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package singleflight

import ""

Package singleflight provides a duplicate function call suppression mechanism.


Package Files


type Group Uses

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 Uses

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 Uses

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 Uses

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 Uses

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

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

type Result Uses

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

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

Package singleflight imports 2 packages (graph) and is imported by 59 packages. Updated 2020-05-08. Refresh now. Tools for package owners.