-}
{- $blocking
-Calling a foreign C procedure (such as @getchar@) that blocks waiting
-for input will block /all/ threads, unless the @threadsafe@ attribute
-is used on the foreign call (and your compiler \/ operating system
-supports it). GHC's I\/O system uses non-blocking I\/O internally to
-implement thread-friendly I\/O, so calling standard Haskell I\/O
-functions blocks only the thread making the call.
+Different Haskell implementations have different characteristics with
+regard to which operations block /all/ threads.
+
+Using GHC without the @-threaded@ option, all foreign calls will block
+all other Haskell threads in the system, although I\/O operations will
+not. With the @-threaded@ option, only foreign calls with the @unsafe@
+attribute will block all other threads.
+
+Using Hugs, all I\/O operations and foreign calls will block all other
+Haskell threads.
-}
#ifndef __HUGS__
-- Bound Threads
{- $boundthreads
+ #boundthreads#
Support for multiple operating system threads and bound threads as described
below is currently only available in the GHC runtime system if you use the
Just to clarify, 'forkOS' is /only/ necessary if you need to associate
a Haskell thread with a particular OS thread. It is not necessary if
-you only need to make non-blocking foreign calls (see "Control.Concurrent#osthreads").
+you only need to make non-blocking foreign calls (see
+"Control.Concurrent#osthreads"). Neither is it necessary if you want
+to run threads in parallel on a multiprocessor: threads created with
+'forkIO' will be shared out amongst the running CPUs (using GHC,
+@-threaded@, and the @+RTS -N@ runtime option).
-}
forkOS :: IO () -> IO ThreadId
worker OS threads. If you need control over which particular OS
thread is used to run a given Haskell thread, perhaps because
you need to call a foreign library that uses OS-thread-local
- state, then you need "bound threads" (see above).
+ state, then you need bound threads (see "Control.Concurrent#boundthreads").
If you don't use the @-threaded@ option, then the runtime does
not make use of multiple OS threads. Foreign calls will block