public void wake(MasterProcedureScheduler scheduler) {
    if (!event.isReady()) {
      event.wake(scheduler);
    }
  }
help assign and release a worker for each remote task. For each worker, concurrent running task
should be no more than maxTasks. If a task failed to acquire a worker, it will suspend and wait
for workers available.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/WorkerAssigner.java