并发编程经历：同步加锁之业务锁

来源：互联网发布：适合女生看的a v 知乎编辑：程序博客网时间：2024/05/22 13:56

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。

以申请中心的venuscore后台申请报名为例：

@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>

<selectid="getLockDbByCode"resultClass="java.lang.Long"parameterClass="string">

<![CDATA[

select get_lock(#value#, 0) as tolock;

]]>

</select>

<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。

以上是一个我在并发编程上的经历。

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