| // Copyright 2016 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Package errgroup provides synchronization, error propagation, and Context |
| // cancelation for groups of goroutines working on subtasks of a common task. |
| package errgroup |
| |
| import ( |
| "context" |
| "sync" |
| ) |
| |
| // A Group is a collection of goroutines working on subtasks that are part of |
| // the same overall task. |
| // |
| // A zero Group is valid and does not cancel on error. |
| type Group struct { |
| cancel func() |
| |
| wg sync.WaitGroup |
| |
| errOnce sync.Once |
| err error |
| } |
| |
| // WithContext returns a new Group and an associated Context derived from ctx. |
| // |
| // 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 WithContext(ctx context.Context) (*Group, context.Context) { |
| ctx, cancel := context.WithCancel(ctx) |
| return &Group{cancel: cancel}, 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() error) { |
| g.wg.Add(1) |
| |
| go func() { |
| defer g.wg.Done() |
| |
| if err := f(); err != nil { |
| g.errOnce.Do(func() { |
| g.err = err |
| if g.cancel != nil { |
| g.cancel() |
| } |
| }) |
| } |
| }() |
| } |