singleflight

type Group ¶

type Group[T any] struct {
	// contains filtered or unexported fields
}

Group represents a class of work and forms a namespace in which units of work can be executed with duplicate suppression. Unlike the original singleflight Group, this version uses generics. A Group[T]’s Do method returns a Result[T], so the value has the same type T used to create the Group.

g := NewGroup[int]()

block := make(chan struct{})
started := make(chan struct{}, 2)

var r1, r2 Result[int]
var wg sync.WaitGroup

wg.Add(2)
go func() {
	defer wg.Done()
	started <- struct{}{}
	r1 = g.Do("key", func() (int, error) {
		<-block
		return 1, nil
	})
}()

go func() {
	defer wg.Done()
	started <- struct{}{}
	r2 = g.Do("key", func() (int, error) {
		<-block
		return 2, nil
	})
}()

<-started
<-started

close(block)
wg.Wait()

fmt.Println("Equal result:", r1.Val == r2.Val)

Output:

Equal result: true

func NewGroup[T any]() *Group[T]

func (g *Group[T]) Do(key string, fn func() (T, error)) Result[T]

func (g *Group[T]) Stats() *Stats

type Result ¶

type Result[T any] struct {
	Err error

	Shared  bool
	Initial bool

	Val T
}

Result is the return value of a singleflight.Do call.

The shared field indicates whether the value was given to multiple callers. The initial field indicates whether this is the first call to Do for the given key.

type Stats ¶

type Stats struct {
	NumCalls           atomic.Int64
	NumSuppressedCalls atomic.Int64
}

Stats contains statistics about the singleflight.Group. NumCalls is the number of calls to Do. NumSuppressedCalls is the number of calls to Do that were suppressed due to a previous call and are waiting for the results.