Bypass http cache for concurrent range requests.

net/http/http_cache_transaction.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_transaction.h"
 
 #include "build/build_config.h"
 
 #if defined(OS_POSIX)
 #include <unistd.h>
@@ skipping 1364 matching lines @@
   cache_pending_ = true;
   next_state_ = STATE_ADD_TO_ENTRY_COMPLETE;
   net_log_.BeginEvent(NetLog::TYPE_HTTP_CACHE_ADD_TO_ENTRY);
   DCHECK(entry_lock_waiting_since_.is_null());
   entry_lock_waiting_since_ = TimeTicks::Now();
   int rv = cache_->AddTransactionToEntry(new_entry_, this);
   if (rv == ERR_IO_PENDING) {
     if (bypass_lock_for_test_) {
       OnAddToEntryTimeout(entry_lock_waiting_since_);
     } else {
-      const int kTimeoutSeconds = 20;
+      int timeout_secs = 20;
+      if (partial_ && new_entry_->writer &&
+          new_entry_->writer->range_requested_) {
+        // Immediately timeout and bypass the cache if we're a range request and
+        // we're blocked by the reader/writer lock. Doing so eliminates a long
+        // running issue, http://crbug.com/31014, where two of the same media
+        // resources could not be played back simultaneously due to one locking
+        // the cache entry until the entire video was downloaded.
+        //
+        // Bypassing the cache is not ideal, as we are now ignoring the cache
+        // entirely for all range requests to a resource beyond the first. This
+        // is however a much more succinct solution than the alternatives, which
+        // would require somewhat significant changes to the http caching logic.
+        timeout_secs = 0;
+      }
       base::MessageLoop::current()->PostDelayedTask(
           FROM_HERE,
           base::Bind(&HttpCache::Transaction::OnAddToEntryTimeout,
                      weak_factory_.GetWeakPtr(), entry_lock_waiting_since_),
-          TimeDelta::FromSeconds(kTimeoutSeconds));
+          TimeDelta::FromSeconds(timeout_secs));
     }
   }
   return rv;
 }
 
 int HttpCache::Transaction::DoAddToEntryComplete(int result) {
   net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HTTP_CACHE_ADD_TO_ENTRY,
                                     result);
   const TimeDelta entry_lock_wait =
       TimeTicks::Now() - entry_lock_waiting_since_;
@@ skipping 1461 matching lines @@
     default:
       NOTREACHED();
   }
 }
 
 void HttpCache::Transaction::OnIOComplete(int result) {
   DoLoop(result);
 }
 
 }  // namespace net