DROP DATABASE IF EXISTS javacodeabcd;
CREATE DATABASE javacodeabcd;
USE javacodeabcd;
DROP TABLE IF EXISTS t_lock;
create table t_lock(
  lock_key varchar(32) PRIMARY KEY NOT NULL COMMENT '鎖唯一標(biāo)志',
  request_id varchar(64) NOT NULL DEFAULT '' COMMENT '用來(lái)標(biāo)識(shí)請(qǐng)求對(duì)象的',
  lock_count INT NOT NULL DEFAULT 0 COMMENT '當(dāng)前上鎖次數(shù)',
  timeout BIGINT NOT NULL DEFAULT 0 COMMENT '鎖超時(shí)時(shí)間',
  version INT NOT NULL DEFAULT 0 COMMENT '版本號(hào)，每次更新+1'
)COMMENT '鎖信息表';

package com.itsoku.sql;

import lombok.Builder;
import lombok.Getter;
import lombok.Setter;
import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

import java.sql.*;
import java.util.Objects;
import java.util.UUID;
import java.util.concurrent.TimeUnit;

@Slf4j
public class LockUtils {

    //將requestid保存在該變量中
    static ThreadLocal<String> requestIdTL = new ThreadLocal<>();

    /**
     * 獲取當(dāng)前線程requestid
     *
     * @return
     */
    public static String getRequestId() {
        String requestId = requestIdTL.get();
        if (requestId == null || "".equals(requestId)) {
            requestId = UUID.randomUUID().toString();
            requestIdTL.set(requestId);
        }
        log.info("requestId:{}", requestId);
        return requestId;
    }

    /**
     * 獲取鎖
     *
     * @param lock_key        鎖key
     * @param locktimeout(毫秒) 持有鎖的有效時(shí)間，防止死鎖
     * @param gettimeout(毫秒)  獲取鎖的超時(shí)時(shí)間，這個(gè)時(shí)間內(nèi)獲取不到將重試
     * @return
     */
    public static boolean lock(String lock_key, long locktimeout, int gettimeout) throws Exception {
        log.info("start");
        boolean lockResult = false;
        String request_id = getRequestId();
        long starttime = System.currentTimeMillis();
        while (true) {
            LockModel lockModel = LockUtils.get(lock_key);
            if (Objects.isNull(lockModel)) {
                //插入一條記錄,重新嘗試獲取鎖
                LockUtils.insert(LockModel.builder().lock_key(lock_key).request_id("").lock_count(0).timeout(0L).version(0).build());
            } else {
                String reqid = lockModel.getRequest_id();
                //如果reqid為空字符，表示鎖未被占用
                if ("".equals(reqid)) {
                    lockModel.setRequest_id(request_id);
                    lockModel.setLock_count(1);
                    lockModel.setTimeout(System.currentTimeMillis() + locktimeout);
                    if (LockUtils.update(lockModel) == 1) {
                        lockResult = true;
                        break;
                    }
                } else if (request_id.equals(reqid)) {
                    //如果request_id和表中request_id一樣表示鎖被當(dāng)前線程持有者，此時(shí)需要加重入鎖
                    lockModel.setTimeout(System.currentTimeMillis() + locktimeout);
                    lockModel.setLock_count(lockModel.getLock_count() + 1);
                    if (LockUtils.update(lockModel) == 1) {
                        lockResult = true;
                        break;
                    }
                } else {
                    //鎖不是自己的，并且已經(jīng)超時(shí)了，則重置鎖，繼續(xù)重試
                    if (lockModel.getTimeout() < System.currentTimeMillis()) {
                        LockUtils.resetLock(lockModel);
                    } else {
                        //如果未超時(shí)，休眠100毫秒，繼續(xù)重試
                        if (starttime + gettimeout > System.currentTimeMillis()) {
                            TimeUnit.MILLISECONDS.sleep(100);
                        } else {
                            break;
                        }
                    }
                }
            }
        }
        log.info("end");
        return lockResult;
    }

    /**
     * 釋放鎖
     *
     * @param lock_key
     * @throws Exception
     */
    public static void unlock(String lock_key) throws Exception {
        //獲取當(dāng)前線程requestId
        String requestId = getRequestId();
        LockModel lockModel = LockUtils.get(lock_key);
        //當(dāng)前線程requestId和庫(kù)中request_id一致 && lock_count>0，表示可以釋放鎖
        if (Objects.nonNull(lockModel) && requestId.equals(lockModel.getRequest_id()) && lockModel.getLock_count() > 0) {
            if (lockModel.getLock_count() == 1) {
                //重置鎖
                resetLock(lockModel);
            } else {
                lockModel.setLock_count(lockModel.getLock_count() - 1);
                LockUtils.update(lockModel);
            }
        }
    }

    /**
     * 重置鎖
     *
     * @param lockModel
     * @return
     * @throws Exception
     */
    public static int resetLock(LockModel lockModel) throws Exception {
        lockModel.setRequest_id("");
        lockModel.setLock_count(0);
        lockModel.setTimeout(0L);
        return LockUtils.update(lockModel);
    }

    /**
     * 更新lockModel信息，內(nèi)部采用樂(lè)觀鎖來(lái)更新
     *
     * @param lockModel
     * @return
     * @throws Exception
     */
    public static int update(LockModel lockModel) throws Exception {
        return exec(conn -> {
            String sql = "UPDATE t_lock SET request_id = ?,lock_count = ?,timeout = ?,version = version + 1 WHERE lock_key = ? AND  version = ?";
            PreparedStatement ps = conn.prepareStatement(sql);
            int colIndex = 1;
            ps.setString(colIndex++, lockModel.getRequest_id());
            ps.setInt(colIndex++, lockModel.getLock_count());
            ps.setLong(colIndex++, lockModel.getTimeout());
            ps.setString(colIndex++, lockModel.getLock_key());
            ps.setInt(colIndex++, lockModel.getVersion());
            return ps.executeUpdate();
        });
    }

    public static LockModel get(String lock_key) throws Exception {
        return exec(conn -> {
            String sql = "select * from t_lock t WHERE t.lock_key=?";
            PreparedStatement ps = conn.prepareStatement(sql);
            int colIndex = 1;
            ps.setString(colIndex++, lock_key);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                return LockModel.builder().
                        lock_key(lock_key).
                        request_id(rs.getString("request_id")).
                        lock_count(rs.getInt("lock_count")).
                        timeout(rs.getLong("timeout")).
                        version(rs.getInt("version")).build();
            }
            return null;
        });
    }

    public static int insert(LockModel lockModel) throws Exception {
        return exec(conn -> {
            String sql = "insert into t_lock (lock_key, request_id, lock_count, timeout, version) VALUES (?,?,?,?,?)";
            PreparedStatement ps = conn.prepareStatement(sql);
            int colIndex = 1;
            ps.setString(colIndex++, lockModel.getLock_key());
            ps.setString(colIndex++, lockModel.getRequest_id());
            ps.setInt(colIndex++, lockModel.getLock_count());
            ps.setLong(colIndex++, lockModel.getTimeout());
            ps.setInt(colIndex++, lockModel.getVersion());
            return ps.executeUpdate();
        });
    }

    public static <T> T exec(SqlExec<T> sqlExec) throws Exception {
        Connection conn = getConn();
        try {
            return sqlExec.exec(conn);
        } finally {
            closeConn(conn);
        }
    }

    @FunctionalInterface
    public interface SqlExec<T> {
        T exec(Connection conn) throws Exception;
    }

    @Getter
    @Setter
    @Builder
    public static class LockModel {
        private String lock_key;
        private String request_id;
        private Integer lock_count;
        private Long timeout;
        private Integer version;
    }

    private static final String url = "jdbc:mysql://localhost:3306/javacodeabcd?useSSL=false";        //數(shù)據(jù)庫(kù)地址
    private static final String username = "root";        //數(shù)據(jù)庫(kù)用戶名
    private static final String password = "root123";        //數(shù)據(jù)庫(kù)密碼
    private static final String driver = "com.mysql.jdbc.Driver";        //mysql驅(qū)動(dòng)

    /**
     * 連接數(shù)據(jù)庫(kù)
     *
     * @return
     */
    public static Connection getConn() {
        Connection conn = null;
        try {
            Class.forName(driver);  //加載數(shù)據(jù)庫(kù)驅(qū)動(dòng)
            try {
                conn = DriverManager.getConnection(url, username, password);  //連接數(shù)據(jù)庫(kù)
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return conn;
    }

    /**
     * 關(guān)閉數(shù)據(jù)庫(kù)鏈接
     *
     * @return
     */
    public static void closeConn(Connection conn) {
        if (conn != null) {
            try {
                conn.close();  //關(guān)閉數(shù)據(jù)庫(kù)鏈接
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

package com.itsoku.sql;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

import static com.itsoku.sql.LockUtils.lock;
import static com.itsoku.sql.LockUtils.unlock;

@Slf4j
public class LockUtilsTest {

    //測(cè)試重復(fù)獲取和重復(fù)釋放
    @Test
    public void test1() throws Exception {
        String lock_key = "key1";
        for (int i = 0; i < 10; i++) {
            lock(lock_key, 10000L, 1000);
        }
        for (int i = 0; i < 9; i++) {
            unlock(lock_key);
        }
    }

    //獲取之后不釋放，超時(shí)之后被thread1獲取
    @Test
    public void test2() throws Exception {
        String lock_key = "key2";
        lock(lock_key, 5000L, 1000);
        Thread thread1 = new Thread(() -> {
            try {
                try {
                    lock(lock_key, 5000L, 7000);
                } finally {
                    unlock(lock_key);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        thread1.setName("thread1");
        thread1.start();
        thread1.join();
    }
}