fix: async snapshot lost file

[bean08]

Motivation:

异步保存snapshot可以提升系统性能。在异步保存snapshot时会存在 多线程并发保存不同的状态机信息到不同文件 的情况，此时com.alipay.sofa.jraft.storage.snapshot.SnapshotWriter#addFile(java.lang.String) 也是并发操作，但对于file信息的存储 com.alipay.sofa.jraft.storage.snapshot.local.LocalSnapshotMetaTable#fileMap 类型是HashMap，它是非线程安全的，在并发调用addFile会出现信息丢失的情况，目前我是靠并发调用addFile前加锁解决的。

Modification:

com.alipay.sofa.jraft.storage.snapshot.local.LocalSnapshotMetaTable#fileMap 的类型改为线程安全的 ConcurrentHashMap

Result:

Summary by CodeRabbit

• Refactor
  • Improved thread safety in snapshot management by utilizing ConcurrentHashMap.

[sofastack-cla]

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[coderabbitai]

Walkthrough

The modification in question transitions the data structure for the fileMap field from a HashMap to a ConcurrentHashMap within the LocalSnapshotMetaTable class. This change enhances thread safety and concurrency control in snapshot metadata management, reflecting a focus on improving the reliability and performance of snapshot operations.

Changes

File Path	Change Summary
.../snapshot/local/LocalSnapshotMetaTable.java	Swapped HashMap with ConcurrentHashMap for fileMap initialization.

🐰✨
In the realm of code, where snapshots lay,
A change was made, one bright day.
From HashMap's embrace, we did depart,
To ConcurrentHashMap, a thread-safe art.
🌟 For concurrency, we hop and cheer,
In our code's garden, improvements appear!
🐾💻

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Recent Review Status

Configuration used: CodeRabbit UI

Commits

Files that changed from the base of the PR and between 890033a and 47854e5.

Files selected for processing (1)

• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotMetaTable.java (2 hunks)

Additional comments not posted (1)

jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotMetaTable.java (1)

54-54: Switching fileMap to ConcurrentHashMap is a solid fix for the concurrency issue. Ensure to assess the performance impact and compatibility of all fileMap interactions.

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[bean08]

已签署CLA但是状态一直是Required

[fengjiachun]

你好，异步保存 snapshot 本身没问题，但是不需要 fileMap 支持并发，我觉得合理的做法应该是上层 join 所有 task，元数据一次写入 fileMap，否则只有部分成功的话我认为是数据损坏

[killme2008]

你好，异步保存 snapshot 本身没问题，但是不需要 fileMap 支持并发，我觉得合理的做法应该是上层 join 所有 task，元数据一次写入 fileMap，否则只有部分成功的话我认为是数据损坏

Agree

[bean08]

你好，异步保存 snapshot 本身没问题，但是不需要 fileMap 支持并发，我觉得合理的做法应该是上层 join 所有 task，元数据一次写入 fileMap，否则只有部分成功的话我认为是数据损坏

感谢您的回复，我的场景是 通过jraft构建了一个框架，框架对内部各个组件的snapshot进行SPI化，SPI的实现自行决定保存的文件内容以及方式，只需要告知框架snapshot结果，框架统一对结果进行判断，如果任意SPI异常则整体异常，因此产生了并发的问题。
有理由相信其他人在未深究源码的情况下也会出现类似的问题，基于框架的鲁棒性考虑，我倒是觉得支持并发是有好处的。