Remove data race in WebDataRequest::CancelRequest.

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/atomicops.h"
 #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
 //
 // Every request is processed using a request object. The object contains
 // both the request parameters and the results.
 //////////////////////////////////////////////////////////////////////////////
 class WebDataRequest {
  public:
   virtual ~WebDataRequest();
 
   // Returns the identifier for this request.
   WebDataServiceBase::Handle GetHandle() const;
 
   // Returns |true| if the request is active and |false| if the request has been
   // cancelled or has already completed.
-  bool IsActive() const;
+  bool IsActive();
 
  private:
   // For access to the web request mutable state under the manager's lock.
   friend class WebDataRequestManager;
 
   // Private constructor called for WebDataRequestManager::NewRequest.
   WebDataRequest(WebDataRequestManager* manager,
-                 WebDataServiceConsumer* consumer);
+                 WebDataServiceConsumer* consumer,
+                 WebDataServiceBase::Handle handle);
 
-  // Internal debugging helper to assert that the request is active and that the
-  // manager's lock is held by the current thread.
-  void AssertThreadSafe() const;
+  // Retrieves the manager set in the constructor, if the request is still
+  // active, or nullptr if the request is inactive. The returned value may
+  // change between calls.
+  WebDataRequestManager* GetManager();
 
   // Retrieves the |consumer_| set in the constructor.
-  WebDataServiceConsumer* GetConsumer() const;
+  WebDataServiceConsumer* GetConsumer();
 
   // Retrieves the original task runner of the request.
-  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() const;
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner();
 
   // Marks the current request as inactive, either due to cancellation or
   // completion.
   void MarkAsInactive();
 
   // Tracks task runner that the request originated on.
   const scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
-  // 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 manager associated with this request. This is stored as a raw (untyped)
+  // pointer value because it does double duty as the flag indicating whether or
+  // not this request is active (non-nullptr => active).
+  base::subtle::AtomicWord atomic_manager_;
 
   // The originator of the service request.
-  WebDataServiceConsumer* consumer_;
+  WebDataServiceConsumer* const consumer_;
 
   // Identifier for this request.
-  WebDataServiceBase::Handle handle_;
+  const WebDataServiceBase::Handle handle_;
 
   DISALLOW_COPY_AND_ASSIGN(WebDataRequest);
 };
 
 //////////////////////////////////////////////////////////////////////////////
 //
 // 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();
 
   // Factory function to create a new WebDataRequest.
   std::unique_ptr<WebDataRequest> NewRequest(WebDataServiceConsumer* consumer);
 
   // 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,
                         std::unique_ptr<WDTypedResult> result);
 
-  // A debugging aid to assert that the pending_lock_ is held by the current
-  // thread.
-  void AssertLockedByCurrentThread() const;
-
  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,
                                 std::unique_ptr<WDTypedResult> result);
 
   // 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__