Ignore disk cache for concurrent byte range requests to a single resource, to prevent stalling.

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index e2d46be45350eec82cb3ec0850f1e792f17e98f2..af21e2bbb9ad8d7e71e7ec2348cddea656af8e56 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -843,6 +843,23 @@ int HttpCache::Transaction::DoGetBackendComplete(int result) {
         mode_ = NONE;
       }
     }
+
+    // If we're already writing to an active entry with this key and it is
+    // a range request, we want to switch to pass-through mode. This
+    // eliminates a long-running issue (crbug.com/31014) where two of the same
+    // video resource could not be played back simultaneously due to one locking
+    // the cache entry until the entire video was downloaded.
+    //
+    // This is not an ideal solution, 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.
+    // TODO(rileya): Support simultaneous transactions on sparse cache entries,
+    // and remove this hack.

[scherkus (not reviewing), 2014/04/10 18:26:06]

if the plan is to close the original bug, then I'd recommending finding an
existing bug / filing a new bug we can link to

[rileya (GONE FROM CHROMIUM), 2014/04/10 19:24:51]

Sounds good, filed crbug.com/362215.

+    if (ActiveEntry* entry = cache_->FindActiveEntry(cache_key_)) {
+      if (partial_ && entry->writer && entry->writer->range_requested_)
+        mode_ = NONE;
+    }
   }
 
   // Use PUT and DELETE only to invalidate existing stored entries.