Alastair Reid wrote:
Design ~~~~~~
Haskell threads may be associated at thread creation time with either zero or one native threads. There are only two ways to create Haskell threads so there are two cases to consider:
Umm, Alastair, I think you've got things a bit mixed up here. Did you mean two ways to create a native thread? There are currently three ways to create a Haskell thread (forkIO, foreign export, finalizers) and Wolfgang has proposed a fourth (forkNativeThread). Or perhaps you're proposing we do away with forkIO and only have forkNativeThread? That was discounted a while back because we want to continue to have light-weight threads independent of OS threads.
1) forkNativeThread :: IO () -> IO ()
The fresh Haskell thread is associated with a fresh native thread.
(ToDo: do we really need to use a fresh native thread or would a pool of threads be ok? The issue could be avoided by separating creation of the native thread from the 'associate' operation.)
2) Calls to a threadsafe foreign export allocate a fresh Haskell thread which is then associated with the Haskell thread.
I don't know what you mean by a "threadsafe foreign export". Did you mean "threadsafe foreign import" perhaps? And I'm not sure how a fresh Haskell thread is associated with a Haskell thread ;-)
Calls to threadsafe foreign imports by threads which have an associated native thread are performed by that native thread.
Calls to any other foreign imports (i.e., 'safe' or 'unsafe' calls) may be made in other threads or, if it exists, in the associated native thread at the implementation's discretion.
[ToDo: can Haskell threads with no associated thread make foreign calls using a thread associated with some other thread?
er... overloading the word "thread" was maybe not such a good idea. I think you're asking whether a green thread can grab a native thread to make a foreign call. The current answer is no... but can you think of a reason we might want this feature? Cheers, Simon