Probably running out of ephemeral ports or hitting fd limit.

@bradfitz:

If I run it with -cpu 32 -parallel 1024 it will print this after a while:
proof_test.go:4037: dial tcp 127.0.0.1:50697: can't assign requested address

If I change my ulimit -n 100, and run it with -cpu 8 -parallel 1024, I get this:
panic: httptest: failed to listen on a port: listen tcp6 [::1]:0: too many open files [recovered]

So I think this is a different error.

cc @mikioh who likes stuff like this.

test-web.go

package main

import "github.com/go-martini/martini"
import "runtime"
import (
    "log"
)

func main() {
    n := runtime.NumCPU()
    log.Println("CPU:", n)
    runtime.GOMAXPROCS(n)

    m := martini.Classic()
    m.Get("/", func() string {
        return "Hello world!"
    })
    m.Run()
}

boom -cpus 8 -n 10000 -c 240 http://127.0.0.1:3000/
10000 / 10000 Booooooooooooooooooooooooooooooooooooooooooooooooooooooo! 100.00 %

Summary:
Total: 6.0928 secs.
Slowest: 3.5828 secs.
Fastest: 0.0006 secs.
Average: 0.0413 secs.
Requests/sec: 1472.8877
Total Data Received: 107688 bytes.
Response Size per Request: 12 bytes.

Status code distribution:
[200] 8974 responses

Response time histogram:
0.001 [1] |
0.359 [8885] |∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
0.717 [3] |
1.075 [16] |
1.433 [10] |
1.792 [1] |
2.150 [7] |
2.508 [6] |
2.866 [6] |
3.225 [0] |
3.583 [39] |

Latency distribution:
10% in 0.0074 secs.
25% in 0.0096 secs.
50% in 0.0126 secs.
75% in 0.0221 secs.
90% in 0.0380 secs.
95% in 0.0477 secs.
99% in 0.2838 secs.

Error distribution:
[2] Get http://127.0.0.1:3000/: write tcp 127.0.0.1:3000: socket is not connected
[841] Get http://127.0.0.1:3000/: dial tcp 127.0.0.1:3000: can't assign requested address
[183] Get http://127.0.0.1:3000/: read tcp 127.0.0.1:3000: connection reset by peer

@hannesroth macs have a reduced number of ephemeral port try

 sudo sysctl -w net.inet.ip.portrange.first=32768

This fixes your example for me.

Reason is the min lifetime of a port on mac os plus the available number of ports, which is bound to run out.

Timeout. And I don't think there's anything actionable here.

We can reopen if anybody disagrees.