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分布式锁Redission

作者:互联网

Redisson 作为分布式锁

官方文档:https://github.com/redisson/redisson/wiki

  1. 引入依赖

     <dependency>
       <groupId>org.redisson</groupId>
       <artifactId>redisson</artifactId>
       <version>3.11.1</version>
    </dependency>
    

    2.配置redission

    @Configuration
    public class MyRedissonConfig {
        /**
         * 所有对 Redisson 的使用都是通过 RedissonClient
         *
         * @return
         * @throws IOException
         */
        @Bean(destroyMethod = "shutdown")
        public RedissonClient redisson() throws IOException {
            // 1、创建配置
            Config config = new Config();
            // Redis url should start with redis:// or rediss://
            config.useSingleServer().setAddress("redis://192.168.163.131:6379");
    
            // 2、根据 Config 创建出 RedissonClient 实例
            return Redisson.create(config);
        }
    }
    

    3.测试

        @Autowired
        RedissonClient redissonClient;
    
        @Test
        public  void redission()
        {
            System.out.println(redissonClient);
        }
    

    4.使用

     @ResponseBody
        @GetMapping("/hello")
        public  String hello()
        {
            // 1. 获取一把锁
            RLock lock = redisson.getLock("my-lock");
            // 2. 加锁, 阻塞式等待
            lock.lock();
            try {
                System.out.println("加锁成功,执行业务...");
                Thread.sleep(15000);
            } catch (Exception e) {
            } finally {
                // 3. 解锁 假设解锁代码没有运行,Redisson 会出现死锁吗?(不会)
                System.out.println("释放锁"+Thread.currentThread().getId());
                lock.unlock();
            }
            return "hello";
        }
    

假设解锁代码没有运行,Redisson 会出现死锁吗?

不会

源码分析-Redission如何解决死锁

Ctrl+Alt查看方法实现

image-20211006120452959

这是一个加锁方法,不传过期时间

    public void lock() {
        try {
            //这里过期时间自动赋值成-1
            this.lock(-1L, (TimeUnit)null, false);
        } catch (InterruptedException var2) {
            throw new IllegalStateException();
        }
    }

然后会调用 this.lock(-1L, (TimeUnit)null, false)方法

private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {
        //得到线程ID
        long threadId = Thread.currentThread().getId();
       //通过线程ID获取到锁
        Long ttl = this.tryAcquire(leaseTime, unit, threadId);
        //如果没有获取到锁
        if (ttl != null) {
            RFuture<RedissonLockEntry> future = this.subscribe(threadId);
            this.commandExecutor.syncSubscription(future);

            try {
                while(true) {
                    ttl = this.tryAcquire(leaseTime, unit, threadId);
                    if (ttl == null) {
                        return;
                    }

                    if (ttl >= 0L) {
                        try {
                            this.getEntry(threadId).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);
                        } catch (InterruptedException var13) {
                            if (interruptibly) {
                                throw var13;
                            }

                            this.getEntry(threadId).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);
                        }
                    } else if (interruptibly) {
                        this.getEntry(threadId).getLatch().acquire();
                    } else {
                        this.getEntry(threadId).getLatch().acquireUninterruptibly();
                    }
                }
            } finally {
                this.unsubscribe(future, threadId);
            }
        }
    }

获取锁方法

    private Long tryAcquire(long leaseTime, TimeUnit unit, long threadId) {
        return (Long)this.get(this.tryAcquireAsync(leaseTime, unit, threadId));
    }

里面又调用了tryAcquireAsync

private <T> RFuture<Long> tryAcquireAsync(long leaseTime, TimeUnit unit, long threadId) {
    //如果传了过期时间    
    if (leaseTime != -1L) {
            return this.tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
        } 
    //没有传过期时间
    else {
            RFuture<Long> ttlRemainingFuture = this.tryLockInnerAsync(this.commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
            ttlRemainingFuture.onComplete((ttlRemaining, e) -> {
                if (e == null) {
                    if (ttlRemaining == null) {
                        this.scheduleExpirationRenewal(threadId);
                    }

                }
            });
            return ttlRemainingFuture;
        }
    }

有指定过期时间走tryLockInnerAsync方法,尝试用异步加锁

    <T> RFuture<T> tryLockInnerAsync(long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
        //先把时间转换成internalLockLeaseTime
        this.internalLockLeaseTime = unit.toMillis(leaseTime);
        //然后执行lua脚本 发给redis执行
        return this.commandExecutor.evalWriteAsync(this.getName(), LongCodec.INSTANCE, command, "if (redis.call('exists', KEYS[1]) == 0) then redis.call('hset', KEYS[1], ARGV[2], 1); redis.call('pexpire', KEYS[1], ARGV[1]); return nil; end; if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then redis.call('hincrby', KEYS[1], ARGV[2], 1); redis.call('pexpire', KEYS[1], ARGV[1]); return nil; end; return redis.call('pttl', KEYS[1]);", Collections.singletonList(this.getName()), new Object[]{this.internalLockLeaseTime, this.getLockName(threadId)});
    }

没有指定过期时间调用getLockWatchdogTimeout()方法,获取锁的默认看门狗时间,30秒

public long getLockWatchdogTimeout() {
    return this.lockWatchdogTimeout;
}
this.lockWatchdogTimeout = 30000L;

还是调用tryLockInnerAsyncredis发送命令,占锁成功返回一个以不变异步编排的RFuture<Long>对象,来进行监听,里面有两个参数ttlRemaining, e

 ttlRemainingFuture.onComplete((ttlRemaining, e) -> {
                if (e == null) {
                    if (ttlRemaining == null) {
                        this.scheduleExpirationRenewal(threadId);
                    }

                }
            });

里面有个scheduleExpirationRenewal方法

    private void scheduleExpirationRenewal(long threadId) {
        RedissonLock.ExpirationEntry entry = new RedissonLock.ExpirationEntry();
        RedissonLock.ExpirationEntry oldEntry = (RedissonLock.ExpirationEntry)EXPIRATION_RENEWAL_MAP.putIfAbsent(this.getEntryName(), entry);
        if (oldEntry != null) {
            oldEntry.addThreadId(threadId);
        } else {
            entry.addThreadId(threadId);
            //重新设置过期时间
            this.renewExpiration();
        }

    }

里面的关键方法renewExpiration执行定时任务,

 private void renewExpiration() {
        RedissonLock.ExpirationEntry ee = (RedissonLock.ExpirationEntry)EXPIRATION_RENEWAL_MAP.get(this.getEntryName());
        if (ee != null) {
            //里面会执行一个定时任务
            Timeout task = this.commandExecutor.getConnectionManager().newTimeout(new TimerTask() {
                public void run(Timeout timeout) throws Exception {
                    RedissonLock.ExpirationEntry ent = (RedissonLock.ExpirationEntry)RedissonLock.EXPIRATION_RENEWAL_MAP.get(RedissonLock.this.getEntryName());
                    if (ent != null) {
                        Long threadId = ent.getFirstThreadId();
                        if (threadId != null) {
                            RFuture<Boolean> future = RedissonLock.this.renewExpirationAsync(threadId);
                            future.onComplete((res, e) -> {
                                if (e != null) {
                                    RedissonLock.log.error("Can't update lock " + RedissonLock.this.getName() + " expiration", e);
                                } else {
                                    if (res) {
                                        RedissonLock.this.renewExpiration();
                                    }

                                }
                            });
                        }
                    }
                }
                //看门狗时间/3 10秒钟重试一次
            }, this.internalLockLeaseTime / 3L, TimeUnit.MILLISECONDS);
            ee.setTimeout(task);
        }
    }

主要是来运行renewExpirationAsync这个方法

 protected RFuture<Boolean> renewExpirationAsync(long threadId) {
        return this.commandExecutor.evalWriteAsync(this.getName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN, "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then redis.call('pexpire', KEYS[1], ARGV[1]); return 1; end; return 0;", Collections.singletonList(this.getName()), new Object[]{this.internalLockLeaseTime, this.getLockName(threadId)});
    }

里面传入了一个internalLockLeaseTime时间参数

image-20211006163310509

又是获取看门狗时间

总结

读写锁测试

@GetMapping("/write")
    @ResponseBody
    public  String writeValue()
    {
        RReadWriteLock readWriteLock = redisson.getReadWriteLock("rw-lock");
        String s="";
        RLock rLock=readWriteLock.writeLock();
        try{
            //加写锁
            rLock.lock();
            s= UUID.randomUUID().toString();
            Thread.sleep(30000);
            redisTemplate.opsForValue().set("writeValue",s);
        }catch (Exception e){
            e.printStackTrace();
        }
        finally {
            rLock.unlock();
        }
        return  s;
    }

    @GetMapping("/read")
    @ResponseBody
    public  String readValue()
    {
        RReadWriteLock readWriteLock = redisson.getReadWriteLock("rw-lock");
        String s="";
        //加读锁
        RLock rLock=readWriteLock.readLock();
        rLock.lock();
        try{
            s=redisTemplate.opsForValue().get("writeValue");
        }catch (Exception e){
            e.printStackTrace();
        }
        finally {
            rLock.unlock();
        }
        return  s;
    }

写锁没释放读锁就必须等待,没有写锁读锁都可以读

保证数据的一致性,写锁是一个排他锁、互斥锁,读锁是共享锁。

读读共享、读写互斥、写写互斥、写读互斥,只要有写的存在都必须等待

信号量测试

像车库停车,每进来一辆车,车库减少一个车位,只有当车库还有车位才可以停车

    @GetMapping("/park")
    @ResponseBody
    public  String park() throws InterruptedException {
        RSemaphore park = redisson.getSemaphore("park");
        //获取一个信号 占一个值
        park.acquire();
        return  "ok";
    }

    @GetMapping("/go")
    @ResponseBody
    public  String go(){
        RSemaphore park = redisson.getSemaphore("park");
        //释放一个车位
        park.release();
        return  "ok";
    }

访问:

gulimall.com/park

gulimall.com/go

信号量可以用作分布式的限流

闭锁

只有等待所有活动都完成才发生,例如当所有班级放学走完才关闭学校大门

    @GetMapping("/lockdoor")
    @ResponseBody
    public  String lockDoor() throws InterruptedException {
        RCountDownLatch door = redisson.getCountDownLatch("door");
        door.trySetCount(5);
        door.await();//等待闭锁都完成
        return  "放假啦....";
    }

    @GetMapping("/gogo/{id}")
    @ResponseBody
    public  String gogogo(@PathVariable("id") Long id) throws InterruptedException {
        RCountDownLatch door = redisson.getCountDownLatch("door");
        door.countDown();
        return  id+"班都走了";
    }

缓存一致性解决

在我们读缓存的时候可能会有数据被修改过,为了让我们能够读到最新的数据,有两种处理方法:

双写模式

在把数据写入数据库的时候,同时写入到缓存中

问题:在写的过程中,可能会在第一个线程缓存还没写进,但是第二个查询到缓存又开始写数据,读到的最新数据有延迟,导致产生脏数据

失效模式

在把数据写入数据更新的时候,把缓存删除,下次查询没有缓存再添加缓存

问题:在线程1更新数据的时候消耗大量时间,还没删缓存,线程2进来也没有缓存,读取到原来老的数据,然后更新缓存

我们系统的一致性解决方案

1、缓存的所有数据都有过期时间,数据过期下一次查询触发主动更新

2、读写数据的时候,加上分布式的读写锁

3、遇到实时性、一致性要求高的数据,就应该查数据库,即使慢点。

标签:return,lock,redis,Redission,RedissonLock,threadId,public,分布式
来源: https://www.cnblogs.com/cg-ww/p/15394175.html