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// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Tests to make sure the runtime doesn't generate futile wakeups. For example,
// it makes sure that a block on a channel send that unblocks briefly only to
// immediately go back to sleep (in such a way that doesn't reveal any useful
// information, and is purely an artifact of the runtime implementation) doesn't
// make it into the trace.
//go:build ignore
package main
import (
"context"
"log"
"os"
"runtime"
"runtime/trace"
"sync"
)
func main() {
if err := trace.Start(os.Stdout); err != nil {
log.Fatalf("failed to start tracing: %v", err)
}
defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(8))
c0 := make(chan int, 1)
c1 := make(chan int, 1)
c2 := make(chan int, 1)
const procs = 2
var done sync.WaitGroup
done.Add(4 * procs)
for p := 0; p < procs; p++ {
const iters = 1e3
go func() {
trace.WithRegion(context.Background(), "special", func() {
for i := 0; i < iters; i++ {
runtime.Gosched()
c0 <- 0
}
done.Done()
})
}()
go func() {
trace.WithRegion(context.Background(), "special", func() {
for i := 0; i < iters; i++ {
runtime.Gosched()
<-c0
}
done.Done()
})
}()
go func() {
trace.WithRegion(context.Background(), "special", func() {
for i := 0; i < iters; i++ {
runtime.Gosched()
select {
case c1 <- 0:
case c2 <- 0:
}
}
done.Done()
})
}()
go func() {
trace.WithRegion(context.Background(), "special", func() {
for i := 0; i < iters; i++ {
runtime.Gosched()
select {
case <-c1:
case <-c2:
}
}
done.Done()
})
}()
}
done.Wait()
trace.Stop()
}
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