Support optimistic Create and Write operations on the SimpleCache.

net/http/http_cache.cc

 // 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.
 
 #include "net/http/http_cache.h"
 
 #include <algorithm>
 
 #include "base/compiler_specific.h"
 
@@ skipping 704 matching lines @@
   if (rv != ERR_IO_PENDING) {
     item->ClearTransaction();
     pending_op->callback.Run(rv);
   }
 
   return rv;
 }
 
 int HttpCache::CreateEntry(const std::string& key, ActiveEntry** entry,
                            Transaction* trans) {
-  DCHECK(!FindActiveEntry(key));
+  if (FindActiveEntry(key)) {
+    return ERR_CACHE_RACE;
+  }
 
   WorkItem* item = new WorkItem(WI_CREATE_ENTRY, trans, entry);
   PendingOp* pending_op = GetPendingOp(key);
   if (pending_op->writer) {
     pending_op->pending_queue.push_back(item);
     return ERR_IO_PENDING;
   }
 
   DCHECK(pending_op->pending_queue.empty());
 
@@ skipping 391 matching lines @@
     building_backend_ = false;
     DeletePendingOp(pending_op);
   }
 
   // The cache may be gone when we return from the callback.
   if (!item->DoCallback(result, backend))
     item->NotifyTransaction(result, NULL);
 }
 
 }  // namespace net