# run

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run.Group is a universal mechanism to manage goroutine lifecycles.

Create a zero-value run.Group, and then add actors to it. Actors are defined as
a pair of functions: an **execute** function, which should run synchronously;
and an **interrupt** function, which, when invoked, should cause the execute
function to return. Finally, invoke Run, which blocks until the first actor
returns. This general-purpose API allows callers to model pretty much any
runnable task, and achieve well-defined lifecycle semantics for the group.

run.Group was written to manage component lifecycles in func main for
[OK Log](https://github.com/oklog/oklog).
But it's useful in any circumstance where you need to orchestrate multiple
goroutines as a unit whole.
[Click here](https://www.youtube.com/watch?v=LHe1Cb_Ud_M&t=15m45s) to see a
video of a talk where run.Group is described.

## Examples

### context.Context

```go
ctx, cancel := context.WithCancel(context.Background())
g.Add(func() error {
	return myProcess(ctx, ...)
}, func(error) {
	cancel()
})
```

### net.Listener

```go
ln, _ := net.Listen("tcp", ":8080")
g.Add(func() error {
	return http.Serve(ln, nil)
}, func(error) {
	ln.Close()
})
```

### io.ReadCloser

```go
var conn io.ReadCloser = ...
g.Add(func() error {
	s := bufio.NewScanner(conn)
	for s.Scan() {
		println(s.Text())
	}
	return s.Err()
}, func(error) {
	conn.Close()
})
```

## Comparisons

Package run is somewhat similar to package
[errgroup](https://godoc.org/golang.org/x/sync/errgroup),
except it doesn't require actor goroutines to understand context semantics.

It's somewhat similar to package
[tomb.v1](https://godoc.org/gopkg.in/tomb.v1) or
[tomb.v2](https://godoc.org/gopkg.in/tomb.v2),
except it has a much smaller API surface, delegating e.g. staged shutdown of
goroutines to the caller.