public void sendGlobalBarrierStart() throws ForeignException {
    // start the procedure
    LOG.debug("Starting procedure '" + procName + "', kicking off acquire phase on members.");
    try {
      // send procedure barrier start to specified list of members. cloning the list to avoid
      // concurrent modification from the controller setting the prepared nodes
      coord.getRpcs().sendGlobalBarrierAcquire(this, args,
        Lists.newArrayList(this.acquiringMembers));
    } catch (IOException e) {
      coord.rpcConnectionFailure("Can't reach controller.", e);
    } catch (IllegalArgumentException e) {
      throw new ForeignException(getName(), e);
    }
  }
Sends a message to Members to create a new {@link Subprocedure} for this Procedure and execute
the {@link Subprocedure#acquireBarrier} step.
hbase-server/src/main/java/org/apache/hadoop/hbase/procedure/Procedure.java