extensions/browser/api/system_info/system_info_provider.h

   1 // Copyright 2013 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 EXTENSIONS_BROWSER_API_SYSTEM_INFO_SYSTEM_INFO_PROVIDER_H_
   6 #define EXTENSIONS_BROWSER_API_SYSTEM_INFO_SYSTEM_INFO_PROVIDER_H_
   7
   8 #include <queue>
   9
  10 #include "base/bind.h"
  11 #include "base/callback.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "base/threading/sequenced_worker_pool.h"
  14
  15 namespace extensions {
  16
  17 // An abstract base class for all kinds of system information providers. Each
  18 // kind of SystemInfoProvider is a single shared instance. It is created if
  19 // needed, and destroyed at exit time. This is done via LazyInstance and
  20 // scoped_refptr.
  21 //
  22 // The SystemInfoProvider is designed to query system information on the worker
  23 // pool. It also maintains a queue of callbacks on the UI thread which are
  24 // waiting for the completion of querying operation. Once the query operation
  25 // is completed, all pending callbacks in the queue get called on the UI
  26 // thread. In this way, it avoids frequent querying operation in case of lots
  27 // of query requests, e.g. calling systemInfo.cpu.get repeatedly in an
  28 // extension process.
  29 //
  30 // Each kind of SystemInfoProvider should satisfy an API query in a subclass on
  31 // the blocking pool.
  32 class SystemInfoProvider
  33     : public base::RefCountedThreadSafe<SystemInfoProvider> {
  34  public:
  35   // Callback type for completing to get information. The argument indicates
  36   // whether its contents are valid, for example, no error occurs in querying
  37   // the information.
  38   typedef base::Callback<void(bool)> QueryInfoCompletionCallback;
  39   typedef std::queue<QueryInfoCompletionCallback> CallbackQueue;
  40
  41   SystemInfoProvider();
  42
  43   // Override to do any prepare work on UI thread before |QueryInfo()| gets
  44   // called.
  45   virtual void PrepareQueryOnUIThread();
  46
  47   // The parameter |do_query_info_callback| is query info task which is posted
  48   // to SystemInfoProvider sequenced worker pool.
  49   //
  50   // You can do any initial things of *InfoProvider before start to query info.
  51   // While overriding this method, |do_query_info_callback| *must* be called
  52   // directly or indirectly.
  53   //
  54   // Sample usage please refer to StorageInfoProvider.
  55   virtual void InitializeProvider(const base::Closure& do_query_info_callback);
  56
  57   // Start to query the system information. Should be called on UI thread.
  58   // The |callback| will get called once the query is completed.
  59   //
  60   // If the parameter |callback| itself calls StartQueryInfo(callback2),
  61   // callback2 will be called immediately rather than triggering another call to
  62   // the system.
  63   void StartQueryInfo(const QueryInfoCompletionCallback& callback);
  64
  65  protected:
  66   virtual ~SystemInfoProvider();
  67
  68  private:
  69   friend class base::RefCountedThreadSafe<SystemInfoProvider>;
  70
  71   // Interface to query the system information synchronously.
  72   // Return true if no error occurs.
  73   // Should be called in the blocking pool.
  74   virtual bool QueryInfo() = 0;
  75
  76   // Called on UI thread. The |success| parameter means whether it succeeds
  77   // to get the information.
  78   void OnQueryCompleted(bool success);
  79
  80   void StartQueryInfoPostInitialization();
  81
  82   // The queue of callbacks waiting for the info querying completion. It is
  83   // maintained on the UI thread.
  84   CallbackQueue callbacks_;
  85
  86   // Indicates if it is waiting for the querying completion.
  87   bool is_waiting_for_completion_;
  88
  89   // Sequenced worker pool to make the operation of querying information get
  90   // executed in order.
  91   scoped_refptr<base::SequencedTaskRunner> worker_pool_;
  92
  93   DISALLOW_COPY_AND_ASSIGN(SystemInfoProvider);
  94 };
  95
  96 }  // namespace extensions
  97
  98 #endif  // EXTENSIONS_BROWSER_API_SYSTEM_INFO_SYSTEM_INFO_PROVIDER_H_