併發編程經歷：同步加鎖之業務鎖

業務鎖

在處理併發問題時,很多情況下需要用到業務鎖來達到按照某個維度同步執行業務塊。

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 {
            //加鎖
            lockResultEnum = lockManager.getLock(lockName, LockTypeEnum.APPLY_LOCK.getCode());
            if (LockResultEnum.沒有獲取到鎖.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 {
            //釋放鎖
            lockManager.releaseLock(lockName, LockTypeEnum.APPLY_LOCK.getCode(),lockResultEnum);
        }
}

 

 

 

LockManager的getLock方法實現如下：

 

@Override
public LockResultEnum getLock(StringlockName,StringlockType){
        if(StringUtil.isEmpty(lockName)){
            LOG.error("getLock()參數爲空,param:" +lockName);
            throw new BizException(ErrorCode.ILLEGAL_ARGUMENT,"參數爲空！");
           
        }
        //只是生成一個數據庫鎖名，純粹的字符串拼接過程
        String lockName_ = getDBLockName(lockName,lockType);
        booleanisGetDbLocked =lockDao.getDbLock(lockName_);
        if (isGetDbLocked) {
            LockDO lock = lockDao.getRowLockByName(lockName);
            if (lock !=null){
                return LockResultEnum.獲取鎖成功;
            } else {
                return LockResultEnum.僅數據庫鎖;
            }
        } else {
            LOG.warn("獲取鎖【" +lockName_+"】失敗");
            return LockResultEnum.沒有獲取到鎖;
        }
}

 

 

 

LockManager的releaseLock方法實現如下：

 

@Override
public void releaseLock(StringlockName,StringlockType,LockResultEnumlockResultEnum) {
        String lockName_ = getDBLockName(lockName,lockType);
        if (StringUtil.isEmpty(lockName)) {
            LOG.error("releaseLock()參數爲空,lockName:{}",lockName);
            throw new BizException(ErrorCode.ILLEGAL_ARGUMENT,"參數爲空！");
        }
        if (LockResultEnum.獲取鎖成功.equals(lockResultEnum)|| LockResultEnum.僅數據庫鎖.equals(lockResultEnum)) {
            booleanisReleased =lockDao.releaseDbLock(lockName_);
            if (!isReleased) {
                LOG.warn("釋放鎖【" +lockName_+"】失敗");
            }
        } else {
            LOG.debug("不需要釋放鎖【" +lockName_+"】");
        }
 }

 

 

 

LockDao的實現如下：

 

@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對應sqlMap文件裏的執行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>
       <!-- 通過指定的代碼取得操作數據鎖-->
   <selectid="getLockDbByCode"resultClass="java.lang.Long"parameterClass="string">
        <![CDATA[
            select get_lock(#value#, 0) as tolock;
        ]]>
   </select>
   <!-- 通過指定的代碼釋放操作數據鎖-->
   <selectid="releaseLockDbByCode"resultClass="java.lang.Long"parameterClass="string">
        <![CDATA[
            select release_lock(#value#) as torelease;
        ]]>
    </select>

 

 

 

通過以上代碼可以很清楚的看出原理了。貸款申請提交時，爲了防止一個人同時提交多筆，要按照以人維度進行業務鎖的加鎖處理。加鎖邏輯就是鎖名和人直接掛鉤(就是鎖名裏有可以直接區分人的字段)，通過執行sql：select get_lock(#鎖名#, 0) as tolock;來獲取數據庫鎖，如果獲取成功，返回1。這裏還去獲取了一下行鎖，獲取的行鎖它鎖住的是venus_lock表的符合where條件的那些行，執行sql: select ID, NAME, REMARK,IS_ENABLED from VENUS_LOCK where NAME = #鎖名#and  IS_ENABLED = 'y' FOR UPDATE;這裏行鎖是否獲取成功其實都沒有關係。獲取到鎖之後就可以執行業務邏輯了，執行完一定要釋放鎖，執行sql：select release_lock(#鎖名#) as torelease;爲了保證釋放鎖操作一定執行，一般在finally子句中執行它即可。通過以上的步驟，當一個人同時申請多筆時，鎖名是一樣的，所以獲取到鎖後返回值就是1、2、3…具體看你是第幾個獲取的了，只有第一個獲取的返回值是1，從lockDao .getDbLock裏的booleanresult = (lock !=null&&lock.longValue()== 1) ? true:false;就可以看出，只有第一個可以執行業務邏輯，其他就認爲是沒有獲取到鎖而拋出異常終止執行：if (LockResultEnum.沒有獲取到鎖.equals(lockResultEnum)){thrownewBizException(ErrorCode.LOCK_FAIL); }

 

還有一個例子：

下面的是任務分發器，它實現了Runnable接口，在任務分發器執行時會去獲取各種異步任務類型的待執行任務列表，這裏也用到了業務鎖，調用的和上面的一樣都是lockManager.getLock(...)方法。

 

public class JobDispatcher implements Runnable {
    private static final Logger LOG                 = LoggerFactory.getLogger("applyCenterJobLog");
    /** 守護線程名稱 */
    private String              name;
    /** 一天秒數 */
    private static final long   ONE_DAY_SEC         = 24 * 60 * 60;
    /** 線程池隊列長度 */
    private int                 queueSize           = 5;
    /** 初始處理線程數 */
    private int                 coreSize            = 5;
    /** 最大處理線程數 */
    private int                 maxSize             = 5;
    /** 空閒線程最大閒置時間 */
    private long                keepAliveTime       = ONE_DAY_SEC;
    /** 線程池接收新任務閥值 */
    private int                 hungrySize          = 2;
    /** 分發器運行狀態標記 */
    private boolean             isRunning           = true;
    /** 無命令處理時休息時常（毫秒） */
    private long                noCmdSleepMillis    = 1000;
    /** 出現系統異常時休息時常（毫秒），防止把系統拖垮 */
    private long                errorCmdSleepMillis = 10000;


    private JobManager          jobManager;
    /** handler產生工廠類 */
    private JobHandlerFactory   jobHandlerFactory;


    private List<String>        jobTypeList;


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


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


    @Override
    public void run() {
        LOG.info("分發器【" + name + "】啓動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 調度異常" + e.getMessage(), e);
                ThreadUtil.sleep(errorCmdSleepMillis, LOG);
            }
        }
        executor.shutdown();
    }


    /**
     * 執行分發
     */
    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()參數非法jobType:{},jobNum:{}", jobType, jobNum);
            throw new BizException(ErrorCode.ILLEGAL_ARGUMENT, "參數非法！");
        }
        LockResultEnum lockResultEnum = null;
        try {
            /** 1、獲取業務鎖 */
    //這裏調用的lockManager.getLock(...)就是之前例子裏的
            lockResultEnum = lockManager.getLock(jobType, LockTypeEnum.JOB_LOCK.getCode());
            if (!LockResultEnum.獲取鎖成功.equals(lockResultEnum)) {//返回emptylist,dispatcher會sleep一定時間，可配置
                return new ArrayList<JobDO>(0);
            }


            return doAssignJob(jobType, jobNum);
        } catch (Exception e) {
            LOG.warn("獲取鎖失敗", e);
        } finally {
            lockManager.releaseLock(jobType, LockTypeEnum.JOB_LOCK.getCode(), lockResultEnum);
        }
        return new ArrayList<JobDO>(0);
    }

 

 

 

 

 

從上可見，這次是要獲取數據庫鎖和行鎖都成功才行： if (!LockResultEnum.獲取鎖成功.equals(lockResultEnum)) {return new ArrayList<JobDO>(0);}

所以需要在venus_lock表中有對應任務類型的數據，才能使sql:select ID, NAME, REMARK,IS_ENABLED from VENUS_LOCK where NAME = #鎖名#and  IS_ENABLED = 'y' FOR UPDATE;執行成功，獲取到行鎖。