GoReplay: record-less semi-deterministic replayer for Go programs

GoReplay replays concurrent Go programs semi-deterministically without recording concrete events.

How it works

GoReplay injects time.Sleep(time.Duration(hash(seed, context, stack)) % maxInterval) to arbitrary execution points of the target Go program.

seed: environmental variable GRSEED. You can replay the execution by remembering and setting GRSEED. The default value is empty value and it disables GoReplay.
context: optional []byte slice.
stack: runtime stack. (planned)
maxInterval: environmental variable GRMAX (should be time.Duration string). The default value is 10ms.

Name	Type	Default	Description
`GRSEED`	`string`	(empty)	The seed value for determining the delay. An empty value disables GoReplay.
`GRMAX`	`time.Duration`	`10ms`	Max delay.
`GRZBIAS`	`float64`	`0.0`	Probability of enforcing the delay to be zero. must be in `[0.0, 1.0)`.

Usage

Follow the example: example/ex01.

package main

import (
	"fmt"
	"sync"

	"github.com/AkihiroSuda/go-replay"
)

func main() {
	n := 8
	var wg sync.WaitGroup
	for i := 0; i < n; i++ {
		wg.Add(1)
		go func(i interface{}) {
			msg := fmt.Sprintf("i=%d", i)
			replay.Inject([]byte(msg))
			fmt.Printf("%s\n", msg)
			wg.Done()
		}(i)
	}
	wg.Wait()
}

The result is non-deterministic without GoReplay:

$ go run example/ex01/main.go
i=7
i=5
i=1
i=6
i=0
i=2
i=3
i=4
$ (for f in $(seq 1 10);do go run example/ex01/main.go | sha512sum -; done) | sort | uniq | wc -l
4

If you set GRSEED, the result becomes deterministic:

$ (for f in $(seq 1 10);do GRSEED=foo go run example/ex01/main.go | sha512sum -; done) | sort | uniq
7ea818bd9e800609ab8e360688d975189033a9b9277d1ad9c9c96c9013f4ffeb1cf05c16ace9de737dcedaa68bc99162d611ac60b7169a43b4f9b17b1665f121  -

$ (for f in $(seq 1 10);do GRSEED=bar go run example/ex01/main.go | sha512sum -; done) | sort | uniq
fc1c177ebbc58baa7e4960102cf26da25173559de0d7a08e00c37a4512eb0a579fc6b4b70f2c708fe1166a1c0641e8839305d5fe7e26624cabbce2cb8274d963  -

Practical Examples

example/etcd-5155: data race (coreos/etcd#5155)

Hint

You may use AspectGo(WIP) for automatic instrumentation.

Related project

Namazu: a programmable fuzzy scheduler for testing distributed systems

GoReplay is planned to be merged to Namazu.

AkihiroSuda / go-replay