Merge pull request #25 from jacob-hughes/uncollectable_bit

Add tag for tracking if object is RAII'd or GC'd
softdevteam · Sep 16, 2024 · a1b1276 · a1b1276
2 parents a69f8b7 + b75dc0b
commit a1b1276
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Showing 3 changed files with 45 additions and 3 deletions.
diff --git a/include/gc/gc_mark.h b/include/gc/gc_mark.h
@@ -374,6 +374,10 @@ GC_API int GC_CALL GC_is_marked(const void *) GC_ATTR_NONNULL(1);
 GC_API void GC_CALL GC_clear_mark_bit(const void *) GC_ATTR_NONNULL(1);
 GC_API void GC_CALL GC_set_mark_bit(const void *) GC_ATTR_NONNULL(1);
 
+GC_API int GC_CALL GC_is_uncollectable(const void *) GC_ATTR_NONNULL(1);
+GC_API void GC_CALL GC_set_uncollectable(const void *) GC_ATTR_NONNULL(1);
+GC_API void GC_CALL GC_clear_uncollectable(const void *) GC_ATTR_NONNULL(1);
+
 /* Push everything in the given range onto the mark stack.              */
 /* (GC_push_conditional pushes either all or only dirty pages depending */
 /* on the third argument.)  GC_push_all_eager also ensures that stack   */

diff --git a/include/private/gc_priv.h b/include/private/gc_priv.h
@@ -1915,9 +1915,16 @@ struct GC_traced_stack_sect_s {
  */
 
 #ifdef USE_MARK_BYTES
-# define mark_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n])
-# define set_mark_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] = 1)
-# define clear_mark_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] = 0)
+# define MARK_TAG 0x1
+# define UNCOLLECTABLE_TAG 0x1
+
+# define mark_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] & MARK_TAG)
+# define set_mark_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] |= MARK_TAG)
+# define clear_mark_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] &= ~MARK_TAG)
+
+# define uncollectable_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] & UNCOLLECTABLE_TAG)
+# define set_uncollectable_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] |= UNCOLLECTABLE_TAG)
+# define clear_uncollectable_bit_from_hdr(hhdr,n) ((hhdr)->hb_marks[n] &= ~UNCOLLECTABLE_TAG)
 #else
 /* Set mark bit correctly, even if mark bits may be concurrently        */
 /* accessed.                                                            */

diff --git a/mark.c b/mark.c
@@ -280,6 +280,37 @@ GC_API int GC_CALL GC_is_marked(const void *p)
     return (int)mark_bit_from_hdr(hhdr, bit_no); /* 0 or 1 */
 }
 
+GC_API void GC_CALL GC_set_uncollectable(const void *p)
+{
+    struct hblk *h = HBLKPTR(p);
+    hdr * hhdr = HDR(h);
+    word bit_no = MARK_BIT_NO((word)((ptr_t)p - (ptr_t)h), hhdr -> hb_sz);
+
+    if (!uncollectable_bit_from_hdr(hhdr, bit_no)) {
+      set_uncollectable_bit_from_hdr(hhdr, bit_no);
+    }
+}
+
+GC_API void GC_CALL GC_clear_uncollectable(const void *p)
+{
+    struct hblk *h = HBLKPTR(p);
+    hdr * hhdr = HDR(h);
+    word bit_no = MARK_BIT_NO((word)((ptr_t)p - (ptr_t)h), hhdr -> hb_sz);
+
+    if (uncollectable_bit_from_hdr(hhdr, bit_no)) {
+      clear_uncollectable_bit_from_hdr(hhdr, bit_no);
+    }
+}
+
+GC_API int GC_CALL GC_is_uncollectable(const void *p)
+{
+    struct hblk *h = HBLKPTR(p);
+    hdr * hhdr = HDR(h);
+    word bit_no = MARK_BIT_NO((word)((ptr_t)p - (ptr_t)h), hhdr -> hb_sz);
+
+    return (int)uncollectable_bit_from_hdr(hhdr, bit_no); /* 0 or 1 */
+}
+
 /* Clear mark bits in all allocated heap blocks.  This invalidates the  */
 /* marker invariant, and sets GC_mark_state to reflect this.  (This     */
 /* implicitly starts marking to reestablish the invariant.)             */