分布式锁原理和使用

 

自旋 

 public Map<String, List<Catelog2Vo>> getCatalogJsonFromDBWithRedisLock() {Boolean b = redisTemplate.opsForValue().setIfAbsent(Lock, Lock, Duration.ofMinutes(1));if (!b) {int i = 10;while (i > 0) {Object result = redisTemplate.opsForValue().get(CATALOG_JSON);try {TimeUnit.MILLISECONDS.sleep(100);} catch (InterruptedException e) {throw new RuntimeException(e);}if (result != null) {System.out.println("命中缓存 db lock");return (Map<String, List<Catelog2Vo>>) result;}i--;}throw new RuntimeException("系统繁忙，请重新访问");}//1.查出所有1级分类List<CategoryEntity> selectList = baseMapper.selectList(null);/*** 将数据库的多次查询变成一次*/System.out.println("查询了数据库");//2. 封装数据List<CategoryEntity> level1Category = selectList.stream().filter(s -> s.getParentCid().equals(0L)).collect(Collectors.toList());Map<String, List<Catelog2Vo>> map = level1Category.stream().collect(Collectors.toMap(k -> k.getCatId().toString(), v -> {//1.每一个的一级分类,查到1级分类的所有二级分类List<CategoryEntity> categoryEntities = selectList.stream().filter(s -> s.getParentCid().equals(v.getCatId())).collect(Collectors.toList());List<Catelog2Vo> catelog2VoList = categoryEntities.stream().map(c -> {Catelog2Vo catelog2Vo = new Catelog2Vo();catelog2Vo.setId(c.getCatId().toString());catelog2Vo.setName(c.getName());catelog2Vo.setCatalog1Id(v.getCatId().toString());List<CategoryEntity> categoryEntities1 = selectList.stream().filter(s -> s.getParentCid().equals(c.getCatId())).collect(Collectors.toList());List<Catelog2Vo.Catelog3Vo> collect = categoryEntities1.stream().map(c3 -> {Catelog2Vo.Catelog3Vo catelog3Vo = new Catelog2Vo.Catelog3Vo();catelog3Vo.setId(c3.getCatId().toString());catelog3Vo.setName(c3.getName());catelog3Vo.setCatalog2Id(c.getCatId().toString());return catelog3Vo;}).collect(Collectors.toList());catelog2Vo.setCatalog3List(collect);return catelog2Vo;}).collect(Collectors.toList());return catelog2VoList;}));if (map == null) {/*** 解决缓存穿透*/map = new HashMap<>();}redisTemplate.opsForValue().set(CATALOG_JSON, map, Duration.ofDays(1));redisTemplate.delete(Lock);return map;}

 public Map<String, List<Catelog2Vo>> getCatalogJsonFromDBWithRedisLock() {String uuid = UUID.randomUUID().toString();Boolean b = redisTemplate.opsForValue().setIfAbsent(Lock, uuid, Duration.ofMinutes(1));if (!b) {int i = 10;while (i > 0) {Object result = redisTemplate.opsForValue().get(CATALOG_JSON);try {TimeUnit.MILLISECONDS.sleep(100);} catch (InterruptedException e) {throw new RuntimeException(e);}if (result != null) {System.out.println("命中缓存 db lock");return (Map<String, List<Catelog2Vo>>) result;}i--;}throw new RuntimeException("系统繁忙，请重新访问");}//1.查出所有1级分类List<CategoryEntity> selectList = baseMapper.selectList(null);/*** 将数据库的多次查询变成一次*/System.out.println("查询了数据库");//2. 封装数据List<CategoryEntity> level1Category = selectList.stream().filter(s -> s.getParentCid().equals(0L)).collect(Collectors.toList());Map<String, List<Catelog2Vo>> map = level1Category.stream().collect(Collectors.toMap(k -> k.getCatId().toString(), v -> {//1.每一个的一级分类,查到1级分类的所有二级分类List<CategoryEntity> categoryEntities = selectList.stream().filter(s -> s.getParentCid().equals(v.getCatId())).collect(Collectors.toList());List<Catelog2Vo> catelog2VoList = categoryEntities.stream().map(c -> {Catelog2Vo catelog2Vo = new Catelog2Vo();catelog2Vo.setId(c.getCatId().toString());catelog2Vo.setName(c.getName());catelog2Vo.setCatalog1Id(v.getCatId().toString());List<CategoryEntity> categoryEntities1 = selectList.stream().filter(s -> s.getParentCid().equals(c.getCatId())).collect(Collectors.toList());List<Catelog2Vo.Catelog3Vo> collect = categoryEntities1.stream().map(c3 -> {Catelog2Vo.Catelog3Vo catelog3Vo = new Catelog2Vo.Catelog3Vo();catelog3Vo.setId(c3.getCatId().toString());catelog3Vo.setName(c3.getName());catelog3Vo.setCatalog2Id(c.getCatId().toString());return catelog3Vo;}).collect(Collectors.toList());catelog2Vo.setCatalog3List(collect);return catelog2Vo;}).collect(Collectors.toList());return catelog2VoList;}));if (map == null) {/*** 解决缓存穿透*/map = new HashMap<>();}redisTemplate.opsForValue().set(CATALOG_JSON, map, Duration.ofDays(1));Object o = redisTemplate.opsForValue().get(Lock);if (o != null && o.equals(uuid)) {redisTemplate.delete(Lock);}return map;}

还是有问题

因为 在传输过程中需要耗时，这时候如果过期KEY，让其他线程进来创建KEY，然后数据返回到之前那个线程，删除KEY，又会把别人新加进来的key给删掉

获取值对比+对比成功删除=原子操作

 redis+lua脚本实现

 public static final String Lock = "Lock";

  public Map<String, List<Catelog2Vo>> getCatalogJsonFromDBWithRedisLock() {String uuid = UUID.randomUUID().toString();Boolean b = redisTemplate.opsForValue().setIfAbsent(Lock, uuid, Duration.ofMinutes(5));if (!b) {System.out.println("获取分布式锁失败，等待重试");int i = 10;while (i > 0) {Object result = redisTemplate.opsForValue().get(CATALOG_JSON);try {TimeUnit.MILLISECONDS.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}if (result != null) {System.out.println("命中缓存 db lock");return (Map<String, List<Catelog2Vo>>) result;}i--;}throw new RuntimeException("系统繁忙，请重新访问");}//1.查出所有1级分类/*** 将数据库的多次查询变成一次*/System.out.println("获取分布式锁成功");//2. 封装数据Map<String, List<Catelog2Vo>> map = null;try {System.out.println("查询了数据库");List<CategoryEntity> selectList = baseMapper.selectList(null);List<CategoryEntity> level1Category = selectList.stream().filter(s -> s.getParentCid().equals(0L)).collect(Collectors.toList());map = level1Category.stream().collect(Collectors.toMap(k -> k.getCatId().toString(), v -> {//1.每一个的一级分类,查到1级分类的所有二级分类List<CategoryEntity> categoryEntities = selectList.stream().filter(s -> s.getParentCid().equals(v.getCatId())).collect(Collectors.toList());List<Catelog2Vo> catelog2VoList = categoryEntities.stream().map(c -> {Catelog2Vo catelog2Vo = new Catelog2Vo();catelog2Vo.setId(c.getCatId().toString());catelog2Vo.setName(c.getName());catelog2Vo.setCatalog1Id(v.getCatId().toString());List<CategoryEntity> categoryEntities1 = selectList.stream().filter(s -> s.getParentCid().equals(c.getCatId())).collect(Collectors.toList());List<Catelog2Vo.Catelog3Vo> collect = categoryEntities1.stream().map(c3 -> {Catelog2Vo.Catelog3Vo catelog3Vo = new Catelog2Vo.Catelog3Vo();catelog3Vo.setId(c3.getCatId().toString());catelog3Vo.setName(c3.getName());catelog3Vo.setCatalog2Id(c.getCatId().toString());return catelog3Vo;}).collect(Collectors.toList());catelog2Vo.setCatalog3List(collect);return catelog2Vo;}).collect(Collectors.toList());return catelog2VoList;}));if (map == null) {/*** 解决缓存穿透*/map = new HashMap<>();}redisTemplate.opsForValue().set(CATALOG_JSON, map, Duration.ofDays(1));} catch (Exception e) {e.printStackTrace();} finally {//lua脚本解锁//如果获取key等于传过来的值，就执行删除操作,否则就不执行String script="if redis.call('get',KEYS[1])==ARGV[1] then return redis.call('del',KEYS[1]) else return 0 end";Long execute = redisTemplate.execute(new DefaultRedisScript<Long>(script, Long.class), Arrays.asList(Lock), uuid);if (execute==1){System.out.println("原子删锁成功");}else {System.out.println("原子删锁失败");}}return map;}

 只有一个查询了数据库