to an arbitrary function (such as an event handler) that ultimately calls methods on the object that are not designed to be called at that point. This is even trickier than thread safety and many class libraries do not get this right. (Worse yet, class libraries are known to poorly document what re-entrancy is allowed.)

For all of these cases, it can be argued that thorough documentation is a solution. However, documentation also can prescribe how to allocate and deallocate memory in unmanaged languages. We know from experience (e.g., with memory allocation) that the difference between documentation and language/runtime enforcement is night and day.

What can we expect from languages and runtimes in the future to protect us from these problems and other subtle problems like them?

Answer 1

I think languages and runtimes will keep moving forward, keep abstracting away issues from the developer, and keep making our lives easier and more productive.

Take your example - threading. There are some great new features on the horizon in the .NET world to simplify the threading model we use daily. STM.NET may eventually make shared state much, much safer to handle, for example. The parallel extensions in .NET 4 make life very easy for threading compared to current technologies.

Answer 2

What can we expect in the future?

Nothing. Thread-state and re-entrancy are not problems I see tools/runtimes solving. Instead I think in the future people will move to styles that avoid programming with mutable state to bypass these issues. Languages and libraries can help make these styles of programming more attractive, but the tools are not the solution - changing the way we write code is the solution.

Answer 3

I think that transactional memory is promising for addressing some of these issues. I'm not sure if this answers your question in some way but this is an interesting topic in any event:

http://en.wikipedia.org/wiki/Software_transactional_memory

There was an episode of Software Engineering Radio on the topic a year or so ago maybe.

Answer 4

First of all, "managed" is a bit of a misnomer: languages like OCaml, Haskell, and SML achieve such protections and safety while being fully compiled. All relevant "management" occurs at compile time through static analysis, which aids optimization and speed.

Anyway, to answer your question: if you look at languages like Erlang and Haskell, state is isolated and immutable by default. With kind of system, threading and reentrancy is safe by default, and because you have to go out of your way to break these rules, it is obvious to see where unsafe code can arise.

By starting with safe defaults but leaving room for advanced unsafe usage, you get the best of both worlds. It seems reasonable that future systems that are safe by your definition may follow some of these practices as well.