[GHC] #2028: STM slightly conservative on write-only transactions

[GHC]

#2028: STM slightly conservative on write-only transactions
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 Reporter:  JulesBean  |          Owner:         
     Type:  proposal   |         Status:  new    
 Priority:  normal     |      Milestone:         
Component:  Compiler   |        Version:  6.8.1  
 Severity:  normal     |     Resolution:         
 Keywords:             |     Difficulty:  Unknown
 Testcase:             |   Architecture:  Unknown
       Os:  Unknown    |  
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Comment (by simonpj):

 Comment from Tim Harris:

 This suggestion is OK from the point of view of correctness.

 There are several special cases where we could allow transactions to
 commit when we currently treat them as conflicting.  E.g. any single-word
 transaction is OK.

 I've avoided dealing with too many of these in the absence of code we care
 about performing badly (it'll add complexity and might slow down the
 hopefully-common case of non-conflicting transactions).

 No strong arguments against adding this one though: we could probably use
 a special value in the old-val field to indicate no-previous-value so we
 won't get a space code.  We could also handle it specially in "retry" --
 we don't need to watch for updates to a `TVar` that has been written to
 but not read.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2028#comment:1>
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