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// Copyright (c) Liam Stanley <me@liamstanley.io>. All rights reserved. Use
// of this source code is governed by the MIT license that can be found in
// the LICENSE file.
package ctxgroup
import (
"context"
"sync"
)
// A Group is a collection of goroutines working on subtasks that are part of
// the same overall task.
type Group struct {
ctx context.Context
cancel func()
wg sync.WaitGroup
errOnce sync.Once
err error
}
// New returns a new Group and an associated context derived from ctx.
// Obtain the derived context from calling Group.Context().
//
// The derived context is canceled the first time a function passed to Go
// returns a non-nil error or the first time Wait returns, whichever occurs
// first.
func New(ctx context.Context) *Group {
nctx, cancel := context.WithCancel(ctx)
return &Group{ctx: nctx, cancel: cancel}
}
// Context returns the context for this group. It may be canceled by the first
// function to return a non-nil error.
func (g *Group) Context() context.Context {
return g.ctx
}
// Wait blocks until all function calls from the Go method have returned, then
// returns the first non-nil error (if any) from them.
func (g *Group) Wait() error {
g.wg.Wait()
if g.cancel != nil {
g.cancel()
}
return g.err
}
// Go calls the given function in a new goroutine. The first call to return a
// non-nil error cancels the group; its error will be returned by Wait.
func (g *Group) Go(f func(ctx context.Context) error) {
g.wg.Add(1)
go func() {
defer g.wg.Done()
if err := f(g.ctx); err != nil {
g.errOnce.Do(func() {
g.err = err
if g.cancel != nil {
g.cancel()
}
})
}
}()
}
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