The thing is : it isn't an "idea" at all. These projects ended up with a big lock, or not tolerating reentrancy due to history -- they were developed at a time, and in an environment where there were no threads (or where support for threads wasn't of interest to the developer). It's just a bug. Not an idea, not a benefit. All the talk of it being the best way is nonsense invented after the fact to try to justify something that's just broken.