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go sync.pool 的实现
https://www.cyhone.com/articles/think-in-sync-pool/#:~:text=sync.Pool%20%E6%98%AFGolang%20%E5%86%85%E7%BD%AE,%E5%88%9B%E5%BB%BA%E7%9A%84%20gin.Context%20%E5%AF%B9%E8%B1%A1%E3%80%82