The problem was we assumed ProcessPendingRequest() would always make progress once the group's releasing socket went down to zero. However, in OnAvailableSocketSlot(), since the top stalled group might still have a releasing socket, it won't necessarily make progress. The algorithmic solution is to simply never do any socket slot processing in DoReleaseSocket() if there are any releasing sockets. This requires us to search for any stalled groups after releasing sockets gets back down to 0, so it requires the full group scan each time num_releasing_sockets goes back to 0. There is a performance hit here, but I think a linear search through 256~ groups in the worst case is ok. TODO(willchan): evaluate the perf hit and consider adding a secondary data structure to improve the stalled group search. BUG=42267 Review URL: http://codereview.chromium.org/2013009 git-svn-id: svn://svn.chromium.org/chrome/trunk/src@46757 0039d316-1c4b-4281-b951-d872f2087c98