singleflight

Documentation

Overview

Package singleflight provides a duplicate function call suppression mechanism.

Index

• type Group
  • func (g *Group) Do(key string, fn func() (interface{}, error)) (v interface{}, shared bool, err error)
  • func (g *Group) DoChan(key string, fn func() (interface{}, error)) (<-chan Result, bool)
  • func (g *Group) Forget(key string)
  • func (g *Group) NumCalls(key string) int
• type Result

Types

type Group

type Group 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.

func (*Group) Do

func (g *Group) Do(
	key string, fn func() (interface{}, error),
) (v interface{}, shared bool, err error)

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) DoChan

func (g *Group) DoChan(key string, fn func() (interface{}, error)) (<-chan Result, bool)

DoChan is like Do but returns a channel that will receive the results when they are ready. The method also returns a boolean specifying whether the caller's fn function will be called or not. This return value lets callers identify a unique "leader" for a flight.

NOTE: DoChan makes it possible to initiate or join a flight while holding a lock without holding it for the duration of the flight. A common usage pattern is: 1. Check some datastructure to see if it contains the value you're looking for. 2. If it doesn't, initiate or join a flight to produce it.

Step one is expected to be done while holding a lock. Modifying the datastructure in the callback is expected to need to take the same lock. Once a caller proceeds to step two, it likely wants to keep the lock until DoChan() returned a channel, in order to ensure that a flight is only started before any modifications to the datastructure occurred (relative to the state observed in step one). Were the lock to be released before calling DoChan(), a previous flight might modify the datastructure before our flight began.

func (*Group) Forget

func (g *Group) Forget(key string)

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.

func (*Group) NumCalls

func (g *Group) NumCalls(key string) int

NumCalls returns the number of in-flight calls for a given key.

type Result

type Result struct {
	Val    interface{}
	Err    error
	Shared bool
}

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