In a typical Go network program, you start by accepting a connection with conn := lis.Accept(), then initiate a goroutine to handle incoming data using go func(net.Conn). Next, you allocate a buffer with buf := make([]byte, 4096) and wait for data with conn.Read(buf).
For a server managing over 10,000 connections with frequent short messages (e.g., <512 bytes), the cost of context switching becomes significantly higher than that of receiving messages—each context switch can require over 1,000 CPU cycles or around 600 ns on a 2.1 GHz processor.
By eliminating one goroutine per connection through Edge-Triggered I/O Multiplexing, you can save the 2KB (R) + 2KB (W) stack space typically used per goroutine. Additionally, by employing an internal swap buffer, you can avoid the need for buf := make([]byte, 4096) at the expense of some performance.
The gaio library implements the proactor pattern, effectively addressing both memory constraints and performance objectives.
- High Performance: Tested in High Frequency Trading environments, handling 30K–40K RPS on a single HVM server.
- Scalability: Designed for over C10K concurrent connections, optimizing both parallelism and single connection throughput.
- Flexible Buffering: Use
Read(ctx, conn, buffer)with a nil buffer to leverage the internal swap buffer. - Non-Intrusive Integration: Compatible with
net.Listenerandnet.Conn(supportssyscall.RawConn), allowing easy integration into existing applications. - Efficient Context Switching: Minimizes context switching costs for small messages, ideal for frequent chat message exchanges.
- Customizable Delegation: Applications can choose when to delegate
net.Connto gaio, such as after a handshake or specificnet.TCPConnsettings. - Back-Pressure Handling: Applications can control when to submit read or write requests, enabling per-connection back-pressure to slow down sending when necessary, particularly useful for transferring data from a faster source (A) to a slower destination (B).
- Lightweight and Maintainable: Approximately 1,000 lines of code, making it easy to debug.
- Cross-Platform Support: Compatible with Linux and BSD.
-
Connection Delegation: Once you submit an async read/write request with a related
net.Conntogaio.Watcher, that connection is delegated to the watcher. Subsequent calls toconn.Readorconn.Writewill return an error, but TCP properties set bySetReadBuffer(),SetWriteBuffer(),SetLinger(),SetKeepAlive(), andSetNoDelay()will be retained. -
Resource Management: If you no longer need a connection, call
Watcher.Free(net.Conn)to immediately close the socket and free resources. If you forget to callWatcher.Free, the runtime garbage collector will clean up system resources ifnet.Connis not referenced elsewhere. Failing to callWatcher.Close()will lead the garbage collector to clean up all related resources if the watcher is unreferenced. -
Load Balancing: For connection load balancing, create multiple
gaio.Watcherinstances to distributenet.Connusing your preferred strategy. For acceptor load balancing, utilizego-reuseportas the listener. -
Safe Read Requests: When submitting read requests with a 'nil' buffer, the returned
[]bytefromWatcher.WaitIO()is safe to use until the next call toWatcher.WaitIO().
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
}
}
}Push server
package mainpackage 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
}
}For complete documentation, see the associated Godoc.
| Test Case | Throughput test with 64KB buffer |
|---|---|
| Description | A client keep on sending 64KB bytes to server, server keeps on reading and sending back whatever it received, the client keeps on receiving whatever the server sent back until all bytes received successfully |
| Command | go test -v -run=^$ -bench Echo |
| Macbook Pro | 1695.27 MB/s 518 B/op 4 allocs/op |
| Linux AMD64 | 1883.23 MB/s 518 B/op 4 allocs/op |
| Raspberry Pi4 | 354.59 MB/s 334 B/op 4 allocs/op |
| Test Case | 8K concurrent connection echo test |
|---|---|
| Description | Start 8192 clients, each client send 1KB data to server, server keeps on reading and sending back whatever it received, the client keeps on receiving whatever the server sent back until all bytes received successfully. |
| Command | go test -v -run=8k |
| Macbook Pro | 1.09s |
| Linux AMD64 | 0.94s |
| Raspberry Pi4 | 2.09s |
On MacOS, you need to increase the max open files limit to run the benchmarks.
sysctl -w kern.ipc.somaxconn=4096
sysctl -w kern.maxfiles=100000
sysctl -w kern.maxfilesperproc=100000
sysctl -w net.inet.ip.portrange.first=1024
sysctl -w net.inet.ip.portrange.last=65535
ulimit -S -n 65536
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
- if you encounter something like:
# github.com/xtaci/gaio [github.com/xtaci/gaio.test]
./aio_linux.go:155:7: undefined: setAffinity
./watcher.go:588:4: undefined: setAffinity
FAIL github.com/xtaci/gaio [build failed]
FAIL
make sure you have gcc/clang installed.
gaio source code is available under the MIT License.
- https://zhuanlan.zhihu.com/p/102890337 -- gaio小记
- golang/go#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
Stable