Fix issue 17514770 (https://b2.corp.google.com/issues/17514770)

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 40392)
+++ runtime/vm/object.cc	(working copy)
@@ -8745,23 +8745,75 @@
 }
 
 
+// Traits for looking up Libraries by url in a hash set.
+class LibraryUrl {
+ public:
+  LibraryUrl(const String& url, String* tmp_string)
+      : url_(url), tmp_string_(tmp_string) {}
+  bool Matches(const Library& library) const {
+    if (url_.IsSymbol()) {
+      return url_.raw() == library.url();
+    } else {
+      *tmp_string_ = library.url();
+      return url_.Equals(*tmp_string_);
+    }
+  }
+  intptr_t Hash() const { return url_.Hash(); }
+ private:
+  const String& url_;
+  String* tmp_string_;
+};
+
+
+class LibraryUrlTraits {
+ public:
+  // Called when growing the table.
+  static bool IsMatch(const Object& a, const Object& b) {
+    ASSERT(a.IsLibrary() && b.IsLibrary());
+    // Library objects are always canonical.
+    return a.raw() == b.raw();
+  }
+  static bool IsMatch(const LibraryUrl& url, const Object& obj) {
+    return url.Matches(Library::Cast(obj));
+  }
+  static uword Hash(const Object& key) {
+    return Library::Cast(key).UrlHash();
+  }
+  static uword Hash(const LibraryUrl& url) {
+    return url.Hash();
+  }
+};
+
+
+typedef UnorderedHashSet<LibraryUrlTraits> LibraryLoadErrorSet;
+
+
 RawInstance* Library::TransitiveLoadError() const {
   if (LoadError() != Instance::null()) {
     return LoadError();
   }
+  Isolate* isolate = Isolate::Current();
+  ObjectStore* object_store = isolate->object_store();
+  LibraryLoadErrorSet set(object_store->library_load_error_table());
+  bool present = false;
+  if (set.GetOrNull(*this, &present) != Object::null()) {
+    object_store->set_library_load_error_table(set.Release());
+    return Instance::null();
+  }
   intptr_t num_imp = num_imports();
-  Library& lib = Library::Handle();
-  Instance& error = Instance::Handle();
+  Library& lib = Library::Handle(isolate);
+  Instance& error = Instance::Handle(isolate);
   for (intptr_t i = 0; i < num_imp; i++) {
+    HANDLESCOPE(isolate);
     lib = ImportLibraryAt(i);
-    // Break potential import cycles while recursing through imports.
-    set_num_imports(0);
+    // Ensure we don't repeatedly visit the same library again.
+    set.Insert(lib);
     error = lib.TransitiveLoadError();
-    set_num_imports(num_imp);
     if (!error.IsNull()) {
       break;
     }
   }
+  object_store->set_library_load_error_table(set.Release());
   return error.raw();
 }
 
@@ -9941,17 +9993,23 @@
 
 
 RawInstance* LibraryPrefix::LoadError() const {
-  Library& lib = Library::Handle();
-  Instance& error = Instance::Handle();
+  const intptr_t kNumLibs = 25;
+  Isolate* isolate = Isolate::Current();
+  ObjectStore* object_store = isolate->object_store();
+  LibraryLoadErrorSet set(HashTables::New<LibraryLoadErrorSet>(kNumLibs));

[Ivan Posva, 2014/09/18 00:58:04]

How about just calling set.Clear() once we are done below and asserting here
that the set is empty before we begin.

[siva, 2014/09/18 01:07:37]

Ignoring this for now.

+  object_store->set_library_load_error_table(set.Release());
+  Library& lib = Library::Handle(isolate);
+  Instance& error = Instance::Handle(isolate);
   for (int32_t i = 0; i < num_imports(); i++) {
     lib = GetLibrary(i);

[Ivan Posva, 2014/09/18 00:58:04]

HANDLESCOPE(isolate);

[siva, 2014/09/18 01:07:37]

Done.

     ASSERT(!lib.IsNull());
     error = lib.TransitiveLoadError();
     if (!error.IsNull()) {
-      return error.raw();
+      break;
     }
   }
-  return Instance::null();
+  object_store->set_library_load_error_table(Object::empty_array());
+  return error.raw();
 }