Java Reference
In-Depth Information
For all these reasons, when you wake up from
wait
you must test the condition predicate
again
, and go back to waiting (or fail) if it is not yet true. Since you can wake up repeatedly
without your condition predicate being true, you must therefore always call
wait
from with-
in a loop, testing the condition predicate in each iteration. The canonical form for a condition
wait is shown in
Listing 14.7
.
Listing 14.7. Canonical Form for State-dependent Methods.
When using condition waits (
Object.wait
or
Condition.await
):
•
Always have a condition predicate—some test of object state that must hold before
proceeding;
•
Always test the condition predicate before calling
wait
, and again after returning
from
wait
;
•
Always call
wait
in a loop;
•
Ensure that the state variables making up the condition predicate are guarded by the
lock associated with the condition queue;
•
Hold the lock associated with the the condition queue when calling
wait
,
notify
,
or
notifyAll
; and
•
Do not release the lock after checking the condition predicate but before acting on it.
