为什么 fasthttp.Client 并发消费一个 API 会变慢？

Question

这是第一种情况。

var fastClient fasthttp.Client

fastClient = fasthttp.Client{
    ReadTimeout: 500 * time.Millisecond,
    MaxConnsPerHost: 500,
}

runtime.GOMAXPROCS(1)

for i := 0; i < 500; i++ {
    req := fasthttp.AcquireRequest()
    req.Header.SetMethod("GET")
    req.SetRequestURI(TEST_REST_API)
    res := fasthttp.AcquireResponse()
    
    start := time.Now()
    err := client.Do(req, res)
    ms := time.Since(start).Milliseconds()

    fasthttp.ReleaseRequest(req)
    fasthttp.ReleaseResponse(res)

    fmt.Printf("%v %v", ms, string(res.Header.Peek("x-real-service-time")))
}

这是第二种情况。

var fastClient fasthttp.Client

fastClient = fasthttp.Client{
    ReadTimeout: 500 * time.Millisecond,
    MaxConnsPerHost: 500,
}

runtime.GOMAXPROCS(1)

for i := 0; i < 500; i++ {
    go func(id int, c *fasthttp.Client) {
       req := c.AcquireRequest()
       req.Header.SetMethod("GET")
       req.SetRequestURI(TEST_REST_API)
       res := c.AcquireResponse()

       start := time.Now()
       err := client.Do(req, res)
       ms := time.Since(start).Milliseconds()

       c.ReleaseRequest(req)
       c.ReleaseResponse(res)

       fmt.Printf("%v %v %v", id, ms, string(res.Header.Peek("x-real-service-time")))
    }(i, &fastClient)

    // waiting for end all goroutine
}

x-real-service-time是一个header，它记录了服务器处理实际请求和响应所花费的时间。

在第一种情况下，ms 与 x-real-service-time 几乎相同。 在第二种情况下，ms 比 x-real-service-time 慢太多，而且随着每个 id 的增加，它变得越来越慢。

你能解释这些差异的原因吗？ 我希望在第二种情况下 ms 和 x-real-service-time 之间的差异也很小。 我应该如何调整它？

编辑：第一种情况的结果。

id: 166 | ms: 115 | x-real-service-time : 105
id: 167 | ms: 103 | x-real-service-time : 97
id: 168 | ms: 89 | x-real-service-time : 73
id: 169 | ms: 92 | x-real-service-time : 76
id: 170 | ms: 79 | x-real-service-time : 73
id: 171 | ms: 81 | x-real-service-time : 73
id: 172 | ms: 84 | x-real-service-time : 76
id: 173 | ms: 84 | x-real-service-time : 78
id: 174 | ms: 81 | x-real-service-time : 73
id: 175 | ms: 82 | x-real-service-time : 76
id: 176 | ms: 82 | x-real-service-time : 75
id: 177 | ms: 80 | x-real-service-time : 74
id: 178 | ms: 79 | x-real-service-time : 71
id: 179 | ms: 75 | x-real-service-time : 69
id: 180 | ms: 87 | x-real-service-time : 78
id: 181 | ms: 81 | x-real-service-time : 72
...

第二种情况的结果。

id: 486 | ms: 516 | x-real-service-time : 72
id: 361 | ms: 620 | x-real-service-time : 100
id: 349 | ms: 620 | x-real-service-time : 96
id: 417 | ms: 621 | x-real-service-time : 100
id: 3 | ms: 631 | x-real-service-time : 76
id: 227 | ms: 634 | x-real-service-time : 90
id: 152 | ms: 639 | x-real-service-time : 77
id: 138 | ms: 640 | x-real-service-time : 78
id: 139 | ms: 640 | x-real-service-time : 84
id: 144 | ms: 640 | x-real-service-time : 79
...
id: 267 | ms: 783 | x-real-service-time : 75
id: 195 | ms: 779 | x-real-service-time : 73
id: 465 | ms: 781 | x-real-service-time : 76
id: 420 | ms: 781 | x-real-service-time : 74
id: 334 | ms: 782 | x-real-service-time : 112
id: 14 | ms: 780 | x-real-service-time : 69
id: 430 | ms: 781 | x-real-service-time : 75
id: 372 | ms: 782 | x-real-service-time : 78
id: 224 | ms: 778 | x-real-service-time : 107
...
id: 481 | ms: 825 | x-real-service-time : 67
id: 105 | ms: 823 | x-real-service-time : 75
id: 467 | ms: 825 | x-real-service-time : 71
id: 67 | ms: 825 | x-real-service-time : 73
id: 460 | ms: 828 | x-real-service-time : 77
id: 142 | ms: 827 | x-real-service-time : 78
id: 58 | ms: 828 | x-real-service-time : 71
id: 311 | ms: 833 | x-real-service-time : 78
id: 414 | ms: 833 | x-real-service-time : 71
id: 289 | ms: 836 | x-real-service-time : 77
...
id: 323 | ms: 1019 | x-real-service-time : 201
id: 211 | ms: 1015 | x-real-service-time : 209
id: 220 | ms: 1015 | x-real-service-time : 203
id: 275 | ms: 1021 | x-real-service-time : 216
id: 477 | ms: 1019 | x-real-service-time : 207
id: 160 | ms: 1017 | x-real-service-time : 197
id: 398 | ms: 1020 | x-real-service-time : 199
id: 253 | ms: 1017 | x-real-service-time : 201
id: 74 | ms: 1019 | x-real-service-time : 204
id: 422 | ms: 1021 | x-real-service-time : 205

id：循环号（变量i）

ms：客户端发出请求后到收到响应的时间（毫秒）

x-real-service-time：在服务器上实际处理所花费的时间（毫秒）

Answer 1

你只使用一个 cpu( runtime.GOMAXPROCS(1) )，

如果你使用 goroutine，cpu 会等待并挂起，

client.Do花费最多的时间。

不是慢而是开始时间太早。

这就是为什么result for second case 。 id⬆ -> 时间⬆