> I'm starting to use threads with my OCaml-Win32 library, and I'd like to
> annotate it with appropriate calls to enter_blocking_section and
> leave_blocking_section.  Clearly, if I make a call to a Win32 API function
> that may take some time, I'll surround the call with enter_blocking_section
> / leave_blocking_section.  But what if that function may make a callback to
> my own code, which may in turn pass control back to OCaml?

I believe the solution you outline in your message is correct:

> LRESULT window_proc(...)
> {
>     leave_blocking_section();
>     callback(...); // call OCaml window proc
>     enter_blocking_section();
> }
> 
> Obviously I'll need to guarantee that whenever window_proc is called, it
> happens during a blocking section.

Agreed.  Moreover, you should make sure that window_proc is always
called from a thread that was created by Caml, and not some other
thread created by the system.  (I don't believe Windows message
handling creates such extra threads, though.)

- Xavier Leroy
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