private synchronized boolean childrenCountDown() {
    assert childrenLatch > 0 : this;
    boolean b = --childrenLatch == 0;
    if (LOG.isTraceEnabled()) {
      LOG.trace("CHILD LATCH DECREMENT " + childrenLatch, new Throwable(this.toString()));
    }
    return b;
  }
Called by the ProcedureExecutor to notify that one of the sub-procedures has completed.
hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/Procedure.java