并发编程经历 同步加锁之业务锁

Posted 2021-01-29 swnchx

业务锁

在处理并发问题时,很多情况下需要用到业务锁来达到按照某个维度同步执行业务块。

例子：

 

@Override
@Transactional(rollbackFor = Exception.class, noRollbackFor = TerminateException.class)
public ApplyDO submitApply(ApplyDOapplyDO) {
        LockResultEnum lockResultEnum =null;
        String lockName = new StringBuffer().append(applyDO.getSite()).append("_").append(applyDO.getSiteMemId()).toString();
        try {
            //加锁
            lockResultEnum = lockManager.getLock(lockName, LockTypeEnum.APPLY_LOCK.getCode());
            if (LockResultEnum.没有获取到锁.equals(lockResultEnum)){
                throw new BizException(ErrorCode.LOCK_FAIL);
            }
            …
            returnapplyDO;
        } catch (TerminateExceptione) {
            throwe;
        } catch (BizExceptione) {
            throw new BizException(e.getErrorCode(),e);
        } catch (Exceptione) {
            throw new BizException(ErrorCode.GENERIC_ERROR,e);
        } finally {
            //释放锁
            lockManager.releaseLock(lockName, LockTypeEnum.APPLY_LOCK.getCode(),lockResultEnum);
        }
}

LockManager的getLock方法实现如下：

 

@Override
public LockResultEnum getLock(StringlockName,StringlockType){
        if(StringUtil.isEmpty(lockName)){
            LOG.error("getLock()参数为空,param:" +lockName);
            throw new BizException(ErrorCode.ILLEGAL_ARGUMENT,"参数为空！");
           
        }
        //只是生成一个数据库锁名，纯粹的字符串拼接过程
        String lockName_ = getDBLockName(lockName,lockType);
        booleanisGetDbLocked =lockDao.getDbLock(lockName_);
        if (isGetDbLocked) {
            LockDO lock = lockDao.getRowLockByName(lockName);
            if (lock !=null){
                return LockResultEnum.获取锁成功;
            } else {
                return LockResultEnum.仅数据库锁;
            }
        } else {
            LOG.warn("获取锁【" +lockName_+"】失败");
            return LockResultEnum.没有获取到锁;
        }
}

LockManager的releaseLock方法实现如下：

 

@Override
public void releaseLock(StringlockName,StringlockType,LockResultEnumlockResultEnum) {
        String lockName_ = getDBLockName(lockName,lockType);
        if (StringUtil.isEmpty(lockName)) {
            LOG.error("releaseLock()参数为空,lockName:{}",lockName);
            throw new BizException(ErrorCode.ILLEGAL_ARGUMENT,"参数为空！");
        }
        if (LockResultEnum.获取锁成功.equals(lockResultEnum)|| LockResultEnum.仅数据库锁.equals(lockResultEnum)) {
            booleanisReleased =lockDao.releaseDbLock(lockName_);
            if (!isReleased) {
                LOG.warn("释放锁【" +lockName_+"】失败");
            }
        } else {
            LOG.debug("不需要释放锁【" +lockName_+"】");
        }
 }

LockDao的实现如下：

 

@Override
public boolean getDbLock(String lockCode){
        Long lock = (Long)super.getSqlMapClientTemplate().queryForObject("LockDO.getLockDbByCode",lockCode);
        booleanresult = (lock !=null&&lock.longValue()== 1) ? true:false;
        returnresult;
}
    @Override
    public boolean releaseDbLock(String lockCode) {
        Long lock = (Long)super.getSqlMapClientTemplate().queryForObject("LockDO.releaseLockDbByCode",lockCode);
        booleanresult = (lock !=null&&lock.longValue()== 1) ? true:false;
        returnresult;
    }
    @Override
    public LockDO getRowLockByName(Stringname) {
       return (LockDO)super.getSqlMapClientTemplate().queryForObject("LockDO.selectForUpdateByLockName",name);
}

LockDao对应sqlMap文件里的执行sql如下：

 

<selectid="selectForUpdateByLockName"resultMap="jobLockMap" parameterClass="java.lang.String" >
        select
               ID, NAME, REMARK, IS_ENABLED
          from VENUS_LOCK
         where NAME = #value# and  IS_ENABLED = ‘y‘
        FOR UPDATE
  </select>
       <!-- 通过指定的代码取得操作数据锁-->
   <selectid="getLockDbByCode"resultClass="java.lang.Long"parameterClass="string">
        <![CDATA[
            select get_lock(#value#, 0) as tolock;
        ]]>
   </select>
   <!-- 通过指定的代码释放操作数据锁-->
   <selectid="releaseLockDbByCode"resultClass="java.lang.Long"parameterClass="string">
        <![CDATA[
            select release_lock(#value#) as torelease;
        ]]>
    </select>

通过以上代码可以很清楚的看出原理了。贷款申请提交时，为了防止一个人同时提交多笔，要按照以人维度进行业务锁的加锁处理。加锁逻辑就是锁名和人直接挂钩(就是锁名里有可以直接区分人的字段)，通过执行sql：select get_lock(#锁名#, 0) as tolock;来获取数据库锁，如果获取成功，返回1。这里还去获取了一下行锁，获取的行锁它锁住的是venus_lock表的符合where条件的那些行，执行sql: select ID, NAME, REMARK,IS_ENABLED from VENUS_LOCK where NAME = #锁名#and  IS_ENABLED = ‘y‘ FOR UPDATE;这里行锁是否获取成功其实都没有关系。获取到锁之后就可以执行业务逻辑了，执行完一定要释放锁，执行sql：select release_lock(#锁名#) as torelease;为了保证释放锁操作一定执行，一般在finally子句中执行它即可。通过以上的步骤，当一个人同时申请多笔时，锁名是一样的，所以获取到锁后返回值就是1、2、3…具体看你是第几个获取的了，只有第一个获取的返回值是1，从lockDao .getDbLock里的booleanresult = (lock !=null&&lock.longValue()== 1) ? true:false;就可以看出，只有第一个可以执行业务逻辑，其他就认为是没有获取到锁而抛出异常终止执行：if (LockResultEnum.没有获取到锁.equals(lockResultEnum)){thrownewBizException(ErrorCode.LOCK_FAIL); }

 

还有一个例子：

下面的是任务分发器，它实现了Runnable接口，在任务分发器执行时会去获取各种异步任务类型的待执行任务列表，这里也用到了业务锁，调用的和上面的一样都是lockManager.getLock(...)方法。

 

public class JobDispatcher implements Runnable {
    private static final Logger LOG                 = LoggerFactory.getLogger("applyCenterJobLog");
    /** 守护线程名称 */
    private String              name;
    /** 一天秒数 */
    private static final long   ONE_DAY_SEC         = 24 * 60 * 60;
    /** 线程池队列长度 */
    private int                 queueSize           = 5;
    /** 初始处理线程数 */
    private int                 coreSize            = 5;
    /** 最大处理线程数 */
    private int                 maxSize             = 5;
    /** 空闲线程最大闲置时间 */
    private long                keepAliveTime       = ONE_DAY_SEC;
    /** 线程池接收新任务阀值 */
    private int                 hungrySize          = 2;
    /** 分发器运行状态标记 */
    private boolean             isRunning           = true;
    /** 无命令处理时休息时常（毫秒） */
    private long                noCmdSleepMillis    = 1000;
    /** 出现系统异常时休息时常（毫秒），防止把系统拖垮 */
    private long                errorCmdSleepMillis = 10000;


    private JobManager          jobManager;
    /** handler产生工厂类 */
    private JobHandlerFactory   jobHandlerFactory;


    private List<String>        jobTypeList;


    /**
     * spring init
     */
    public void init() {
        LOG.info("分发器【" + name + "】init!!!!!");
        jobTypeList = jobHandlerFactory.getJobTypeList();
    }


    /**
     * spring destroy
     */
    public void destroy() {
        LOG.warn("收到分发器【" + name + "】停止通知!!!!!");
        isRunning = false;
    }


    @Override
    public void run() {
        LOG.info("分发器【" + name + "】启动ing...");
        BlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(queueSize);
        ThreadPoolExecutor executor = new ThreadPoolExecutor(coreSize, maxSize, keepAliveTime, TimeUnit.SECONDS, queue);
        while (isRunning) {
            try {
                int i = 0;
                if (queue.size() < hungrySize) {
                    for (String jobType : jobTypeList) {
                        List<JobDO> jobDOList = jobManager.assignJob(jobType, queueSize - queue.size());
                        for (JobDO jobDO : jobDOList) {
                            i++;
                            JobHandler<JobDO> tmpJobHandler = jobHandlerFactory.getHandler(jobDO);
                            ExecuteJobThread<JobDO> executeCmdThread = new ExecuteJobThread<JobDO>(jobDO, tmpJobHandler);
                            executor.execute(executeCmdThread);
                        }
                    }
                } else {
                    ThreadUtil.sleep(noCmdSleepMillis, LOG);
                }
                if (i == 0) {
                    ThreadUtil.sleep(noCmdSleepMillis, LOG);
                } else {
                    i = 0;
                }
            } catch (Exception e) {
                LOG.error("dispacher 调度异常" + e.getMessage(), e);
                ThreadUtil.sleep(errorCmdSleepMillis, LOG);
            }
        }
        executor.shutdown();
    }


    /**
     * 执行分发
     */
    public void dispatcher() {
        Thread thread = new Thread(this);
        isRunning = true;
        thread.start();
    }
...//一些set方法
}

jobManager的assignJob方法如下：

 

public List<JobDO> assignJob(String jobType, int jobNum) {
        if (StringUtil.isBlank(jobType) || jobNum <= 0) {
            LOG.error("assignJob()参数非法jobType:{},jobNum:{}", jobType, jobNum);
            throw new BizException(ErrorCode.ILLEGAL_ARGUMENT, "参数非法！");
        }
        LockResultEnum lockResultEnum = null;
        try {
            /** 1、获取业务锁 */
    //这里调用的lockManager.getLock(...)就是之前例子里的
            lockResultEnum = lockManager.getLock(jobType, LockTypeEnum.JOB_LOCK.getCode());
            if (!LockResultEnum.获取锁成功.equals(lockResultEnum)) {//返回emptylist,dispatcher会sleep一定时间，可配置
                return new ArrayList<JobDO>(0);
            }


            return doAssignJob(jobType, jobNum);
        } catch (Exception e) {
            LOG.warn("获取锁失败", e);
        } finally {
            lockManager.releaseLock(jobType, LockTypeEnum.JOB_LOCK.getCode(), lockResultEnum);
        }
        return new ArrayList<JobDO>(0);
    }

从上可见，这次是要获取数据库锁和行锁都成功才行： if (!LockResultEnum.获取锁成功.equals(lockResultEnum)) {return new ArrayList<JobDO>(0);}

所以需要在venus_lock表中有对应任务类型的数据，才能使sql:select ID, NAME, REMARK,IS_ENABLED from VENUS_LOCK where NAME = #锁名#and  IS_ENABLED = ‘y‘ FOR UPDATE;执行成功，获取到行锁。

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