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Update Conservative GC section of manual

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* doc/ref/data-rep.texi (Conservative GC): Update notes with more
  details.
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Andy Wingo 2018-09-27 09:50:37 +02:00
parent 179f6610a2
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@ -1,6 +1,6 @@
@c -*-texinfo-*- @c -*-texinfo-*-
@c This is part of the GNU Guile Reference Manual. @c This is part of the GNU Guile Reference Manual.
@c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2010, 2015 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2010, 2015, 2018
@c Free Software Foundation, Inc. @c Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions. @c See the file guile.texi for copying conditions.
@ -324,11 +324,11 @@ is a nightmare to maintain. Thus, the BDW-GC uses a technique called
@dfn{conservative garbage collection}, to make the local variable list @dfn{conservative garbage collection}, to make the local variable list
unnecessary. unnecessary.
The trick to conservative collection is to treat the stack as an 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 stack ordinary range of memory, and assume that @emph{every} word on the C
is a pointer into the heap. Thus, the collector marks all objects whose stack is a pointer into the heap. Thus, the collector marks all objects
addresses appear anywhere in the stack, without knowing for sure how whose addresses appear anywhere in the C stack, without knowing for sure
that word is meant to be interpreted. how that word is meant to be interpreted.
In addition to the stack, the BDW-GC will also scan static data In addition to the stack, the BDW-GC will also scan static data
sections. This means that global variables are also scanned when looking sections. This means that global variables are also scanned when looking
@ -336,12 +336,16 @@ for live Scheme objects.
Obviously, such a system will occasionally retain objects that are Obviously, such a system will occasionally retain objects that are
actually garbage, and should be freed. In practice, this is not a actually garbage, and should be freed. In practice, this is not a
problem. The alternative, an explicitly maintained list of local problem, as the set of conservatively-scanned locations is fixed; the
variable addresses, is effectively much less reliable, due to programmer Scheme stack is maintained apart from the C stack, and is scanned
error. Interested readers should see the BDW-GC web page at precisely (as opposed to conservatively). The GC-managed heap is also
@uref{http://www.hboehm.info/gc/}, for more partitioned into parts that can contain pointers (such as vectors) and
information. 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
@uref{http://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 @node The SCM Type in Guile
@subsection The SCM Type in Guile @subsection The SCM Type in Guile