Automated rollback of commit 5fc0e22.

PiperOrigin-RevId: 734287833

Author: tanx16

src/google/protobuf/descriptor.h

@@ -2530,22 +2530,18 @@ class PROTOBUF_EXPORT DescriptorPool {
     auto key = std::pair<const void*, const void*>(field, &type_key);
     {
       absl::ReaderMutexLock lock(&field_memo_table_mutex_);
-      auto it = field_memo_table_.find(key);
-      if (it != field_memo_table_.end()) {
+      auto it = field_memo_table_->find(key);
+      if (it != field_memo_table_->end()) {
         return internal::DownCast<const MemoData<ResultT>&>(*it->second).value;
       }
     }
     auto result = std::make_unique<MemoData<ResultT>>();
     result->value = func(field);
     {
       absl::MutexLock lock(&field_memo_table_mutex_);
-      auto& res = field_memo_table_[key];
-      // Only initialize the first time. We don't want to invalidate old
-      // references.
-      if (res == nullptr) {
-        res = std::move(result);
-      }
-      return internal::DownCast<const MemoData<ResultT>&>(*res).value;
+      auto insert_result = field_memo_table_->insert({key, std::move(result)});
+      auto it = insert_result.first;
+      return internal::DownCast<const MemoData<ResultT>&>(*it->second).value;
     }
   }
   // Return true if the given name is a sub-symbol of any non-package
@@ -2608,9 +2604,12 @@ class PROTOBUF_EXPORT DescriptorPool {
 
 #ifndef SWIG
   mutable absl::Mutex field_memo_table_mutex_;
-  mutable absl::flat_hash_map<std::pair<const void*, const void*>,
-                              std::unique_ptr<MemoBase>>
-      field_memo_table_ ABSL_GUARDED_BY(field_memo_table_mutex_);
+  mutable std::unique_ptr<absl::flat_hash_map<
+      std::pair<const void*, const void*>, std::unique_ptr<MemoBase>>>
+      field_memo_table_ ABSL_GUARDED_BY(field_memo_table_mutex_) =
+          std::make_unique<
+              absl::flat_hash_map<std::pair<const void*, const void*>,
+                                  std::unique_ptr<MemoBase>>>();
 #endif  // SWIG
 
   // If fallback_database_ is nullptr, this is nullptr.  Otherwise, this is a

src/google/protobuf/descriptor_unittest.cc

@@ -12178,6 +12178,27 @@ TEST_F(DescriptorPoolMemoizationTest, MemoizeProjectionMultithreaded) {
   }
 }
 
+TEST_F(DescriptorPoolMemoizationTest, MemoizeProjectionInsertionRace) {
+  auto name_lambda = [](const FieldDescriptor* field) {
+    return field->full_name();
+  };
+  proto2_unittest::TestAllTypes message;
+  const Descriptor* descriptor = message.GetDescriptor();
+  std::vector<std::thread> threads;
+  for (int i = 0; i < descriptor->field_count(); ++i) {
+    for (int j = 0; j < 3; ++j) {
+      threads.emplace_back([this, name_lambda, descriptor, i]() {
+        auto name = DescriptorPoolMemoizationTest::MemoizeProjection(
+            descriptor->file()->pool(), descriptor->field(i), name_lambda);
+        ASSERT_THAT(name, HasSubstr("proto2_unittest.TestAllTypes"));
+      });
+    }
+  }
+  for (auto& thread : threads) {
+    thread.join();
+  }
+}
+