mask, catch, myThreadId, throwTo
Felipe Almeida Lessa
felipe.lessa at gmail.com
Tue Apr 16 23:27:15 CEST 2013
Nice, thanks, Edward =).
On Tue, Apr 16, 2013 at 6:20 PM, Edward Z. Yang <ezyang at mit.edu> wrote:
> OK, I've updated the docus.
> Excerpts from Felipe Almeida Lessa's message of Mon Apr 15 13:34:50 -0700 2013:
>> Thanks a lot, you're correct! The trouble is, I was misguided by the
>> "Interruptible operations" note  which states that
>> The following operations are guaranteed not to be interruptible:
>> ... * everything from Control.Exception ...
>> Well, it seems that not everything from Control.Exception fits the bill.
>> Thanks, =)
>>  http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Exception.html#g:14
>> On Mon, Apr 15, 2013 at 5:25 PM, Bertram Felgenhauer
>> <bertram.felgenhauer at googlemail.com> wrote:
>> > Felipe Almeida Lessa wrote:
>> >> I have some code that is not behaving the way I thought it should.
>> >> The gist of it is
>> >> sleeper =
>> >> mask_ $
>> >> forkIOWithUnmask $ \restore ->
>> >> forever $
>> >> restore sleep `catch` throwBack
>> >> throwBack (Ping tid) = myThreadId >>= throwTo tid . Pong
>> >> throwBack (Pong tid) = myThreadId >>= throwTo tid . Ping
>> >> Since (a) throwBack is executed on a masked state, (b) myThreadId is
>> >> uninterruptible, and (c) throwTo is uninterruptible, my understanding
>> >> is that the sleeper thread should catch all PingPong exceptions and
>> >> never let any one of them through.
>> > (c) is wrong, throwTo may block, and blocking operations are interruptible.
>> > http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Exception.html#v:throwTo
>> > explains this in some more detail.
>> > The simplest way that throwTo can actually block in your program, as
>> > far as I can see, and one that will only affect the threaded RTS, is
>> > if the sleeper thread and whichever thread is running the other
>> > throwBack are executing on different capabilities; this will always
>> > cause throwTo to block. (You could try looking at a ghc event log to
>> > find out more.)
>> > I last ran into trouble like that with System.Timeout.timeout; for
>> > that function I finally convinced myself that uninterruptibleMask
>> > is the only way to avoid such problems; then throwTo will not be
>> > interrupted by exceptions even when it blocks. Maybe this is the
>> > solution for your problem, too.
>> > Hope that helps,
>> > Bertram
>> > _______________________________________________
>> > Glasgow-haskell-users mailing list
>> > Glasgow-haskell-users at haskell.org
>> > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
More information about the Glasgow-haskell-users