func main(){
    var wg sync.WaitGroup
    for i:=0; i < 10; i++{
        wg.Add(1)
        go func() {
            defer wg.Done()
            defer func() {
                // recover panic
                err := recover()
                if err != nil {
                    fmt.Println(err)
                }
            }
            // do something
            handle()
        }
    }
    wg.Wait()
}

func main() {
 wg := conc.NewWaitGroup()
 for i := 0; i < 10; i++ {
  wg.Go(doSomething)
 }
 wg.Wait()
}

func doSomething() {
 fmt.Println("test")
}

type WaitGroup struct {
 wg sync.WaitGroup
 pc panics.Catcher
}

type Catcher struct {
 recovered atomic.Pointer[RecoveredPanic]
}

type RecoveredPanic struct {
 // The original value of the panic.
 Value any
 // The caller list as returned by runtime.Callers when the panic was
 // recovered. Can be used to produce a more detailed stack information with
 // runtime.CallersFrames.
 Callers []uintptr
 // The formatted stacktrace from the goroutine where the panic was recovered.
 // Easier to use than Callers.
 Stack []byte
}

func (p *Catcher) Try(f func()) {
 defer p.tryRecover()
 f()
}

func (p *Catcher) tryRecover() {
 if val := recover(); val != nil {
  rp := NewRecoveredPanic(1, val)
        // 只會(huì)記錄第一個(gè)panic的goroutine信息
  p.recovered.CompareAndSwap(nil, &rp)
 }
}

func (p *Catcher) Repanic() {
 if val := p.Recovered(); val != nil {
  panic(val)
 }
}

func (p *Catcher) Recovered() *RecoveredPanic {
 return p.recovered.Load()
}

func (h *WaitGroup) Wait() {
 h.wg.Wait()

 // Propagate a panic if we caught one from a child goroutine.
 h.pc.Repanic()
}

func (h *WaitGroup) WaitAndRecover() *panics.RecoveredPanic {
 h.wg.Wait()

 // Return a recovered panic if we caught one from a child goroutine.
 return h.pc.Recovered()
}

import "github.com/sourcegraph/conc/pool"

func ExampleContextPool_WithCancelOnError() {
 p := pool.New().
  WithMaxGoroutines(4).
  WithContext(context.Background()).
  WithCancelOnError()
 for i := 0; i < 3; i++ {
  i := i
  p.Go(func(ctx context.Context) error {
   if i == 2 {
    return errors.New("I will cancel all other tasks!")
   }
   <-ctx.Done()
   return nil
  })
 }
 err := p.Wait()
 fmt.Println(err)
 // Output:
 // I will cancel all other tasks!
}

type Pool struct {
 handle   conc.WaitGroup
 limiter  limiter
 tasks    chan func()
 initOnce sync.Once
}

type limiter chan struct{}

func (l limiter) limit() int {
 return cap(l)
}

func (l limiter) release() {
 if l != nil {
  <-l
 }
}

func (p *Pool) Go(f func()) {
 p.init()

 if p.limiter == nil {
  // 沒有限制
  select {
  case p.tasks <- f:
   // A goroutine was available to handle the task.
  default:
   // No goroutine was available to handle the task.
   // Spawn a new one and send it the task.
   p.handle.Go(p.worker)
   p.tasks <- f
  }
 } else {
  select {
  case p.limiter <- struct{}{}:
   // If we are below our limit, spawn a new worker rather
   // than waiting for one to become available.
   p.handle.Go(p.worker)

   // We know there is at least one worker running, so wait
   // for it to become available. This ensures we never spawn
   // more workers than the number of tasks.
   p.tasks <- f
  case p.tasks <- f:
   // A worker is available and has accepted the task.
   return
  }
 }

}

func ExampleStream() {
 times := []int{20, 52, 16, 45, 4, 80}

 stream := stream2.New()
 for _, millis := range times {
  dur := time.Duration(millis) * time.Millisecond
  stream.Go(func() stream2.Callback {
   time.Sleep(dur)
   // This will print in the order the tasks were submitted
   return func() { fmt.Println(dur) }
  })
 }
 stream.Wait()

 // Output:
 // 20ms
 // 52ms
 // 16ms
 // 45ms
 // 4ms
 // 80ms
}

type Stream struct {
 pool             pool.Pool
 callbackerHandle conc.WaitGroup
 queue            chan callbackCh

 initOnce sync.Once
}

type callbackCh chan func()

func (s *Stream) Go(f Task) {
 s.init()

 // Get a channel from the cache.
 ch := getCh()

 // Queue the channel for the callbacker.
 s.queue <- ch

 // Submit the task for execution.
 s.pool.Go(func() {
  defer func() {
   // In the case of a panic from f, we don't want the callbacker to
   // starve waiting for a callback from this channel, so give it an
   // empty callback.
   if r := recover(); r != nil {
    ch <- func() {}
    panic(r)
   }
  }()

  // Run the task, sending its callback down this task's channel.
  callback := f()
  ch <- callback
 })
}

var callbackChPool = sync.Pool{
 New: func() any {
  return make(callbackCh, 1)
 },
}

func getCh() callbackCh {
 return callbackChPool.Get().(callbackCh)
}

func putCh(ch callbackCh) {
 callbackChPool.Put(ch)
}

func main() {
 input := []int{1, 2, 3, 4}
 iterator := iter.Iterator[int]{
  MaxGoroutines: len(input) / 2,
 }

 iterator.ForEach(input, func(v *int) {
  if *v%2 != 0 {
   *v = -1
  }
 })

 fmt.Println(input)
}

type Iterator[T any] struct {
 MaxGoroutines int
}
func (iter Iterator[T]) ForEachIdx(input []T, f func(int, *T)) {
 if iter.MaxGoroutines == 0 {
  // iter is a value receiver and is hence safe to mutate
  iter.MaxGoroutines = defaultMaxGoroutines()
 }

 numInput := len(input)
 if iter.MaxGoroutines > numInput {
  // No more concurrent tasks than the number of input items.
  iter.MaxGoroutines = numInput
 }

 var idx atomic.Int64
 // 通過atomic控制僅創(chuàng)建一個(gè)閉包
 task := func() {
  i := int(idx.Add(1) - 1)
  for ; i < numInput; i = int(idx.Add(1) - 1) {
   f(i, &input[i])
  }
 }

 var wg conc.WaitGroup
 for i := 0; i < iter.MaxGoroutines; i++ {
  wg.Go(task)
 }
 wg.Wait()
}

func main() {
 input := []int{1, 2, 3, 4}
 mapper := iter.Mapper[int, bool]{
  MaxGoroutines: len(input) / 2,
 }

 results := mapper.Map(input, func(v *int) bool { return *v%2 == 0 })
 fmt.Println(results)
 // Output:
 // [false true false true]
}