[GHC] #2786: Blackhole loops are not detected and reported in GHCi

[GHC]

#2786: Blackhole loops are not detected and reported in GHCi
---------------------------------+------------------------------------------
    Reporter:  simonmar          |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  normal            |   Milestone:  _|_             
   Component:  GHCi              |     Version:  6.8.3           
    Severity:  normal            |    Keywords:                  
  Difficulty:  Unknown           |    Testcase:                  
Architecture:  Unknown/Multiple  |          Os:  Unknown/Multiple
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 While looking into #2783 I noticed this.  It has never worked, and I was
 vaguely aware of it, but it seems we don't have a ticket.

 {{{
 let x = x in x
 }}}

 in GHCi should report `<<loop>>`.  One issue is that the
 `interruptTargetThread` global var points to the `ThreadId` running the
 expression, which will keep it alive and prevent it from being detected as
 deadlocked.  But that's not all: I think the expression itself is being
 retained by the main thread (perhaps because it is bound to `it`), which
 will cause the child thread to also stay alive.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2786>
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