It seems the p4 plugin is simply hung on this p4 command. This is the second time it has happened, the first time was probably about two months ago (don't have logs from that time). We usually have at least one build occur every day, if not multiple. So it seems very infrequent but when it does happen, hitting the 'x' to cancel the build does not affect it and that Jenkins executor stays hung. So my only course of action that I know of is to kill the Jenkins service and restart it.
Here is the last output on the Jenkins console:
P4 Task: reverting all pending and shelved revisions. ... p4 revert C:\Jenkins\jobs\Sepac_x.58\workspace\buildType\standard\osType\linux\spec___ - p4 revert C:\Jenkins\jobs\Sepac_x.58\workspace\buildType\standard\osType\linux\specialBuild\none/... C:\Jenkins\jobs\Sepac_x.58\workspace\buildType\standard\osType\linux\specialBuild\none/... - file(s) not opened on this client. ... rm [abandoned files] duration: (78ms) P4 Task: cleaning workspace to match have list. ... p4 reconcile -w -f C:\Jenkins\jobs\Sepac_x.58\workspace\buildType\standard\osType\l___ - p4 reconcile -w -f C:\Jenkins\jobs\Sepac_x.58\workspace\buildType\standard\osType\linux\specialBuild\none/...
Attached is a thread dump of my Jenkins.