feat: adds close state checking for snapshot reader and writer

[killme2008]

Motivation:

• Adds note about thread safety for SnapshotReader and SnapshopWriter
• Adds close state checking for SnapshotReader and SnapshopWriter

Modification:

Describe the idea and modifications you've done.

Result:

After this PR, i think we can close #1099

If there is no issue then describe the changes introduced by this PR.

Summary by CodeRabbit

• Documentation

  • Added notes indicating that SnapshotReader, SnapshotWriter, and SnapshotFileReader are not thread-safe.

• New Features

  • Introduced state management with a closed boolean field in LocalSnapshotReader and LocalSnapshotWriter.
  • Added checkState() method to LocalSnapshotReader and LocalSnapshotWriter to ensure operations are not performed on closed instances.

[coderabbitai]

Walkthrough

The updates enhance the thread-safety and state management of snapshot-related classes in the JRaft library. Critical modifications include marking multiple classes as not thread-safe and introducing state checks for proper resource handling in snapshot reader and writer classes.

Changes

Files	Change Summary
.../jraft/storage/snapshot/SnapshotReader.java .../jraft/storage/snapshot/SnapshotWriter.java .../jraft/storage/snapshot/local/SnapshotFileReader.java	Added notes in documentation to indicate that the classes are not thread-safe, improving clarity about the limitations of these classes.
.../jraft/storage/snapshot/local/LocalSnapshotReader.java	Added a closed field, a checkState() method, and updated the close() method to check state before closing, enhancing state management to avoid operating on closed readers.
.../jraft/storage/snapshot/local/LocalSnapshotWriter.java	Introduced a closed field, a checkState() method, and state checks in multiple methods (close(), saveMeta(), sync(), addFile(), removeFile()) to ensure proper state handling.

Assessment against linked issues

Objective (Issues)	Addressed	Explanation
Improve thread-safety of snapshot classes (#1099)	✅

In code we trust, we make it right,
Ensuring threads won't clash with might.
A reader closed, a state that's known,
Our snapshots safe, stability shown.

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[coderabbitai]

Actionable comments posted: 0

Review details

Configuration used: CodeRabbit UI
Review profile: CHILL

Commits

Files that changed from the base of the PR and between 6be4448 and f01fabe.

Files selected for processing (5)

• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/SnapshotReader.java (1 hunks)
• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/SnapshotWriter.java (1 hunks)
• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotReader.java (3 hunks)
• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotWriter.java (3 hunks)
• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/SnapshotFileReader.java (1 hunks)

Files not reviewed due to errors (1)

• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotReader.java (no review received)

Files skipped from review due to trivial changes (3)

• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/SnapshotReader.java
• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/SnapshotWriter.java
• jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/SnapshotFileReader.java

Additional comments not posted (4)

jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotWriter.java (4)

50-57: Implementation of state management for LocalSnapshotWriter.

The addition of the closed field and its initialization in the constructor are crucial for state management, ensuring that no operations are performed on a closed writer. This is a good practice, especially for error handling and resource management in multi-threaded environments.

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100-103: Enhanced safety in the close method.

The checkState call before proceeding with the close operations ensures that the writer does not perform redundant actions if it is already closed. Setting the closed flag after the operations is a good practice to maintain the state accurately.
[APROVED]

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105-108: Robust state checking with checkState.

The checkState method throws an IllegalStateException if an operation is attempted on a closed writer. This is an effective way to prevent erroneous operations on an already closed resource, enhancing the robustness of the class.

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113-113: Consistent use of state checking across methods.

The consistent use of checkState in methods like saveMeta, sync, addFile, and removeFile ensures that these operations are safe and do not occur on a closed writer. This practice helps in maintaining the integrity and reliability of the writer's operations.

Also applies to: 119-119, 125-125, 136-136