On 22 June 2004 06:11, Bernard James POPE wrote:
Ideally I'd like this function:
blockThread :: ThreadId -> IO ()
and thus:
unBlockThread :: ThreadId -> IO ()
Hmm, might be possible. Can the blocked thread be woken up by an exception? (this is usually the case for blocked threads). Note that if you block a thread and then drop all references to it, the garbage collector will wake up the thread with a BlockedOnDeadMVar exception. I think I'd be tempted to call these functions {stop,continue}Thread to avoid overloading the block/unblock terms any more. Stop/continue is used in Unix land too. To implement this you'll need another StgTSOBlockReason state for stopped threads. Stopping already blocked threads might not be a problem, since (in some cases at least) the blocking operation will be retried when the thread is started again. I'm not sure whether this is always the case though. Stopping a thread blocked on a foreign call cannot be done. Stopping a thread blocked on I/O or delay# will need to remove the thread from the appropriate queue. You'll need two new primops: stopThread#, continueThread#. Take a look at the implementation of killThread# for clues (in ghc/rts/Exception.hc). Don't forget to take into account the case when a thread stops itself (that's the tricky one). Let us know if you need any more guidance... Cheers, Simon