# devopsgym / codegen__prometheus__prometheus-10710

- taskset: [devopsgym](https://harnessreport.com/tasks/devopsgym.md)
- difficulty: hard
- category: code-generation
- language: 
- runnable from the site: no
- agent timeout: 3000s

## Results by harness

_none yet_

## Instruction

```
This is a code generation task. You are expected to write working code that solves the described problem.
<issue>
      I notice that Thanos ruler API (`/api/v1/rules`) some times slow.
The rules api will iterate all rules, for each rule call `(*AlertingRule).LastError()` https://github.com/prometheus/prometheus/blob/v2.35.0/rules/alerting.go#L187 and  `(*AlertingRule).Health()` https://github.com/prometheus/prometheus/blob/v2.35.0/rules/alerting.go#L201 to get the error state and health state, this function will call `(*AlertingRule).mtx.Lock()`.
At the same time, ruler may eval rules, call the `(*AlertingRule).Eval` https://github.com/prometheus/prometheus/blob/v2.35.0/rules/alerting.go#L341 , it will also call  `(*AlertingRule).mtx.Lock()`, in the `(*AlertingRule).Eval` function, the `tmpl.Expand()` https://github.com/prometheus/prometheus/blob/v2.35.0/rules/alerting.go#L378  will be a slow operation if we using `query` https://github.com/prometheus/prometheus/blob/main/template/template.go#L150 function in template. 

## Proposal
1. use sync.RWMutex.
2. make template expanding out of the lock.

## My Work plan
1. write a unit test to minimum produce.
2. fix it.

</issue>
Focus on implementing the required functionality correctly and efficiently. Treat this as a programming challenge.
You are not allowed to read git history.
```
---
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