IndexedDB: Fix cursor prefetching edge cases

content/child/indexed_db/webidbcursor_impl_unittest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
 #include "content/child/indexed_db/indexed_db_dispatcher.h"
 #include "content/child/indexed_db/indexed_db_key_builders.h"
 #include "content/child/indexed_db/webidbcursor_impl.h"
 #include "content/child/thread_safe_sender.h"
@@ skipping 12 matching lines @@
 namespace content {
 
 namespace {
 
 class MockDispatcher : public IndexedDBDispatcher {
  public:
   MockDispatcher(ThreadSafeSender* thread_safe_sender)
       : 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) {}
 
   virtual void RequestIDBCursorPrefetch(int n,
                                         WebIDBCallbacks* callbacks,
                                         int32 ipc_cursor_id) OVERRIDE {
     ++prefetch_calls_;
     last_prefetch_count_ = n;
     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 {
     ++advance_calls_;
     callbacks_.reset(callbacks);
   }
 
   virtual void RequestIDBCursorContinue(const IndexedDBKey& key,
                                         const IndexedDBKey& primary_key,
                                         WebIDBCallbacks* callbacks,
                                         int32 ipc_cursor_id) OVERRIDE {
     ++continue_calls_;
     callbacks_.reset(callbacks);
   }
 
   virtual void CursorDestroyed(int32 ipc_cursor_id) OVERRIDE {
     destroyed_cursor_id_ = ipc_cursor_id;
   }
 
   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_;
   scoped_ptr<WebIDBCallbacks> callbacks_;
 };
 
 class MockContinueCallbacks : public WebIDBCallbacks {
  public:
   MockContinueCallbacks(IndexedDBKey* key = 0) : key_(key) {}
 
@@ skipping 157 matching lines @@
 
   // IDBCursor.advance(lots) - beyond the fetched amount
   cursor.advance(WebIDBCursorImpl::kMaxPrefetchAmount,
                  new MockContinueCallbacks(&key));
   EXPECT_EQ(1, dispatcher_->advance_calls());
   EXPECT_EQ(1, dispatcher_->prefetch_calls());
   EXPECT_EQ(static_cast<int>(WebIDBCursorImpl::kPrefetchContinueThreshold),
             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