waiters.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  	"fmt"
     9  	"io"
    10  	"log"
    11  	"net"
    12  	"runtime/internal/atomic"
    13  	"sync"
    14  	"time"
    15  	_ "unsafe" // for go:linkname
    16  )
    17  
    18  // The bug is that netpollWaiters increases monotonically.
    19  // This doesn't cause a problem until it overflows.
    20  // Use linkname to see the value.
    21  //
    22  //go:linkname netpollWaiters runtime.netpollWaiters
    23  var netpollWaiters atomic.Uint32
    24  
    25  func init() {
    26  	register("NetpollWaiters", NetpollWaiters)
    27  }
    28  
    29  func NetpollWaiters() {
    30  	listener, err := net.Listen("tcp", "127.0.0.1:0")
    31  	if err != nil {
    32  		log.Fatal(err)
    33  	}
    34  
    35  	var wg sync.WaitGroup
    36  	wg.Add(1)
    37  	go func() {
    38  		defer wg.Done()
    39  		conn, err := listener.Accept()
    40  		if err != nil {
    41  			log.Fatal(err)
    42  		}
    43  		defer conn.Close()
    44  		if _, err := io.Copy(io.Discard, conn); err != nil {
    45  			log.Fatal(err)
    46  		}
    47  	}()
    48  
    49  	wg.Add(1)
    50  	go func() {
    51  		defer wg.Done()
    52  		conn, err := net.Dial("tcp", listener.Addr().String())
    53  		if err != nil {
    54  			log.Fatal(err)
    55  		}
    56  		defer conn.Close()
    57  		for i := 0; i < 10; i++ {
    58  			fmt.Fprintf(conn, "%d\n", i)
    59  			time.Sleep(time.Millisecond)
    60  		}
    61  	}()
    62  
    63  	wg.Wait()
    64  	if v := netpollWaiters.Load(); v != 0 {
    65  		log.Fatalf("current waiters %v", v)
    66  	}
    67  
    68  	fmt.Println("OK")
    69  }
    70
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