Fix threading issues in WebDataRequestManager.

components/webdata/common/web_data_request_manager.h

 // Copyright 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.
 
 // Chromium settings and storage represent user-selected preferences and
 // information and MUST not be extracted, overwritten or modified except
 // through Chromium defined APIs.
 
 #ifndef COMPONENTS_WEBDATA_COMMON_WEB_DATA_REQUEST_MANAGER_H__
 #define COMPONENTS_WEBDATA_COMMON_WEB_DATA_REQUEST_MANAGER_H__
 
 #include <map>
 #include <memory>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "components/webdata/common/web_data_results.h"
 #include "components/webdata/common/web_data_service_base.h"
 #include "components/webdata/common/web_data_service_consumer.h"
 #include "components/webdata/common/web_database_service.h"
 
 class WebDataServiceConsumer;
 class WebDataRequestManager;
 
 //////////////////////////////////////////////////////////////////////////////
 //
-// Webdata requests
+// WebData requests
 //
 // Every request is processed using a request object. The object contains
 // both the request parameters and the results.
 //////////////////////////////////////////////////////////////////////////////
 class WebDataRequest {
  public:
   WebDataRequest(WebDataServiceConsumer* consumer,
                  WebDataRequestManager* manager);
 
   virtual ~WebDataRequest();
 
+  // Returns the identifier for this request.
   WebDataServiceBase::Handle GetHandle() const;
 
+  // Returns |true| if the request was cancelled (or has already completed).
+  bool IsCancelled() const;
+
+ private:
+  // Internal debugging helper to assert that the manager pointer is valid and
+  // that the manager's lock is held by the current thread.
+  void AssertThreadSafe() const;
+
   // Retrieves the |consumer_| set in the constructor.
   WebDataServiceConsumer* GetConsumer() const;
 
   // Retrieves the original task runner of the request.
   scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() const;
 
-  // Returns |true| if the request was cancelled via the |Cancel()| method.
-  bool IsCancelled() const;
-
-  // This can be invoked from any thread. From this point we assume that
-  // our consumer_ reference is invalid.
-  void Cancel();
-
-  // Invoked when the request has been completed.
-  void OnComplete();
+  // Marks the current request as inactive, either due to cancellation or
+  // completion.
+  void MarkAsInactive();
 
   // The result is owned by the request.
   void SetResult(std::unique_ptr<WDTypedResult> r);
 
-  // Transfers ownership pof result to caller. Should only be called once per
+  // Transfers ownership of result to caller. Should only be called once per
   // result.
   std::unique_ptr<WDTypedResult> GetResult();
 
- private:
-  // Used to notify manager if request is cancelled. Uses a raw ptr instead of
-  // a ref_ptr so that it can be set to NULL when a request is cancelled.
-  WebDataRequestManager* manager_;
-
   // Tracks task runner that the request originated on.
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+  const scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
   // Identifier for this request.
-  WebDataServiceBase::Handle handle_;
+  const WebDataServiceBase::Handle handle_;
 
-  // A lock to protect against simultaneous cancellations of the request.
-  // Cancellation affects both the |cancelled_| flag and |consumer_|.
-  mutable base::Lock cancel_lock_;
-  bool cancelled_;
+  // Used to notify manager if request is cancelled. Uses a raw ptr instead of
+  // a ref_ptr so that it can be set to NULL when a request is cancelled or
+  // completed.
+  WebDataRequestManager* manager_;
 
   // The originator of the service request.
   WebDataServiceConsumer* consumer_;
 
   std::unique_ptr<WDTypedResult> result_;
 
+  // For access to the web request mutable state under the manager's lock.
+  friend class WebDataRequestManager;

[Mathieu, 2016/12/14 01:13:46]

I've seen those statements be right under the private: line

https://cs.chromium.org/search/?q=%22friend+class%22+file:components&sq=packa...

[Roger McFarlane (Chromium), 2016/12/14 14:02:49]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(WebDataRequest);
 };
 
 //////////////////////////////////////////////////////////////////////////////
 //
-// Webdata Request Manager
+// WebData Request Manager
 //
 // Tracks all WebDataRequests for a WebDataService.
 //
 // Note: This is an internal interface, not to be used outside of webdata/
 //////////////////////////////////////////////////////////////////////////////
 class WebDataRequestManager
     : public base::RefCountedThreadSafe<WebDataRequestManager> {
  public:
   WebDataRequestManager();
 
   // Cancel any pending request.
   void CancelRequest(WebDataServiceBase::Handle h);
 
   // Invoked by the WebDataService when |request| has been completed.
-  void RequestCompleted(std::unique_ptr<WebDataRequest> request);
+  void RequestCompleted(std::unique_ptr<WebDataRequest> request,
+                        std::unique_ptr<WDTypedResult> result);
 
   // Register the request as a pending request.
   void RegisterRequest(WebDataRequest* request);
 
   // Return the next request handle.
   int GetNextRequestHandle();
 
+  // A debugging aid to assert that the pending_lock_ is held by the current
+  // thread.
+  void AssertLockedByCurrentThread() const { pending_lock_.AssertAcquired(); }
+
  private:
   friend class base::RefCountedThreadSafe<WebDataRequestManager>;
 
   ~WebDataRequestManager();
 
   // This will notify the consumer in whatever thread was used to create this
   // request.
   void RequestCompletedOnThread(std::unique_ptr<WebDataRequest> request);
 
   // A lock to protect pending requests and next request handle.
   base::Lock pending_lock_;
 
   // Next handle to be used for requests. Incremented for each use.
   WebDataServiceBase::Handle next_request_handle_;
 
   std::map<WebDataServiceBase::Handle, WebDataRequest*> pending_requests_;
 
   DISALLOW_COPY_AND_ASSIGN(WebDataRequestManager);
 };
 
 #endif  // COMPONENTS_WEBDATA_COMMON_WEB_DATA_REQUEST_MANAGER_H__