sync with w3m-0.2.2-inu-1.1/gc

1 files changed, 447 insertions, 0 deletions

diff --git a/gc/backgraph.c b/gc/backgraph.c
new file mode 100644
index 0000000..01ab738
--- /dev/null
+++ b/gc/backgraph.c
@@ -0,0 +1,447 @@
+/*
+ * Copyright (c) 2001 by Hewlett-Packard Company. All rights reserved.
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program
+ * for any purpose,  provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is granted,
+ * provided the above notices are retained, and a notice that the code was
+ * modified is included with the above copyright notice.
+ *
+ */
+
+/*
+ * This implements a full, though not well-tuned, representation of the
+ * backwards points-to graph.  This is used to test for non-GC-robust
+ * data structures; the code is not used during normal garbage collection.
+ *
+ * One restriction is that we drop all back-edges from nodes with very
+ * high in-degree, and simply add them add them to a list of such
+ * nodes.  They are then treated as permanent roots.  Id this by itself
+ * doesn't introduce a space leak, then such nodes can't contribute to
+ * a growing space leak.
+ */
+
+#ifdef MAKE_BACK_GRAPH
+
+#define MAX_IN	10	/* Maximum in-degree we handle directly */
+
+#include "private/dbg_mlc.h"
+#include <unistd.h>
+
+#if !defined(DBG_HDRS_ALL) || (ALIGNMENT != CPP_WORDSZ/8) || !defined(UNIX_LIKE)
+# error Configuration doesnt support MAKE_BACK_GRAPH
+#endif
+
+/* We store single back pointers directly in the object's oh_bg_ptr field.   */
+/* If there is more than one ptr to an object, we store q | FLAG_MANY, 	     */
+/* where q is a pointer to a back_edges object.				     */
+/* Every once in a while we use a back_edges object even for a single	     */
+/* pointer, since we need the other fields in the back_edges structure to    */
+/* be present in some fraction of the objects.  Otherwise we get serious     */
+/* performance issues.							     */
+#define FLAG_MANY 2
+
+typedef struct back_edges_struct {
+  word n_edges;	/* Number of edges, including those in continuation	*/
+  		/* structures.						*/
+  unsigned short flags;
+#	define RETAIN 1	/* Directly points to a reachable object;	*/
+  			/* retain for next GC.				*/
+  unsigned short height_gc_no;
+  		/* If height > 0, then the GC_gc_no value when it	*/
+  		/* was computed.  If it was computed this cycle, then	*/
+  		/* it is current.  If it was computed during the	*/
+  		/* last cycle, then it represents the old height,	*/
+  		/* which is only saved for live objects referenced by	*/
+  		/* dead ones.  This may grow due to refs from newly	*/
+		/* dead objects.				        */
+  signed_word height;
+  		/* Longest path through unreachable nodes to this node	*/
+  		/* that we found using depth first search.		*/
+  
+#   define HEIGHT_UNKNOWN ((signed_word)(-2))
+#   define HEIGHT_IN_PROGRESS ((signed_word)(-1))
+  ptr_t edges[MAX_IN];
+  struct back_edges_struct *cont;
+  		/* Pointer to continuation structure; we use only the	*/
+  		/* edges field in the continuation.			*/
+  		/* also used as free list link.				*/
+} back_edges;
+
+/* Allocate a new back edge structure.  Should be more sophisticated	*/
+/* if this were production code.					*/
+#define MAX_BACK_EDGE_STRUCTS 100000
+static back_edges *back_edge_space = 0;
+int GC_n_back_edge_structs = 0;	/* Serves as pointer to never used	*/
+				/* back_edges space.			*/
+static back_edges *avail_back_edges = 0;
+				/* Pointer to free list of deallocated	*/
+				/* back_edges structures.		*/
+
+static back_edges * new_back_edges(void)
+{
+  if (0 == back_edge_space) {
+    back_edge_space = (back_edges *)
+	    		sbrk(MAX_BACK_EDGE_STRUCTS*sizeof(back_edges));
+  }
+  if (0 != avail_back_edges) {
+    back_edges * result = avail_back_edges;
+    avail_back_edges = result -> cont;
+    result -> cont = 0;
+    return result;
+  }
+  if (GC_n_back_edge_structs >= MAX_BACK_EDGE_STRUCTS - 1) {
+    ABORT("needed too much space for back edges: adjust "
+	  "MAX_BACK_EDGE_STRUCTS");
+  }
+  return back_edge_space + (GC_n_back_edge_structs++);
+}
+
+/* Deallocate p and its associated continuation structures.	*/
+static void deallocate_back_edges(back_edges *p)
+{
+   back_edges *last = p;
+
+   while (0 != last -> cont) last = last -> cont;
+   last -> cont = avail_back_edges;
+   avail_back_edges = p;
+}
+
+/* Table of objects that are currently on the depth-first search	*/
+/* stack.  Only objects with in-degree one are in this table.		*/
+/* Other objects are identified using HEIGHT_IN_PROGRESS.		*/
+/* This data structure NEEDS IMPROVEMENT.				*/
+#define MAX_IN_PROGRESS 10000
+static ptr_t * in_progress_space = 0;
+static int n_in_progress = 0;
+
+static void push_in_progress(ptr_t p)
+{
+  if (in_progress_space == 0)
+      in_progress_space = sbrk(MAX_IN_PROGRESS * sizeof(ptr_t));
+  if (n_in_progress == MAX_IN_PROGRESS)
+      ABORT("Exceeded MAX_IN_PROGRESS");
+  in_progress_space[n_in_progress++] = p;
+}
+
+static GC_bool is_in_progress(ptr_t p)
+{
+  int i;
+  for (i = 0; i < n_in_progress; ++i) {
+    if (in_progress_space[i] == p) return TRUE;
+  }
+  return FALSE;
+}
+
+static void pop_in_progress(ptr_t p)
+{
+  --n_in_progress;
+  GC_ASSERT(in_progress_space[n_in_progress] == p);
+}
+
+#define GET_OH_BG_PTR(p) \
+		(ptr_t)REVEAL_POINTER(((oh *)(p)) -> oh_bg_ptr)
+#define SET_OH_BG_PTR(p,q) (((oh *)(p)) -> oh_bg_ptr) = HIDE_POINTER(q)
+
+/* Execute s once for each predecessor q of p in the points-to graph. 	*/
+/* s should be a bracketed statement.  We declare q.			*/
+#define FOR_EACH_PRED(q, p, s) \
+  { \
+    ptr_t q = GET_OH_BG_PTR(p); \
+    if (!((word)q & FLAG_MANY)) { \
+      if (q && !((word)q & 1)) s \
+	      /* !((word)q & 1) checks for a misnterpreted freelist link */ \
+    } else { \
+      back_edges *orig_be_ = (back_edges *)((word)q & ~FLAG_MANY); \
+      back_edges *be_ = orig_be_; \
+      int total_, local_; \
+      int n_edges_ = be_ -> n_edges; \
+      for (total_ = 0, local_ = 0; total_ < n_edges_; ++local_, ++total_) { \
+	  if (local_ == MAX_IN) { \
+	      be_ = be_ -> cont; \
+	      local_ = 0; \
+	  } \
+	  q = be_ -> edges[local_]; s \
+      } \
+    } \
+  }
+
+/* Ensure that p has a back_edges structure associated with it.	*/
+static void ensure_struct(ptr_t p)
+{
+  ptr_t old_back_ptr = GET_OH_BG_PTR(p);
+
+  if (!((word)old_back_ptr & FLAG_MANY)) {
+    back_edges *be = new_back_edges();
+    be -> flags = 0;
+    if (0 == old_back_ptr) {
+      be -> n_edges = 0;
+    } else {
+      be -> n_edges = 1;
+      be -> edges[0] = old_back_ptr;
+    }
+    be -> height = HEIGHT_UNKNOWN;
+    be -> height_gc_no = GC_gc_no - 1;
+    GC_ASSERT(be >= back_edge_space);
+    SET_OH_BG_PTR(p, (word)be | FLAG_MANY);
+  }
+}
+
+/* Add the (forward) edge from p to q to the backward graph.  Both p	*/
+/* q are pointers to the object base, i.e. pointers to an oh.		*/
+static void add_edge(ptr_t p,  ptr_t q)
+{
+    ptr_t old_back_ptr = GET_OH_BG_PTR(q);
+    back_edges * be, *be_cont;
+    word i;
+    static unsigned random_number = 13;
+#   define GOT_LUCKY_NUMBER (((++random_number) & 0x7f) == 0)
+      /* A not very random number we use to occasionally allocate a	*/
+      /* back_edges structure even for a single backward edge.  This	*/
+      /* prevents us from repeatedly tracing back through very long	*/
+      /* chains, since we will have some place to store height and	*/
+      /* in_progress flags along the way.				*/
+
+    GC_ASSERT(p == GC_base(p) && q == GC_base(q));
+    if (!GC_HAS_DEBUG_INFO(q) || !GC_HAS_DEBUG_INFO(p)) {
+      /* This is really a misinterpreted free list link, since we saw */
+      /* a pointer to a free list.  Dont overwrite it!		      */
+      return;
+    }
+    if (0 == old_back_ptr) {
+	SET_OH_BG_PTR(q, p);
+	if (GOT_LUCKY_NUMBER) ensure_struct(q);
+	return;
+    }
+    /* Check whether it was already in the list of predecessors. */
+      FOR_EACH_PRED(pred, q, { if (p == pred) return; });
+    ensure_struct(q);
+    old_back_ptr = GET_OH_BG_PTR(q);
+    be = (back_edges *)((word)old_back_ptr & ~FLAG_MANY);
+    for (i = be -> n_edges, be_cont = be; i > MAX_IN;
+	be_cont = be_cont -> cont, i -= MAX_IN) {}
+    if (i == MAX_IN) {
+	be_cont -> cont = new_back_edges();
+	be_cont = be_cont -> cont;
+	i = 0;
+    }
+    be_cont -> edges[i] = p;
+    be -> n_edges++;
+    if (be -> n_edges == 100) {
+#       if 0
+	  if (GC_print_stats) {
+	    GC_err_printf0("The following object has in-degree >= 100:\n");
+	    GC_print_heap_obj(q);
+	  }
+#	endif
+    }
+}
+
+typedef void (*per_object_func)(ptr_t p, word n_words, word gc_descr);
+
+static void per_object_helper(struct hblk *h, word fn)
+{
+  hdr * hhdr = HDR(h);
+  word sz = hhdr -> hb_sz;
+  word descr = hhdr -> hb_descr;
+  per_object_func f = (per_object_func)fn;
+  int i = 0;
+
+  do {
+    f((ptr_t)(h -> hb_body + i), sz, descr);
+    i += sz;
+  } while (i + sz <= BYTES_TO_WORDS(HBLKSIZE));
+}
+
+void GC_apply_to_each_object(per_object_func f)
+{
+  GC_apply_to_all_blocks(per_object_helper, (word)f);
+}
+
+static void reset_back_edge(ptr_t p, word n_words, word gc_descr)
+{
+  /* Skip any free list links, or dropped blocks */
+  if (GC_HAS_DEBUG_INFO(p)) {
+    ptr_t old_back_ptr = GET_OH_BG_PTR(p);
+    if ((word)old_back_ptr & FLAG_MANY) {
+      back_edges *be = (back_edges *)((word)old_back_ptr & ~FLAG_MANY);
+      if (!(be -> flags & RETAIN)) {
+	deallocate_back_edges(be);
+        SET_OH_BG_PTR(p, 0); 
+      } else {
+        word *currentp;
+
+	GC_ASSERT(GC_is_marked(p));
+
+	/* Back edges may point to objects that will not be retained. 	*/
+	/* Delete them for now, but remember the height.		*/
+	/* Some will be added back at next GC.				*/
+	  be -> n_edges = 0;
+	  if (0 != be -> cont) {
+	    deallocate_back_edges(be -> cont);
+	    be -> cont = 0;
+	  }
+
+	GC_ASSERT(GC_is_marked(p));
+
+	/* We only retain things for one GC cycle at a time.		*/
+	  be -> flags &= ~RETAIN;
+      }
+    } else /* Simple back pointer */ {
+      /* Clear to avoid dangling pointer. */
+      SET_OH_BG_PTR(p, 0);
+    }
+  }
+}
+
+static void add_back_edges(ptr_t p, word n_words, word gc_descr)
+{
+  word *currentp = (word *)(p + sizeof(oh));
+
+  /* For now, fix up non-length descriptors conservatively.	*/
+    if((gc_descr & GC_DS_TAGS) != GC_DS_LENGTH) {
+      gc_descr = WORDS_TO_BYTES(n_words);
+    }
+  while (currentp < (word *)(p + gc_descr)) {
+    word current = *currentp++;
+    if (current >= (word)GC_least_plausible_heap_addr && 
+	current <= (word)GC_greatest_plausible_heap_addr) {
+       ptr_t target = GC_base((GC_PTR)current);
+       if (0 != target) {
+	 add_edge(p, target);
+       }
+    }
+  }
+}
+
+/* Rebuild the reprentation of the backward reachability graph.	*/
+/* Does not examine mark bits.  Can be called before GC.	*/
+void GC_build_back_graph(void)
+{
+  GC_apply_to_each_object(add_back_edges);
+}
+
+/* Return an approximation to the length of the longest simple path	*/
+/* through unreachable objects to p.  We refer to this as the height	*/
+/* of p.								*/
+static word backwards_height(ptr_t p)
+{
+  word result;
+  ptr_t back_ptr = GET_OH_BG_PTR(p);
+  back_edges *be;
+
+  if (0 == back_ptr) return 1;
+  if (!((word)back_ptr & FLAG_MANY)) {
+    if (is_in_progress(p)) return 0;  /* DFS back edge, i.e. we followed  */
+    				      /* an edge to an object already	  */
+    				      /* on our stack: ignore		  */
+    push_in_progress(p);
+    result = backwards_height(back_ptr)+1;
+    pop_in_progress(p);
+    return result;
+  }
+  be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
+  if (be -> height >= 0 && be -> height_gc_no == GC_gc_no)
+      return be -> height;
+  /* Ignore back edges in DFS */
+    if (be -> height == HEIGHT_IN_PROGRESS) return 0;
+  result = (be -> height > 0? be -> height : 1);
+  be -> height = HEIGHT_IN_PROGRESS;
+  FOR_EACH_PRED(q, p, {
+    word this_height;
+    if (GC_is_marked(q) && !(FLAG_MANY & (word)GET_OH_BG_PTR(p))) {
+      if (GC_print_stats)
+	  GC_printf2("Found bogus pointer from 0x%lx to 0x%lx\n", q, p);
+	/* Reachable object "points to" unreachable one.		*/
+	/* Could be caused by our lax treatment of GC descriptors.	*/
+      this_height = 1;
+    } else {
+        this_height = backwards_height(q);
+    }
+    if (this_height >= result) result = this_height + 1;
+  });
+  be -> height = result;
+  be -> height_gc_no = GC_gc_no;
+  return result;
+}
+
+word GC_max_height;
+ptr_t GC_deepest_obj;
+
+/* Compute the maximum height of every unreachable predecessor p of  a 	*/
+/* reachable object.  Arrange to save the heights of all such objects p	*/
+/* so that they can be used in calculating the height of objects in the	*/
+/* next GC.								*/
+/* Set GC_max_height to be the maximum height we encounter, and 	*/
+/* GC_deepest_obj to be the corresponding object.			*/
+static void update_max_height(ptr_t p, word n_words, word gc_descr)
+{
+  if (GC_is_marked(p) && GC_HAS_DEBUG_INFO(p)) {
+    int i;
+    word p_height = 0;
+    ptr_t p_deepest_obj = 0;
+    ptr_t back_ptr;
+    back_edges *be = 0;
+
+    /* If we remembered a height last time, use it as a minimum.	*/
+    /* It may have increased due to newly unreachable chains pointing	*/
+    /* to p, but it can't have decreased.				*/
+    back_ptr = GET_OH_BG_PTR(p);
+    if (0 != back_ptr && ((word)back_ptr & FLAG_MANY)) {
+      be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
+      if (be -> height != HEIGHT_UNKNOWN) p_height = be -> height;
+    }
+    FOR_EACH_PRED(q, p, {
+      if (!GC_is_marked(q) && GC_HAS_DEBUG_INFO(q)) {
+        word q_height;
+
+        q_height = backwards_height(q);
+	if (q_height > p_height) {
+	  p_height = q_height;
+	  p_deepest_obj = q;
+	}
+      }
+    });
+    if (p_height > 0) {
+      /* Remember the height for next time. */
+	if (be == 0) {
+    	  ensure_struct(p);
+    	  back_ptr = GET_OH_BG_PTR(p);
+  	  be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
+	}
+	be -> flags |= RETAIN;
+	be -> height = p_height;
+	be -> height_gc_no = GC_gc_no;
+    }
+    if (p_height > GC_max_height) {
+	GC_max_height = p_height;
+	GC_deepest_obj = p_deepest_obj;
+    }
+  }
+}
+
+void GC_traverse_back_graph(void)
+{
+  static word max_max_height = 0;
+  GC_max_height = 0;
+  GC_apply_to_each_object(update_max_height);
+  GC_printf2("Maximum backwards height of reachable objects at GC %lu is %ld\n",
+	     (unsigned long) GC_gc_no, GC_max_height);
+  if (GC_max_height > max_max_height) {
+    max_max_height = GC_max_height;
+    GC_printf0("The following unreachable object is last in a longest chain "
+	       "of unreachable objects:\n");
+    GC_print_heap_obj(GC_deepest_obj);
+  }
+  if (GC_print_stats) {
+    GC_printf1("Needed max total of %ld back-edge structs\n",
+	       GC_n_back_edge_structs);
+  }
+  GC_apply_to_each_object(reset_back_edge);
+  GC_deepest_obj = 0;
+}
+
+#endif /* MAKE_BACK_GRAPH */