[IndexedDB] Pool and evict leveldb iterators, to save memory

content/browser/indexed_db/leveldb/leveldb_transaction_unittest.cc

Index: content/browser/indexed_db/leveldb/leveldb_transaction_unittest.cc
diff --git a/content/browser/indexed_db/leveldb/leveldb_transaction_unittest.cc b/content/browser/indexed_db/leveldb/leveldb_transaction_unittest.cc
index 2052d1ab9b4388b9c6ee9b322975b779db053507..60f0b732d65ea2566860c69f4e63a62e569a307d 100644
--- a/content/browser/indexed_db/leveldb/leveldb_transaction_unittest.cc
+++ b/content/browser/indexed_db/leveldb/leveldb_transaction_unittest.cc
@@ -24,6 +24,7 @@
 namespace content {
 
 namespace {
+static const size_t kTestingMaxOpenCursors = 3;
 
 class SimpleComparator : public LevelDBComparator {
  public:
@@ -35,12 +36,17 @@ class SimpleComparator : public LevelDBComparator {
   const char* Name() const override { return "temp_comparator"; }
 };
 
+}  // namespace
+
 class LevelDBTransactionTest : public testing::Test {
  public:
   LevelDBTransactionTest() {}
   void SetUp() override {
     ASSERT_TRUE(temp_directory_.CreateUniqueTempDir());
-    LevelDBDatabase::Open(temp_directory_.GetPath(), &comparator_, &leveldb_);
+    leveldb::Status s =
+        LevelDBDatabase::Open(temp_directory_.GetPath(), &comparator_,
+                              &leveldb_, kTestingMaxOpenCursors);
+    ASSERT_TRUE(s.ok());
     ASSERT_TRUE(leveldb_);
   }
   void TearDown() override {}
@@ -96,6 +102,10 @@ class LevelDBTransactionTest : public testing::Test {
 
   LevelDBDatabase* db() { return leveldb_.get(); }
 
+  scoped_refptr<LevelDBTransaction> CreateTransaction() {
+    return new LevelDBTransaction(db());
+  }
+
  private:
   base::ScopedTempDir temp_directory_;
   SimpleComparator comparator_;
@@ -104,8 +114,6 @@ class LevelDBTransactionTest : public testing::Test {
   DISALLOW_COPY_AND_ASSIGN(LevelDBTransactionTest);
 };
 
-}  // namespace
-
 TEST_F(LevelDBTransactionTest, GetAndPut) {
   leveldb::Status status;
 
@@ -210,6 +218,72 @@ TEST_F(LevelDBTransactionTest, Commit) {
   EXPECT_EQ(value3, got_value);
 }
 
+TEST_F(LevelDBTransactionTest, IterationWithEvictedCursors) {
+  leveldb::Status status;
+
+  const std::string key1("key1");

[pwnall, 2017/03/24 09:16:03]

You don't seem to reuse these strings (which is perfectly fine, the literals are
expressive enough). How about inlining them in the Put calls below?

[dmurph, 2017/03/24 23:33:39]

Done.

+  const std::string key2("key2");
+  const std::string key3("key3");
+  const std::string value1("value1");
+  const std::string value2("value2");
+  const std::string value3("value3");
+
+  Put(key1, value1);
+  Put(key2, value2);
+  Put(key3, value3);
+
+  scoped_refptr<LevelDBTransaction> transaction = CreateTransaction();
+
+  std::unique_ptr<LevelDBIterator> evicted_normal_location =
+      transaction->CreateIterator();
+
+  std::unique_ptr<LevelDBIterator> evicted_before_start =
+      transaction->CreateIterator();
+
+  std::unique_ptr<LevelDBIterator> evicted_after_end =
+      transaction->CreateIterator();
+
+  std::unique_ptr<LevelDBIterator> it1 = transaction->CreateIterator();
+  std::unique_ptr<LevelDBIterator> it2 = transaction->CreateIterator();
+  std::unique_ptr<LevelDBIterator> it3 = transaction->CreateIterator();
+
+  evicted_normal_location->Seek("key1");
+  evicted_before_start->Seek("key1");
+  evicted_before_start->Prev();
+  evicted_after_end->SeekToLast();
+  evicted_after_end->Next();
+
+  // Nothing is purged, as we just have 3 iterators used.
+  EXPECT_FALSE(evicted_normal_location->IsEvicted());
+  EXPECT_FALSE(evicted_before_start->IsEvicted());
+  EXPECT_FALSE(evicted_after_end->IsEvicted());
+  EXPECT_FALSE(evicted_before_start->IsValid());
+  EXPECT_FALSE(evicted_after_end->IsValid());
+
+  // Should purge all of our earlier iterators.
+  it1->Seek("key1");
+  it2->Seek("key2");
+  it3->Seek("key3");
+
+  EXPECT_TRUE(evicted_normal_location->IsEvicted());
+  EXPECT_TRUE(evicted_before_start->IsEvicted());
+  EXPECT_TRUE(evicted_after_end->IsEvicted());
+
+  // Check we don't need to reload for just the key.
+  EXPECT_EQ(key1, evicted_normal_location->Key());
+  EXPECT_TRUE(evicted_normal_location->IsEvicted());
+
+  // Make sure iterators are reloaded correctly.
+  EXPECT_TRUE(evicted_normal_location->IsValid());
+  EXPECT_EQ(value1, evicted_normal_location->Value());
+  EXPECT_FALSE(evicted_normal_location->IsEvicted());
+  EXPECT_FALSE(evicted_before_start->IsValid());
+  EXPECT_FALSE(evicted_after_end->IsValid());
+
+  // And our |Value()| call purged the earlier iterator.
+  EXPECT_TRUE(it1->IsEvicted());
+}
+
 namespace {
 enum RangePrepareMode {
   DataInMemory,