Fixed the synchronization issue for cancel() operations
Fixed the synchronization issue for cancel() operations

Locking operations may affect hudson.remoting.Request::get() handlers
The issue may cause the JENKINS-21932, which seems to be caused by unhandled locks().

Signed-off-by: Oleg Nenashev <4ee7d312f1006a91e3e4abf62d17d00b82d791a2@gmail.com>

jenkinsci/remoting,oleg-nenashev/remoting,oleg-nenashev/remoting,jenkinsci/remoting