Updates to FFI spec: performGC

[Manuel M T Chakravarty]

Alastair Reid <alastair at reid-consulting-uk.ltd.uk> wrote,

> George Russell <ger at tzi.de> writes:
> > Also there are probably hard-real-time GC algorithms (like Baker's
> > treadmill) or algorithms which are close to being hard-real-time
> > (like the train algorithm) where doing a "full GC" would be a major
> > pain.
> 
> The desired property is that the runtime system releases all
> unreachable objects.  

I like that phrase, so I put

  Finally, \code{hs\_perform\_gc()} advices the Haskell
  storage manager to perform a garbage collection, where the
  storage manager makes an effort to releases all
  unreachable objects.  This function must not be invoked
  from C functions that are imported \code{unsafe} into
  Haskell code nor may it be used from a finalizer.

into the spec.  It's signals the intent, but still leaves an
implementation some freedom.

Manuel