Unlike most other java.util.concurrent Queues,
SynchronousQueue does not allow control of fairness parameter, which
makes it impossible to fine-tune its use, especially in thread
pools. As pointed out in JSR166 user feedback, relying on default
policy, which cannot be changed, can keep too many threads alive in
ThreadPoolExecutor. Additionally, the class was not amenable to the
future addition of any such improvement because its serialization spec
did not allow restoration of policy.