Merge branch 'master' of github.com:robert-strandh/LispOS

Documentation/chap-garbage-collection.tex

@@ -70,3 +70,20 @@ is never moved as a result of a garbage collection.  Therefore, any
 reference to an object that is shared between several threads, remains
 valid after a garbage collection of the global heap.
 
+The marking phase is done by first requesting each thread to do a
+garbage collection and to mark any object in the global heap that is
+referred to by local objects.  When all threads have responded, a
+global collection is started.  The global collection is done
+concurrently with thread activity.  For that reason, objects allocated
+in the global heap during this phase are marked as being live.
+The global collection traces the global heap starting with objects
+marked by the mutator threads.  This tracing uses a standard
+three-color algorithm.  Write operations to the global heap are caught
+by a write barrier.
+
+When tracing in the global heap is finished, the part of the global
+heap that contains two-word headers and \texttt{cons} cells is scanned
+and unmarked cells are collected into a free list.  If an unmarked
+cell is a \texttt{cons} cell, then no further action is needed.  If an
+unmarked cell is a header object, then the corresponding rack is
+returned to the rack part of the global heap.