breakit.go

package main

import (
	"fmt"
	"log"
	"net"
	"time"
)

func main() {
	n := 0
	t := time.NewTicker(time.Second)
	c, err := net.Dial("tcp", "localhost:8888")
	if err != nil {
		log.Fatal(err)
	}
	for {
		select {
		case <-t.C:
			fmt.Println(n, "req/sec")
			n = 0
		default:
			fmt.Fprintln(c, "10")
			n = n + 1
		}
	}
}

stupid_fib_server.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"net"
	"strconv"
)

func main() {
	ln, err := net.Listen("tcp", ":8888")
	if err != nil {
		log.Fatal(err)
	}
	for {
		c, err := ln.Accept()
		if err == nil {
			go serve(c)
		}
	}
}

func fib(n int) int {
	if n <= 2 {
		return 1
	} else {
		return fib(n-1) + fib(n-2)
	}
}

func serve(c net.Conn) {
	bs := bufio.NewScanner(c)
	for bs.Scan() {
		n, _ := strconv.Atoi(bs.Text())
		go func() {
			res := fib(n)
			fmt.Fprintf(c, "%d: %s\n", n, strconv.Itoa(res))
		}()
	}
	if bs.Err() != nil {
		log.Println("error")
	}
}

What have I done?

panic: net: inconsistent fdMutex

goroutine 1145194 [running]:
panic(0x126cc0, 0xc94cf02860)
	/usr/local/Cellar/go/1.6/libexec/src/runtime/panic.go:464 +0x3e6
net.(*fdMutex).RWLock(0xc8200620e0, 0x0, 0xc94d37f61e)
	/usr/local/Cellar/go/1.6/libexec/src/net/fd_mutex.go:136 +0x20c
net.(*netFD).writeLock(0xc8200620e0, 0x0, 0x0)
	/usr/local/Cellar/go/1.6/libexec/src/net/fd_unix.go:194 +0x39
net.(*netFD).Write(0xc8200620e0, 0xc94cf02848, 0x7, 0x8, 0x0, 0x0, 0x0)
	/usr/local/Cellar/go/1.6/libexec/src/net/fd_unix.go:319 +0x6c
net.(*conn).Write(0xc820088020, 0xc94cf02848, 0x7, 0x8, 0x0, 0x0, 0x0)
	/usr/local/Cellar/go/1.6/libexec/src/net/net.go:184 +0xe4
fmt.Fprintf(0x440028, 0xc820088020, 0x18bf18, 0x7, 0xc94d9e0f70, 0x2, 0x2, 0x0, 0x0, 0x0)
	/usr/local/Cellar/go/1.6/libexec/src/fmt/print.go:189 +0xb2
main.serve.func1(0xa, 0x489440, 0xc820088020)
	/Users/twexler/dev/tmp/fib.go:38 +0x1d1
created by main.serve
	/Users/twexler/dev/tmp/fib.go:39 +0x18d
exit status 2

Interestingly enough, the script that broke it continued sending data to a socket that wasn't being listened on anymore:

⏚ [twexler:~/dev/tmp] 1 $ go run breakit.go
46110 req/sec
38331 req/sec
42625 req/sec
52618 req/sec
62030 req/sec
58850 req/sec
59278 req/sec
90486 req/sec
39302 req/sec
59480 req/sec
53790 req/sec
61662 req/sec
43035 req/sec
61134 req/sec
58688 req/sec
82457 req/sec
33726 req/sec
42164 req/sec
44805 req/sec
42312 req/sec
41992 req/sec
38499 req/sec
56298 req/sec
132634 req/sec
144863 req/sec
150092 req/sec
130998 req/sec
165556 req/sec