1 files changed, 75 insertions, 0 deletions
diff --git a/src/runtime/testdata/testprog/preempt.go b/src/runtime/testdata/testprog/preempt.go
new file mode 100644
index 0000000..fb6755a
--- /dev/null
+++ b/src/runtime/testdata/testprog/preempt.go
@@ -0,0 +1,75 @@
+// Copyright 2019 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.
+
+package main
+
+import (
+	"runtime"
+	"runtime/debug"
+	"sync/atomic"
+)
+
+func init() {
+	register("AsyncPreempt", AsyncPreempt)
+}
+
+func AsyncPreempt() {
+	// Run with just 1 GOMAXPROCS so the runtime is required to
+	// use scheduler preemption.
+	runtime.GOMAXPROCS(1)
+	// Disable GC so we have complete control of what we're testing.
+	debug.SetGCPercent(-1)
+	// Out of an abundance of caution, also make sure that there are
+	// no GCs actively in progress. The sweep phase of a GC cycle
+	// for instance tries to preempt Ps at the very beginning.
+	runtime.GC()
+
+	// Start a goroutine with no sync safe-points.
+	var ready, ready2 uint32
+	go func() {
+		for {
+			atomic.StoreUint32(&ready, 1)
+			dummy()
+			dummy()
+		}
+	}()
+	// Also start one with a frameless function.
+	// This is an especially interesting case for
+	// LR machines.
+	go func() {
+		atomic.AddUint32(&ready2, 1)
+		frameless()
+	}()
+	// Also test empty infinite loop.
+	go func() {
+		atomic.AddUint32(&ready2, 1)
+		for {
+		}
+	}()
+
+	// Wait for the goroutine to stop passing through sync
+	// safe-points.
+	for atomic.LoadUint32(&ready) == 0 || atomic.LoadUint32(&ready2) < 2 {
+		runtime.Gosched()
+	}
+
+	// Run a GC, which will have to stop the goroutine for STW and
+	// for stack scanning. If this doesn't work, the test will
+	// deadlock and timeout.
+	runtime.GC()
+
+	println("OK")
+}
+
+//go:noinline
+func frameless() {
+	for i := int64(0); i < 1<<62; i++ {
+		out += i * i * i * i * i * 12345
+	}
+}
+
+var out int64
+
+//go:noinline
+func dummy() {}