1 files changed, 84 insertions, 0 deletions
diff --git a/src/internal/trace/v2/testdata/testprog/futile-wakeup.go b/src/internal/trace/v2/testdata/testprog/futile-wakeup.go
new file mode 100644
index 0000000..cc48981
--- /dev/null
+++ b/src/internal/trace/v2/testdata/testprog/futile-wakeup.go
@@ -0,0 +1,84 @@
+// 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()
+}