Use worker pool for IO in JsonPrefStore.

chrome/common/json_pref_store.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/common/json_pref_store.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop_proxy.h"
+#include "base/sequenced_task_runner.h"
 #include "base/values.h"
 
 namespace {
 
 // Some extensions we'll tack on to copies of the Preferences files.
 const FilePath::CharType* kBadExtension = FILE_PATH_LITERAL("bad");
 
 // Differentiates file loading between origin thread and passed
 // (aka file) thread.
 class FileThreadDeserializer
     : public base::RefCountedThreadSafe<FileThreadDeserializer> {
  public:
   FileThreadDeserializer(JsonPrefStore* delegate,
-                         base::MessageLoopProxy* file_loop_proxy)
+                         base::SequencedTaskRunner* blocking_task_runner)
       : no_dir_(false),
         error_(PersistentPrefStore::PREF_READ_ERROR_NONE),
         delegate_(delegate),
-        file_loop_proxy_(file_loop_proxy),
+        blocking_task_runner_(blocking_task_runner),
         origin_loop_proxy_(base::MessageLoopProxy::current()) {
   }
 
   void Start(const FilePath& path) {
     DCHECK(origin_loop_proxy_->BelongsToCurrentThread());
-    file_loop_proxy_->PostTask(
+    blocking_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&FileThreadDeserializer::ReadFileAndReport,
                    this, path));
   }
 
   // Deserializes JSON on the file thread.
   void ReadFileAndReport(const FilePath& path) {
-    DCHECK(file_loop_proxy_->BelongsToCurrentThread());
-
     value_.reset(DoReading(path, &error_, &no_dir_));
 
     origin_loop_proxy_->PostTask(
         FROM_HERE,
         base::Bind(&FileThreadDeserializer::ReportOnOriginThread, this));
   }
 
   // Reports deserialization result on the origin thread.
   void ReportOnOriginThread() {
     DCHECK(origin_loop_proxy_->BelongsToCurrentThread());
@@ skipping 19 matching lines @@
                            PersistentPrefStore::PrefReadError* error);
 
  private:
   friend class base::RefCountedThreadSafe<FileThreadDeserializer>;
   ~FileThreadDeserializer() {}
 
   bool no_dir_;
   PersistentPrefStore::PrefReadError error_;
   scoped_ptr<Value> value_;
   scoped_refptr<JsonPrefStore> delegate_;
-  scoped_refptr<base::MessageLoopProxy> file_loop_proxy_;
+  scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
   scoped_refptr<base::MessageLoopProxy> origin_loop_proxy_;
 };
 
 // static
 void FileThreadDeserializer::HandleErrors(
     const Value* value,
     const FilePath& path,
     int error_code,
     const std::string& error_msg,
     PersistentPrefStore::PrefReadError* error) {
@@ skipping 32 matching lines @@
         break;
     }
   } else if (!value->IsType(Value::TYPE_DICTIONARY)) {
     *error = PersistentPrefStore::PREF_READ_ERROR_JSON_TYPE;
   }
 }
 
 }  // namespace
 
 JsonPrefStore::JsonPrefStore(const FilePath& filename,
-                             base::MessageLoopProxy* file_message_loop_proxy)
+                             base::SequencedTaskRunner* blocking_task_runner)
     : path_(filename),
-      file_message_loop_proxy_(file_message_loop_proxy),
+      blocking_task_runner_(blocking_task_runner),
       prefs_(new DictionaryValue()),
       read_only_(false),
-      writer_(filename, file_message_loop_proxy),
+      writer_(filename, blocking_task_runner),
       error_delegate_(NULL),
       initialized_(false),
       read_error_(PREF_READ_ERROR_OTHER) {
 }
 
 PrefStore::ReadResult JsonPrefStore::GetValue(const std::string& key,
                                               const Value** result) const {
   Value* tmp = NULL;
   if (prefs_->Get(key, &tmp)) {
     if (result)
@@ skipping 81 matching lines @@
   initialized_ = false;
   error_delegate_.reset(error_delegate);
   if (path_.empty()) {
     OnFileRead(NULL, PREF_READ_ERROR_FILE_NOT_SPECIFIED, false);
     return;
   }
 
   // Start async reading of the preferences file. It will delete itself
   // in the end.
   scoped_refptr<FileThreadDeserializer> deserializer(
-      new FileThreadDeserializer(this, file_message_loop_proxy_.get()));
+      new FileThreadDeserializer(this, blocking_task_runner_));
   deserializer->Start(path_);
 }
 
 void JsonPrefStore::CommitPendingWrite() {
   if (writer_.HasPendingWrite() && !read_only_)
     writer_.DoScheduledWrite();
 }
 
 void JsonPrefStore::ReportValueChanged(const std::string& key) {
   FOR_EACH_OBSERVER(PrefStore::Observer, observers_, OnPrefValueChanged(key));
@@ skipping 75 matching lines @@
         copy->Set(key, new base::ListValue);
     } else if (value->IsType(base::Value::TYPE_DICTIONARY)) {
       const base::DictionaryValue* dict = NULL;
       if (value->GetAsDictionary(&dict) && dict->empty())
         copy->Set(key, new base::DictionaryValue);
     }
   }
 
   return serializer.Serialize(*(copy.get()));
 }