原理
通过线程安全findAndModify 实现锁
实现
定义锁存储对象：
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/** * mongodb 分布式锁 */ @Data @NoArgsConstructor @AllArgsConstructor @Document (collection = "distributed-lock-doc" ) public class LockDocument { @Id private String id; private long expireAt; private String token; } |
定义Lock API：
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public interface LockService {
String acquire(String key, long expiration);
boolean release(String key, String token);
boolean refresh(String key, String token, long expiration); } |
获取锁：
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@Override public String acquire(String key, long expiration) { Query query = Query.query(Criteria.where( "_id" ).is(key)); String token = this .generateToken(); Update update = new Update() .setOnInsert( "_id" , key) .setOnInsert( "expireAt" , System.currentTimeMillis() + expiration) .setOnInsert( "token" , token);
FindAndModifyOptions options = new FindAndModifyOptions().upsert( true ) .returnNew( true ); LockDocument doc = mongoTemplate.findAndModify(query, update, options, LockDocument. class ); boolean locked = doc.getToken() != null && doc.getToken().equals(token);
// 如果已过期 if (!locked && doc.getExpireAt() < System.currentTimeMillis()) { DeleteResult deleted = this .mongoTemplate.remove( Query.query(Criteria.where( "_id" ).is(key) .and( "token" ).is(doc.getToken()) .and( "expireAt" ).is(doc.getExpireAt())), LockDocument. class ); if (deleted.getDeletedCount() >= 1 ) { // 成功释放锁， 再次尝试获取锁 return this .acquire(key, expiration); } }
log.debug( "Tried to acquire lock for key {} with token {} . Locked: {}" , key, token, locked); return locked ? token : null ; } |
原理：
先尝试upsert锁对象，如果成功且token一致，说明拿到锁 否则加锁失败 如果未拿到锁，但是锁已过期，尝试删除锁 如果删除成功，再次尝试拿锁 如果失败，说明锁可能已经续期了释放和续期锁：
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@Override public boolean release(String key, String token) { Query query = Query.query(Criteria.where( "_id" ).is(key) .and( "token" ).is(token)); DeleteResult deleted = mongoTemplate.remove(query, LockDocument. class ); boolean released = deleted.getDeletedCount() == 1 ; if (released) { log.debug( "Remove query successfully affected 1 record for key {} with token {}" , key, token); } else if (deleted.getDeletedCount() > 0 ) { log.error( "Unexpected result from release for key {} with token {}, released {}" , key, token, deleted); } else { log.error( "Remove query did not affect any records for key {} with token {}" , key, token); }
return released; }
@Override public boolean refresh(String key, String token, long expiration) { Query query = Query.query(Criteria.where( "_id" ).is(key) .and( "token" ).is(token)); Update update = Update.update( "expireAt" , System.currentTimeMillis() + expiration); UpdateResult updated = mongoTemplate.updateFirst(query, update, LockDocument. class );
final boolean refreshed = updated.getModifiedCount() == 1 ; if (refreshed) { log.debug( "Refresh query successfully affected 1 record for key {} " + "with token {}" , key, token); } else if (updated.getModifiedCount() > 0 ) { log.error( "Unexpected result from refresh for key {} with token {}, " + "released {}" , key, token, updated); } else { log.warn( "Refresh query did not affect any records for key {} with token {}. " + "This is possible when refresh interval fires for the final time " + "after the lock has been released" , key, token); }
return refreshed; } |
使用
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private LockService lockService;
private void tryAcquireLockAndSchedule() { while (! this .stopSchedule) { // 尝试拿锁 this .token = this .lockService.acquire(SCHEDULER_LOCK, 20000 ); if ( this .token != null ) { // 拿到锁 } else { // 等待LOCK_EXPIRATION, 再次尝试 Thread.sleep(LOCK_EXPIRATION); } } } |
先尝试拿锁，如果获取到token，说明拿锁成功 否则可以sleep一段时间后再拿锁
完整代码，可到github查看 https://github测试数据/jadepeng/docker-pipeline/blob/main/pipeline-master/src/main/java/com/github/jadepeng/pipeline/service/impl/MongoLockService.java
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原文链接：https://HdhCmsTestcnblogs测试数据/xiaoqi/p/mongodb-lock.html
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