On a number of the slaves at builds.apache.org, we're seeing slaves hanging after a while, both Linux and Windows slaves. The common thread seems to be Maven jobs being run on them and eventually hanging, causing everything else on the slave to hang (including, in some cases, attempts to get the threaddump from within Jenkins). The original Maven build hangs indefinitely, and any subsequent builds trying to run on the same slave get to the point of starting the git clone/svn checkout/etc and then just hang. The Linux slaves are running Java 1.8.0_05, and the Windows are running some Java 7 version - not sure which.
Threaddump for Linux is at https://gist.github.com/abayer/3d567b56776e1ce78ad7 (one job hanging for over a day, another that started an hour or so ago but is now hanging), threaddump for Windows is at https://gist.github.com/abayer/c99f72ca1232e4d8acfa (only one job running at all on there, hanging for 17 hours or so).