Revert 141514 - Remove CachingValueStore in favor of an async ValueStoreFrontend.

Caused massive number of use-after-free crashes on ClusterFuzz.

After actually seeing the use cases for the value store in extension code, I
realized that an async version would be more appropriate. This one will use
less memory as well, since we won't need to keep the cache in memory.

BUG=123366
TEST=no


Review URL: https://chromiumcodereview.appspot.com/10539073

TBR=mpcomplete@chromium.org
Review URL: https://chromiumcodereview.appspot.com/10537116

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141603 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/value_store/value_store_frontend.cc → chrome/browser/value_store/caching_value_store.cc

@@ -2,42 +2,31 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/value_store/value_store_frontend.h"
+#include "chrome/browser/value_store/caching_value_store.h"
 
 #include "chrome/browser/value_store/leveldb_value_store.h"
 #include "content/public/browser/browser_thread.h"
 
 using content::BrowserThread;
 
-class ValueStoreFrontend::Backend : public base::RefCountedThreadSafe<Backend> {
+class CachingValueStore::Backend : public base::RefCountedThreadSafe<Backend> {
  public:
-  explicit Backend(const FilePath& db_path) : storage_(NULL) {
-    BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
-        base::Bind(&ValueStoreFrontend::Backend::InitOnFileThread,
-                   this, db_path));
-  }
+  typedef base::Callback<void(scoped_ptr<base::DictionaryValue>)> ReadyCallback;
+  Backend() : storage_(NULL) {}
 
-  void Get(const std::string& key,
-           const ValueStoreFrontend::ReadCallback& callback) {
-    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
-    ValueStore::ReadResult result = storage_->Get(key);
-
-    // Extract the value from the ReadResult and pass ownership of it to the
-    // callback.
-    base::Value* value = NULL;
-    if (!result->HasError())
-      result->settings()->RemoveWithoutPathExpansion(key, &value);
-
-    scoped_ptr<base::Value> passed_value(value);
-    BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
-        base::Bind(&ValueStoreFrontend::Backend::RunCallback,
-                   this, callback, base::Passed(passed_value.Pass())));
+  void Init(const FilePath& db_path, ReadyCallback callback) {
+    BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+        base::Bind(&CachingValueStore::Backend::InitOnFileThread,
+                   this, db_path, callback));
   }
 
   void Set(const std::string& key, scoped_ptr<base::Value> value) {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
-    // We don't need the old value, so skip generating changes.
-    storage_->Set(ValueStore::IGNORE_QUOTA | ValueStore::NO_GENERATE_CHANGES,
+    // We've already checked that the value has changed, so don't bother
+    // checking again. Also, skip changes to avoid wasted copies.
+    storage_->Set(ValueStore::IGNORE_QUOTA |
+                      ValueStore::NO_GENERATE_CHANGES |
+                      ValueStore::NO_CHECK_OLD_VALUE,
                   key, *value.get());
   }
 
@@ -57,16 +46,17 @@ class ValueStoreFrontend::Backend : public base::RefCountedThreadSafe<Backend> {
     }
   }
 
-  void InitOnFileThread(const FilePath& db_path) {
+  void InitOnFileThread(const FilePath& db_path, ReadyCallback callback) {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
     DCHECK(!storage_);
     storage_ = LeveldbValueStore::Create(db_path);
-  }
 
-  void RunCallback(const ValueStoreFrontend::ReadCallback& callback,
-                   scoped_ptr<base::Value> value) {
-    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-    callback.Run(value.Pass());
+    ValueStore::ReadResult result = storage_->Get();
+    if (result->HasError()) {
+      callback.Run(scoped_ptr<base::DictionaryValue>(NULL));
+    } else {
+      callback.Run(result->settings().Pass());
+    }
   }
 
   // The actual ValueStore that handles persisting the data to disk. Used
@@ -76,36 +66,76 @@ class ValueStoreFrontend::Backend : public base::RefCountedThreadSafe<Backend> {
   DISALLOW_COPY_AND_ASSIGN(Backend);
 };
 
-ValueStoreFrontend::ValueStoreFrontend(const FilePath& db_path)
-    : backend_(new Backend(db_path)) {
+CachingValueStore::CachingValueStore(const FilePath& db_path)
+    : backend_(new Backend()) {
+  backend_->Init(db_path,
+                 base::Bind(&CachingValueStore::OnBackendReady, AsWeakPtr()));
 }
 
-ValueStoreFrontend::~ValueStoreFrontend() {
+CachingValueStore::~CachingValueStore() {
+}
+
+bool CachingValueStore::Get(const std::string& key,
+                            const base::Value** result) {
   DCHECK(CalledOnValidThread());
+  DCHECK(IsInitialized());
+
+  base::Value* value = NULL;
+  if (cache_->GetWithoutPathExpansion(key, &value)) {
+    *result = value;
+    return true;
+  }
+  return false;
 }
 
-void ValueStoreFrontend::Get(const std::string& key,
-                             const ReadCallback& callback) {
+void CachingValueStore::Set(const std::string& key, base::Value* value) {
   DCHECK(CalledOnValidThread());
+  DCHECK(IsInitialized());
+
+  scoped_ptr<base::Value> new_value(value);
+  base::Value* old_value = NULL;
+  if (!cache_->GetWithoutPathExpansion(key, &old_value) ||
+      !value->Equals(old_value)) {
+    cache_->SetWithoutPathExpansion(key, new_value.release());
 
-  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
-      base::Bind(&ValueStoreFrontend::Backend::Get,
-                 backend_, key, callback));
+    scoped_ptr<base::Value> passed_value(value->DeepCopy());
+    BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+        base::Bind(&CachingValueStore::Backend::Set,
+                   backend_, key, base::Passed(passed_value.Pass())));
+  }
+}
+
+void CachingValueStore::Remove(const std::string& key) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(IsInitialized());
+
+  if (cache_->RemoveWithoutPathExpansion(key, NULL)) {
+    BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+        base::Bind(&CachingValueStore::Backend::Remove,
+                   backend_, key));
+  }
+}
+
+bool CachingValueStore::IsInitialized() {
+  DCHECK(CalledOnValidThread());
+  return !!cache_.get();
 }
 
-void ValueStoreFrontend::Set(const std::string& key,
-                             scoped_ptr<base::Value> value) {
+void CachingValueStore::AddObserver(Observer* observer) {
   DCHECK(CalledOnValidThread());
+  observers_.AddObserver(observer);
+}
 
-  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
-      base::Bind(&ValueStoreFrontend::Backend::Set,
-                 backend_, key, base::Passed(value.Pass())));
+void CachingValueStore::RemoveObserver(Observer* observer) {
+  DCHECK(CalledOnValidThread());
+  observers_.RemoveObserver(observer);
 }
 
-void ValueStoreFrontend::Remove(const std::string& key) {
+void CachingValueStore::OnBackendReady(
+    scoped_ptr<base::DictionaryValue> values) {
   DCHECK(CalledOnValidThread());
+  DCHECK(!cache_.get());
+  cache_.swap(values);
 
-  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
-      base::Bind(&ValueStoreFrontend::Backend::Remove,
-                 backend_, key));
+  FOR_EACH_OBSERVER(Observer, observers_, OnInitializationComplete());
 }

chrome/browser/value_store/caching_value_store.h

+// Copyright (c) 2012 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.
+
+#ifndef CHROME_BROWSER_VALUE_STORE_CACHING_VALUE_STORE_H_
+#define CHROME_BROWSER_VALUE_STORE_CACHING_VALUE_STORE_H_
+#pragma once
+
+#include <string>
+
+#include "base/file_path.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
+#include "base/threading/non_thread_safe.h"
+#include "base/values.h"
+
+// Value store area with caching, backed by a LeveldbValueStore on the FILE
+// thread. The key/value store is flat with no path expansion, meaning "foo"
+// and "foo.bar" are completely separate keys.
+class CachingValueStore
+    : public base::SupportsWeakPtr<CachingValueStore>,
+      public base::NonThreadSafe {
+ public:
+  class Observer {
+   public:
+    virtual ~Observer() {}
+
+    // Notification that the Store is ready to use.
+    virtual void OnInitializationComplete() = 0;
+  };
+
+  explicit CachingValueStore(const FilePath& db_path);
+  ~CachingValueStore();
+
+  // Retrieves a value from the cache, returning true if value with the given
+  // key exists. The returned value is a reference to the value in the cache,
+  // i.e. no copies are made.
+  bool Get(const std::string& key, const base::Value** result);
+
+  // Sets a value with the given key. Ownership of |value| is transferred to
+  // the store.
+  void Set(const std::string& key, base::Value* value);
+
+  // Removes the value with the given key.
+  void Remove(const std::string& key);
+
+  // Returns true if the store has finished initializing.
+  bool IsInitialized();
+
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+ private:
+  class Backend;
+
+  // Called when our backend finishes reading the database.
+  void OnBackendReady(scoped_ptr<base::DictionaryValue> values);
+
+  // A cache of the value store. This is always up-to-date, with changes
+  // persisted to disk as they are made.
+  scoped_ptr<base::DictionaryValue> cache_;
+
+  // A helper class to manage lifetime of the backing ValueStore, which lives
+  // on the FILE thread.
+  scoped_refptr<Backend> backend_;
+
+  ObserverList<Observer, true> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(CachingValueStore);
+};
+
+#endif  // CHROME_BROWSER_VALUE_STORE_CACHING_VALUE_STORE_H_

chrome/browser/value_store/value_store_frontend_unittest.cc → chrome/browser/value_store/caching_value_store_unittest.cc

@@ -7,7 +7,7 @@
 #include "base/message_loop.h"
 #include "base/path_service.h"
 #include "base/scoped_temp_dir.h"
-#include "chrome/browser/value_store/value_store_frontend.h"
+#include "chrome/browser/value_store/caching_value_store.h"
 #include "chrome/common/chrome_paths.h"
 #include "content/public/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -16,9 +16,11 @@ using content::BrowserThread;
 
 // Test suite for CachingValueStore, using a test database with a few simple
 // entries.
-class ValueStoreFrontendTest : public testing::Test {
+class CachingValueStoreTest
+    : public testing::Test,
+      public CachingValueStore::Observer {
  public:
-  ValueStoreFrontendTest()
+  CachingValueStoreTest()
       : ui_thread_(BrowserThread::UI, MessageLoop::current()),
         file_thread_(BrowserThread::FILE, MessageLoop::current()) {
   }
@@ -37,29 +39,26 @@ class ValueStoreFrontendTest : public testing::Test {
 
   virtual void TearDown() {
     MessageLoop::current()->RunAllPending();  // wait for storage to delete
+    storage_->RemoveObserver(this);
     storage_.reset();
   }
 
-  // Reset the value store, reloading the DB from disk.
-  void ResetStorage() {
-    storage_.reset(new ValueStoreFrontend(db_path_));
+  // CachingValueStore::Observer
+  virtual void OnInitializationComplete() {
+    MessageLoop::current()->Quit();
   }
 
-  bool Get(const std::string& key, scoped_ptr<base::Value>* output) {
-    storage_->Get(key, base::Bind(&ValueStoreFrontendTest::GetAndWait,
-                                  base::Unretained(this), output));
-    MessageLoop::current()->Run();  // wait for GetAndWait
-    return !!output->get();
+  // Reset the value store, reloading the DB from disk.
+  void ResetStorage() {
+    if (storage_.get())
+      storage_->RemoveObserver(this);
+    storage_.reset(new CachingValueStore(db_path_));
+    storage_->AddObserver(this);
+    MessageLoop::current()->Run();  // wait for OnInitializationComplete
   }
 
  protected:
-  void GetAndWait(scoped_ptr<base::Value>* output,
-                  scoped_ptr<base::Value> result) {
-    *output = result.Pass();
-    MessageLoop::current()->Quit();
-  }
-
-  scoped_ptr<ValueStoreFrontend> storage_;
+  scoped_ptr<CachingValueStore> storage_;
   ScopedTempDir temp_dir_;
   FilePath db_path_;
   MessageLoop message_loop_;
@@ -67,50 +66,48 @@ class ValueStoreFrontendTest : public testing::Test {
   content::TestBrowserThread file_thread_;
 };
 
-TEST_F(ValueStoreFrontendTest, GetExistingData) {
-  scoped_ptr<base::Value> value(NULL);
-  ASSERT_FALSE(Get("key0", &value));
+TEST_F(CachingValueStoreTest, GetExistingData) {
+  const base::Value* value = NULL;
+  ASSERT_FALSE(storage_->Get("key0", &value));
 
   // Test existing keys in the DB.
   {
-    ASSERT_TRUE(Get("key1", &value));
+    ASSERT_TRUE(storage_->Get("key1", &value));
     std::string result;
     ASSERT_TRUE(value->GetAsString(&result));
     EXPECT_EQ("value1", result);
   }
 
   {
-    ASSERT_TRUE(Get("key2", &value));
+    ASSERT_TRUE(storage_->Get("key2", &value));
     int result;
     ASSERT_TRUE(value->GetAsInteger(&result));
     EXPECT_EQ(2, result);
   }
 }
 
-TEST_F(ValueStoreFrontendTest, ChangesPersistAfterReload) {
-  storage_->Set("key0",
-      scoped_ptr<base::Value>(base::Value::CreateIntegerValue(0)));
-  storage_->Set("key1",
-      scoped_ptr<base::Value>(base::Value::CreateStringValue("new1")));
+TEST_F(CachingValueStoreTest, ChangesPersistAfterReload) {
+  storage_->Set("key0", base::Value::CreateIntegerValue(0));
+  storage_->Set("key1", base::Value::CreateStringValue("new1"));
   storage_->Remove("key2");
 
   // Reload the DB and test our changes.
   ResetStorage();
 
-  scoped_ptr<base::Value> value(NULL);
+  const base::Value* value = NULL;
   {
-    ASSERT_TRUE(Get("key0", &value));
+    ASSERT_TRUE(storage_->Get("key0", &value));
     int result;
     ASSERT_TRUE(value->GetAsInteger(&result));
     EXPECT_EQ(0, result);
   }
 
   {
-    ASSERT_TRUE(Get("key1", &value));
+    ASSERT_TRUE(storage_->Get("key1", &value));
     std::string result;
     ASSERT_TRUE(value->GetAsString(&result));
     EXPECT_EQ("new1", result);
   }
 
-  ASSERT_FALSE(Get("key2", &value));
+  ASSERT_FALSE(storage_->Get("key2", &value));
 }

chrome/browser/value_store/value_store_frontend.h

-// Copyright (c) 2012 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.
-
-#ifndef CHROME_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_
-#define CHROME_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_
-#pragma once
-
-#include <string>
-
-#include "base/callback.h"
-#include "base/file_path.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
-#include "base/threading/non_thread_safe.h"
-#include "base/values.h"
-
-// A frontend for a LeveldbValueStore, for use on the UI thread.
-class ValueStoreFrontend
-    : public base::SupportsWeakPtr<ValueStoreFrontend>,
-      public base::NonThreadSafe {
- public:
-  typedef base::Callback<void(scoped_ptr<base::Value>)> ReadCallback;
-
-  explicit ValueStoreFrontend(const FilePath& db_path);
-  ~ValueStoreFrontend();
-
-  // Retrieves a value from the database asynchronously, passing a copy to
-  // |callback| when ready. NULL is passed if no matching entry is found.
-  void Get(const std::string& key, const ReadCallback& callback);
-
-  // Sets a value with the given key.
-  void Set(const std::string& key, scoped_ptr<base::Value> value);
-
-  // Removes the value with the given key.
-  void Remove(const std::string& key);
-
- private:
-  class Backend;
-
-  // A helper class to manage lifetime of the backing ValueStore, which lives
-  // on the FILE thread.
-  scoped_refptr<Backend> backend_;
-
-  DISALLOW_COPY_AND_ASSIGN(ValueStoreFrontend);
-};
-
-#endif  // CHROME_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_

chrome/chrome_browser.gypi

@@ -4055,6 +4055,8 @@
         'browser/user_style_sheet_watcher.h',
         'browser/user_style_sheet_watcher_factory.cc',
         'browser/user_style_sheet_watcher_factory.h',
+        'browser/value_store/caching_value_store.cc',
+        'browser/value_store/caching_value_store.h',
         'browser/value_store/failing_value_store.cc',
         'browser/value_store/failing_value_store.h',
         'browser/value_store/leveldb_value_store.cc',
@@ -4063,8 +4065,6 @@
         'browser/value_store/testing_value_store.h',
         'browser/value_store/value_store_change.cc',
         'browser/value_store/value_store_change.h',
-        'browser/value_store/value_store_frontend.cc',
-        'browser/value_store/value_store_frontend.h',
         'browser/value_store/value_store.cc',
         'browser/value_store/value_store.h',
         'browser/view_type_utils.cc',

chrome/chrome_tests.gypi

@@ -1816,9 +1816,9 @@
         'browser/ui/window_snapshot/window_snapshot_mac_unittest.mm',
         'browser/chrome_to_mobile_service_unittest.cc',
         'browser/user_style_sheet_watcher_unittest.cc',
+        'browser/value_store/caching_value_store_unittest.cc',
         'browser/value_store/leveldb_value_store_unittest.cc',
         'browser/value_store/testing_value_store_unittest.cc',
-        'browser/value_store/value_store_frontend_unittest.cc',
         'browser/value_store/value_store_unittest.cc',
         'browser/value_store/value_store_unittest.h',
         'browser/visitedlink/visitedlink_unittest.cc',