Go Concurrency with Limit

A goal

To provide a simple example on the question "how to do a limited concurrency in Go?".

What does this example do?

1. Read a file with domains of mail providers.
2. Extract subdomain, domain and TLD for each domain and get their IP addresses via DNS concurrently.
3. Print results.

Run

go run main.go

Benchmark

Results for 6100 domains

Concurrency=500:

Time start: 2020-09-11 17:16:00.857152197 +0300 EEST m=+0.000333288
Time end: 2020-09-11 17:16:13.591289057 +0300 EEST m=+12.734470178
Time difference: 12.73413689s

Concurrency=100:

Time start: 2020-09-11 17:15:03.606068609 +0300 EEST m=+0.000312989
Time end: 2020-09-11 17:15:30.193861802 +0300 EEST m=+26.588106172
Time difference: 26.587793183s

Concurrency=1:

No results, because I am not a crazy man.

Results for 500 domains

Concurrency=100:

Time start: 2020-09-11 16:58:32.909812603 +0300 EEST m=+0.000545235
Time end: 2020-09-11 16:58:42.947877372 +0300 EEST m=+10.038609975
Time difference: 10.03806474s

Concurrency=10:

Time start: 2020-09-11 16:57:09.509066626 +0300 EEST m=+0.000300896
Time end: 2020-09-11 16:57:27.794322435 +0300 EEST m=+18.285556776
Time difference: 18.28525588s

Concurrency=1:

Time start: 2020-09-11 16:59:06.880638779 +0300 EEST m=+0.000315233
Time end: 2020-09-11 17:00:11.641919047 +0300 EEST m=+64.761595541
Time difference: 1m4.761280308s