136 lines
3.3 KiB
Go
136 lines
3.3 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package errgroup provides synchronization, error propagation, and Context
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// cancelation for groups of goroutines working on subtasks of a common task.
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//
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// [errgroup.Group] is related to [sync.WaitGroup] but adds handling of tasks
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// returning errors.
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package errgroup
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import (
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"context"
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"fmt"
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"sync"
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)
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type token struct{}
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// A Group is a collection of goroutines working on subtasks that are part of
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// the same overall task.
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//
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// A zero Group is valid, has no limit on the number of active goroutines,
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// and does not cancel on error.
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type Group struct {
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cancel func(error)
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wg sync.WaitGroup
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sem chan token
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errOnce sync.Once
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err error
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}
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func (g *Group) done() {
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if g.sem != nil {
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<-g.sem
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}
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g.wg.Done()
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}
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// WithContext returns a new Group and an associated Context derived from ctx.
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//
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// The derived Context is canceled the first time a function passed to Go
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// returns a non-nil error or the first time Wait returns, whichever occurs
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// first.
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func WithContext(ctx context.Context) (*Group, context.Context) {
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ctx, cancel := withCancelCause(ctx)
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return &Group{cancel: cancel}, ctx
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}
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// Wait blocks until all function calls from the Go method have returned, then
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// returns the first non-nil error (if any) from them.
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func (g *Group) Wait() error {
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g.wg.Wait()
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if g.cancel != nil {
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g.cancel(g.err)
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}
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return g.err
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}
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// Go calls the given function in a new goroutine.
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// It blocks until the new goroutine can be added without the number of
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// active goroutines in the group exceeding the configured limit.
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//
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// The first call to return a non-nil error cancels the group's context, if the
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// group was created by calling WithContext. The error will be returned by Wait.
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func (g *Group) Go(f func() error) {
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if g.sem != nil {
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g.sem <- token{}
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}
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g.wg.Add(1)
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go func() {
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defer g.done()
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if err := f(); err != nil {
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g.errOnce.Do(func() {
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g.err = err
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if g.cancel != nil {
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g.cancel(g.err)
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}
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})
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}
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}()
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}
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// TryGo calls the given function in a new goroutine only if the number of
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// active goroutines in the group is currently below the configured limit.
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//
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// The return value reports whether the goroutine was started.
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func (g *Group) TryGo(f func() error) bool {
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if g.sem != nil {
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select {
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case g.sem <- token{}:
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// Note: this allows barging iff channels in general allow barging.
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default:
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return false
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}
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}
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g.wg.Add(1)
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go func() {
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defer g.done()
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if err := f(); err != nil {
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g.errOnce.Do(func() {
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g.err = err
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if g.cancel != nil {
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g.cancel(g.err)
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}
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})
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}
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}()
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return true
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}
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// SetLimit limits the number of active goroutines in this group to at most n.
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// A negative value indicates no limit.
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//
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// Any subsequent call to the Go method will block until it can add an active
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// goroutine without exceeding the configured limit.
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//
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// The limit must not be modified while any goroutines in the group are active.
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func (g *Group) SetLimit(n int) {
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if n < 0 {
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g.sem = nil
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return
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}
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if len(g.sem) != 0 {
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panic(fmt.Errorf("errgroup: modify limit while %v goroutines in the group are still active", len(g.sem)))
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}
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g.sem = make(chan token, n)
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}
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