commit 52a7f5caebdf359ab877f1928aad59f1e9ad29fa
author Mathieu Chartier <mathieuc@google.com> Tue Aug 18 18:35:52 2015 -0700
committer Mathieu Chartier <mathieuc@google.com> Fri Aug 21 10:25:36 2015 -0700
tree fe23aeb3682128a31c62324e427b906c9804afd3
parent 944973e56fd3c04c92d902b05d0148f77ed28a78

Add class flags to class to help GC scanning

Reduces GC time and pauses by reducing the number of loads required
to scan an object.

Average total GC time before on EvaluateAndApplyChanges (EAAC): 7.452s
After: 7.144s

Average GC pause times before on EAAC: 860.67us
After: 722.75us

Adding the class flags field cause a memory increase of ~24k system
wide on low memory devices.

Change-Id: I3f04212d5787bfbf5e55026584d149f55476105e

runtime/class_linker.cc

diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index c179c64..b547d07 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -358,9 +358,9 @@
   // Setup String.
   Handle<mirror::Class> java_lang_String(hs.NewHandle(
       AllocClass(self, java_lang_Class.Get(), mirror::String::ClassSize(image_pointer_size_))));
+  java_lang_String->SetStringClass();
   mirror::String::SetClass(java_lang_String.Get());
   mirror::Class::SetStatus(java_lang_String, mirror::Class::kStatusResolved, self);
-  java_lang_String->SetStringClass();
 
   // Setup java.lang.ref.Reference.
   Handle<mirror::Class> java_lang_ref_Reference(hs.NewHandle(
@@ -570,16 +570,13 @@
   CHECK_EQ(java_lang_ref_Reference->GetClassSize(),
            mirror::Reference::ClassSize(image_pointer_size_));
   class_root = FindSystemClass(self, "Ljava/lang/ref/FinalizerReference;");
-  class_root->SetAccessFlags(class_root->GetAccessFlags() |
-                             kAccClassIsReference | kAccClassIsFinalizerReference);
+  class_root->SetClassFlags(class_root->GetClassFlags() | mirror::kClassFlagFinalizerReference);
   class_root = FindSystemClass(self, "Ljava/lang/ref/PhantomReference;");
-  class_root->SetAccessFlags(class_root->GetAccessFlags() | kAccClassIsReference |
-                             kAccClassIsPhantomReference);
+  class_root->SetClassFlags(class_root->GetClassFlags() | mirror::kClassFlagPhantomReference);
   class_root = FindSystemClass(self, "Ljava/lang/ref/SoftReference;");
-  class_root->SetAccessFlags(class_root->GetAccessFlags() | kAccClassIsReference);
+  class_root->SetClassFlags(class_root->GetClassFlags() | mirror::kClassFlagSoftReference);
   class_root = FindSystemClass(self, "Ljava/lang/ref/WeakReference;");
-  class_root->SetAccessFlags(class_root->GetAccessFlags() | kAccClassIsReference |
-                             kAccClassIsWeakReference);
+  class_root->SetClassFlags(class_root->GetClassFlags() | mirror::kClassFlagWeakReference);
 
   // Setup the ClassLoader, verifying the object_size_.
   class_root = FindSystemClass(self, "Ljava/lang/ClassLoader;");
@@ -2701,6 +2698,11 @@
   new_class->SetVTable(java_lang_Object->GetVTable());
   new_class->SetPrimitiveType(Primitive::kPrimNot);
   new_class->SetClassLoader(component_type->GetClassLoader());
+  if (component_type->IsPrimitive()) {
+    new_class->SetClassFlags(mirror::kClassFlagNoReferenceFields);
+  } else {
+    new_class->SetClassFlags(mirror::kClassFlagObjectArray);
+  }
   mirror::Class::SetStatus(new_class, mirror::Class::kStatusLoaded, self);
   {
     ArtMethod* imt[mirror::Class::kImtSize];
@@ -4385,9 +4387,9 @@
   }
 
   // Inherit reference flags (if any) from the superclass.
-  int reference_flags = (super->GetAccessFlags() & kAccReferenceFlagsMask);
+  int reference_flags = (super->GetClassFlags() & mirror::kClassFlagReference);
   if (reference_flags != 0) {
-    klass->SetAccessFlags(klass->GetAccessFlags() | reference_flags);
+    klass->SetClassFlags(klass->GetClassFlags() | reference_flags);
   }
   // Disallow custom direct subclasses of java.lang.ref.Reference.
   if (init_done_ && super == GetClassRoot(kJavaLangRefReference)) {
@@ -5227,6 +5229,22 @@
     *class_size = size;
   } else {
     klass->SetNumReferenceInstanceFields(num_reference_fields);
+    mirror::Class* super_class = klass->GetSuperClass();
+    if (num_reference_fields == 0 || super_class == nullptr) {
+      // object has one reference field, klass, but we ignore it since we always visit the class.
+      // If the super_class is null then we are java.lang.Object.
+      if (super_class == nullptr ||
+          (super_class->GetClassFlags() & mirror::kClassFlagNoReferenceFields) != 0) {
+        klass->SetClassFlags(klass->GetClassFlags() | mirror::kClassFlagNoReferenceFields);
+      } else if (kIsDebugBuild) {
+        size_t total_reference_instance_fields = 0;
+        while (super_class != nullptr) {
+          total_reference_instance_fields += super_class->NumReferenceInstanceFields();
+          super_class = super_class->GetSuperClass();
+        }
+        CHECK_GT(total_reference_instance_fields, 1u);
+      }
+    }
     if (!klass->IsVariableSize()) {
       std::string temp;
       DCHECK_GE(size, sizeof(mirror::Object)) << klass->GetDescriptor(&temp);