singleflight: increase concurrency efficieny of dochan

[0xdoomxy]

In Singlelight, the function of mutex is to protect the atomic access of critical resources in the map. In the following optimization, after deleting the key of the map, the mutex can be released without being responsible for each chan

Benchmark code

type user struct {
	Name string
}

func BenchmarkSingleflight(b *testing.B) {
	group := singleflight.Group{}
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			for i := 0; i < 1000; i++ {
				_ = <-group.DoChan(strconv.FormatInt(int64(i), 10), func() (inner interface{}, err error) {
					inner = user{
						Name: "hello",
					}
					return
				})
			}
		}
	})

}

Before optimization

After optimization

summary

Overall, this has a significant performance improvement for singlelight, with an average decrease of about 15% in time overhead

In a production environment, we do not want to use a global lock for sending results to every channel of doChan. This global lock is not necessarily responsible for this, and it is clearly stated in the performance analysis report that this can effectively reduce time overhead

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