Expose whether two arrays are shared

* array.c (rb_ary_shared_with_p): new function.
  Expose whether two arrays are shared (read-only, C only).

* include/ruby/intern.h (rb_ary_shared_with_p): declare.
  Patch by Greg Price.
  [ruby-core:47970] [Bug #7158]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37478 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,12 @@
+Mon Nov  5 23:23:51 2012  Greg Price  <price@mit.edu>
+
+	* array.c (rb_ary_shared_with_p): new function.
+	  Expose whether two arrays are shared (read-only, C only).
+
+	* include/ruby/intern.h (rb_ary_shared_with_p): declare.
+	  Patch by Greg Price.
+	  [ruby-core:47970] [Bug #7158]
+
 Mon Nov  5 23:21:14 2012  Greg Price  <price@mit.edu>
 
 	* load.c (loaded_feature_path): clarify and briefly comment

array.c

@@ -305,6 +305,22 @@ rb_ary_frozen_p(VALUE ary)
     return Qfalse;
 }
 
+/* This can be used to take a snapshot of an array (with
+   e.g. rb_ary_replace) and check later whether the array has been
+   modified from the snapshot.  The snapshot is cheap, though if
+   something does modify the array it will pay the cost of copying
+   it. */
+VALUE
+rb_ary_shared_with_p(VALUE ary1, VALUE ary2)
+{
+    if (!ARY_EMBED_P(ary1) && ARY_SHARED_P(ary1)
+     && !ARY_EMBED_P(ary2) && ARY_SHARED_P(ary2)
+     && RARRAY(ary1)->as.heap.aux.shared == RARRAY(ary2)->as.heap.aux.shared) {
+	return Qtrue;
+    }
+    return Qfalse;
+}
+
 static VALUE
 ary_alloc(VALUE klass)
 {

include/ruby/intern.h

@@ -56,6 +56,7 @@ VALUE rb_ary_tmp_new(long);
 void rb_ary_free(VALUE);
 void rb_ary_modify(VALUE);
 VALUE rb_ary_freeze(VALUE);
+VALUE rb_ary_shared_with_p(VALUE, VALUE);
 VALUE rb_ary_aref(int, VALUE*, VALUE);
 VALUE rb_ary_subseq(VALUE, long, long);
 void rb_ary_store(VALUE, long, VALUE);

load.c

@@ -88,7 +88,7 @@ loaded_feature_path(const char *name, long vlen, const char *feature, long len,
     long plen;
     const char *e;
 
-    if (vlen < len+1) return 0
+    if (vlen < len+1) return 0;
     if (!strncmp(name+(vlen-len), feature, len)) {
 	plen = vlen - len - 1;
     }