chrome/browser/extensions/external_loader.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_
   6 #define CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_
   7
   8 #include "base/files/file_path.h"
   9 #include "base/memory/ref_counted.h"
  10 #include "base/memory/scoped_ptr.h"
  11
  12 namespace base {
  13 class DictionaryValue;
  14 }
  15
  16 namespace extensions {
  17 class ExternalProviderImpl;
  18
  19 // Base class for gathering a list of external extensions. Subclasses
  20 // implement loading from registry, JSON file, policy.
  21 // Instances are owned by ExternalProviderImpl objects.
  22 // Instances are created on the UI thread and expect public method calls from
  23 // the UI thread. Some subclasses introduce new methods that are executed on the
  24 // FILE thread.
  25 // The sequence of loading the extension list:
  26 // 1.) StartLoading() - checks if a loading task is already running
  27 // 2.) Load() - implemented in subclasses
  28 // 3.) LoadFinished()
  29 // 4.) owner_->SetPrefs()
  30 class ExternalLoader : public base::RefCountedThreadSafe<ExternalLoader> {
  31  public:
  32   ExternalLoader();
  33
  34   // Specifies the provider that owns this object.
  35   void Init(ExternalProviderImpl* owner);
  36
  37   // Called by the owner before it gets deleted.
  38   void OwnerShutdown();
  39
  40   // Initiates the possibly asynchronous loading of extension list.
  41   // It is the responsibility of the caller to ensure that calls to
  42   // this method do not overlap with each other.
  43   // Implementations of this method should save the loaded results
  44   // in prefs_ and then call LoadFinished.
  45   virtual void StartLoading() = 0;
  46
  47   // Some external providers allow relative file paths to local CRX files.
  48   // Subclasses that want this behavior should override this method to
  49   // return the absolute path from which relative paths should be resolved.
  50   // By default, return an empty path, which indicates that relative paths
  51   // are not allowed.
  52   virtual const base::FilePath GetBaseCrxFilePath();
  53
  54  protected:
  55   virtual ~ExternalLoader();
  56
  57   // Notifies the provider that the list of extensions has been loaded.
  58   virtual void LoadFinished();
  59
  60   // Used for passing the list of extensions from the method that loads them
  61   // to |LoadFinished|. To ensure thread safety, the rules are the following:
  62   // if this value is written on another thread than the UI, then it should
  63   // only be written in a task that was posted from |StartLoading|. After that,
  64   // this task should invoke |LoadFinished| with a PostTask. This scheme of
  65   // posting tasks will avoid concurrent access and imply the necessary memory
  66   // barriers.
  67   scoped_ptr<base::DictionaryValue> prefs_;
  68
  69  private:
  70   friend class base::RefCountedThreadSafe<ExternalLoader>;
  71
  72   ExternalProviderImpl* owner_;  // weak
  73
  74   DISALLOW_COPY_AND_ASSIGN(ExternalLoader);
  75 };
  76
  77 }  // namespace extensions
  78
  79 #endif  // CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_