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      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_
     80