[GHC] #12347: Parallel make should eagerly report when compilation of a module starts

[GHC]

#12347: Parallel make should eagerly report when compilation of a module starts
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           Reporter:  ezyang         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Steps to reproduce:

 1. Create a small project which has some parallelism, but the individual
 files take some time to compile. For my testing, I used the module from
 https://ghc.haskell.org/trac/ghc/ticket/9630#comment:22 and set things up
 so that I had:

 {{{
 -- A.hs
 -- contents of #9630 test-case
 -- B.hs
 -- contents of #9630 test-case
 -- C.hs
 -- contents of #9630 test-case
 -- All.hs
 module All where
 import A
 import B
 import C
 }}}

 2. Run `ghc --make All A B C -j4 +RTS -N4`

 Expected results: GHC immediately reports that it is building `A`, `B`,
 and `C`; some time later `All` begins compiling.

 Actual results: Only one module is reported at first; only after it
 completes are the rest reported (quickly!)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12347>
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