From 17ed49b5605ed9b9fcf7fbef8a59ca9594dfef01 Mon Sep 17 00:00:00 2001
From: Michael Lippautz <mlippautz@chromium.org>
Date: Mon, 30 Nov 2020 22:30:55 +0100
Subject: [PATCH] heap, cppgc: Add write barrier for TracedReference

Adds publicly callable version of write barrier for TracedReferenceBase.

Bug: chromium:1056170
Change-Id: Ie45b4ebbe91d9f0e8f76b521dcbfd931232adcf6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2565248
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71524}
---
 include/DEPS                           |  1 +
 include/cppgc/internal/write-barrier.h | 12 ++---
 include/v8-cppgc.h                     | 61 +++++++++++++++++++++++++-
 src/heap/cppgc-js/cpp-heap.cc          |  6 +++
 4 files changed, 73 insertions(+), 7 deletions(-)

diff --git a/include/DEPS b/include/DEPS
index c5b95537d9..9f4002059b 100644
--- a/include/DEPS
+++ b/include/DEPS
@@ -4,5 +4,6 @@ include_rules = [
   "+cppgc/common.h",
   # Used by v8-cppgc.h to bridge to cppgc.
   "+cppgc/custom-space.h",
+  "+cppgc/internal/write-barrier.h",
   "+cppgc/visitor.h",
 ]
diff --git a/include/cppgc/internal/write-barrier.h b/include/cppgc/internal/write-barrier.h
index 5edd04caab..e3cc4c989d 100644
--- a/include/cppgc/internal/write-barrier.h
+++ b/include/cppgc/internal/write-barrier.h
@@ -73,6 +73,12 @@ class V8_EXPORT WriteBarrier final {
                                             const void* slot) {}
 #endif  // CPPGC_YOUNG_GENERATION
 
+#if V8_ENABLE_CHECKS
+  static void CheckParams(Type expected_type, const Params& params);
+#else   // !V8_ENABLE_CHECKS
+  static void CheckParams(Type expected_type, const Params& params) {}
+#endif  // !V8_ENABLE_CHECKS
+
  private:
   WriteBarrier() = delete;
 
@@ -92,12 +98,6 @@ class V8_EXPORT WriteBarrier final {
   static void SteeleMarkingBarrierSlow(const void* value);
   static void SteeleMarkingBarrierSlowWithSentinelCheck(const void* value);
 
-#if V8_ENABLE_CHECKS
-  static void CheckParams(Type expected_type, const Params& params);
-#else   // !V8_ENABLE_CHECKS
-  static void CheckParams(Type expected_type, const Params& params) {}
-#endif  // !V8_ENABLE_CHECKS
-
 #if defined(CPPGC_YOUNG_GENERATION)
   static void GenerationalBarrierSlow(const CagedHeapLocalData& local_data,
                                       const AgeTable& ageTable,
diff --git a/include/v8-cppgc.h b/include/v8-cppgc.h
index 01ded7f622..8a0d9cb9a0 100644
--- a/include/v8-cppgc.h
+++ b/include/v8-cppgc.h
@@ -9,9 +9,10 @@
 #include <vector>
 
 #include "cppgc/custom-space.h"
+#include "cppgc/internal/write-barrier.h"
 #include "cppgc/visitor.h"
 #include "v8-internal.h"  // NOLINT(build/include_directory)
-#include "v8.h"  // NOLINT(build/include_directory)
+#include "v8.h"           // NOLINT(build/include_directory)
 
 namespace cppgc {
 class AllocationHandle;
@@ -68,6 +69,64 @@ class JSVisitor : public cppgc::Visitor {
   virtual void Visit(const TracedReferenceBase& ref) {}
 };
 
+/**
+ * **DO NOT USE: Use the appropriate managed types.**
+ *
+ * Consistency helpers that aid in maintaining a consistent internal state of
+ * the garbage collector.
+ */
+class JSHeapConsistency final {
+ public:
+  using WriteBarrierParams = cppgc::internal::WriteBarrier::Params;
+  using WriteBarrierType = cppgc::internal::WriteBarrier::Type;
+
+  /**
+   * Gets the required write barrier type for a specific write.
+   *
+   * \param ref The reference being written to.
+   * \param params Parameters that may be used for actual write barrier calls.
+   *   Only filled if return value indicates that a write barrier is needed. The
+   *   contents of the `params` are an implementation detail.
+   * \returns whether a write barrier is needed and which barrier to invoke.
+   */
+  static V8_INLINE WriteBarrierType GetWriteBarrierType(
+      const TracedReferenceBase& ref, WriteBarrierParams& params) {
+    if (ref.IsEmpty()) return WriteBarrierType::kNone;
+    return cppgc::internal::WriteBarrier::GetWriteBarrierType(&ref, params);
+  }
+
+  /**
+   * Conservative Dijkstra-style write barrier that processes an object if it
+   * has not yet been processed.
+   *
+   * \param params The parameters retrieved from `GetWriteBarrierType()`.
+   * \param ref The reference being written to.
+   */
+  static V8_INLINE void DijkstraMarkingBarrier(const WriteBarrierParams& params,
+                                               cppgc::HeapHandle& heap_handle,
+                                               const TracedReferenceBase& ref) {
+    cppgc::internal::WriteBarrier::CheckParams(WriteBarrierType::kMarking,
+                                               params);
+    DijkstraMarkingBarrierSlow(heap_handle, ref);
+  }
+
+  /**
+   * Generational barrier for maintaining consistency when running with multiple
+   * generations.
+   *
+   * \param params The parameters retrieved from `GetWriteBarrierType()`.
+   * \param ref The reference being written to.
+   */
+  static V8_INLINE void GenerationalBarrier(const WriteBarrierParams& params,
+                                            const TracedReferenceBase& ref) {}
+
+ private:
+  JSHeapConsistency() = delete;
+
+  static void DijkstraMarkingBarrierSlow(cppgc::HeapHandle&,
+                                         const TracedReferenceBase& ref);
+};
+
 }  // namespace v8
 
 namespace cppgc {
diff --git a/src/heap/cppgc-js/cpp-heap.cc b/src/heap/cppgc-js/cpp-heap.cc
index 34449032f2..c8f62c89e5 100644
--- a/src/heap/cppgc-js/cpp-heap.cc
+++ b/src/heap/cppgc-js/cpp-heap.cc
@@ -42,6 +42,12 @@ cppgc::HeapHandle& CppHeap::GetHeapHandle() {
   return *internal::CppHeap::From(this);
 }
 
+void JSHeapConsistency::DijkstraMarkingBarrierSlow(
+    cppgc::HeapHandle& heap_handle, const TracedReferenceBase& ref) {
+  auto& heap_base = cppgc::internal::HeapBase::From(heap_handle);
+  static_cast<JSVisitor*>(&heap_base.marker()->Visitor())->Trace(ref);
+}
+
 namespace internal {
 
 namespace {