Shared keyword and the GC?

[deadalnix]

Why not definitively adopt the following (and already proposed) memory 
scheme (some practice are now considered valid when this scheme is not 
respected) :

Thread local head (one by thread) -> shared heap -> immutable heap

This model have multiple benefices :
  - TL heap only can be processed by only interacting with one thread.
  - immutable head can be collected 100% concurently if we allow some 
floating garbage.
  - shared heap is the only problem, but as its size stay small, the 
problem stay small.