cppgc: Allow multiple calls to InitializeProcess/ShutdownProcess

Model cppgc::InitializeProcess()/cppgc::ShutdownProcess() similar to
V8's InitializePlatform()/ShutdownPlatform() in that we allow the pair
to be called multiple times.

GCInfoTable will not be freed on ShutdownProcess though as the current
global design uses static indices to retrieve per-type metadata.

Drive-by: Remove stale ShutdownProcess() call.

Change-Id: Ia9b50325a964e85a72f3ef218e72bc386b69be51
Bug: chromium:1176416, chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2685171
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72630}

include/cppgc/platform.h

@@ -125,12 +125,19 @@ class V8_EXPORT Platform {
 
 /**
  * Process-global initialization of the garbage collector. Must be called before
- * creating a Heap. Must only be called once per process.
+ * creating a Heap.
+ *
+ * Can be called multiple times when paired with `ShutdownProcess()`.
+ *
+ * \param page_allocator The allocator used for maintaining meta data. Must not
+ *   change between multiple calls to InitializeProcess.
  */
-V8_EXPORT void InitializeProcess(PageAllocator*);
+V8_EXPORT void InitializeProcess(PageAllocator* page_allocator);
 
 /**
- * Must be called after destroying the last used heap.
+ * Must be called after destroying the last used heap. Some process-global
+ * metadata may not be returned and reused upon a subsequent
+ * `InitializeProcess()` call.
  */
 V8_EXPORT void ShutdownProcess();
 

src/heap/cppgc/gc-info-table.cc

@@ -29,14 +29,7 @@ static_assert(v8::base::bits::IsPowerOfTwo(kEntrySize),
               "GCInfoTable entries size must be power of "
               "two");
 
-}  // namespace
-
-GCInfoTable* GlobalGCInfoTable::global_table_ = nullptr;
-constexpr GCInfoIndex GCInfoTable::kMaxIndex;
-constexpr GCInfoIndex GCInfoTable::kMinIndex;
-constexpr GCInfoIndex GCInfoTable::kInitialWantedLimit;
-
-void GlobalGCInfoTable::Create(PageAllocator* page_allocator) {
+PageAllocator* GetAllocator(PageAllocator* page_allocator) {
   if (!page_allocator) {
     static v8::base::LeakyObject<v8::base::PageAllocator>
         default_page_allocator;
@@ -44,9 +37,23 @@ void GlobalGCInfoTable::Create(PageAllocator* page_allocator) {
   }
   // TODO(chromium:1056170): Wrap page_allocator into LsanPageAllocator when
   // running with LEAK_SANITIZER.
-  static v8::base::LeakyObject<GCInfoTable> table(page_allocator);
+  return page_allocator;
+}
+
+}  // namespace
+
+GCInfoTable* GlobalGCInfoTable::global_table_ = nullptr;
+constexpr GCInfoIndex GCInfoTable::kMaxIndex;
+constexpr GCInfoIndex GCInfoTable::kMinIndex;
+constexpr GCInfoIndex GCInfoTable::kInitialWantedLimit;
+
+// static
+void GlobalGCInfoTable::Initialize(PageAllocator* page_allocator) {
+  static v8::base::LeakyObject<GCInfoTable> table(GetAllocator(page_allocator));
   if (!global_table_) {
     global_table_ = table.get();
+  } else {
+    CHECK_EQ(page_allocator, global_table_->allocator());
   }
 }
 

src/heap/cppgc/gc-info-table.h

@@ -67,6 +67,8 @@ class V8_EXPORT GCInfoTable final {
   GCInfoIndex LimitForTesting() const { return limit_; }
   GCInfo& TableSlotForTesting(GCInfoIndex index) { return table_[index]; }
 
+  PageAllocator* allocator() const { return page_allocator_; }
+
  private:
   void Resize();
 
@@ -93,8 +95,10 @@ class V8_EXPORT GlobalGCInfoTable final {
   GlobalGCInfoTable(const GlobalGCInfoTable&) = delete;
   GlobalGCInfoTable& operator=(const GlobalGCInfoTable&) = delete;
 
-  // Sets up a singleton table that can be acquired using Get().
-  static void Create(PageAllocator* page_allocator);
+  // Sets up the table with the provided `page_allocator`. Will use an internal
+  // allocator in case no PageAllocator is provided. May be called multiple
+  // times with the same `page_allocator` argument.
+  static void Initialize(PageAllocator* page_allocator);
 
   // Accessors for the singleton table.
   static GCInfoTable& GetMutable() { return *global_table_; }

src/heap/cppgc/platform.cc

@@ -10,19 +10,22 @@
 
 namespace cppgc {
 
+namespace {
+PageAllocator* g_page_allocator = nullptr;
+}  // namespace
+
 TracingController* Platform::GetTracingController() {
   static v8::base::LeakyObject<TracingController> tracing_controller;
   return tracing_controller.get();
 }
 
 void InitializeProcess(PageAllocator* page_allocator) {
-  static PageAllocator* allocator = nullptr;
-  CHECK(!allocator);
-  internal::GlobalGCInfoTable::Create(page_allocator);
-  allocator = page_allocator;
+  CHECK(!g_page_allocator);
+  internal::GlobalGCInfoTable::Initialize(page_allocator);
+  g_page_allocator = page_allocator;
 }
 
-void ShutdownProcess() {}
+void ShutdownProcess() { g_page_allocator = nullptr; }
 
 namespace internal {
 

src/init/v8.cc

@@ -169,7 +169,6 @@ void V8::ShutdownPlatform() {
   v8::tracing::TracingCategoryObserver::TearDown();
   v8::base::SetPrintStackTrace(nullptr);
   platform_ = nullptr;
-  cppgc::ShutdownProcess();
 }
 
 v8::Platform* V8::GetCurrentPlatform() {