Get rid of FileThreadDeserializer.

Replace it with modern threading constructs:
 - PostTaskAndReplyWithResult gets rid of most of the logic FileThreadDeserializer was implementing.
 - The remainder logic didn't require any class state so it was moved to anonymous methods.

Also declare JsonPrefStore explicitly NonThreadSafe (the only actions outside the UI thread should happen by posting anonymous tasks to the |sequenced_task_runner_|).

This is a stepping stone in cleaning up JsonPrefStore to eventually get rid of PrefStore's ref-counting scheme.

BUG=393081

Review URL: https://codereview.chromium.org/400673008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284754 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 121 insertions, 128 deletions

diff --git a/base/prefs/json_pref_store.cc b/base/prefs/json_pref_store.cc
index fd95b73..f615933 100644
--- a/base/prefs/json_pref_store.cc
+++ b/base/prefs/json_pref_store.cc
@@ -13,124 +13,62 @@
 #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/message_loop_proxy.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_filter.h"
 #include "base/sequenced_task_runner.h"
 #include "base/strings/string_util.h"
+#include "base/task_runner_util.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/values.h"
 
-namespace {
-
-// Some extensions we'll tack on to copies of the Preferences files.
-const base::FilePath::CharType* kBadExtension = FILE_PATH_LITERAL("bad");
-
-// Differentiates file loading between origin thread and passed
-// (aka file) thread.
-class FileThreadDeserializer
-    : public base::RefCountedThreadSafe<FileThreadDeserializer> {
+// Result returned from internal read tasks.
+struct JsonPrefStore::ReadResult {
  public:
-  FileThreadDeserializer(JsonPrefStore* delegate,
-                         base::SequencedTaskRunner* sequenced_task_runner)
-      : no_dir_(false),
-        error_(PersistentPrefStore::PREF_READ_ERROR_NONE),
-        delegate_(delegate),
-        sequenced_task_runner_(sequenced_task_runner),
-        origin_loop_proxy_(base::MessageLoopProxy::current()) {
-  }
-
-  void Start(const base::FilePath& path,
-             const base::FilePath& alternate_path) {
-    DCHECK(origin_loop_proxy_->BelongsToCurrentThread());
-    // TODO(gab): This should use PostTaskAndReplyWithResult instead of using
-    // the |error_| member to pass data across tasks.
-    sequenced_task_runner_->PostTask(
-        FROM_HERE,
-        base::Bind(&FileThreadDeserializer::ReadFileAndReport,
-                   this, path, alternate_path));
-  }
+  ReadResult();
+  ~ReadResult();
 
-  // Deserializes JSON on the sequenced task runner.
-  void ReadFileAndReport(const base::FilePath& path,
-                         const base::FilePath& alternate_path) {
-    DCHECK(sequenced_task_runner_->RunsTasksOnCurrentThread());
-
-    value_.reset(DoReading(path, alternate_path, &error_, &no_dir_));
-
-    origin_loop_proxy_->PostTask(
-        FROM_HERE,
-        base::Bind(&FileThreadDeserializer::ReportOnOriginThread, this));
-  }
+  scoped_ptr<base::Value> value;
+  PrefReadError error;
+  bool no_dir;
 
-  // Reports deserialization result on the origin thread.
-  void ReportOnOriginThread() {
-    DCHECK(origin_loop_proxy_->BelongsToCurrentThread());
-    delegate_->OnFileRead(value_.Pass(), error_, no_dir_);
-  }
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ReadResult);
+};
 
-  static base::Value* DoReading(const base::FilePath& path,
-                                const base::FilePath& alternate_path,
-                                PersistentPrefStore::PrefReadError* error,
-                                bool* no_dir) {
-    if (!base::PathExists(path) && !alternate_path.empty() &&
-        base::PathExists(alternate_path)) {
-      base::Move(alternate_path, path);
-    }
+JsonPrefStore::ReadResult::ReadResult()
+    : error(PersistentPrefStore::PREF_READ_ERROR_NONE), no_dir(false) {
+}
 
-    int error_code;
-    std::string error_msg;
-    JSONFileValueSerializer serializer(path);
-    base::Value* value = serializer.Deserialize(&error_code, &error_msg);
-    HandleErrors(value, path, error_code, error_msg, error);
-    *no_dir = !base::PathExists(path.DirName());
-    return value;
-  }
+JsonPrefStore::ReadResult::~ReadResult() {
+}
 
-  static void HandleErrors(const base::Value* value,
-                           const base::FilePath& path,
-                           int error_code,
-                           const std::string& error_msg,
-                           PersistentPrefStore::PrefReadError* error);
+namespace {
 
- private:
-  friend class base::RefCountedThreadSafe<FileThreadDeserializer>;
-  ~FileThreadDeserializer() {}
-
-  bool no_dir_;
-  PersistentPrefStore::PrefReadError error_;
-  scoped_ptr<base::Value> value_;
-  const scoped_refptr<JsonPrefStore> delegate_;
-  const scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;
-  const scoped_refptr<base::MessageLoopProxy> origin_loop_proxy_;
-};
+// Some extensions we'll tack on to copies of the Preferences files.
+const base::FilePath::CharType kBadExtension[] = FILE_PATH_LITERAL("bad");
 
-// static
-void FileThreadDeserializer::HandleErrors(
+PersistentPrefStore::PrefReadError HandleReadErrors(
     const base::Value* value,
     const base::FilePath& path,
     int error_code,
-    const std::string& error_msg,
-    PersistentPrefStore::PrefReadError* error) {
-  *error = PersistentPrefStore::PREF_READ_ERROR_NONE;
+    const std::string& error_msg) {
   if (!value) {
     DVLOG(1) << "Error while loading JSON file: " << error_msg
              << ", file: " << path.value();
     switch (error_code) {
       case JSONFileValueSerializer::JSON_ACCESS_DENIED:
-        *error = PersistentPrefStore::PREF_READ_ERROR_ACCESS_DENIED;
+        return PersistentPrefStore::PREF_READ_ERROR_ACCESS_DENIED;
         break;
       case JSONFileValueSerializer::JSON_CANNOT_READ_FILE:
-        *error = PersistentPrefStore::PREF_READ_ERROR_FILE_OTHER;
+        return PersistentPrefStore::PREF_READ_ERROR_FILE_OTHER;
         break;
       case JSONFileValueSerializer::JSON_FILE_LOCKED:
-        *error = PersistentPrefStore::PREF_READ_ERROR_FILE_LOCKED;
+        return PersistentPrefStore::PREF_READ_ERROR_FILE_LOCKED;
         break;
       case JSONFileValueSerializer::JSON_NO_SUCH_FILE:
-        *error = PersistentPrefStore::PREF_READ_ERROR_NO_FILE;
+        return PersistentPrefStore::PREF_READ_ERROR_NO_FILE;
         break;
       default:
-        *error = PersistentPrefStore::PREF_READ_ERROR_JSON_PARSE;
         // JSON errors indicate file corruption of some sort.
         // Since the file is corrupt, move it to the side and continue with
         // empty preferences.  This will result in them losing their settings.
@@ -142,18 +80,40 @@ void FileThreadDeserializer::HandleErrors(
         // If they've ever had a parse error before, put them in another bucket.
         // TODO(erikkay) if we keep this error checking for very long, we may
         // want to differentiate between recent and long ago errors.
-        if (base::PathExists(bad))
-          *error = PersistentPrefStore::PREF_READ_ERROR_JSON_REPEAT;
+        bool bad_existed = base::PathExists(bad);
         base::Move(path, bad);
-        break;
+        return bad_existed ? PersistentPrefStore::PREF_READ_ERROR_JSON_REPEAT
+                           : PersistentPrefStore::PREF_READ_ERROR_JSON_PARSE;
     }
   } else if (!value->IsType(base::Value::TYPE_DICTIONARY)) {
-    *error = PersistentPrefStore::PREF_READ_ERROR_JSON_TYPE;
+    return PersistentPrefStore::PREF_READ_ERROR_JSON_TYPE;
+  }
+  return PersistentPrefStore::PREF_READ_ERROR_NONE;
+}
+
+scoped_ptr<JsonPrefStore::ReadResult> ReadPrefsFromDisk(
+    const base::FilePath& path,
+    const base::FilePath& alternate_path) {
+  if (!base::PathExists(path) && !alternate_path.empty() &&
+      base::PathExists(alternate_path)) {
+    base::Move(alternate_path, path);
   }
+
+  int error_code;
+  std::string error_msg;
+  scoped_ptr<JsonPrefStore::ReadResult> read_result(
+      new JsonPrefStore::ReadResult);
+  JSONFileValueSerializer serializer(path);
+  read_result->value.reset(serializer.Deserialize(&error_code, &error_msg));
+  read_result->error =
+      HandleReadErrors(read_result->value.get(), path, error_code, error_msg);
+  read_result->no_dir = !base::PathExists(path.DirName());
+  return read_result.Pass();
 }
 
 }  // namespace
 
+// static
 scoped_refptr<base::SequencedTaskRunner> JsonPrefStore::GetTaskRunnerForFile(
     const base::FilePath& filename,
     base::SequencedWorkerPool* worker_pool) {
@@ -196,6 +156,8 @@ JsonPrefStore::JsonPrefStore(const base::FilePath& filename,
 
 bool JsonPrefStore::GetValue(const std::string& key,
                              const base::Value** result) const {
+  DCHECK(CalledOnValidThread());
+
   base::Value* tmp = NULL;
   if (!prefs_->Get(key, &tmp))
     return false;
@@ -206,27 +168,39 @@ bool JsonPrefStore::GetValue(const std::string& key,
 }
 
 void JsonPrefStore::AddObserver(PrefStore::Observer* observer) {
+  DCHECK(CalledOnValidThread());
+
   observers_.AddObserver(observer);
 }
 
 void JsonPrefStore::RemoveObserver(PrefStore::Observer* observer) {
+  DCHECK(CalledOnValidThread());
+
   observers_.RemoveObserver(observer);
 }
 
 bool JsonPrefStore::HasObservers() const {
+  DCHECK(CalledOnValidThread());
+
   return observers_.might_have_observers();
 }
 
 bool JsonPrefStore::IsInitializationComplete() const {
+  DCHECK(CalledOnValidThread());
+
   return initialized_;
 }
 
 bool JsonPrefStore::GetMutableValue(const std::string& key,
                                     base::Value** result) {
+  DCHECK(CalledOnValidThread());
+
   return prefs_->Get(key, result);
 }
 
 void JsonPrefStore::SetValue(const std::string& key, base::Value* value) {
+  DCHECK(CalledOnValidThread());
+
   DCHECK(value);
   scoped_ptr<base::Value> new_value(value);
   base::Value* old_value = NULL;
@@ -239,6 +213,8 @@ void JsonPrefStore::SetValue(const std::string& key, base::Value* value) {
 
 void JsonPrefStore::SetValueSilently(const std::string& key,
                                      base::Value* value) {
+  DCHECK(CalledOnValidThread());
+
   DCHECK(value);
   scoped_ptr<base::Value> new_value(value);
   base::Value* old_value = NULL;
@@ -251,63 +227,76 @@ void JsonPrefStore::SetValueSilently(const std::string& key,
 }
 
 void JsonPrefStore::RemoveValue(const std::string& key) {
+  DCHECK(CalledOnValidThread());
+
   if (prefs_->RemovePath(key, NULL))
     ReportValueChanged(key);
 }
 
 void JsonPrefStore::RemoveValueSilently(const std::string& key) {
+  DCHECK(CalledOnValidThread());
+
   prefs_->RemovePath(key, NULL);
   if (!read_only_)
     writer_.ScheduleWrite(this);
 }
 
 bool JsonPrefStore::ReadOnly() const {
+  DCHECK(CalledOnValidThread());
+
   return read_only_;
 }
 
 PersistentPrefStore::PrefReadError JsonPrefStore::GetReadError() const {
+  DCHECK(CalledOnValidThread());
+
   return read_error_;
 }
 
 PersistentPrefStore::PrefReadError JsonPrefStore::ReadPrefs() {
+  DCHECK(CalledOnValidThread());
+
   if (path_.empty()) {
-    OnFileRead(
-        scoped_ptr<base::Value>(), PREF_READ_ERROR_FILE_NOT_SPECIFIED, false);
+    scoped_ptr<ReadResult> no_file_result;
+    no_file_result->error = PREF_READ_ERROR_FILE_NOT_SPECIFIED;
+    OnFileRead(no_file_result.Pass());
     return PREF_READ_ERROR_FILE_NOT_SPECIFIED;
   }
 
-  PrefReadError error;
-  bool no_dir;
-  scoped_ptr<base::Value> value(
-      FileThreadDeserializer::DoReading(path_, alternate_path_, &error,
-                                        &no_dir));
-  OnFileRead(value.Pass(), error, no_dir);
-  return filtering_in_progress_ ? PREF_READ_ERROR_ASYNCHRONOUS_TASK_INCOMPLETE :
-                                  error;
+  OnFileRead(ReadPrefsFromDisk(path_, alternate_path_));
+  return filtering_in_progress_ ? PREF_READ_ERROR_ASYNCHRONOUS_TASK_INCOMPLETE
+                                : read_error_;
 }
 
 void JsonPrefStore::ReadPrefsAsync(ReadErrorDelegate* error_delegate) {
+  DCHECK(CalledOnValidThread());
+
   initialized_ = false;
   error_delegate_.reset(error_delegate);
   if (path_.empty()) {
-    OnFileRead(
-        scoped_ptr<base::Value>(), PREF_READ_ERROR_FILE_NOT_SPECIFIED, false);
+    scoped_ptr<ReadResult> no_file_result;
+    no_file_result->error = PREF_READ_ERROR_FILE_NOT_SPECIFIED;
+    OnFileRead(no_file_result.Pass());
     return;
   }
 
-  // Start async reading of the preferences file. It will delete itself
-  // in the end.
-  scoped_refptr<FileThreadDeserializer> deserializer(
-      new FileThreadDeserializer(this, sequenced_task_runner_.get()));
-  deserializer->Start(path_, alternate_path_);
+  base::PostTaskAndReplyWithResult(
+      sequenced_task_runner_,
+      FROM_HERE,
+      base::Bind(&ReadPrefsFromDisk, path_, alternate_path_),
+      base::Bind(&JsonPrefStore::OnFileRead, this));
 }
 
 void JsonPrefStore::CommitPendingWrite() {
+  DCHECK(CalledOnValidThread());
+
   if (writer_.HasPendingWrite() && !read_only_)
     writer_.DoScheduledWrite();
 }
 
 void JsonPrefStore::ReportValueChanged(const std::string& key) {
+  DCHECK(CalledOnValidThread());
+
   if (pref_filter_)
     pref_filter_->FilterUpdate(key);
 
@@ -319,17 +308,21 @@ void JsonPrefStore::ReportValueChanged(const std::string& key) {
 
 void JsonPrefStore::RegisterOnNextSuccessfulWriteCallback(
     const base::Closure& on_next_successful_write) {
+  DCHECK(CalledOnValidThread());
+
   writer_.RegisterOnNextSuccessfulWriteCallback(on_next_successful_write);
 }
 
-void JsonPrefStore::OnFileRead(scoped_ptr<base::Value> value,
-                               PersistentPrefStore::PrefReadError error,
-                               bool no_dir) {
+void JsonPrefStore::OnFileRead(scoped_ptr<ReadResult> read_result) {
+  DCHECK(CalledOnValidThread());
+
+  DCHECK(read_result);
+
   scoped_ptr<base::DictionaryValue> unfiltered_prefs(new base::DictionaryValue);
 
-  read_error_ = error;
+  read_error_ = read_result->error;
 
-  bool initialization_successful = !no_dir;
+  bool initialization_successful = !read_result->no_dir;
 
   if (initialization_successful) {
     switch (read_error_) {
@@ -341,9 +334,9 @@ void JsonPrefStore::OnFileRead(scoped_ptr<base::Value> value,
         read_only_ = true;
         break;
       case PREF_READ_ERROR_NONE:
-        DCHECK(value.get());
+        DCHECK(read_result->value.get());
         unfiltered_prefs.reset(
-            static_cast<base::DictionaryValue*>(value.release()));
+            static_cast<base::DictionaryValue*>(read_result->value.release()));
         break;
       case PREF_READ_ERROR_NO_FILE:
         // If the file just doesn't exist, maybe this is first run.  In any case
@@ -386,6 +379,8 @@ JsonPrefStore::~JsonPrefStore() {
 }
 
 bool JsonPrefStore::SerializeData(std::string* output) {
+  DCHECK(CalledOnValidThread());
+
   if (pref_filter_)
     pref_filter_->FilterSerializeData(prefs_.get());
 
@@ -417,6 +412,8 @@ bool JsonPrefStore::SerializeData(std::string* output) {
 void JsonPrefStore::FinalizeFileRead(bool initialization_successful,
                                      scoped_ptr<base::DictionaryValue> prefs,
                                      bool schedule_write) {
+  DCHECK(CalledOnValidThread());
+
   filtering_in_progress_ = false;
 
   if (!initialization_successful) {
diff --git a/base/prefs/json_pref_store.h b/base/prefs/json_pref_store.h
index 6ceea68..6df9e23 100644
--- a/base/prefs/json_pref_store.h
+++ b/base/prefs/json_pref_store.h
@@ -19,6 +19,7 @@
 #include "base/observer_list.h"
 #include "base/prefs/base_prefs_export.h"
 #include "base/prefs/persistent_pref_store.h"
+#include "base/threading/non_thread_safe.h"
 
 class PrefFilter;
 
@@ -30,13 +31,15 @@ class SequencedWorkerPool;
 class Value;
 }
 
-
 // A writable PrefStore implementation that is used for user preferences.
 class BASE_PREFS_EXPORT JsonPrefStore
     : public PersistentPrefStore,
       public base::ImportantFileWriter::DataSerializer,
-      public base::SupportsWeakPtr<JsonPrefStore> {
+      public base::SupportsWeakPtr<JsonPrefStore>,
+      public base::NonThreadSafe {
  public:
+  struct ReadResult;
+
   // Returns instance of SequencedTaskRunner which guarantees that file
   // operations on the same file will be executed in sequenced order.
   static scoped_refptr<base::SequencedTaskRunner> GetTaskRunnerForFile(
@@ -94,23 +97,16 @@ class BASE_PREFS_EXPORT JsonPrefStore
   void RegisterOnNextSuccessfulWriteCallback(
       const base::Closure& on_next_successful_write);
 
+ private:
+  virtual ~JsonPrefStore();
+
   // This method is called after the JSON file has been read.  It then hands
   // |value| (or an empty dictionary in some read error cases) to the
   // |pref_filter| if one is set. It also gives a callback pointing at
   // FinalizeFileRead() to that |pref_filter_| which is then responsible for
   // invoking it when done. If there is no |pref_filter_|, FinalizeFileRead()
   // is invoked directly.
-  // Note, this method is used with asynchronous file reading, so this class
-  // exposes it only for the internal needs (read: do not call it manually).
-  // TODO(gab): Move this method to the private section and hand a callback to
-  // it to FileThreadDeserializer rather than exposing this public method and
-  // giving a JsonPrefStore* to FileThreadDeserializer.
-  void OnFileRead(scoped_ptr<base::Value> value,
-                  PrefReadError error,
-                  bool no_dir);
-
- private:
-  virtual ~JsonPrefStore();
+  void OnFileRead(scoped_ptr<ReadResult> read_result);
 
   // ImportantFileWriter::DataSerializer overrides:
   virtual bool SerializeData(std::string* output) OVERRIDE;