nonblock.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  package main
     6  
     7  import (
     8  	"os"
     9  	"sync"
    10  	"syscall"
    11  )
    12  
    13  func main() {
    14  	if len(os.Args) < 2 {
    15  		panic("usage: nonblock <MODE> [PATH...]")
    16  	}
    17  	mode := os.Args[1]
    18  
    19  	ready := make(chan struct{})
    20  
    21  	var wg sync.WaitGroup
    22  	for _, path := range os.Args[2:] {
    23  		f, err := os.Open(path)
    24  		if err != nil {
    25  			panic(err)
    26  		}
    27  		switch mode {
    28  		case "os.OpenFile":
    29  		case "os.NewFile":
    30  			fd := f.Fd()
    31  			if err := syscall.SetNonblock(int(fd), true); err != nil {
    32  				panic(err)
    33  			}
    34  			f = os.NewFile(fd, path)
    35  		default:
    36  			panic("invalid test mode")
    37  		}
    38  
    39  		spawnWait := make(chan struct{})
    40  
    41  		wg.Add(1)
    42  		go func(f *os.File) {
    43  			defer f.Close()
    44  			defer wg.Done()
    45  
    46  			close(spawnWait)
    47  
    48  			<-ready
    49  
    50  			var buf [256]byte
    51  			n, err := f.Read(buf[:])
    52  			if err != nil {
    53  				panic(err)
    54  			}
    55  			os.Stderr.Write(buf[:n])
    56  		}(f)
    57  
    58  		// Spawn one goroutine at a time.
    59  		<-spawnWait
    60  	}
    61  
    62  	println("waiting")
    63  	close(ready)
    64  	wg.Wait()
    65  }
    66
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