python system_error ai_generated true

警告：事件循环被阻塞，异步路由中检测到阻塞调用，事件循环停滞 5.2 秒。

WARNING: (tracemalloc) ... asyncio: Task was destroyed but it is pending! Blocking call detected in async def route, event loop stalled for 5.2s

ID: python/fastapi-async-route-blocking-event-loop

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80%修复率
86%置信度
0证据数
2025-05-27首次发现

版本兼容性

版本状态引入弃用备注
0.100.x active — — —
0.110.x active — — —

根因分析

`async def` 路由直接调用了同步/阻塞函数（requests、time.sleep、重 CPU 操作），冻结了事件循环。

English

An `async def` route calls a synchronous/blocking function (requests, time.sleep, heavy CPU) directly, freezing the event loop.

generic

解决方案

  1. 95% 成功率 
    Use httpx.AsyncClient: `async with httpx.AsyncClient() as c: r = await c.get(url)`
  2. 90% 成功率 
    Offload with `await asyncio.to_thread(blocking_fn, args)` or `run_in_executor`.

无效尝试

常见但无效的做法:

  1. 80% 失败

    Each worker still blocks its own loop under load.

  2. 90% 失败

    Does not yield for blocking I/O; loop still stalls.