Initial commit

LICENSE

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+MIT License
+
+Copyright (c) 2023 pkg
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Group
+
+A group provides a way manage the lifetime of a group of related goroutines.

group.go

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+// package group provides a way to manage the lifecycle of a group of goroutines.
+package group
+
+import (
+	"context"
+	"sync"
+)
+
+// A G manages the lifetime of a set of goroutines from a common context.
+// The first goroutine in the group to return will cause the context to be canceled,
+// terminating the remaining goroutines.
+type G struct {
+	// ctx is the context passed to all goroutines in the group.
+	ctx    context.Context
+	cancel context.CancelFunc
+	done   sync.WaitGroup
+
+	errOnce sync.Once
+	err     error
+}
+
+// New returns a new group using the given context.
+func New(ctx context.Context) *G {
+	ctx, cancel := context.WithCancel(ctx)
+	return &G{
+		ctx:    ctx,
+		cancel: cancel,
+	}
+}
+
+// Add runs fn in a new goroutine and adds it to the group.
+// The goroutine should exit when the context passed to it is canceled.
+func (g *G) Add(fn func(context.Context) error) {
+	g.done.Add(1)
+	go func() {
+		defer g.done.Done()
+		defer g.cancel()
+		if err := fn(g.ctx); err != nil {
+			g.errOnce.Do(func() { g.err = err })
+		}
+	}()
+}
+
+// Wait waits for all goroutines in the group to exit.
+// If any of the goroutines fail with an error, Wait will return the first error.
+func (g *G) Wait() error {
+	g.done.Wait()
+	g.errOnce.Do(func() {
+		// noop, required to synchronise on the errOnce mutex.
+	})
+	return g.err
+}