x/sync/errgroup: WithContext leads to cancellation of task B with a confusing error message about failed task A

[lvhuat]

Go version

go version go1.23.6 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/keto/Library/Caches/go-build'
GOENV='/Users/keto/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/keto/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/keto/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.6'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/keto/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/gv/cc7_9vk54ms322pmygll676m0000gn/T/go-build3989342279=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/keto/Library/Caches/go-build'
GOENV='/Users/keto/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/keto/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/keto/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.6'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/keto/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/gv/cc7_9vk54ms322pmygll676m0000gn/T/go-build3989342279=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you see happen?

package main

import (
	"context"
	"fmt"
	"net/http"

	"golang.org/x/sync/errgroup"
)

func main() {
	group, egCtx := errgroup.WithContext(context.Background())

	group.Go(func() error {
		return fmt.Errorf("too many pending order")
	})

	// resty
	group.Go(func() error {
		req, _ := http.NewRequest("GET", "https://baidu.com", nil)
		req = req.WithContext(egCtx)
		_, err := http.DefaultClient.Do(req)
		fmt.Println("-------------", err) // it return too many pending order,very strange!!!
		return nil
	})

	fmt.Println("############", group.Wait())
}

http return an error info is trigger by other routine

What did you expect to see?

http request return error: context cancelled

[gabyhelp]

Related Issues

• bug #75944 (closed)
• yaffaliu #56935 (closed)
• import/path: issue title #70442 (closed)
• import/path: issue title #70159 (closed)
• import/path: Loops no longer share loop variablesRunning them in different ways gives different results #69704 (closed)
• import/path: issue title #71265 (closed)
• import/path: issue title #73371 (closed)
• import/path: issue title #71243 (closed)
• go env #52280 (closed)
• import/path: issue title #68317 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[adonovan]

I agree this is a little surprising. To clarify: an errgroup runs two independent tasks. One fails with an error message; this causes the second to have its context canceled with the first error as its "cause", resulting in failure of the second operation with no obvious sign that context cancelation was the intermediating mechanism. So an error message from task A leaks into task B, even though they seem to be independent.

I haven't studied the implementation yet, but perhaps there is room to augment the cause error with "context cancelled because $CAUSE" or somesuch.

[adonovan]

@neild

[qiulaidongfeng]

Maybe https://github.com/golang/go/blob/master/src/net/http/transport.go#L677 modification can add prompt information for this issue

[qiulaidongfeng]

Or a more universal solution, https://github.com/golang/sync/blob/master/errgroup/errgroup.go#L97 modification Group.cancel Implementing Err will return prompt information as a prefix