If there is a job that gets very rapidly scheduled, since a Run.id currently must be unique to the second, a lot of the time the Queue will be locked:
... waiting on condition [...]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at hudson.model.AbstractProject.newBuild(AbstractProject.java:1121)
- locked <...> (a hudson.model.FreeStyleProject)
at hudson.model.AbstractProject.createExecutable(AbstractProject.java:1349)
at hudson.model.AbstractProject.createExecutable(AbstractProject.java:156)
at hudson.model.Executor.run(Executor.java:211)
- locked <...> (a hudson.model.Queue)
which can prevent other things from happening, such as routine queue maintenance, or even rendering of the queue widget (which expects a fresh snapshot every second):
"Handling ..." ... waiting for monitor entry [...]
java.lang.Thread.State: BLOCKED (on object monitor)
at hudson.model.Queue.getItems(Queue.java:685)
- waiting to lock <...> (a hudson.model.Queue)
at hudson.model.Queue$CachedItemList.get(Queue.java:217)
at hudson.model.Queue.getApproximateItemsQuickly(Queue.java:715)
at hudson.model.View.getApproximateQueueItemsQuickly(View.java:483)
(This also artificially slows down some functional tests.)