singleflight

README

Singleflight with Generics!

Package singleflight provides a duplicate function call suppression mechanism.

This fork adds generics support (Group[K comparable, V any] and Result[V any]) to the original x/sync/singleflight package.

Updates & Versioning

• I will keep this package up-to-date with the original one, at least until x/sync/singleflight adds support for generics. If you notice an update before I do, please open an issue or submit a pull request.
• Versions will be tagged to align with the same versioning as the x/sync/singleflight package.

Usage

For example usage, see:

• Group.Do
• Group.DoChan
• Group.DoForget

Documentation

Overview

Package singleflight provides a duplicate function call suppression mechanism.

This is a fork of Go's golang.org/x/sync/singleflight package, with the following changes: - Adds support for generics with Group[K comparable, V any] and Result[V any].

Index

• type Group
  • func (g *Group[K, V]) Do(key K, fn func() (V, error)) (v V, err error, shared bool)
  • func (g *Group[K, V]) DoChan(key K, fn func() (V, error)) <-chan Result[V]
  • func (g *Group[K, V]) Forget(key K)
• type Result

Examples

• Group

Types

type Group

type Group[K comparable, V 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.

Example

g := new(Group[string, string])

block := make(chan struct{})
res1c := g.DoChan("key", func() (string, error) {
	<-block
	return "func 1", nil
})
res2c := g.DoChan("key", func() (string, error) {
	<-block
	return "func 2", nil
})
close(block)

res1 := <-res1c
res2 := <-res2c

// Results are shared by functions executed with duplicate keys.
fmt.Println("Shared:", res2.Shared)
// Only the first function is executed: it is registered and started with "key",
// and doesn't complete before the second funtion is registered with a duplicate key.
fmt.Println("Equal results:", res1.Val == res2.Val)
fmt.Println("Result:", res1.Val)

Output:

Shared: true
Equal results: true
Result: func 1

func (*Group[K, V]) Do

func (g *Group[K, V]) Do(key K, fn func() (V, error)) (v V, err error, shared bool)

Do executes and returns the results of the given function, making sure that only one execution is in-flight for a given key at a time. If a duplicate comes in, the duplicate caller waits for the original to complete and receives the same results. The return value shared indicates whether v was given to multiple callers.

func (*Group[K, V]) DoChan

func (g *Group[K, V]) DoChan(key K, fn func() (V, error)) <-chan Result[V]

DoChan is like Do but returns a channel that will receive the results when they are ready.

The returned channel will not be closed.

func (*Group[K, V]) Forget

func (g *Group[K, V]) Forget(key K)

Forget tells the singleflight to forget about a key. Future calls to Do for this key will call the function rather than waiting for an earlier call to complete.

type Result

type Result[V any] struct {
	Val    V
	Err    error
	Shared bool
}

Result holds the results of Do, so they can be passed on a channel.