IndexedDB: Fix cursor prefetching edge cases

content/child/indexed_db/webidbcursor_impl_unittest.cc

Index: content/child/indexed_db/webidbcursor_impl_unittest.cc
diff --git a/content/child/indexed_db/webidbcursor_impl_unittest.cc b/content/child/indexed_db/webidbcursor_impl_unittest.cc
index 14842df9c3e802a8ec50ed8f444fd04d1ddbeeab..111595048cb52eaffa7aee16dee97bc9a1e61700 100644
--- a/content/child/indexed_db/webidbcursor_impl_unittest.cc
+++ b/content/child/indexed_db/webidbcursor_impl_unittest.cc
@@ -30,6 +30,8 @@ class MockDispatcher : public IndexedDBDispatcher {
       : IndexedDBDispatcher(thread_safe_sender),
         prefetch_calls_(0),
         last_prefetch_count_(0),
+        reset_calls_(0),
+        last_used_count_(0),
         advance_calls_(0),
         continue_calls_(0),
         destroyed_cursor_id_(0) {}
@@ -42,6 +44,13 @@ class MockDispatcher : public IndexedDBDispatcher {
     callbacks_.reset(callbacks);
   }
 
+  virtual void RequestIDBCursorPrefetchReset(int used_prefetches,
+                                             int unused_prefetches,
+                                             int32 ipc_cursor_id) OVERRIDE {
+    ++reset_calls_;
+    last_used_count_ = used_prefetches;
+  }
+
   virtual void RequestIDBCursorAdvance(unsigned long count,
                                        WebIDBCallbacks* callbacks,
                                        int32 ipc_cursor_id) OVERRIDE {
@@ -62,14 +71,18 @@ class MockDispatcher : public IndexedDBDispatcher {
   }
 
   int prefetch_calls() { return prefetch_calls_; }
+  int last_prefetch_count() { return last_prefetch_count_; }
+  int reset_calls() { return reset_calls_; }
+  int last_used_count() { return last_used_count_; }
   int advance_calls() { return advance_calls_; }
   int continue_calls() { return continue_calls_; }
-  int last_prefetch_count() { return last_prefetch_count_; }
   int32 destroyed_cursor_id() { return destroyed_cursor_id_; }
 
  private:
   int prefetch_calls_;
   int last_prefetch_count_;
+  int reset_calls_;
+  int last_used_count_;
   int advance_calls_;
   int continue_calls_;
   int32 destroyed_cursor_id_;
@@ -247,4 +260,48 @@ TEST_F(WebIDBCursorImplTest, AdvancePrefetchTest) {
             dispatcher_->continue_calls());
 }
 
+TEST_F(WebIDBCursorImplTest, PrefetchReset) {
+  WebIDBCursorImpl cursor(WebIDBCursorImpl::kInvalidCursorId,
+                          thread_safe_sender_.get());
+
+  // Call continue() until prefetching should kick in.
+  int continue_calls = 0;
+  EXPECT_EQ(dispatcher_->continue_calls(), 0);
+  for (int i = 0; i < WebIDBCursorImpl::kPrefetchContinueThreshold; ++i) {
+    cursor.continueFunction(null_key_, new MockContinueCallbacks());
+    EXPECT_EQ(++continue_calls, dispatcher_->continue_calls());
+    EXPECT_EQ(0, dispatcher_->prefetch_calls());
+  }
+
+  // Initiate the prefetch
+  cursor.continueFunction(null_key_, new MockContinueCallbacks());
+  EXPECT_EQ(continue_calls, dispatcher_->continue_calls());
+  EXPECT_EQ(1, dispatcher_->prefetch_calls());
+  EXPECT_EQ(0, dispatcher_->reset_calls());
+
+  // Now invalidate it
+  cursor.ResetPrefetchCache();
+
+  // No reset should have been sent since nothing has been received yet.
+  EXPECT_EQ(0, dispatcher_->reset_calls());
+
+  // Fill the prefetch cache as requested.
+  int prefetch_count = dispatcher_->last_prefetch_count();
+  std::vector<IndexedDBKey> keys(prefetch_count);
+  std::vector<IndexedDBKey> primary_keys(prefetch_count);
+  std::vector<WebData> values(prefetch_count);
+  cursor.SetPrefetchData(keys, primary_keys, values);
+
+  // No reset should have been sent since prefetch data hasn't been used.
+  EXPECT_EQ(0, dispatcher_->reset_calls());
+
+  // The real dispatcher would call cursor->CachedContinue(), so do that:
+  scoped_ptr<WebIDBCallbacks> callbacks(new MockContinueCallbacks());
+  cursor.CachedContinue(callbacks.get());
+
+  // Now the cursor should have reset the rest of the cache.
+  EXPECT_EQ(1, dispatcher_->reset_calls());
+  EXPECT_EQ(1, dispatcher_->last_used_count());
+}
+
 }  // namespace content