cppgc: Introduce HeapVisitor

HeapVisitor is a simple visitor implementing both visitation and accept
interfaces. HeapVisitor is aimed to replace functions that traverse the
heap in Blink: PrepareForSweep, Sweep, FinalizeSweep, MakeConsistentForGC,
ObjectPayloadSize, VerifyObjectStartBitmap, CollectStatistics, etc.

This CL also introduces a Heap::ObjectPayloadSize function.

Bug: chromium:1056170
Change-Id: I85a2b8b572486bea29704fc436b002d8f7405201
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2165733
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67458}

BUILD.gn

@@ -4033,6 +4033,7 @@ v8_source_set("cppgc_base") {
     "src/heap/cppgc/heap-page.h",
     "src/heap/cppgc/heap-space.cc",
     "src/heap/cppgc/heap-space.h",
+    "src/heap/cppgc/heap-visitor.h",
     "src/heap/cppgc/heap.cc",
     "src/heap/cppgc/heap.h",
     "src/heap/cppgc/liveness-broker.cc",

src/heap/cppgc/heap-page.cc

@@ -80,6 +80,19 @@ NormalPage::NormalPage(Heap* heap, BaseSpace* space)
 
 NormalPage::~NormalPage() = default;
 
+NormalPage::iterator NormalPage::begin() {
+  const auto& lab = NormalPageSpace::From(space())->linear_allocation_buffer();
+  return iterator(reinterpret_cast<HeapObjectHeader*>(PayloadStart()),
+                  lab.start(), lab.size());
+}
+
+NormalPage::const_iterator NormalPage::begin() const {
+  const auto& lab = NormalPageSpace::From(space())->linear_allocation_buffer();
+  return const_iterator(
+      reinterpret_cast<const HeapObjectHeader*>(PayloadStart()), lab.start(),
+      lab.size());
+}
+
 Address NormalPage::PayloadStart() {
   return AlignAddress((reinterpret_cast<Address>(this + 1)),
                       kAllocationGranularity);

src/heap/cppgc/heap-page.h

@@ -7,6 +7,7 @@
 
 #include "src/base/iterator.h"
 #include "src/base/macros.h"
+#include "src/heap/cppgc/globals.h"
 #include "src/heap/cppgc/heap-object-header.h"
 
 namespace cppgc {
@@ -49,7 +50,15 @@ class V8_EXPORT_PRIVATE NormalPage final : public BasePage {
   template <typename T>
   class IteratorImpl : v8::base::iterator<std::forward_iterator_tag, T> {
    public:
-    explicit IteratorImpl(T* p) : p_(p) {}
+    explicit IteratorImpl(T* p, ConstAddress lab_start = nullptr,
+                          size_t lab_size = 0)
+        : p_(p), lab_start_(lab_start), lab_size_(lab_size) {
+      DCHECK(p);
+      DCHECK_EQ(0, (lab_size & (sizeof(T) - 1)));
+      if (reinterpret_cast<ConstAddress>(p_) == lab_start_) {
+        p_ += (lab_size_ / sizeof(T));
+      }
+    }
 
     T& operator*() { return *p_; }
     const T& operator*() const { return *p_; }
@@ -58,19 +67,26 @@ class V8_EXPORT_PRIVATE NormalPage final : public BasePage {
     bool operator!=(IteratorImpl other) const { return !(*this == other); }
 
     IteratorImpl& operator++() {
-      p_ += (p_->GetSize() / sizeof(T));
+      const size_t size = p_->GetSize();
+      DCHECK_EQ(0, (size & (sizeof(T) - 1)));
+      p_ += (size / sizeof(T));
+      if (reinterpret_cast<ConstAddress>(p_) == lab_start_) {
+        p_ += (lab_size_ / sizeof(T));
+      }
       return *this;
     }
     IteratorImpl operator++(int) {
       IteratorImpl temp(*this);
-      p_ += (p_->GetSize() / sizeof(T));
+      ++(*this);
       return temp;
     }
 
-    T* base() { return p_; }
+    T* base() const { return p_; }
 
    private:
     T* p_;
+    ConstAddress lab_start_;
+    size_t lab_size_;
   };
 
  public:
@@ -83,13 +99,17 @@ class V8_EXPORT_PRIVATE NormalPage final : public BasePage {
   // corresponding space (i.e. be swept when called).
   static void Destroy(NormalPage*);
 
-  iterator begin() {
+  static NormalPage* From(BasePage* page) {
-    return iterator(reinterpret_cast<HeapObjectHeader*>(PayloadStart()));
+    DCHECK(!page->is_large());
+    return static_cast<NormalPage*>(page);
   }
-  const_iterator begin() const {
+  static const NormalPage* From(const BasePage* page) {
-    return const_iterator(
+    return From(const_cast<BasePage*>(page));
-        reinterpret_cast<const HeapObjectHeader*>(PayloadStart()));
   }
+
+  iterator begin();
+  const_iterator begin() const;
+
   iterator end() {
     return iterator(reinterpret_cast<HeapObjectHeader*>(PayloadEnd()));
   }
@@ -118,6 +138,14 @@ class V8_EXPORT_PRIVATE LargePage final : public BasePage {
   // corresponding space (i.e. be swept when called).
   static void Destroy(LargePage*);
 
+  static LargePage* From(BasePage* page) {
+    DCHECK(page->is_large());
+    return static_cast<LargePage*>(page);
+  }
+  static const LargePage* From(const BasePage* page) {
+    return From(const_cast<BasePage*>(page));
+  }
+
   HeapObjectHeader* ObjectHeader();
   const HeapObjectHeader* ObjectHeader() const;
 

src/heap/cppgc/heap-space.h

@@ -60,27 +60,35 @@ class V8_EXPORT_PRIVATE NormalPageSpace final : public BaseSpace {
  public:
   class LinearAllocationBuffer {
    public:
-    void* Allocate(size_t alloc_size) {
+    Address Allocate(size_t alloc_size) {
       DCHECK_GE(size_, alloc_size);
-      void* result = start_;
+      Address result = start_;
       start_ += alloc_size;
       size_ -= alloc_size;
       return result;
     }
 
-    void Set(void* ptr, size_t size) {
+    void Set(Address ptr, size_t size) {
-      start_ = static_cast<uint8_t*>(ptr);
+      start_ = ptr;
       size_ = size;
     }
 
-    void* start() const { return start_; }
+    Address start() const { return start_; }
     size_t size() const { return size_; }
 
    private:
-    uint8_t* start_ = nullptr;
+    Address start_ = nullptr;
     size_t size_ = 0;
   };
 
+  static NormalPageSpace* From(BaseSpace* space) {
+    DCHECK(!space->is_large());
+    return static_cast<NormalPageSpace*>(space);
+  }
+  static const NormalPageSpace* From(const BaseSpace* space) {
+    return From(const_cast<BaseSpace*>(space));
+  }
+
   NormalPageSpace(RawHeap* heap, size_t index);
 
   LinearAllocationBuffer& linear_allocation_buffer() { return current_lab_; }
@@ -98,6 +106,14 @@ class V8_EXPORT_PRIVATE NormalPageSpace final : public BaseSpace {
 
 class V8_EXPORT_PRIVATE LargePageSpace final : public BaseSpace {
  public:
+  static LargePageSpace* From(BaseSpace* space) {
+    DCHECK(space->is_large());
+    return static_cast<LargePageSpace*>(space);
+  }
+  static const LargePageSpace* From(const BaseSpace* space) {
+    return From(const_cast<BaseSpace*>(space));
+  }
+
   LargePageSpace(RawHeap* heap, size_t index);
 };
 

src/heap/cppgc/heap-visitor.h

@@ -0,0 +1,88 @@
+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_HEAP_CPPGC_HEAP_VISITOR_H_
+#define V8_HEAP_CPPGC_HEAP_VISITOR_H_
+
+#include "src/heap/cppgc/heap-page.h"
+#include "src/heap/cppgc/heap-space.h"
+#include "src/heap/cppgc/raw-heap.h"
+
+namespace cppgc {
+namespace internal {
+
+// Visitor for heap, which also implements the accept (traverse) interface.
+// Implements preorder traversal of the heap. The order of traversal is defined.
+// Implemented as a CRTP visitor to avoid virtual calls and support better
+// inlining.
+template <typename Derived>
+class HeapVisitor {
+ public:
+  void Traverse(RawHeap* heap) {
+    if (VisitHeapImpl(heap)) return;
+    for (auto& space : *heap) {
+      Traverse(space.get());
+    }
+  }
+
+  void Traverse(BaseSpace* space) {
+    const bool is_stopped =
+        space->is_large()
+            ? VisitLargePageSpaceImpl(LargePageSpace::From(space))
+            : VisitNormalPageSpaceImpl(NormalPageSpace::From(space));
+    if (is_stopped) return;
+    for (auto* page : *space) {
+      Traverse(page);
+    }
+  }
+
+  void Traverse(BasePage* page) {
+    if (page->is_large()) {
+      auto* large_page = LargePage::From(page);
+      if (VisitLargePageImpl(large_page)) return;
+      VisitHeapObjectHeaderImpl(large_page->ObjectHeader());
+    } else {
+      auto* normal_page = NormalPage::From(page);
+      if (VisitNormalPageImpl(normal_page)) return;
+      for (auto& header : *normal_page) {
+        VisitHeapObjectHeaderImpl(&header);
+      }
+    }
+  }
+
+ protected:
+  // Visitor functions return true if no deeper processing is required.
+  // Users are supposed to override functions that need special treatment.
+  bool VisitHeap(RawHeap*) { return false; }
+  bool VisitNormalPageSpace(NormalPageSpace*) { return false; }
+  bool VisitLargePageSpace(LargePageSpace*) { return false; }
+  bool VisitNormalPage(NormalPage*) { return false; }
+  bool VisitLargePage(LargePage*) { return false; }
+  bool VisitHeapObjectHeader(HeapObjectHeader*) { return false; }
+
+ private:
+  Derived& ToDerived() { return static_cast<Derived&>(*this); }
+
+  bool VisitHeapImpl(RawHeap* heap) { return ToDerived().VisitHeap(heap); }
+  bool VisitNormalPageSpaceImpl(NormalPageSpace* space) {
+    return ToDerived().VisitNormalPageSpace(space);
+  }
+  bool VisitLargePageSpaceImpl(LargePageSpace* space) {
+    return ToDerived().VisitLargePageSpace(space);
+  }
+  bool VisitNormalPageImpl(NormalPage* page) {
+    return ToDerived().VisitNormalPage(page);
+  }
+  bool VisitLargePageImpl(LargePage* page) {
+    return ToDerived().VisitLargePage(page);
+  }
+  bool VisitHeapObjectHeaderImpl(HeapObjectHeader* hoh) {
+    return ToDerived().VisitHeapObjectHeader(hoh);
+  }
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // V8_HEAP_CPPGC_HEAP_VISITOR_H_

src/heap/cppgc/heap.cc

@@ -8,7 +8,9 @@
 
 #include "src/base/platform/platform.h"
 #include "src/heap/cppgc/heap-object-header-inl.h"
+#include "src/heap/cppgc/heap-object-header.h"
 #include "src/heap/cppgc/heap-page.h"
+#include "src/heap/cppgc/heap-visitor.h"
 #include "src/heap/cppgc/stack.h"
 
 namespace cppgc {
@@ -25,6 +27,35 @@ constexpr bool NeedsConservativeStackScan(Heap::GCConfig config) {
   return config.stack_state == Heap::GCConfig::StackState::kNonEmpty;
 }
 
+class ObjectSizeCounter : public HeapVisitor<ObjectSizeCounter> {
+  friend class HeapVisitor<ObjectSizeCounter>;
+
+ public:
+  size_t GetSize(RawHeap* heap) {
+    Traverse(heap);
+    return accumulated_size_;
+  }
+
+ private:
+  static size_t ObjectSize(const HeapObjectHeader* header) {
+    const size_t size =
+        header->IsLargeObject()
+            ? static_cast<const LargePage*>(BasePage::FromPayload(header))
+                  ->PayloadSize()
+            : header->GetSize();
+    DCHECK_GE(size, sizeof(HeapObjectHeader));
+    return size - sizeof(HeapObjectHeader);
+  }
+
+  bool VisitHeapObjectHeader(HeapObjectHeader* header) {
+    if (header->IsFree()) return true;
+    accumulated_size_ += ObjectSize(header);
+    return true;
+  }
+
+  size_t accumulated_size_ = 0;
+};
+
 }  // namespace
 
 // static
@@ -93,6 +124,10 @@ void Heap::CollectGarbage(GCConfig config) {
   }
 }
 
+size_t Heap::ObjectPayloadSize() const {
+  return ObjectSizeCounter().GetSize(const_cast<RawHeap*>(&raw_heap()));
+}
+
 Heap::NoGCScope::NoGCScope(Heap* heap) : heap_(heap) { heap_->no_gc_scope_++; }
 
 Heap::NoGCScope::~NoGCScope() { heap_->no_gc_scope_--; }

src/heap/cppgc/heap.h

@@ -98,6 +98,8 @@ class V8_EXPORT_PRIVATE Heap final : public cppgc::Heap {
   PageBackend* page_backend() { return page_backend_.get(); }
   const PageBackend* page_backend() const { return page_backend_.get(); }
 
+  size_t ObjectPayloadSize() const;
+
  private:
   bool in_no_gc_scope() const { return no_gc_scope_ > 0; }
   bool is_allocation_allowed() const { return no_allocation_scope_ == 0; }

src/heap/cppgc/object-allocator-inl.h

@@ -20,9 +20,8 @@ void* ObjectAllocator::AllocateObject(size_t size, GCInfoIndex gcinfo) {
   const size_t allocation_size =
       RoundUp(size + sizeof(HeapObjectHeader), kAllocationGranularity);
   const RawHeap::SpaceType type = GetSpaceIndexForSize(allocation_size);
-  return AllocateObjectOnSpace(
+  return AllocateObjectOnSpace(NormalPageSpace::From(raw_heap_->Space(type)),
-      static_cast<NormalPageSpace*>(raw_heap_->Space(type)), allocation_size,
+                               allocation_size, gcinfo);
-      gcinfo);
 }
 
 // static

src/heap/cppgc/object-allocator.cc

@@ -46,8 +46,8 @@ void* ObjectAllocator::OutOfLineAllocate(NormalPageSpace* space, size_t size,
 
   // 1. If this allocation is big enough, allocate a large object.
   if (size >= kLargeObjectSizeThreshold) {
-    auto* large_space = static_cast<LargePageSpace*>(
+    auto* large_space =
-        raw_heap_->Space(RawHeap::SpaceType::kLarge));
+        LargePageSpace::From(raw_heap_->Space(RawHeap::SpaceType::kLarge));
     return AllocateLargeObject(raw_heap_, large_space, size, gcinfo);
   }
 
@@ -84,7 +84,7 @@ void* ObjectAllocator::AllocateFromFreeList(NormalPageSpace* space, size_t size,
     space->free_list().Add({current_lab.start(), current_lab.size()});
   }
 
-  current_lab.Set(entry.address, entry.size);
+  current_lab.Set(static_cast<Address>(entry.address), entry.size);
   return AllocateObjectOnSpace(space, size, gcinfo);
 }
 

test/unittests/heap/cppgc/heap_unittest.cc

@@ -3,7 +3,13 @@
 // found in the LICENSE file.
 
 #include "src/heap/cppgc/heap.h"
+
+#include <algorithm>
+#include <iterator>
+#include <numeric>
+
 #include "include/cppgc/allocation.h"
+#include "src/heap/cppgc/globals.h"
 #include "test/unittests/heap/cppgc/tests.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -34,6 +40,13 @@ class Foo : public GarbageCollected<Foo> {
 
 size_t Foo::destructor_callcount;
 
+template <size_t Size>
+class GCed : public GarbageCollected<Foo> {
+ public:
+  void Visit(cppgc::Visitor*) {}
+  char buf[Size];
+};
+
 }  // namespace
 
 TEST_F(GCHeapTest, PreciseGCReclaimsObjectOnStack) {
@@ -57,7 +70,7 @@ const void* ConservativeGCReturningObject(cppgc::Heap* heap,
 
 }  // namespace
 
-TEST_F(GCHeapTest, ConservaitveGCRetainsObjectOnStack) {
+TEST_F(GCHeapTest, ConservativeGCRetainsObjectOnStack) {
   Foo* volatile object = MakeGarbageCollected<Foo>(GetHeap());
   EXPECT_EQ(0u, Foo::destructor_callcount);
   EXPECT_EQ(object, ConservativeGCReturningObject(GetHeap(), object));
@@ -68,5 +81,35 @@ TEST_F(GCHeapTest, ConservaitveGCRetainsObjectOnStack) {
   EXPECT_EQ(1u, Foo::destructor_callcount);
 }
 
+TEST_F(GCHeapTest, ObjectPayloadSize) {
+  static constexpr size_t kNumberOfObjectsPerArena = 16;
+  static constexpr size_t kObjectSizes[] = {1, 32, 64, 128,
+                                            2 * kLargeObjectSizeThreshold};
+
+  Heap::From(GetHeap())->CollectGarbage();
+
+  for (size_t k = 0; k < kNumberOfObjectsPerArena; ++k) {
+    MakeGarbageCollected<GCed<kObjectSizes[0]>>(GetHeap());
+    MakeGarbageCollected<GCed<kObjectSizes[1]>>(GetHeap());
+    MakeGarbageCollected<GCed<kObjectSizes[2]>>(GetHeap());
+    MakeGarbageCollected<GCed<kObjectSizes[3]>>(GetHeap());
+    MakeGarbageCollected<GCed<kObjectSizes[4]>>(GetHeap());
+  }
+
+  size_t aligned_object_sizes[arraysize(kObjectSizes)];
+  std::transform(std::cbegin(kObjectSizes), std::cend(kObjectSizes),
+                 std::begin(aligned_object_sizes), [](size_t size) {
+                   return RoundUp(size, kAllocationGranularity);
+                 });
+  const size_t expected_size = std::accumulate(
+      std::cbegin(aligned_object_sizes), std::cend(aligned_object_sizes), 0u,
+      [](size_t acc, size_t size) {
+        return acc + kNumberOfObjectsPerArena * size;
+      });
+  // TODO(chromium:1056170): Change to EXPECT_EQ when proper sweeping is
+  // implemented.
+  EXPECT_LE(expected_size, Heap::From(GetHeap())->ObjectPayloadSize());
+}
+
 }  // namespace internal
 }  // namespace cppgc