This document describes code for a Memcached server written in Go. It uses TCP listeners and handlers to accept connections from clients. It maintains an in-memory key-value store using a map. It can handle get and set requests by parsing the request header and building responses. It uses channels for communication between the main listener routine and a backend handler for the key-value store.

1. Moriyoshi Koizumi

4. net.Listen("tcp", "127.0.0.1:11211")
net.Accept()

5. go handleConn(sock);

6. func main() {
if len(os.Args) < 2 {
fmt.Fprintf(os.Stderr, "usage: %s addr:portn", os.Args[0]);
os.Exit(255);
}
l, e := net.Listen("tcp", os.Args[1]);
if e != nil {
error("An error occurred (%s)", e.String());
os.Exit(1);
}
// blocking channel
backend_ch := make(chan *kvsBackendConn);
go backend(backend_ch);
for {
ch, e := l.Accept();
if e != nil {
error("An error occurred (%s)", e.String());
os.Exit(1);
}
go handleConn(ch, backend_ch, false);
}
os.Exit(0)
}

7. opcode := int(header[1]);
key_length := (int(header[2]) << 8) | int(header[3]);
extra_length := int(header[4]);
data_type := int(header[5]);
body_length := (int(header[8]) << 24)
| (int(header[9]) << 16)
| (int(header[10]) << 8)
| int(header[11]);

9. func backend(ch <-chan *kvsBackendConn) {
kvs := make(map[string] []byte);
for req := range ch {
switch (req.command) {
case 0: // get
value, e := kvs[string(req.key)];
if e {
req.resp_ch<- (&kvsBackendConn{command:0, value:value})
} else {
req.resp_ch<- (&kvsBackendConn{command:0, value:nil})
}
break;
case 1: // set
kvs[string(req.key)] = req.value;
break;
backend_ch<-
} (&kvsBackendConn{
} command: 0,
} key: key,
value: nil,
resp_ch: recv_ch
});
result := <-recv_ch;
resp_extra := make([]byte, 4);
if result != nil {
resp = buildResponse(opcode, 0, ...)
} else {
resp = buildResponse(opcode, 1, ...)
}

11. memslap --test=get --concurrency=4 --binary --verbose
--servers=127.0.0.1 --execute-number=100 --initial-load=10000
--tcp-nodelay
GOMAXPROCS=1
GOMAXPROCS=2
GOMAXPROCS=3
GOMAXPROCS=4

12. epoll(2)/
Poll server kqueue(2)
Write() FD
FD FD FD once.Do(startServer)
FD FD FD FD
Read() FD
FD
Read()
Write()
channel
communication

13. pipe(2) eventfd(2)

14. moriyoshi