Unrevert 141514: Remove CachingValueStore in favor of an async ValueStoreFrontend.

chrome/browser/value_store/value_store_frontend.cc

+// 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.
+
+#include "chrome/browser/value_store/value_store_frontend.h"
+
+#include "chrome/browser/value_store/failing_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> {
+ public:
+  explicit Backend(const FilePath& db_path) : storage_(NULL) {
+  }
+
+  void Init(const FilePath& db_path) {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    DCHECK(!storage_);
+    storage_ = LeveldbValueStore::Create(db_path);
+    if (!storage_)
+      storage_ = new FailingValueStore();
+  }
+
+  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 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,
+                  key, *value.get());
+  }
+
+  void Remove(const std::string& key) {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    storage_->Remove(key);
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<Backend>;
+
+  virtual ~Backend() {
+    if (BrowserThread::CurrentlyOn(BrowserThread::FILE)) {
+      delete storage_;
+    } else {
+      BrowserThread::DeleteSoon(BrowserThread::FILE, FROM_HERE, storage_);
+    }
+  }
+
+  void RunCallback(const ValueStoreFrontend::ReadCallback& callback,
+                   scoped_ptr<base::Value> value) {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    callback.Run(value.Pass());
+  }
+
+  // The actual ValueStore that handles persisting the data to disk. Used
+  // exclusively on the FILE thread.
+  ValueStore* storage_;
+
+  DISALLOW_COPY_AND_ASSIGN(Backend);
+};
+
+ValueStoreFrontend::ValueStoreFrontend(const FilePath& db_path)
+    : backend_(new Backend(db_path)) {
+  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+      base::Bind(&ValueStoreFrontend::Backend::Init,
+                 backend_, db_path));

[Matt Perry, 2012/06/12 20:42:16]

This is what changed since last round. Moving the PostTask to here (instead of
the Backend constructor) ensures that backend_ holds a reference before
PostTask. Now if PostTask fails and releases its reference, backend_ still keeps
the object alive.

+}
+
+ValueStoreFrontend::~ValueStoreFrontend() {
+  DCHECK(CalledOnValidThread());
+}
+
+void ValueStoreFrontend::Get(const std::string& key,
+                             const ReadCallback& callback) {
+  DCHECK(CalledOnValidThread());
+
+  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+      base::Bind(&ValueStoreFrontend::Backend::Get,
+                 backend_, key, callback));
+}
+
+void ValueStoreFrontend::Set(const std::string& key,
+                             scoped_ptr<base::Value> value) {
+  DCHECK(CalledOnValidThread());
+
+  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+      base::Bind(&ValueStoreFrontend::Backend::Set,
+                 backend_, key, base::Passed(value.Pass())));
+}
+
+void ValueStoreFrontend::Remove(const std::string& key) {
+  DCHECK(CalledOnValidThread());
+
+  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+      base::Bind(&ValueStoreFrontend::Backend::Remove,
+                 backend_, key));
+}