These costs, though, are generally trivial compared to the lifecycle costs of dealing with multithreaded code. Isolation in processes greatly enhances debuggability, and it's almost impossible to produce a truly bug-free threaded program. Even a heavily tested threaded program will often break mysteriously when compiled with a different compiler/libraries, or even when seemingly irrelevant code changes are made. It's a tar pit.
Maybe, but, on Linux, processes and threads are almost the same thing.
Additionally, even where a process is a bit more expensive to create, it is not enough to block the UI thread from being responsive. I have first hand experience with this on different operating systems, including Windows, and it is more than fast enough to keep the UI completely responsive.
> and far more expensive and complex and restrictive to move data around.
Not necessarily. For threading, synchronization patterns are not necessarily simple. (This is why computer science instruction spend time on these principles.)
Furthermore, some languages and frameworks provide really nice IPC mechanisms. Apple's new XPC frameworks are pretty nice and make it pretty easy to do.
> Either the tasks aee broken into ridiculously fine-grained bits that are hard to make sense or keep track,or you still get a blocking UI.
As I mentioned, coroutines make this dirt easy. It principle, this doesn't have to be hard.
> Furthermore, the solution is computationally more expensive.
That doesn't really follow. The underlying task is the where the computation is. You are just moving it, either to a process, a thread, or dividing it up, or something else (e.g. send it to a server to process). At the end of the day, it is the same work, just moved.
Yes, you might need some state flags for breaking up the work, but threading also requires resources such as creating and running the thread, the locks and protecting your shared data, and so forth. There is no free lunch any way you do this.
If you do use a lot of CPU time, spawning a process instead of a thread might not have any noticeable impact at all.
Additionally, IPC isolates the process, meaning it can be more resistant to hostile takeover (if you drop privs correctly) and additionally you avoid any and all shared state that could possible result in unforeseen bugs.
More expensive to start than threads, and far more expensive and complex and restrictive to move data around. Sounds like with the exception of some specific corner cases, threads are a better solution.
> Another solution is break up the work and processing in increments
Either the tasks aee broken into ridiculously fine-grained bits that are hard to make sense or keep track,or you still get a blocking UI. Furthermore, the solution is computationally more expensive.