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

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 8727 matching lines @@
 
 
 void Library::SetLoadError(const Instance& error) const {
   // Should not be already successfully loaded or just allocated.
   ASSERT(LoadInProgress() || LoadRequested() || LoadFailed());
   raw_ptr()->load_state_ = RawLibrary::kLoadError;
   StorePointer(&raw_ptr()->load_error_, error.raw());
 }
 
 
+// Traits for looking up Libraries by url in a hash set.
+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 uword Hash(const Object& key) {
+    return Library::Cast(key).UrlHash();
+  }
+};
+
+
+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();
+  }
+  // Ensure we don't repeatedly visit the same library again.
+  set.Insert(*this);
+  object_store->set_library_load_error_table(set.Release());
   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);
     error = lib.TransitiveLoadError();
-    set_num_imports(num_imp);
     if (!error.IsNull()) {
       break;
     }
   }
   return error.raw();
 }
 
 
 static RawString* MakeClassMetaName(const Class& cls) {
   String& cname = String::Handle(cls.Name());
@@ skipping 1163 matching lines @@
     const Array& imports = Array::Handle(this->imports());
     Namespace& import = Namespace::Handle();
     import ^= imports.At(index);
     return import.library();
   }
   return Library::null();
 }
 
 
 RawInstance* LibraryPrefix::LoadError() const {
-  Library& lib = Library::Handle();
-  Instance& error = Instance::Handle();
+  Isolate* isolate = Isolate::Current();
+  ObjectStore* object_store = isolate->object_store();
+  GrowableObjectArray& libs =
+      GrowableObjectArray::Handle(isolate, object_store->libraries());
+  ASSERT(!libs.IsNull());
+  LibraryLoadErrorSet set(HashTables::New<LibraryLoadErrorSet>(libs.Length()));
+  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);
     ASSERT(!lib.IsNull());
+    HANDLESCOPE(isolate);
     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();
 }
 
 
 bool LibraryPrefix::ContainsLibrary(const Library& library) const {
   int32_t num_current_imports = num_imports();
   if (num_current_imports > 0) {
     Library& lib = Library::Handle();
     const String& url = String::Handle(library.url());
     String& lib_url = String::Handle();
     for (int32_t i = 0; i < num_current_imports; i++) {
@@ skipping 10401 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart