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// 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.
#ifndef CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_
#define CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_
#include <memory>
#include "base/files/file_path.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
namespace base {
class DictionaryValue;
}
namespace extensions {
class ExternalProviderImpl;
// Base class for gathering a list of external extensions. Subclasses
// implement loading from registry, JSON file, policy.
// Instances are owned by ExternalProviderImpl objects.
// Instances are created on the UI thread and expect public method calls from
// the UI thread. Some subclasses introduce new methods that are executed on the
// FILE thread.
// The sequence of loading the extension list:
// 1.) StartLoading() - checks if a loading task is already running
// 2.) Load() - implemented in subclasses
// 3.) LoadFinished()
// 4.) owner_->SetPrefs()
class ExternalLoader : public base::RefCountedThreadSafe<ExternalLoader> {
public:
ExternalLoader();
// Specifies the provider that owns this object.
void Init(ExternalProviderImpl* owner);
// Called by the owner before it gets deleted.
void OwnerShutdown();
// Initiates the possibly asynchronous loading of extension list.
// It is the responsibility of the caller to ensure that calls to
// this method do not overlap with each other.
// Implementations of this method should save the loaded results
// in prefs_ and then call LoadFinished.
virtual void StartLoading() = 0;
// Some external providers allow relative file paths to local CRX files.
// Subclasses that want this behavior should override this method to
// return the absolute path from which relative paths should be resolved.
// By default, return an empty path, which indicates that relative paths
// are not allowed.
virtual const base::FilePath GetBaseCrxFilePath();
protected:
virtual ~ExternalLoader();
// Notifies the provider that the list of extensions has been loaded.
virtual void LoadFinished();
// Notifies the provider that the list of extensions has been updated.
virtual void OnUpdated(std::unique_ptr<base::DictionaryValue> updated_prefs);
// Used for passing the list of extensions from the method that loads them
// to |LoadFinished|. To ensure thread safety, the rules are the following:
// if this value is written on another thread than the UI, then it should
// only be written in a task that was posted from |StartLoading|. After that,
// this task should invoke |LoadFinished| with a PostTask. This scheme of
// posting tasks will avoid concurrent access and imply the necessary memory
// barriers.
std::unique_ptr<base::DictionaryValue> prefs_;
private:
friend class base::RefCountedThreadSafe<ExternalLoader>;
ExternalProviderImpl* owner_; // weak
DISALLOW_COPY_AND_ASSIGN(ExternalLoader);
};
} // namespace extensions
#endif // CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_
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