黑马点评演练：程序中断后，异步订单怎样恢复

connection.setAutoCommit(false); // 后续本库写入进入显式事务。
try {
    persistIdempotentOrder(connection, event); // 应用逻辑检查稳定身份、唯一约束和条件库存。
    connection.commit(); // 提交完成后才进入确认投递阶段。
} catch (SQLException failure) {
    rollbackAndPreserveOriginalFailure(connection, failure); // 应用辅助函数，需保留回滚失败与原异常。
    throw failure;
}
acknowledgeOnOriginalStreamGroup(event); // 另一个系统的操作，提交与ACK之间允许崩溃。
// 示例假定专用事务连接；连接池归还和提交结果未知需要外层策略。

import java.util.*;
public class Main {
    record State(int phase,int orders,boolean ack,int crashes){}
    record Node(State state,List<String> path){}
    static Node next(Node from,State state,String action){List<String> path=new ArrayList<>(from.path());path.add(action);return new Node(state,List.copyOf(path));}
    static Optional<List<String>> counterexample(boolean ackFirst,boolean idempotent,int maxCrashes){
        if(maxCrashes<0||maxCrashes>3)throw new IllegalArgumentException("bound");
        Deque<Node> q=new ArrayDeque<>();Set<State> seen=new HashSet<>();q.add(new Node(new State(0,0,false,0),List.of()));
        while(!q.isEmpty()){
            Node node=q.removeFirst();State s=node.state();if(!seen.add(s))continue;
            if(s.orders()>1||s.ack()&&s.orders()==0)return Optional.of(node.path()); // 核对持久效果与确认顺序。
            if(s.phase()==0&&!s.ack())q.addLast(next(node,new State(1,s.orders(),false,s.crashes()),"READ"));
            else if(s.phase()==1){
                if(ackFirst)q.addLast(next(node,new State(2,s.orders(),true,s.crashes()),"ACK"));
                else q.addLast(next(node,new State(2,idempotent?1:s.orders()+1,false,s.crashes()),"COMMIT")); // 重放是否增加第二单由幂等策略决定。
            }else if(s.phase()==2){
                if(ackFirst)q.addLast(next(node,new State(3,idempotent?1:s.orders()+1,true,s.crashes()),"COMMIT"));
                else q.addLast(next(node,new State(3,s.orders(),true,s.crashes()),"ACK"));
            }
            if(s.phase()>0&&s.phase()<3&&s.crashes()<maxCrashes)q.addLast(next(node,new State(0,s.orders(),s.ack(),s.crashes()+1),"CRASH")); // 崩溃丢程序位置，不丢本模型持久事实。
        }return Optional.empty();
    }
    public static void main(String[] args){
        if(counterexample(false,true,2).isPresent())throw new AssertionError();
        if(!counterexample(true,true,1).equals(Optional.of(List.of("READ","ACK"))))throw new AssertionError();
        if(!counterexample(false,false,1).equals(Optional.of(List.of("READ","COMMIT","CRASH","READ","COMMIT"))))throw new AssertionError();
        if(counterexample(false,false,0).isPresent())throw new AssertionError();
        if(counterexample(false,true,3).isPresent())throw new AssertionError();
        try{counterexample(false,true,-1);throw new AssertionError();}catch(IllegalArgumentException expected){}
        System.out.println("PASS 6 tests");
    }
}