iter-pull.go

     1  // Copyright 2023 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Tests coroutine switches.
     6  
     7  //go:build ignore
     8  
     9  package main
    10  
    11  import (
    12  	"iter"
    13  	"log"
    14  	"os"
    15  	"runtime/trace"
    16  	"sync"
    17  )
    18  
    19  func main() {
    20  	// Start tracing.
    21  	if err := trace.Start(os.Stdout); err != nil {
    22  		log.Fatalf("failed to start tracing: %v", err)
    23  	}
    24  
    25  	// Try simple pull iteration.
    26  	i := pullRange(100)
    27  	for {
    28  		_, ok := i.next()
    29  		if !ok {
    30  			break
    31  		}
    32  	}
    33  
    34  	// Try bouncing the pull iterator between two goroutines.
    35  	var wg sync.WaitGroup
    36  	var iterChans [2]chan intIter
    37  	wg.Add(2)
    38  	iterChans[0] = make(chan intIter)
    39  	iterChans[1] = make(chan intIter)
    40  	go func() {
    41  		defer wg.Done()
    42  
    43  		iter := pullRange(100)
    44  		iterChans[1] <- iter
    45  
    46  		for i := range iterChans[0] {
    47  			_, ok := i.next()
    48  			if !ok {
    49  				close(iterChans[1])
    50  				break
    51  			}
    52  			iterChans[1] <- i
    53  		}
    54  	}()
    55  	go func() {
    56  		defer wg.Done()
    57  
    58  		for i := range iterChans[1] {
    59  			_, ok := i.next()
    60  			if !ok {
    61  				close(iterChans[0])
    62  				break
    63  			}
    64  			iterChans[0] <- i
    65  		}
    66  	}()
    67  	wg.Wait()
    68  
    69  	// End of traced execution.
    70  	trace.Stop()
    71  }
    72  
    73  func pullRange(n int) intIter {
    74  	next, stop := iter.Pull(func(yield func(v int) bool) {
    75  		for i := range n {
    76  			yield(i)
    77  		}
    78  	})
    79  	return intIter{next: next, stop: stop}
    80  }
    81  
    82  type intIter struct {
    83  	next func() (int, bool)
    84  	stop func()
    85  }
    86
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