Xavier's first sentence states that they two operating systems have a visibly different philosophy, not that one is better than the other. The second sentence should be interpreted in the context of this first sentence: if you try to emulate Unix's primitive with Windows', and especially if you want to do this and write a user-level scheduler that does not occasionally deadlock without reason, you will get stuck in a couple of places.

This doesn't mean that Windows' philosophy does not give you optimal performance in PyParallel. It simply means that OCaml had chosen for its low-level system primitives a Unix model and that it was difficult to make a Windows version of the same primitives so that OCaml programmers could write this kind of program portably between Windows and Unix.

NOTE: without, at the time it is in my timezone, looking up the full post, I have to say that I don't think that the quoted two sentences have anything to do with the discussion. It seems to me that the two sentences assume that a multicore (multiprocessor, at the time the post was written) OCaml runtime is not available, and discusses the options to still provide threads. A user-level scheduler is one option to provide threads to OCaml programs without a concurrent OCaml runtime. Another option is to use Windows' native threads and superior philosophy for blocking primitives to run each OCaml thread as a native thread (although at most one of these will be running at any given time. All the others will be waiting on the heap mutex).

OCaml ended up providing threads under Windows and a Unix-like “Unix” module around 1996-ish, way before the linked discussion. So thanks for the explanation about VMS, but I think it is off-topic, too.

NOTE 2: I have now read the original post. You should, too. It starts with:

> Threads have at least three different purposes:

>

> 1- Parallelism on shared-memory multiprocessors.

> 2- Overlapping I/O and computation (while a thread is blocked on a network

> read, other threads may proceed).

>3- Supporting the "coroutine" programming style

> (e.g. if a program has a GUI but performs long computations,

> using threads is a nicer way to structure the program than

> trying to wrap the long computation around the GUI event loop).

>

> The goals of OCaml threads are (2) and (3) but not (1) (for reasons

> that I'll get into later)

What makes it relevant to the current discussion is (1), but Xavier is discussing (2) and (3) at the time of the quote you chose to take out of context.