patch for http://bugs.ruby-lang.org/issues/3924

load.c.patch

Index: load.c
===================================================================
--- load.c	(revision 34564)
+++ load.c	(working copy)
@@ -8,6 +8,96 @@
 #include "dln.h"
 #include "eval_intern.h"
 
+struct expander {
+    VALUE hash;
+};
+
+struct expander_alive_values {
+    VALUE *ptr;
+    long len;
+};
+
+static struct expander *expander;
+
+static int
+expander_collect_i(st_data_t key, st_data_t value, st_data_t arg)
+{
+    struct expander_alive_values *alive_values = (void*)arg;
+    long i;
+
+    /* delete dead values using information in the alive_values */
+    for (i = 0; i < alive_values->len; i++) {
+	if (alive_values->ptr[i] == (VALUE)value) {
+	    /* value is alive */
+	    return ST_CONTINUE;
+	}
+    }
+    /* value is dead */
+    return ST_DELETE;
+}
+
+static void
+expander_collect(struct expander *e)
+{
+    st_table *st = RHASH(e->hash)->ntbl;
+    VALUE load_path = rb_get_load_path();
+    struct expander_alive_values alive_values;
+    VALUE *ptr = ALLOCA_N(VALUE, RARRAY_LEN(load_path));
+    long i, len = 0;
+
+    /* remember alive values */
+    for (i = 0; i < RARRAY_LEN(load_path); i++) {
+	/* alive values can be found by rb_hash_lookup2 */
+	VALUE key = RARRAY_PTR(load_path)[i];
+	VALUE value = rb_hash_lookup2(e->hash, key, Qfalse);
+	if (RTEST(value)) {
+	    ptr[len] = value;
+	    len++;
+	}
+    }
+    alive_values.ptr = ptr;
+    alive_values.len = len;
+    st_foreach(st, expander_collect_i, (st_data_t)&alive_values);
+}
+
+#define EXPANDER_COLLECTION_SPAN 10
+static void
+expander_mark(void *ptr)
+{
+    struct expander *e = ptr;
+    static int count = 0;
+
+    if (!e) return;
+    rb_gc_mark(e->hash);
+    if (++count < EXPANDER_COLLECTION_SPAN) return;
+    count = 0;
+    /* do collection in EXPANDER_COLLECTION_SPAN times once */
+    expander_collect(e);
+}
+
+static void
+expander_free(void *p)
+{
+    if (p) xfree(p);
+}
+
+static const rb_data_type_t expander_data_type = {
+    "expander",
+    {expander_mark, expander_free, NULL,},
+};
+
+static VALUE
+expander_alloc(VALUE klass)
+{
+    VALUE obj;
+    struct expander *e;
+
+    obj = TypedData_Make_Struct(klass, struct expander, &expander_data_type, e);
+    e->hash = rb_hash_new();
+
+    return obj;
+}
+
 VALUE ruby_dln_librefs;
 
 #define IS_RBEXT(e) (strcmp((e), ".rb") == 0)
@@ -43,8 +133,18 @@
 
     ary = rb_ary_new2(RARRAY_LEN(load_path));
     for (i = 0; i < RARRAY_LEN(load_path); ++i) {
+#if 0
 	VALUE path = rb_file_expand_path(RARRAY_PTR(load_path)[i], Qnil);
 	rb_str_freeze(path);
+#else
+	VALUE orig = RARRAY_PTR(load_path)[i];
+	VALUE path = rb_hash_lookup2(expander->hash, orig, Qfalse);
+	if (!RTEST(path)) {
+	    path = rb_file_expand_path(orig, Qnil);
+	    rb_str_freeze(path);
+	    rb_hash_aset(expander->hash, orig, path);
+	}
+#endif
 	rb_ary_push(ary, path);
     }
     rb_obj_freeze(ary);
@@ -784,6 +884,9 @@
     rb_vm_t *vm = GET_VM();
     static const char var_load_path[] = "$:";
     ID id_load_path = rb_intern2(var_load_path, sizeof(var_load_path)-1);
+    VALUE expander_parent = rb_class_new(rb_cObject);
+    VALUE rb_cLoadPathExpander = rb_define_class_under(expander_parent, "Expander", rb_cObject);
+    VALUE expander_value;
 
     rb_define_hooked_variable(var_load_path, (VALUE*)vm, load_path_getter, rb_gvar_readonly_setter);
     rb_alias_variable(rb_intern("$-I"), id_load_path);
@@ -804,4 +907,10 @@
 
     ruby_dln_librefs = rb_ary_new();
     rb_gc_register_mark_object(ruby_dln_librefs);
+
+    rb_define_alloc_func(rb_cLoadPathExpander, expander_alloc);
+    expander_value = rb_obj_alloc(rb_cLoadPathExpander);
+    rb_gc_register_mark_object(expander_parent);
+    rb_gc_register_mark_object(expander_value);
+    expander = DATA_PTR(expander_value);
 }