gaio

gaio

Introduction

中文介绍

For a typical golang network program, you would first conn := lis.Accept() to get a connection and go func(net.Conn) to start a goroutine for handling the incoming data, then you would buf:=make([]byte, 4096) to allocate some buffer and finally waits on conn.Read(buf).

For a server holding >10K connections with frequent short messages(e.g. < 512B), cost for context switching is much more expensive than receiving message(a context switch needs at least 1000 CPU cycles or 600ns on 2.1GHz).

And by eliminating one goroutine per one connection scheme with Edge-Triggered IO Multiplexing, the 2KB(R)+2KB(W) per connection goroutine stack can be saved. By using internal swap buffer, buf:=make([]byte, 4096) can be saved(at the cost of performance).

gaio is an proactor pattern networking library satisfy both memory constraints and performance goals.

Features

1. Designed for >C10K concurrent connections, maximized parallelism, and nice single connection throughput.
2. Read(ctx, conn, buffer) can be called with nil buffer to make use of internal swap buffer.
3. Non-intrusive design, this library works with net.Listener and net.Conn. (with syscall.RawConn support), easy to be integrated into your existing software.
4. Amortized context switching cost for tiny messages, able to handle frequent chat message exchanging.
5. Application can decide when to delegate net.Conn to gaio, for example, you can delegate net.Conn to gaio after some handshaking procedure, or having some net.TCPConn settings done.
6. Application can decide when to submit read or write requests, per-connection back-pressure can be propagated to peer to slow down sending. This features is particular useful to transmit data from A to B via gaio, which B is slower than A.
7. Tiny, around 1000 LOC, easy to debug.
8. Support for Linux, BSD.

Conventions

1. Once you submit an async read/write requests with related net.Conn to gaio.Watcher, this conn will be delegated to gaio.Watcher at first submit. Future use of this conn like conn.Read or conn.Write will return error, but TCP properties set by SetReadBuffer(), SetWriteBuffer(), SetLinger(), SetKeepAlive(), SetNoDelay() will be inherited.
2. If you decide not to use this connection anymore, you could call Watcher.Free(net.Conn) to close socket and free related resources immediately.
3. If you forget to call Watcher.Free(net.Conn), runtime garbage collector will cleanup related system resources if nowhere in the system holds the net.Conn.
4. If you forget to call Watcher.Close(), runtime garbage collector will cleanup ALL related system resources if nowhere in the system holds this Watcher.
5. For connection Load-Balance, you can create multiple gaio.Watcher with your own strategy to distribute net.Conn.
6. For acceptor Load-Balance, you can use go-reuseport as the listener.
7. For read requests submitted with 'nil' buffer, the returning []byte from Watcher.WaitIO() is SAFE to use before next call to Watcher.WaitIO() returned.

TL;DR

package main

import (
        "log"
        "net"

        "github.com/xtaci/gaio"
)

// this goroutine will wait for all io events, and sents back everything it received
// in async way
func echoServer(w *gaio.Watcher) {
        for {
                // loop wait for any IO events
                results, err := w.WaitIO()
                if err != nil {
                        log.Println(err)
                        return
                }

                for _, res := range results {
                        switch res.Operation {
                        case gaio.OpRead: // read completion event
                                if res.Error == nil {
                                        // send back everything, we won't start to read again until write completes.
                                        // submit an async write request
                                        w.Write(nil, res.Conn, res.Buffer[:res.Size])
                                }
                        case gaio.OpWrite: // write completion event
                                if res.Error == nil {
                                        // since write has completed, let's start read on this conn again
                                        w.Read(nil, res.Conn, res.Buffer[:cap(res.Buffer)])
                                }
                        }
                }
        }
}

func main() {
        w, err := gaio.NewWatcher()
        if err != nil {
              log.Fatal(err)
        }
        defer w.Close()
	
        go echoServer(w)

        ln, err := net.Listen("tcp", "localhost:0")
        if err != nil {
                log.Fatal(err)
        }
        log.Println("echo server listening on", ln.Addr())

        for {
                conn, err := ln.Accept()
                if err != nil {
                        log.Println(err)
                        return
                }
                log.Println("new client", conn.RemoteAddr())

                // submit the first async read IO request
                err = w.Read(nil, conn, make([]byte, 128))
                if err != nil {
                        log.Println(err)
                        return
                }
        }
}

More examples

package main

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

        "github.com/xtaci/gaio"
)

func main() {
        // by simply replace net.Listen with reuseport.Listen, everything is the same as in push-server
        // ln, err := reuseport.Listen("tcp", "localhost:0")
        ln, err := net.Listen("tcp", "localhost:0")
        if err != nil {
                log.Fatal(err)
        }

        log.Println("pushing server listening on", ln.Addr(), ", use telnet to receive push")

        // create a watcher
        w, err := gaio.NewWatcher()
        if err != nil {
                log.Fatal(err)
        }

        // channel
        ticker := time.NewTicker(time.Second)
        chConn := make(chan net.Conn)
        chIO := make(chan gaio.OpResult)

        // watcher.WaitIO goroutine
        go func() {
                for {
                        results, err := w.WaitIO()
                        if err != nil {
                                log.Println(err)
                                return
                        }

                        for _, res := range results {
                                chIO <- res
                        }
                }
        }()

        // main logic loop, like your program core loop.
        go func() {
                var conns []net.Conn
                for {
                        select {
                        case res := <-chIO: // receive IO events from watcher
                                if res.Error != nil {
                                        continue
                                }
                                conns = append(conns, res.Conn)
                        case t := <-ticker.C: // receive ticker events
                                push := []byte(fmt.Sprintf("%s\n", t))
                                // all conn will receive the same 'push' content
                                for _, conn := range conns {
                                        w.Write(nil, conn, push)
                                }
                                conns = nil
                        case conn := <-chConn: // receive new connection events
                                conns = append(conns, conn)
                        }
                }
        }()

        // this loop keeps on accepting connections and send to main loop
        for {
                conn, err := ln.Accept()
                if err != nil {
                        log.Println(err)
                        return
                }
                chConn <- conn
        }
}

Documentation

For complete documentation, see the associated Godoc.

Benchmarks

Regression

X -> number of concurrent connections, Y -> time of completion in seconds

Best-fit values	 
Slope	8.613e-005 ± 5.272e-006
Y-intercept	0.08278 ± 0.03998
X-intercept	-961.1
1/Slope	11610
 
95% Confidence Intervals	 
Slope	7.150e-005 to 0.0001008
Y-intercept	-0.02820 to 0.1938
X-intercept	-2642 to 287.1
 
Goodness of Fit	 
R square	0.9852
Sy.x	0.05421
 
Is slope significantly non-zero?	 
F	266.9
DFn,DFd	1,4
P Value	< 0.0001
Deviation from horizontal?	Significant
 
Data	 
Number of XY pairs	6
Equation	Y = 8.613e-005*X + 0.08278

License

gaio source code is available under the MIT License.

References

• https://zhuanlan.zhihu.com/p/102890337 -- gaio小记
• https://github.com/golang/go/issues/15735 -- net: add mechanism to wait for readability on a TCPConn
• https://en.wikipedia.org/wiki/C10k_problem -- C10K
• https://golang.org/src/runtime/netpoll_epoll.go -- epoll in golang
• https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2 -- kqueue
• https://idea.popcount.org/2017-02-20-epoll-is-fundamentally-broken-12/ -- epoll is fundamentally broken
• https://en.wikipedia.org/wiki/Transmission_Control_Protocol#Flow_control -- TCP Flow Control
• http://www.idc-online.com/technical_references/pdfs/data_communications/Congestion_Control.pdf -- Back-pressure

Status

Stable