[GHC] #13452: Lock .tix file

[GHC]

#13452: Lock .tix file
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Code Coverage     |              Version:  8.0.1
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Indeed file locking is non-trivial, as our experiences with #13194 has
 taught us. If HPC records were written by Haskell code then we could
 simply piggy-back on the file locking interfaces in `base`. However, this
 isn't the case; `tix` files are written by the RTS. One option would be to
 change this, implementing the tix I/O bits in Haskell. Another would be to
 introduce file locking logic into the RTS.

 Regardless of how the locking itself will be implemented, the real
 question is how contention will be dealt with without either losing
 samples from one of the processes or causing one of the processes to
 block. It seems to me like this will likely require some refactoring of
 how TIX samples are read/accumulated/written; IIRC they are currently read
 by the RTS during startup, accumulated as the program runs, and written
 during shutdown.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13452#comment:4>
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