This question already has answers here:
cancel a blocking operation in Go
(2 answers)
Closed 3 years ago.
I have a pool of goroutines which I want to kill a specific one of them from outside.
Thanks for your help
You cannot "kill" a goroutine. You can use one of the synchronizations primitives, or the context to tell the goroutine that you want it to end.
ctx,cancel:=context.WithCancel(context.Background())
go func(ctx context.Context) {
for {
select {
case <-ctx.Done():
return
default
}
// Do stuff
}
}(ctx)
...
// Tell that goroutine to stop
cancel()
You can use sync.atomic as well:
die:=make([]int32,nGoroutines)
go func(i int) {
if atomic.LoadInt32(&die[i])==1 {
return
}
// Do stuff
if atomic.LoadInt32(&die[i])==1 {
return
}
// Do more stuff
}(0) // 0'th goroutine
...
// Tell goroutine n to stop
atomic.StoreInt32(&die[n],1)
I found an answer. There is a concept named Context which carries deadlines, cancelation signals, and other request-scoped values across API boundaries and between processes. This is sample codes:
type Job struct {
ID int
Context context.Context
Cancel context.CancelFunc
}
var jobs = make(map[int] Job)
func worker(ctx context.Context, index int) {
fmt.Printf("starting job with id %d\n", index)
<-ctx.Done()
}
func main() {
var err error
id := 0
r := gin.Default()
r.POST("/start", func(c *gin.Context) {
var job Job
err := json.NewDecoder(c.Request.Body).Decode(&job)
if err != nil{ fmt.Println(err)}
ctx, cancel := context.WithCancel(context.Background())
job.ID = id
job.Context = ctx
job.Cancel = cancel
jobs[job.ID] = job
c.JSON(http.StatusOK, gin.H{"message": "job received"})
go worker(ctx, job.ID)
id ++
})
r.GET("/cancel/:id", func(c *gin.Context) {
id := c.Param("id")
idInt, err := strconv.Atoi(id)
if err != nil {fmt.Println(err)}
jobs[idInt].Cancel()
})
err = endless.ListenAndServe(":8080", r)
if err != nil{ fmt.Printf("Could not run server : %v", err.Error())}
}
You could use a channel
endRoutine:= make(chan bool)
go func() {
<-endRoutine
}()
//To end one thread waiting on the channel
endRoutine<-true
https://play.golang.org/p/IRARfywOLZX
If you are processing data in a loop and need to check if you should exit on each iteration, you can use a switch
go func() {
for {
switch {
case <-endRoutine:
return //exit
default:
break
}
}
}()
https://play.golang.org/p/18eOHpilnFi
Related
I have the following code:
i have a list to go through and do something with a value from that list, and so i thought of using go routines, but i need to use a max number of go routines, and then in go routine i need to make a call that will get a return of response, err, when the err is different from null I need to terminate all the go routines and return an http response, and if there is no err I need to terminate the go routines and return an http response,
When I have few values it works ok, but when I have many values I have a problem, because when I call cancel I will still have go routines trying to send to the response channel that is already closed and I keep getting errors from:
goroutine 36 [chan send]:
type response struct {
value string
}
func Testing() []response {
fakeValues := getFakeValues()
maxParallel := 25
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
if len(fakeValues) < maxParallel {
maxParallel = len(fakeValues)
}
type responseChannel struct {
Response response
Err error
}
reqChan := make(chan string) //make this an unbuffered channel
resChan := make(chan responseChannel)
wg := &sync.WaitGroup{}
wg.Add(maxParallel)
for i := 0; i < maxParallel; i++ {
go func(ctx context.Context, ch chan string, resChan chan responseChannel) {
for {
select {
case val := <-ch:
resp, err := getFakeResult(val)
resChan <- responseChannel{
Response: resp,
Err: err,
}
case <-ctx.Done():
wg.Done()
return
}
}
}(ctx, reqChan, resChan)
}
go func() {
for _, body := range fakeValues {
reqChan <- body
}
close(reqChan)
cancel()
}()
go func() {
wg.Wait()
close(resChan)
}()
var hasErr error
response := make([]response, 0, len(fakeValues))
for res := range resChan {
if res.Err != nil {
hasErr = res.Err
cancel()
break
}
response = append(response, res.Response)
}
if hasErr != nil {
// return responses.ErrorResponse(hasErr) // returns http response
}
// return responses.Accepted(response, nil) // returns http response
return nil
}
func getFakeValues() []string {
return []string{"a"}
}
func getFakeResult(val string) (response, error) {
if val == "" {
return response{}, fmt.Errorf("ooh noh:%s", val)
}
return response{
value: val,
}, nil
}
The workers end up blocked on sending to resChan because it's not buffered, and after an error, nothing reads from it.
You can either make resChan buffered, with a size at least as large as maxParallel. Or check to see if the context was canceled, e.g. change the resChan <- to
select {
case resChan <- responseChannel{
Response: resp,
Err: err,
}:
case <-ctx.Done():
}
There are two main problems with your solution:
First, if your fakeValues slice has more items than maxParallel+1, your program will block on this part:
for _, body := range fakeValues {
reqChan <- body
}
How does this happen? As you start putting values in reqChan, each started goroutine will read one value from the reqChan and try to write the response to resChan. But, since resChan is still not reading responses, each goroutine will block there (writing to resChan). Eventually, once each goroutine is blocked, reading from the reqChan is blocked as well and you cannot put any more values in it (apart from one buffered value).
Second, you are passing the context to your goroutines, but you are not doing anything with it. You can use ctx.Done() channel to get a signal to exit the goroutine. Something like this:
go func(ctx context.Context, ch chan string, resChan chan responseChannel) {
for {
select {
case val := <-ch:
resp, err := getFakeResult(val)
resChan <- responseChannel{
Response: resp,
Err: err,
}
case <- ctx.Done():
return
}
}
}(ctx, reqChan, resChan)
Now, to tie everything together so that there are no deadlocks, no race conditions, and no situations where values are not processed, a few other changes need to be made. I've posted the entire code below.
func Testing() []response {
fakeValues := getFakeValues()
maxParallel := 25
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
if len(fakeValues) < maxParallel {
maxParallel = len(fakeValues)
}
type responseChannel struct {
Response response
Err error
}
reqChan := make(chan string) //make this an unbuffered channel
resChan := make(chan responseChannel)
wg := &sync.WaitGroup{}
wg.Add(maxParallel)
for i := 0; i < maxParallel; i++ {
go func(ctx context.Context, ch chan string, resChan chan responseChannel) {
for {
select {
case val := <-ch:
resp, err := getFakeResult(val)
resChan <- responseChannel{
Response: resp,
Err: err,
}
case <- ctx.Done():
wg.Done()
return
}
}
wg.Done()
}(ctx, reqChan, resChan)
}
go func() {
for _, body := range fakeValues {
reqChan <- body
}
close(reqChan)
//putting cancel here so that it can terminate all goroutines when all values are read from reqChan
cancel()
}()
go func() {
wg.Wait()
close(resChan)
}()
var hasErr error
response := make([]response, 0, len(fakeValues))
for res := range resChan {
if res.Err != nil {
hasErr = res.Err
cancel()
break
}
response = append(response, res.Response)
}
if hasErr != nil {
return responses.ErrorResponse(hasErr) // returns http response
}
return responses.Accepted(response, nil) // returns http response
}
In short, the changes are:
reqChan is an unbuffered channel, as this will help in cases where values might not get processed when we close goroutines that read data from buffered channels.
worker goroutines have been changed to accommodate the cases of both exiting when error happens and when there is no more data from reqChan to process. wg.Done() is executed when the context is canceled to ensure that resChan is eventually closed.
separate goroutine is created to put the data in the reqChan without blocking the program, close it afterward, and cancel the context.
In go I have two callbacks that eventually do not fire.
registerCb(func() {...})
registerCb(func() {...})
/* Wait for both func to execute with timeout */
I want to wait for both of them but having a timeout if one is not executed.
sync.WaitGroup does not work, since it is blocking and not channel based. Also you call WaitGroup.Done() without the risk of panic outside the callbacks.
My current solution is using just two booleans and a busy wait loop. But that's not satisfying.
Is there any idiomatic way that do not use polling or busy waiting?
Update:
Here is some code that demonstrates a busy wait solution but should return as soon as both callbacks are fired or after the timeout, without using polling
package main
import (
"fmt"
"log"
"sync"
"time"
)
var cbOne func()
var cbTwo func()
func registerCbOne(cb func()) {
cbOne = cb
}
func registerCbTwo(cb func()) {
cbTwo = cb
}
func executeCallbacks() {
<-time.After(1 * time.Second)
cbOne()
// Might never happen
//<-time.After(1 * time.Second)
//cbTwo()
}
func main() {
// Some process in background will execute our callbacks
go func() {
executeCallbacks()
}()
err := WaitAllOrTimeout(3 * time.Second)
if err != nil {
fmt.Println("Error: ", err.Error())
}
fmt.Println("Hello, playground")
}
func WaitAllOrTimeout(to time.Duration) error {
cbOneDoneCh := make(chan bool, 1)
cbTwoDoneCh := make(chan bool, 1)
cbOneDone := false
cbTwoDone := false
registerCbOne(func() {
fmt.Println("cb One");
cbOneDoneCh <- true
})
registerCbTwo(func() {
fmt.Println("cb Two");
cbTwoDoneCh <- true
})
// Wait for cbOne and cbTwo to be executed or a timeout
// Busywait solution
for {
select {
case <-time.After(to):
if cbOneDone && cbTwoDone {
fmt.Println("Both CB executed (we could poll more often)")
return nil
}
fmt.Println("Timeout!")
return fmt.Errorf("Timeout")
case <-cbOneDoneCh:
cbOneDone = true
case <-cbTwoDoneCh:
cbTwoDone = true
}
}
}
This is a followup to my comment, added after you added your example solution. To be clearer than I can in comments, your example code is actually not that bad. Here is your original example:
// Busywait solution
for {
select {
case <-time.After(to):
if cbOneDone && cbTwoDone {
fmt.Println("Both CB executed (we could poll more often)")
return nil
}
fmt.Println("Timeout!")
return fmt.Errorf("Timeout")
case <-cbOneDoneCh:
cbOneDone = true
case <-cbTwoDoneCh:
cbTwoDone = true
}
}
This isn't a "busy wait" but it does have several bugs (including the fact that you need an only-once send semantic for the done channels, or maybe easier and at least as good, to just close them once when done, perhaps using sync.Once). What we want to do is:
Start a timer with to as the timeout.
Enter a select loop, using the timer's channel and the two "done" channels.
We want to exit the select loop when the first of the following events occurs:
the timer fires, or
both "done" channels have been signaled.
If we're going to close the two done channels we'll want to have the Ch variables cleared (set to nil) as well so that the selects don't spin—that would turn this into a true busy-wait—but for the moment let's just assume instead that we send exactly once on them on callback, and otherwise just leak the channels, so that we can use your code as written as those selects will only ever return once. Here's the updated code:
t := timer.NewTimer(to)
for !cbOneDone || !cbTwoDone {
select {
case <-t.C:
fmt.Println("Timeout!")
return fmt.Errorf("timeout")
}
case <-cbOneDoneCh:
cbOneDone = true
case <-cbTwoDoneCh:
cbTwoDone = true
}
}
// insert t.Stop() and receive here to drain t.C if desired
fmt.Println("Both CB executed")
return nil
Note that we will go through the loop at most two times:
If we receive from both Done channels, once each, the loop stops without a timeout. There's no spinning/busy-waiting: we never received anything from t.C. We return nil (no error).
If we receive from one Done channel, the loop resumes but blocks waiting for the timer or the other Done channel.
If we ever receive from t.C, it means we didn't get both callbacks yet. We may have had one, but there's been a timeout and we choose to give up, which was our goal. We return an error, without going back through the loop.
A real version needs a bit more work to clean up properly and avoid leaking "done" channels (and the timer channel and its goroutine; see comment), but this is the general idea. You're already turning the callbacks into channel operations, and you already have a timer with its channel.
func wait(ctx context.Context, wg *sync.WaitGroup) error {
done := make(chan struct{}, 1)
go func() {
wg.Wait()
done <- struct{}{}
}()
select {
case <-done:
// Counter is 0, so all callbacks completed.
return nil
case <-ctx.Done():
// Context cancelled.
return ctx.Err()
}
}
Alternatively, you can pass a time.Duration and block on <-time.After(d) rather than on <-ctx.Done(), but I would argue that using context is more idiomatic.
below code present two variations,
the first is the regular pattern, nothing fancy, it does the job and does it well. You launch your callbacks into a routine, you make them push to a sink, listen that sink for a result or timeout. Take care to the sink channel initial capacity, to prevent leaking a routine it must match the number of callbacks.
the second factories out the synchronization mechanisms into small functions to assemble, two wait methods are provided, waitAll and waitOne. Nice to write, but definitely less efficient, more allocations, more back and forth with more channels, more complex to reason about, more subtle.
package main
import (
"fmt"
"log"
"sync"
"time"
)
func main() {
ExampleOne()
ExampleTwo()
ExampleThree()
fmt.Println("Hello, playground")
}
func ExampleOne() {
log.Println("start reg")
errs := make(chan error, 2)
go func() {
fn := callbackWithOpts("reg: so slow", 2*time.Second, nil)
errs <- fn()
}()
go func() {
fn := callbackWithOpts("reg: too fast", time.Millisecond, fmt.Errorf("broke!"))
errs <- fn()
}()
select {
case err := <-errs: // capture only one result,
// the fastest to finish.
if err != nil {
log.Println(err)
}
case <-time.After(time.Second): // or wait that many amount of time,
// in case they are all so slow.
}
log.Println("done reg")
}
func ExampleTwo() {
log.Println("start wait")
errs := waitAll(
withTimeout(time.Second,
callbackWithOpts("waitAll: so slow", 2*time.Second, nil),
),
withTimeout(time.Second,
callbackWithOpts("waitAll: too fast", time.Millisecond, nil),
),
)
for err := range trim(errs) {
if err != nil {
log.Println(err)
}
}
log.Println("done wait")
}
func ExampleThree() {
log.Println("start waitOne")
errs := waitOne(
withTimeout(time.Second,
callbackWithOpts("waitOne: so slow", 2*time.Second, nil),
),
withTimeout(time.Second,
callbackWithOpts("waitOne: too fast", time.Millisecond, nil),
),
)
for err := range trim(errs) {
if err != nil {
log.Println(err)
}
}
log.Println("done waitOne")
}
// a configurable callback for playing
func callbackWithOpts(msg string, tout time.Duration, err error) func() error {
return func() error {
<-time.After(tout)
fmt.Println(msg)
return err
}
}
// withTimeout return a function that returns first error or times out and return nil
func withTimeout(tout time.Duration, h func() error) func() error {
return func() error {
d := make(chan error, 1)
go func() {
d <- h()
}()
select {
case err := <-d:
return err
case <-time.After(tout):
}
return nil
}
}
// wait launches all func() and return their errors into the returned error channel; (merge)
// It is the caller responsability to drain the output error channel.
func waitAll(h ...func() error) chan error {
d := make(chan error, len(h))
var wg sync.WaitGroup
for i := 0; i < len(h); i++ {
wg.Add(1)
go func(h func() error) {
defer wg.Done()
d <- h()
}(h[i])
}
go func() {
wg.Wait()
close(d)
}()
return d
}
// wait launches all func() and return the first error into the returned error channel
// It is the caller responsability to drain the output error channel.
func waitOne(h ...func() error) chan error {
d := make(chan error, len(h))
one := make(chan error, 1)
var wg sync.WaitGroup
for i := 0; i < len(h); i++ {
wg.Add(1)
go func(h func() error) {
defer wg.Done()
d <- h()
}(h[i])
}
go func() {
for err := range d {
one <- err
close(one)
break
}
}()
go func() {
wg.Wait()
close(d)
}()
return one
}
func trim(err chan error) chan error {
out := make(chan error)
go func() {
for e := range err {
out <- e
}
close(out)
}()
return out
}
i'm setting up a service, provide http server and run goroutine to deal with some job, look code
once in a cycle, a sub job seems like interrupt， there is no logs after one func call
it didn't catch any panic err, and the defer seems not trigger because the mutex lock is not unlock
the log is not interrupted or lost
log of other job is complete
there is no restart or exit or oom kill on those time
this is for a CentOS 7.5, my service running in docker
go1.11
docker 18.09
this is an occasional bug, i add more log and open pprof, and try to reproduce this bug
main.go
func main() {
....
// this is a cycle job, with custom time intervals
router.Cycle(r)
....
endless.ListenAndServe(":"+conf.Conf.Port, r)
}
router/cycle.go
// this is a loop job, when job end, sleep custom time intervals and run again
// implemented by encapsulating a goroutine, and create a context
func Cycle(g *gin.Engine) {
cyclec := cli.InitCycle(g)
cyclec.AddFunc(time.Second, schedule.RunSomeDeal)
cyclec.Start()
}
///RunSomeDeal
func RunSomeDeal(c *gin.Context) error {
...
// deal some sub job
for i := 0; i < missionLen; i++ {
// this is once job, like cycle but only run once
// a new context is generated by passing the exist context and a goroutine executes the callback function
helpers.Job.Run(c, func(newCtx *gin.Context) error {
return DealMission(newCtx, someparams...)
})
}
return nil
}
// Job.Run
func (c *Job) Run(ctx *gin.Context, f func(ctx *gin.Context) error) {
e := &Entry{
Job: FuncJob(f),
}
if c.getJobContext != nil {
e.span = c.getJobContext(ctx)
}
go c.runWithRecovery(e)
}
func (c *Job) runWithRecovery(e *Entry) {
ctx := gin.CreateNewContext(c.gin)
...
defer func() {
if r := recover(); r != nil {
const size = 64 << 10
buf := make([]byte, size)
buf = buf[:runtime.Stack(buf, false)]
requestId, _ := ctx.Get("requestId")
handleName := ctx.CustomContext.HandlerName()
info, _ := json.Marshal(map[string]interface{}{
...some kv for log
})
log.Printf(...)
}
gin.RecycleContext(c.gin, ctx)
}()
if c.beforeRun != nil {
ok := c.beforeRun(ctx, e.span)
if !ok {
return
}
}
error := e.Job.Run(ctx)
...
if c.afterRun != nil {
c.afterRun(ctx)
}
}
// DealMission
func DealMission(c *gin.Context, params...) {
// lock something use sync.mutex
doSomeLock()
defer func() {
// ...not trigger
unlockErr := unlockxxxxx(...)
if unlockErr != nil {
panic("some error info")
}
} ()
base.DebugLog(...)
err := SomeOtherFunc(c, params...)
base.DebugLog(...)
}
// some other func
func SomeOtherFunc(ctx *gin.Context, params...) error {
err := CallOther()
base.DebugLog(...)
err := CallOther()
base.DebugLog(...)
// there is no logs after this call func, and Job.runWithRecovery not catch any panic error
err := CallOther()
// print log...
base.DebugLog(...)
}
in this sub job, the log stop at a certain line， and no panic，no error， and the defer seems not trigger because the mutex lock is not unlock
log for other job is well, and log of next cycle job is well too
I'm trying to follow along the bounded goroutine example that is posted at http://blog.golang.org/pipelines/bounded.go. The problem that I'm having is that if there are more workers spun up then the amount of work to do, the extra workers never get cancelled. Everything else seems to work, the values get computed and logged, but when I close the groups channel, the workers just hang at the range statement.
I guess what I don't understand (in both my code and the example code) is how do the workers know when there is no more work to do and that they should exit?
Update
A working (i.e. non-working) example is posted at http://play.golang.org/p/T7zBCYLECp. It shows the deadlock on the workers since they are all asleep and there is no work to do. What I'm confused about is that I think the example code would have the same problem.
Here is the code that I'm currently using:
// Creates a pool of workers to do a bunch of computations
func computeAll() error {
done := make(chan struct{})
defer close(done)
groups, errc := findGroups(done)
// start a fixed number of goroutines to schedule with
const numComputers = 20
c := make(chan result)
var wg sync.WaitGroup
wg.Add(numComputers)
for i := 0; i < numComputers; i++ {
go func() {
compute(done, groups, c)
wg.Done()
}()
}
go func() {
wg.Wait()
close(c)
}()
// log the results of the computation
for r := range c { // log the results }
if err := <-errc; err != nil {
return err
}
return nil
}
Here is the code that fills up the channel with data:
// Retrieves the groups of data the must be computed
func findGroups(done <-chan struct{}) (<-chan model, <-chan error) {
groups := make(chan model)
errc := make(chan error, 1)
go func() {
// close the groups channel after find returns
defer close(groups)
group, err := //... code to get the group ...
if err == nil {
// add the group to the channel
select {
case groups <- group:
}
}
}()
return groups, errc
}
And here is the code that reads the channel to do the computations.
// Computes the results for the groups of data
func compute(done <-chan struct{}, groups <-chan model, c chan<- result) {
for group := range groups {
value := compute(group)
select {
case c <- result{value}:
case <-done:
return
}
}
}
Because you're trying to read from errc and it's empty unless there's an error.
//edit
computeAll() will always block on <- errc if there are no errors, another approach is to use something like:
func computeAll() (err error) {
.........
select {
case err = <-errc:
default: //don't block
}
return
}
Try to close the errc as OneOfOne says
go func() {
wg.Wait()
close(c)
close(errc)
}()
// log the results of the computation
for r := range c { // log the results }
if err := range errc {
if err != nil {
return err
}
}
I got a problem using sync.WaitGroup and select together. If you take a look at following http request pool you will notice that if an error occurs it will never be reported as wg.Done() will block and there is no read from the channel anymore.
package pool
import (
"fmt"
"log"
"net/http"
"sync"
)
var (
MaxPoolQueue = 100
MaxPoolWorker = 10
)
type Pool struct {
wg *sync.WaitGroup
queue chan *http.Request
errors chan error
}
func NewPool() *Pool {
return &Pool{
wg: &sync.WaitGroup{},
queue: make(chan *http.Request, MaxPoolQueue),
errors: make(chan error),
}
}
func (p *Pool) Add(r *http.Request) {
p.wg.Add(1)
p.queue <- r
}
func (p *Pool) Run() error {
for i := 0; i < MaxPoolWorker; i++ {
go p.doWork()
}
select {
case err := <-p.errors:
return err
default:
p.wg.Wait()
}
return nil
}
func (p *Pool) doWork() {
for r := range p.queue {
fmt.Printf("Request to %s\n", r.Host)
p.wg.Done()
_, err := http.DefaultClient.Do(r)
if err != nil {
log.Fatal(err)
p.errors <- err
} else {
fmt.Printf("no error\n")
}
}
}
Source can be found here
How can I still use WaitGroup but also get errors from go routines?
Just got the answer my self as I wrote the question and as I think it is an interesting case I would like to share it with you.
The trick to use sync.WaitGroup and chan together is that we wrap:
select {
case err := <-p.errors:
return err
default:
p.wg.Done()
}
Together in a for loop:
for {
select {
case err := <-p.errors:
return err
default:
p.wg.Done()
}
}
In this case select will always check for errors and wait if nothing happens :)
It looks a bit like the fail-fast mechanism enabled by the Tomb library (Tomb V2 GoDoc):
The tomb package handles clean goroutine tracking and termination.
If any of the tracked goroutines returns a non-nil error, or the Kill or Killf method is called by any goroutine in the system (tracked or not), the tomb Err is set, Alive is set to false, and the Dying channel is closed to flag that all tracked goroutines are supposed to willingly terminate as soon as possible.
Once all tracked goroutines terminate, the Dead channel is closed, and Wait unblocks and returns the first non-nil error presented to the tomb via a result or an explicit Kill or Killf method call, or nil if there were no errors.
You can see an example in this playground:
(extract)
// start runs all the given functions concurrently
// until either they all complete or one returns an
// error, in which case it returns that error.
//
// The functions are passed a channel which will be closed
// when the function should stop.
func start(funcs []func(stop <-chan struct{}) error) error {
var tomb tomb.Tomb
var wg sync.WaitGroup
allDone := make(chan struct{})
// Start all the functions.
for _, f := range funcs {
f := f
wg.Add(1)
go func() {
defer wg.Done()
if err := f(tomb.Dying()); err != nil {
tomb.Kill(err)
}
}()
}
// Start a goroutine to wait for them all to finish.
go func() {
wg.Wait()
close(allDone)
}()
// Wait for them all to finish, or one to fail
select {
case <-allDone:
case <-tomb.Dying():
}
tomb.Done()
return tomb.Err()
}
A simpler implementation would be like below. (Check in play.golang: https://play.golang.org/p/TYxxsDRt5Wu)
package main
import "fmt"
import "sync"
import "time"
type Error struct {
message string
}
func (e Error) Error() string {
return e.message
}
func main() {
var wg sync.WaitGroup
waitGroupLength := 8
errChannel := make(chan error, 1)
// Setup waitgroup to match the number of go routines we'll launch off
wg.Add(waitGroupLength)
finished := make(chan bool, 1) // this along with wg.Wait() are why the error handling works and doesn't deadlock
for i := 0; i < waitGroupLength; i++ {
go func(i int) {
fmt.Printf("Go routine %d executed\n", i+1)
time.Sleep(time.Duration(waitGroupLength - i))
time.Sleep(0) // only here so the time import is needed
if i%4 == 1 {
errChannel <- Error{fmt.Sprintf("Errored on routine %d", i+1)}
}
// Mark the wait group as Done so it does not hang
wg.Done()
}(i)
}
go func() {
wg.Wait()
close(finished)
}()
L:
for {
select {
case <-finished:
break L // this will break from loop
case err := <-errChannel:
if err != nil {
fmt.Println("error ", err)
// handle your error
}
}
}
fmt.Println("Executed all go routines")
}