concurrent requests to ruby proxy at /api/v1/dependencies resource using the same url can hang

Configure a rubygems.org proxy repository
Send concurrent requests to this url.

/nexus/content/repositories/rubygems.org/api/v1/dependencies?gems=gem_version,rake,nexus,gherkin,cucumber,bundler,qa_lib_store,qa_steps_support_jruby,qa_steps_files_jruby,qa_steps_remote_jruby,qa_steps_httpcalls_jruby,qa_lib_dbservices_jruby,qa_gridconfig_jruby

• nexus sends outbound requests one at a time for the same url
• most of these timeout after 30 seconds
• client starts to get 503 and 500 responses for some requests
• thread dumps show multiple threads waiting for uid locks

The same test using Nexus 2.5 and OSS rubygems plugin worked fine in this scenario