Make it possible to read CLD data from a file

chrome/browser/translate/translate_tab_helper.h

 // Copyright 2011 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_TRANSLATE_TRANSLATE_TAB_HELPER_H_
 #define CHROME_BROWSER_TRANSLATE_TRANSLATE_TAB_HELPER_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/platform_file.h"
+#include "base/synchronization/lock.h"
+#include "base/task_runner.h"
 #include "chrome/browser/ui/translate/translate_bubble_model.h"
 #include "components/translate/content/browser/content_translate_driver.h"
 #include "components/translate/core/browser/translate_client.h"
 #include "components/translate/core/common/translate_errors.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 namespace content {
 class BrowserContext;
 class WebContents;
@@ skipping 70 matching lines @@
   virtual void WebContentsDestroyed(
       content::WebContents* web_contents) OVERRIDE;
 
   void OnLanguageDetermined(const LanguageDetectionDetails& details,
                             bool page_needs_translation);
   void OnPageTranslated(int32 page_id,
                         const std::string& original_lang,
                         const std::string& translated_lang,
                         TranslateErrors::Type error_type);
 
+#if defined(CLD2_DYNAMIC_MODE)
+  // Called when we receive ChromeViewHostMsg_NeedCLDData from a renderer.
+  // If we have already cached the data, responds immediately; else, enqueues
+  // a HandleCLDDataRequest on the blocking pool to cache the data.
+  // Acquires and releases s_file_lock_ in a non-blocking manner; queries
+  // handled while the file is being cached will gracefully and immediately
+  // fail.
+  // It is up to the originator of the message to poll again later if required;
+  // no "negative response" will be generated.
+  void OnCLDDataRequested();
+
+  // Invoked on the blocking pool in order to cache the data. When successful,
+  // immediately responds to the request that initiated OnCLDDataRequested.
+  // Holds s_file_lock_ while the file is being cached.
+  void HandleCLDDataRequest();
+
+  // Sends the renderer a response containing the data file handle. No locking.
+  void SendCLDDataAvailable(const base::PlatformFile handle);
+
+  // Necessary for binding the callback to HandleCLDDataRequest on the blocking
+  // pool.
+  base::WeakPtrFactory<TranslateTabHelper> weak_pointer_factory_;
+
+  // The data file, cached as long as the process stays alive.
+  static base::PlatformFile s_cached_platform_file_; // guarded by file_lock_
+
+  // Guards s_cached_platform_file_
+  static base::Lock s_file_lock_;

[Philippe, 2014/03/19 16:42:35]

JFYI, this static member would generate a static initializer. You would have
here to use a LazyInstance for your global state in translate_tab_helper.cc :)

The LazyInstance will also give you thread-safe initialization which allows you
to get rid of the mutex. You can have the file descriptor const and initialize
it once as in:

struct DataFile {
  DataFile() : fd(OpenFile()) {}
  
  const int fd;

 private:
  static int OpenFile() {
    int fd = open(...);
    // ...
    return fd;
  }
};

base::LazyInstance<DataFile>::Leaky g_file = LAZY_INSTANCE_INITIALIZER;

I haven't looked at the full picture though so please ignore this comment if it
doesn't make sense :)

+#endif
+
   // Shows the translate bubble.
   void ShowBubble(TranslateStep step, TranslateErrors::Type error_type);
 
   ContentTranslateDriver translate_driver_;
   scoped_ptr<TranslateManager> translate_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(TranslateTabHelper);
 };
 
 #endif  // CHROME_BROWSER_TRANSLATE_TRANSLATE_TAB_HELPER_H_