avoid cpu occupied

[yihaoDeng]

Description

Please briefly describe the code changes in this pull request.

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

Hello @yihaoDeng, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on improving the stability and resource management of character set conversion operations. It introduces a retry limit to prevent the taosAcquireConv function from potentially entering an infinite loop, thereby mitigating CPU occupation issues. Concurrently, the system's capacity for handling conversion objects has been substantially expanded to support more concurrent operations. These changes aim to make the conversion process more resilient and efficient.

Highlights

• CPU Occupation Prevention: Implemented a retry mechanism with a limit of 100 attempts in the taosAcquireConv function to prevent indefinite looping and potential CPU occupation when acquiring conversion objects. If the limit is reached, an error is logged.
• Increased Conversion Capacity: The maximum number of conversion objects (CONV_MAX_NUM) has been significantly increased from 32 to 512, allowing for greater concurrency in character set conversion operations.
• Robust Thread ID Calculation: Added a uint32_t cast to the taosGetSelfPthreadId() return value when calculating startId in taosAcquireConv, enhancing the robustness of the modulo operation.

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[gemini-code-assist]

Code Review

This pull request aims to prevent high CPU usage in taosAcquireConv by introducing a retry limit to a busy-wait loop. While this is a good step, the change is incomplete. A second busy-wait loop in the same function remains, which can still lead to 100% CPU utilization under contention. I have raised a critical issue about this incomplete fix. I also have a minor suggestion to improve code maintainability by replacing a magic number with a named constant. The related change to increase the converter pool size in tconv.c seems appropriate.

[gemini-code-assist]

While this pull request aims to prevent high CPU usage by adding a retry limit to the first while loop, the while (true) loop immediately following this line (starting on line 403) remains a busy-wait loop without any yielding mechanism or retry limit. If all converters happen to be in use, this loop will spin indefinitely and consume an entire CPU core, defeating the purpose of this PR.

To fully resolve the CPU occupation issue, this second loop must also be modified. A simple fix would be to add a sched_yield() call within the loop to prevent it from hogging the CPU, for instance after a full scan of all converters without finding a free one.

[gemini-code-assist]

The retry limit 100 is a magic number. It's better to define it as a named constant at the top of the file or in a relevant header file to improve readability and maintainability. For example: #define TAOS_ACQUIRE_CONV_RETRY_LIMIT 100.