src/internal/trace/v2/testdata/testprog/futile-wakeup.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 to make sure the runtime doesn't generate futile wakeups. For example,
   6 // it makes sure that a block on a channel send that unblocks briefly only to
   7 // immediately go back to sleep (in such a way that doesn't reveal any useful
   8 // information, and is purely an artifact of the runtime implementation) doesn't
   9 // make it into the trace.
  10
  11 //go:build ignore
  12
  13 package main
  14
  15 import (
  16         "context"
  17         "log"
  18         "os"
  19         "runtime"
  20         "runtime/trace"
  21         "sync"
  22 )
  23
  24 func main() {
  25         if err := trace.Start(os.Stdout); err != nil {
  26                 log.Fatalf("failed to start tracing: %v", err)
  27         }
  28
  29         defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(8))
  30         c0 := make(chan int, 1)
  31         c1 := make(chan int, 1)
  32         c2 := make(chan int, 1)
  33         const procs = 2
  34         var done sync.WaitGroup
  35         done.Add(4 * procs)
  36         for p := 0; p < procs; p++ {
  37                 const iters = 1e3
  38                 go func() {
  39                         trace.WithRegion(context.Background(), "special", func() {
  40                                 for i := 0; i < iters; i++ {
  41                                         runtime.Gosched()
  42                                         c0 <- 0
  43                                 }
  44                                 done.Done()
  45                         })
  46                 }()
  47                 go func() {
  48                         trace.WithRegion(context.Background(), "special", func() {
  49                                 for i := 0; i < iters; i++ {
  50                                         runtime.Gosched()
  51                                         <-c0
  52                                 }
  53                                 done.Done()
  54                         })
  55                 }()
  56                 go func() {
  57                         trace.WithRegion(context.Background(), "special", func() {
  58                                 for i := 0; i < iters; i++ {
  59                                         runtime.Gosched()
  60                                         select {
  61                                         case c1 <- 0:
  62                                         case c2 <- 0:
  63                                         }
  64                                 }
  65                                 done.Done()
  66                         })
  67                 }()
  68                 go func() {
  69                         trace.WithRegion(context.Background(), "special", func() {
  70                                 for i := 0; i < iters; i++ {
  71                                         runtime.Gosched()
  72                                         select {
  73                                         case <-c1:
  74                                         case <-c2:
  75                                         }
  76                                 }
  77                                 done.Done()
  78                         })
  79                 }()
  80         }
  81         done.Wait()
  82
  83         trace.Stop()
  84 }