原理
通過線程安全findAndModify 實現(xiàn)鎖
實現(xiàn)
定義鎖存儲對象：
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/** * mongodb 分布式鎖 */@Data@NoArgsConstructor@AllArgsConstructor@Document(collection = "distributed-lock-doc")public class LockDocument { @Id private String id; private long expireAt; private String token;} |
定義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);} |
獲取鎖：
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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); // 如果已過期 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) { // 成功釋放鎖， 再次嘗試獲取鎖 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：
- 先嘗試upsert鎖對象，如果成功且token一致，說明拿到鎖
- 否則加鎖失敗
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如果未拿到鎖，但是鎖已過期，嘗試刪除鎖
- 如果刪除成功，再次嘗試拿鎖
- 如果失敗，說明鎖可能已經(jīng)續(xù)期了
釋放和續(xù)期鎖：
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@Overridepublic 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;}@Overridepublic 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) { // 嘗試拿鎖 this.token = this.lockService.acquire(SCHEDULER_LOCK, 20000); if (this.token != null) { // 拿到鎖 } else { // 等待LOCK_EXPIRATION, 再次嘗試 Thread.sleep(LOCK_EXPIRATION); } } } |
- 先嘗試拿鎖，如果獲取到token，說明拿鎖成功
- 否則可以sleep一段時間后再拿鎖
完整代碼，可到github查看 https://github.com/jadepeng/docker-pipeline/blob/main/pipeline-master/src/main/java/com/github/jadepeng/pipeline/service/impl/MongoLockService.java
到此這篇關于java基于mongodb實現(xiàn)分布式鎖的示例代碼的文章就介紹到這了,更多相關java mongodb實現(xiàn)分布式鎖內(nèi)容請搜索服務器之家以前的文章或繼續(xù)瀏覽下面的相關文章希望大家以后多多支持服務器之家！
原文鏈接：https://www.cnblogs.com/xiaoqi/p/mongodb-lock.html
