From 479e880b30fd81f8aed44d7b5c990e190cfe6295 Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Thu, 5 Mar 2020 13:26:17 -0500
Subject: [PATCH] Allow optional collection of opaque pointers

---
 CHANGELOG.md              | 6 ++++++
 gc.c                      | 6 ++++++
 include/cyclone/types.h   | 8 +++++++-
 scheme/cyclone/common.sld | 2 +-
 4 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ef9f0515..908b40ea 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## 0.16 - TBD
+
+Features
+
+- Updated the C API to optionally allow the GC to free memory pointed to by an Opaque object.
+
 ## 0.15 - February 26, 2020
 
 Features
diff --git a/gc.c b/gc.c
index abfec252..4d7465ee 100644
--- a/gc.c
+++ b/gc.c
@@ -534,6 +534,11 @@ static size_t gc_convert_heap_page_to_free_list(gc_heap *h, gc_thread_data *thd)
         fprintf(stderr, "mp_clear from sweep\n");
 #endif
         mp_clear(&(((bignum_type *)p)->bn));
+      } else if (type_of(p) == c_opaque_tag && opaque_collect_ptr(p)) {
+#if GC_DEBUG_VERBOSE
+        fprintf(stderr, "free opaque pointer %p from sweep\n", opaque_ptr(p));
+#endif
+        free( opaque_ptr(p) );
       }
 
       // Free block
@@ -956,6 +961,7 @@ char *gc_copy_obj(object dest, char *obj, gc_thread_data * thd)
       mark(hp) = thd->gc_alloc_color;
       immutable(hp) = immutable(obj);
       type_of(hp) = c_opaque_tag;
+      hp->collect_ptr = ((c_opaque_type *) obj)->collect_ptr;
       hp->ptr = ((c_opaque_type *) obj)->ptr;
       return (char *)hp;
     }
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index f659a865..5860d234 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -692,7 +692,9 @@ typedef cvar_type *cvar;
 typedef struct {
   gc_header_type hdr;
   tag_type tag;
-  /** This pointer can be anything, GC will not collect it */
+  unsigned char collect_ptr;
+  /** This pointer can be anything, GC will not collect it
+      unless collect_ptr is set */
   void *ptr;
 } c_opaque_type;
 typedef c_opaque_type *c_opaque;
@@ -704,11 +706,15 @@ typedef c_opaque_type *c_opaque;
   var.hdr.grayed = 0; \
   var.hdr.immutable = 0; \
   var.tag = c_opaque_tag; \
+  var.collect_ptr = 0; \
   var.ptr = p;
 
 /** Access the Opaque's pointer */
 #define opaque_ptr(x) (((c_opaque)x)->ptr)
 
+/** Access the Opaque's "collect pointer" field */
+#define opaque_collect_ptr(x) (((c_opaque)x)->collect_ptr)
+
 /**
  * @brief The mutex thread synchronization type
  *
diff --git a/scheme/cyclone/common.sld b/scheme/cyclone/common.sld
index a60ee443..1c5e735f 100644
--- a/scheme/cyclone/common.sld
+++ b/scheme/cyclone/common.sld
@@ -15,7 +15,7 @@
     *version-banner*
     *c-file-header-comment*)
   (begin
-(define *version-number* "0.15")
+(define *version-number* "0.16")
 (define *version-name* "")
 (define *version* (string-append *version-number* " " *version-name* ""))