#10414: Buggy behavior with threaded runtime (-N1 working, -N2 getting into <<loop>>) -------------------------------------+------------------------------------- Reporter: exio4 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by rwbarton): The actual cause of the <<loop>> here seems to be that two threads are each blocking on a black hole that is being evaluated, or more likely has been evaluated but not updated, by the other thread. I attached a complete `-Ds` log above, but the relevant lines are {{{ ... 0.011574 7ff6be7fc700: cap 1: thread 6 stopped (blocked on black hole owned by thread 5) ... 0.011808 7ff6c6700740: cap 0: thread 5 stopped (blocked on black hole owned by thread 6) ... }}} I didn't work out exactly how this can arise, but it probably involves two single-entry thunks and two ordinary thunks whose evaluations force both of the single-entry thunks, but in different orders. Changing `blackHoleOnEntry` for single-entry thunks as suggested did fix `par2.hs`. I'm going to test the other examples in this ticket now. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10414#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler