stale-while-revalidate experimental implementation.

net/http/http_cache.h

 // 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.
 
 // This file declares a HttpTransactionFactory implementation that can be
 // layered on top of another HttpTransactionFactory to add HTTP caching.  The
 // caching logic follows RFC 2616 (any exceptions are called out in the code).
 //
 // The HttpCache takes a disk_cache::Backend as a parameter, and uses that for
 // the cache storage.
@@ skipping 183 matching lines @@
 
   // Initializes the Infinite Cache, if selected by the field trial.
   void InitializeInfiniteCache(const base::FilePath& path);
 
   // Causes all transactions created after this point to effectively bypass
   // the cache lock whenever there is lock contention.
   void BypassLockForTest() {
     bypass_lock_for_test_ = true;
   }
 
+  bool use_stale_while_revalidate() const {
+    return use_stale_while_revalidate_;
+  }
+
+  // Enable stale_while_revalidate functionality for testing purposes.
+  void set_use_stale_while_revalidate_for_testing(
+      bool use_stale_while_revalidate) {
+    use_stale_while_revalidate_ = use_stale_while_revalidate;
+  }
+
   // HttpTransactionFactory implementation:
   virtual int CreateTransaction(RequestPriority priority,
                                 scoped_ptr<HttpTransaction>* trans) OVERRIDE;
   virtual HttpCache* GetCache() OVERRIDE;
   virtual HttpNetworkSession* GetSession() OVERRIDE;
 
   base::WeakPtr<HttpCache> GetWeakPtr() { return weak_factory_.GetWeakPtr(); }
 
   // Resets the network layer to allow for tests that probe
   // network changes (e.g. host unreachable).  The old network layer is
@@ skipping 16 matching lines @@
     kNumCacheEntryDataIndices
   };
 
   class MetadataWriter;
   class QuicServerInfoFactoryAdaptor;
   class Transaction;
   class WorkItem;
   friend class Transaction;
   friend class ViewCacheHelper;
   struct PendingOp;  // Info for an entry under construction.
+  class AsyncValidation;  // Encapsulates a single async revalidation.
 
   typedef std::list<Transaction*> TransactionList;
   typedef std::list<WorkItem*> WorkItemList;
+  typedef std::set<AsyncValidation*> AsyncValidationSet;
 
   struct ActiveEntry {
     explicit ActiveEntry(disk_cache::Entry* entry);
     ~ActiveEntry();
 
     disk_cache::Entry* disk_entry;
     Transaction*       writer;
     TransactionList    readers;
     TransactionList    pending_queue;
     bool               will_process_pending_queue;
@@ skipping 114 matching lines @@
   // Removes the transaction |trans|, from the pending list of |pending_op|.
   bool RemovePendingTransactionFromPendingOp(PendingOp* pending_op,
                                              Transaction* trans);
 
   // Instantiates and sets QUIC server info factory.
   void SetupQuicServerInfoFactory(HttpNetworkSession* session);
 
   // Resumes processing the pending list of |entry|.
   void ProcessPendingQueue(ActiveEntry* entry);
 
+  // Called by Transaction to perform an asynchronous revalidation. Creates a
+  // new independent transaction as a copy of the original.
+  void PerformAsyncValidation(const HttpRequestInfo& original_request,
+                              const BoundNetLog& net_log);
+
+  // Remove |async_validation| from the |async_validations_| set and delete it.
+  void DeleteAsyncValidation(AsyncValidation* async_validation);
+
   // Events (called via PostTask) ---------------------------------------------
 
   void OnProcessPendingQueue(ActiveEntry* entry);
 
   // Callbacks ----------------------------------------------------------------
 
   // Processes BackendCallback notifications.
   void OnIOComplete(int result, PendingOp* entry);
 
   // Helper to conditionally delete |pending_op| if the HttpCache object it
@@ skipping 11 matching lines @@
 
   // Variables ----------------------------------------------------------------
 
   NetLog* net_log_;
 
   // Used when lazily constructing the disk_cache_.
   scoped_ptr<BackendFactory> backend_factory_;
   bool building_backend_;
   bool bypass_lock_for_test_;
 
+  // true if the implementation of Cache-Control: stale-while-revalidate
+  // directive is enabled (either via command-line flag or experiment).
+  bool use_stale_while_revalidate_;
+
   Mode mode_;
 
   scoped_ptr<QuicServerInfoFactoryAdaptor> quic_server_info_factory_;
 
   scoped_ptr<HttpTransactionFactory> network_layer_;
 
   scoped_ptr<disk_cache::Backend> disk_cache_;
 
   scoped_ptr<DiskBasedCertCache> cert_cache_;
 
   // The set of active entries indexed by cache key.
   ActiveEntriesMap active_entries_;
 
   // The set of doomed entries.
   ActiveEntriesSet doomed_entries_;
 
   // The set of entries "under construction".
   PendingOpsMap pending_ops_;
 
   scoped_ptr<PlaybackCacheMap> playback_cache_map_;
 
+  // The set of async validations currently in progress. Invariant: all
+  // live AsyncValidation objects connected to this cache are in this set.

[rvargas (doing something else), 2014/09/05 22:52:39]

Isn't the invariant the expected behavior? Why document something that would be
extremely weird to violate?

[Adam Rice, 2014/09/09 12:36:45]

I have seen people do a lot of weird things in my time.

+  AsyncValidationSet async_validations_;
+
   base::WeakPtrFactory<HttpCache> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HttpCache);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_H_