[Guile-commits] 02/08: Update Conservative GC section of manual

[Andy Wingo]

wingo pushed a commit to branch master
in repository guile.

commit a691540703d5e3606bbe7b4d540a1addf1cd4553
Author: Andy Wingo <address@hidden>
Date:   Thu Sep 27 09:50:37 2018 +0200

    Update Conservative GC section of manual
    
    * doc/ref/data-rep.texi (Conservative GC): Update notes with more
      details.
---
 doc/ref/data-rep.texi | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/doc/ref/data-rep.texi b/doc/ref/data-rep.texi
index bb7f74a..32c337d 100644
--- a/doc/ref/data-rep.texi
+++ b/doc/ref/data-rep.texi
@@ -1,6 +1,6 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Guile Reference Manual.
address@hidden Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2010, 
2015
address@hidden Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2010, 
2015, 2018
 @c   Free Software Foundation, Inc.
 @c See the file guile.texi for copying conditions.
 
@@ -324,24 +324,28 @@ is a nightmare to maintain. Thus, the BDW-GC uses a 
technique called
 @dfn{conservative garbage collection}, to make the local variable list
 unnecessary.
 
-The trick to conservative collection is to treat the stack as an
-ordinary range of memory, and assume that @emph{every} word on the stack
-is a pointer into the heap.  Thus, the collector marks all objects whose
-addresses appear anywhere in the stack, without knowing for sure how
-that word is meant to be interpreted.
+The trick to conservative collection is to treat the C stack as an
+ordinary range of memory, and assume that @emph{every} word on the C
+stack is a pointer into the heap.  Thus, the collector marks all objects
+whose addresses appear anywhere in the C stack, without knowing for sure
+how that word is meant to be interpreted.
 
 In addition to the stack, the BDW-GC will also scan static data
 sections. This means that global variables are also scanned when looking
 for live Scheme objects.
 
 Obviously, such a system will occasionally retain objects that are
-actually garbage, and should be freed. In practice, this is not a
-problem. The alternative, an explicitly maintained list of local
-variable addresses, is effectively much less reliable, due to programmer
-error. Interested readers should see the BDW-GC web page at
address@hidden://www.hboehm.info/gc/}, for more
-information.
-
+actually garbage, and should be freed.  In practice, this is not a
+problem, as the set of conservatively-scanned locations is fixed; the
+Scheme stack is maintained apart from the C stack, and is scanned
+precisely (as opposed to conservatively).  The GC-managed heap is also
+partitioned into parts that can contain pointers (such as vectors) and
+parts that can't (such as bytevectors), limiting the potential for
+confusing a raw integer with a pointer to a live object.
+
+Interested readers should see the BDW-GC web page at
address@hidden://www.hboehm.info/gc/}, for more information on conservative
+GC in general and the BDW-GC implementation in particular.
 
 @node The SCM Type in Guile
 @subsection The SCM Type in Guile