Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1090 insertions, 0 deletions

diff --git a/src/runtime/proc_test.go b/src/runtime/proc_test.go
new file mode 100644
index 0000000..767bde1
--- /dev/null
+++ b/src/runtime/proc_test.go
@@ -0,0 +1,1090 @@
+// Copyright 2011 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 runtime_test
+
+import (
+	"fmt"
+	"internal/race"
+	"internal/testenv"
+	"math"
+	"net"
+	"runtime"
+	"runtime/debug"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"syscall"
+	"testing"
+	"time"
+)
+
+var stop = make(chan bool, 1)
+
+func perpetuumMobile() {
+	select {
+	case <-stop:
+	default:
+		go perpetuumMobile()
+	}
+}
+
+func TestStopTheWorldDeadlock(t *testing.T) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no preemption on wasm yet")
+	}
+	if testing.Short() {
+		t.Skip("skipping during short test")
+	}
+	maxprocs := runtime.GOMAXPROCS(3)
+	compl := make(chan bool, 2)
+	go func() {
+		for i := 0; i != 1000; i += 1 {
+			runtime.GC()
+		}
+		compl <- true
+	}()
+	go func() {
+		for i := 0; i != 1000; i += 1 {
+			runtime.GOMAXPROCS(3)
+		}
+		compl <- true
+	}()
+	go perpetuumMobile()
+	<-compl
+	<-compl
+	stop <- true
+	runtime.GOMAXPROCS(maxprocs)
+}
+
+func TestYieldProgress(t *testing.T) {
+	testYieldProgress(false)
+}
+
+func TestYieldLockedProgress(t *testing.T) {
+	testYieldProgress(true)
+}
+
+func testYieldProgress(locked bool) {
+	c := make(chan bool)
+	cack := make(chan bool)
+	go func() {
+		if locked {
+			runtime.LockOSThread()
+		}
+		for {
+			select {
+			case <-c:
+				cack <- true
+				return
+			default:
+				runtime.Gosched()
+			}
+		}
+	}()
+	time.Sleep(10 * time.Millisecond)
+	c <- true
+	<-cack
+}
+
+func TestYieldLocked(t *testing.T) {
+	const N = 10
+	c := make(chan bool)
+	go func() {
+		runtime.LockOSThread()
+		for i := 0; i < N; i++ {
+			runtime.Gosched()
+			time.Sleep(time.Millisecond)
+		}
+		c <- true
+		// runtime.UnlockOSThread() is deliberately omitted
+	}()
+	<-c
+}
+
+func TestGoroutineParallelism(t *testing.T) {
+	if runtime.NumCPU() == 1 {
+		// Takes too long, too easy to deadlock, etc.
+		t.Skip("skipping on uniprocessor")
+	}
+	P := 4
+	N := 10
+	if testing.Short() {
+		P = 3
+		N = 3
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(P))
+	// If runtime triggers a forced GC during this test then it will deadlock,
+	// since the goroutines can't be stopped/preempted.
+	// Disable GC for this test (see issue #10958).
+	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+	for try := 0; try < N; try++ {
+		done := make(chan bool)
+		x := uint32(0)
+		for p := 0; p < P; p++ {
+			// Test that all P goroutines are scheduled at the same time
+			go func(p int) {
+				for i := 0; i < 3; i++ {
+					expected := uint32(P*i + p)
+					for atomic.LoadUint32(&x) != expected {
+					}
+					atomic.StoreUint32(&x, expected+1)
+				}
+				done <- true
+			}(p)
+		}
+		for p := 0; p < P; p++ {
+			<-done
+		}
+	}
+}
+
+// Test that all runnable goroutines are scheduled at the same time.
+func TestGoroutineParallelism2(t *testing.T) {
+	//testGoroutineParallelism2(t, false, false)
+	testGoroutineParallelism2(t, true, false)
+	testGoroutineParallelism2(t, false, true)
+	testGoroutineParallelism2(t, true, true)
+}
+
+func testGoroutineParallelism2(t *testing.T, load, netpoll bool) {
+	if runtime.NumCPU() == 1 {
+		// Takes too long, too easy to deadlock, etc.
+		t.Skip("skipping on uniprocessor")
+	}
+	P := 4
+	N := 10
+	if testing.Short() {
+		N = 3
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(P))
+	// If runtime triggers a forced GC during this test then it will deadlock,
+	// since the goroutines can't be stopped/preempted.
+	// Disable GC for this test (see issue #10958).
+	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+	for try := 0; try < N; try++ {
+		if load {
+			// Create P goroutines and wait until they all run.
+			// When we run the actual test below, worker threads
+			// running the goroutines will start parking.
+			done := make(chan bool)
+			x := uint32(0)
+			for p := 0; p < P; p++ {
+				go func() {
+					if atomic.AddUint32(&x, 1) == uint32(P) {
+						done <- true
+						return
+					}
+					for atomic.LoadUint32(&x) != uint32(P) {
+					}
+				}()
+			}
+			<-done
+		}
+		if netpoll {
+			// Enable netpoller, affects schedler behavior.
+			laddr := "localhost:0"
+			if runtime.GOOS == "android" {
+				// On some Android devices, there are no records for localhost,
+				// see https://golang.org/issues/14486.
+				// Don't use 127.0.0.1 for every case, it won't work on IPv6-only systems.
+				laddr = "127.0.0.1:0"
+			}
+			ln, err := net.Listen("tcp", laddr)
+			if err != nil {
+				defer ln.Close() // yup, defer in a loop
+			}
+		}
+		done := make(chan bool)
+		x := uint32(0)
+		// Spawn P goroutines in a nested fashion just to differ from TestGoroutineParallelism.
+		for p := 0; p < P/2; p++ {
+			go func(p int) {
+				for p2 := 0; p2 < 2; p2++ {
+					go func(p2 int) {
+						for i := 0; i < 3; i++ {
+							expected := uint32(P*i + p*2 + p2)
+							for atomic.LoadUint32(&x) != expected {
+							}
+							atomic.StoreUint32(&x, expected+1)
+						}
+						done <- true
+					}(p2)
+				}
+			}(p)
+		}
+		for p := 0; p < P; p++ {
+			<-done
+		}
+	}
+}
+
+func TestBlockLocked(t *testing.T) {
+	const N = 10
+	c := make(chan bool)
+	go func() {
+		runtime.LockOSThread()
+		for i := 0; i < N; i++ {
+			c <- true
+		}
+		runtime.UnlockOSThread()
+	}()
+	for i := 0; i < N; i++ {
+		<-c
+	}
+}
+
+func TestTimerFairness(t *testing.T) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no preemption on wasm yet")
+	}
+
+	done := make(chan bool)
+	c := make(chan bool)
+	for i := 0; i < 2; i++ {
+		go func() {
+			for {
+				select {
+				case c <- true:
+				case <-done:
+					return
+				}
+			}
+		}()
+	}
+
+	timer := time.After(20 * time.Millisecond)
+	for {
+		select {
+		case <-c:
+		case <-timer:
+			close(done)
+			return
+		}
+	}
+}
+
+func TestTimerFairness2(t *testing.T) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no preemption on wasm yet")
+	}
+
+	done := make(chan bool)
+	c := make(chan bool)
+	for i := 0; i < 2; i++ {
+		go func() {
+			timer := time.After(20 * time.Millisecond)
+			var buf [1]byte
+			for {
+				syscall.Read(0, buf[0:0])
+				select {
+				case c <- true:
+				case <-c:
+				case <-timer:
+					done <- true
+					return
+				}
+			}
+		}()
+	}
+	<-done
+	<-done
+}
+
+// The function is used to test preemption at split stack checks.
+// Declaring a var avoids inlining at the call site.
+var preempt = func() int {
+	var a [128]int
+	sum := 0
+	for _, v := range a {
+		sum += v
+	}
+	return sum
+}
+
+func TestPreemption(t *testing.T) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no preemption on wasm yet")
+	}
+
+	// Test that goroutines are preempted at function calls.
+	N := 5
+	if testing.Short() {
+		N = 2
+	}
+	c := make(chan bool)
+	var x uint32
+	for g := 0; g < 2; g++ {
+		go func(g int) {
+			for i := 0; i < N; i++ {
+				for atomic.LoadUint32(&x) != uint32(g) {
+					preempt()
+				}
+				atomic.StoreUint32(&x, uint32(1-g))
+			}
+			c <- true
+		}(g)
+	}
+	<-c
+	<-c
+}
+
+func TestPreemptionGC(t *testing.T) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no preemption on wasm yet")
+	}
+
+	// Test that pending GC preempts running goroutines.
+	P := 5
+	N := 10
+	if testing.Short() {
+		P = 3
+		N = 2
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(P + 1))
+	var stop uint32
+	for i := 0; i < P; i++ {
+		go func() {
+			for atomic.LoadUint32(&stop) == 0 {
+				preempt()
+			}
+		}()
+	}
+	for i := 0; i < N; i++ {
+		runtime.Gosched()
+		runtime.GC()
+	}
+	atomic.StoreUint32(&stop, 1)
+}
+
+func TestAsyncPreempt(t *testing.T) {
+	if !runtime.PreemptMSupported {
+		t.Skip("asynchronous preemption not supported on this platform")
+	}
+	output := runTestProg(t, "testprog", "AsyncPreempt")
+	want := "OK\n"
+	if output != want {
+		t.Fatalf("want %s, got %s\n", want, output)
+	}
+}
+
+func TestGCFairness(t *testing.T) {
+	output := runTestProg(t, "testprog", "GCFairness")
+	want := "OK\n"
+	if output != want {
+		t.Fatalf("want %s, got %s\n", want, output)
+	}
+}
+
+func TestGCFairness2(t *testing.T) {
+	output := runTestProg(t, "testprog", "GCFairness2")
+	want := "OK\n"
+	if output != want {
+		t.Fatalf("want %s, got %s\n", want, output)
+	}
+}
+
+func TestNumGoroutine(t *testing.T) {
+	output := runTestProg(t, "testprog", "NumGoroutine")
+	want := "1\n"
+	if output != want {
+		t.Fatalf("want %q, got %q", want, output)
+	}
+
+	buf := make([]byte, 1<<20)
+
+	// Try up to 10 times for a match before giving up.
+	// This is a fundamentally racy check but it's important
+	// to notice if NumGoroutine and Stack are _always_ out of sync.
+	for i := 0; ; i++ {
+		// Give goroutines about to exit a chance to exit.
+		// The NumGoroutine and Stack below need to see
+		// the same state of the world, so anything we can do
+		// to keep it quiet is good.
+		runtime.Gosched()
+
+		n := runtime.NumGoroutine()
+		buf = buf[:runtime.Stack(buf, true)]
+
+		nstk := strings.Count(string(buf), "goroutine ")
+		if n == nstk {
+			break
+		}
+		if i >= 10 {
+			t.Fatalf("NumGoroutine=%d, but found %d goroutines in stack dump: %s", n, nstk, buf)
+		}
+	}
+}
+
+func TestPingPongHog(t *testing.T) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no preemption on wasm yet")
+	}
+	if testing.Short() {
+		t.Skip("skipping in -short mode")
+	}
+	if race.Enabled {
+		// The race detector randomizes the scheduler,
+		// which causes this test to fail (#38266).
+		t.Skip("skipping in -race mode")
+	}
+
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
+	done := make(chan bool)
+	hogChan, lightChan := make(chan bool), make(chan bool)
+	hogCount, lightCount := 0, 0
+
+	run := func(limit int, counter *int, wake chan bool) {
+		for {
+			select {
+			case <-done:
+				return
+
+			case <-wake:
+				for i := 0; i < limit; i++ {
+					*counter++
+				}
+				wake <- true
+			}
+		}
+	}
+
+	// Start two co-scheduled hog goroutines.
+	for i := 0; i < 2; i++ {
+		go run(1e6, &hogCount, hogChan)
+	}
+
+	// Start two co-scheduled light goroutines.
+	for i := 0; i < 2; i++ {
+		go run(1e3, &lightCount, lightChan)
+	}
+
+	// Start goroutine pairs and wait for a few preemption rounds.
+	hogChan <- true
+	lightChan <- true
+	time.Sleep(100 * time.Millisecond)
+	close(done)
+	<-hogChan
+	<-lightChan
+
+	// Check that hogCount and lightCount are within a factor of
+	// 5, which indicates that both pairs of goroutines handed off
+	// the P within a time-slice to their buddy. We can use a
+	// fairly large factor here to make this robust: if the
+	// scheduler isn't working right, the gap should be ~1000X.
+	const factor = 5
+	if hogCount > lightCount*factor || lightCount > hogCount*factor {
+		t.Fatalf("want hogCount/lightCount in [%v, %v]; got %d/%d = %g", 1.0/factor, factor, hogCount, lightCount, float64(hogCount)/float64(lightCount))
+	}
+}
+
+func BenchmarkPingPongHog(b *testing.B) {
+	if b.N == 0 {
+		return
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
+
+	// Create a CPU hog
+	stop, done := make(chan bool), make(chan bool)
+	go func() {
+		for {
+			select {
+			case <-stop:
+				done <- true
+				return
+			default:
+			}
+		}
+	}()
+
+	// Ping-pong b.N times
+	ping, pong := make(chan bool), make(chan bool)
+	go func() {
+		for j := 0; j < b.N; j++ {
+			pong <- <-ping
+		}
+		close(stop)
+		done <- true
+	}()
+	go func() {
+		for i := 0; i < b.N; i++ {
+			ping <- <-pong
+		}
+		done <- true
+	}()
+	b.ResetTimer()
+	ping <- true // Start ping-pong
+	<-stop
+	b.StopTimer()
+	<-ping // Let last ponger exit
+	<-done // Make sure goroutines exit
+	<-done
+	<-done
+}
+
+var padData [128]uint64
+
+func stackGrowthRecursive(i int) {
+	var pad [128]uint64
+	pad = padData
+	for j := range pad {
+		if pad[j] != 0 {
+			return
+		}
+	}
+	if i != 0 {
+		stackGrowthRecursive(i - 1)
+	}
+}
+
+func TestPreemptSplitBig(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in -short mode")
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+	stop := make(chan int)
+	go big(stop)
+	for i := 0; i < 3; i++ {
+		time.Sleep(10 * time.Microsecond) // let big start running
+		runtime.GC()
+	}
+	close(stop)
+}
+
+func big(stop chan int) int {
+	n := 0
+	for {
+		// delay so that gc is sure to have asked for a preemption
+		for i := 0; i < 1e9; i++ {
+			n++
+		}
+
+		// call bigframe, which used to miss the preemption in its prologue.
+		bigframe(stop)
+
+		// check if we've been asked to stop.
+		select {
+		case <-stop:
+			return n
+		}
+	}
+}
+
+func bigframe(stop chan int) int {
+	// not splitting the stack will overflow.
+	// small will notice that it needs a stack split and will
+	// catch the overflow.
+	var x [8192]byte
+	return small(stop, &x)
+}
+
+func small(stop chan int, x *[8192]byte) int {
+	for i := range x {
+		x[i] = byte(i)
+	}
+	sum := 0
+	for i := range x {
+		sum += int(x[i])
+	}
+
+	// keep small from being a leaf function, which might
+	// make it not do any stack check at all.
+	nonleaf(stop)
+
+	return sum
+}
+
+func nonleaf(stop chan int) bool {
+	// do something that won't be inlined:
+	select {
+	case <-stop:
+		return true
+	default:
+		return false
+	}
+}
+
+func TestSchedLocalQueue(t *testing.T) {
+	runtime.RunSchedLocalQueueTest()
+}
+
+func TestSchedLocalQueueSteal(t *testing.T) {
+	runtime.RunSchedLocalQueueStealTest()
+}
+
+func TestSchedLocalQueueEmpty(t *testing.T) {
+	if runtime.NumCPU() == 1 {
+		// Takes too long and does not trigger the race.
+		t.Skip("skipping on uniprocessor")
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
+
+	// If runtime triggers a forced GC during this test then it will deadlock,
+	// since the goroutines can't be stopped/preempted during spin wait.
+	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+
+	iters := int(1e5)
+	if testing.Short() {
+		iters = 1e2
+	}
+	runtime.RunSchedLocalQueueEmptyTest(iters)
+}
+
+func benchmarkStackGrowth(b *testing.B, rec int) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			stackGrowthRecursive(rec)
+		}
+	})
+}
+
+func BenchmarkStackGrowth(b *testing.B) {
+	benchmarkStackGrowth(b, 10)
+}
+
+func BenchmarkStackGrowthDeep(b *testing.B) {
+	benchmarkStackGrowth(b, 1024)
+}
+
+func BenchmarkCreateGoroutines(b *testing.B) {
+	benchmarkCreateGoroutines(b, 1)
+}
+
+func BenchmarkCreateGoroutinesParallel(b *testing.B) {
+	benchmarkCreateGoroutines(b, runtime.GOMAXPROCS(-1))
+}
+
+func benchmarkCreateGoroutines(b *testing.B, procs int) {
+	c := make(chan bool)
+	var f func(n int)
+	f = func(n int) {
+		if n == 0 {
+			c <- true
+			return
+		}
+		go f(n - 1)
+	}
+	for i := 0; i < procs; i++ {
+		go f(b.N / procs)
+	}
+	for i := 0; i < procs; i++ {
+		<-c
+	}
+}
+
+func BenchmarkCreateGoroutinesCapture(b *testing.B) {
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		const N = 4
+		var wg sync.WaitGroup
+		wg.Add(N)
+		for i := 0; i < N; i++ {
+			i := i
+			go func() {
+				if i >= N {
+					b.Logf("bad") // just to capture b
+				}
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+	}
+}
+
+func BenchmarkClosureCall(b *testing.B) {
+	sum := 0
+	off1 := 1
+	for i := 0; i < b.N; i++ {
+		off2 := 2
+		func() {
+			sum += i + off1 + off2
+		}()
+	}
+	_ = sum
+}
+
+func benchmarkWakeupParallel(b *testing.B, spin func(time.Duration)) {
+	if runtime.GOMAXPROCS(0) == 1 {
+		b.Skip("skipping: GOMAXPROCS=1")
+	}
+
+	wakeDelay := 5 * time.Microsecond
+	for _, delay := range []time.Duration{
+		0,
+		1 * time.Microsecond,
+		2 * time.Microsecond,
+		5 * time.Microsecond,
+		10 * time.Microsecond,
+		20 * time.Microsecond,
+		50 * time.Microsecond,
+		100 * time.Microsecond,
+	} {
+		b.Run(delay.String(), func(b *testing.B) {
+			if b.N == 0 {
+				return
+			}
+			// Start two goroutines, which alternate between being
+			// sender and receiver in the following protocol:
+			//
+			// - The receiver spins for `delay` and then does a
+			// blocking receive on a channel.
+			//
+			// - The sender spins for `delay+wakeDelay` and then
+			// sends to the same channel. (The addition of
+			// `wakeDelay` improves the probability that the
+			// receiver will be blocking when the send occurs when
+			// the goroutines execute in parallel.)
+			//
+			// In each iteration of the benchmark, each goroutine
+			// acts once as sender and once as receiver, so each
+			// goroutine spins for delay twice.
+			//
+			// BenchmarkWakeupParallel is used to estimate how
+			// efficiently the scheduler parallelizes goroutines in
+			// the presence of blocking:
+			//
+			// - If both goroutines are executed on the same core,
+			// an increase in delay by N will increase the time per
+			// iteration by 4*N, because all 4 delays are
+			// serialized.
+			//
+			// - Otherwise, an increase in delay by N will increase
+			// the time per iteration by 2*N, and the time per
+			// iteration is 2 * (runtime overhead + chan
+			// send/receive pair + delay + wakeDelay). This allows
+			// the runtime overhead, including the time it takes
+			// for the unblocked goroutine to be scheduled, to be
+			// estimated.
+			ping, pong := make(chan struct{}), make(chan struct{})
+			start := make(chan struct{})
+			done := make(chan struct{})
+			go func() {
+				<-start
+				for i := 0; i < b.N; i++ {
+					// sender
+					spin(delay + wakeDelay)
+					ping <- struct{}{}
+					// receiver
+					spin(delay)
+					<-pong
+				}
+				done <- struct{}{}
+			}()
+			go func() {
+				for i := 0; i < b.N; i++ {
+					// receiver
+					spin(delay)
+					<-ping
+					// sender
+					spin(delay + wakeDelay)
+					pong <- struct{}{}
+				}
+				done <- struct{}{}
+			}()
+			b.ResetTimer()
+			start <- struct{}{}
+			<-done
+			<-done
+		})
+	}
+}
+
+func BenchmarkWakeupParallelSpinning(b *testing.B) {
+	benchmarkWakeupParallel(b, func(d time.Duration) {
+		end := time.Now().Add(d)
+		for time.Now().Before(end) {
+			// do nothing
+		}
+	})
+}
+
+// sysNanosleep is defined by OS-specific files (such as runtime_linux_test.go)
+// to sleep for the given duration. If nil, dependent tests are skipped.
+// The implementation should invoke a blocking system call and not
+// call time.Sleep, which would deschedule the goroutine.
+var sysNanosleep func(d time.Duration)
+
+func BenchmarkWakeupParallelSyscall(b *testing.B) {
+	if sysNanosleep == nil {
+		b.Skipf("skipping on %v; sysNanosleep not defined", runtime.GOOS)
+	}
+	benchmarkWakeupParallel(b, func(d time.Duration) {
+		sysNanosleep(d)
+	})
+}
+
+type Matrix [][]float64
+
+func BenchmarkMatmult(b *testing.B) {
+	b.StopTimer()
+	// matmult is O(N**3) but testing expects O(b.N),
+	// so we need to take cube root of b.N
+	n := int(math.Cbrt(float64(b.N))) + 1
+	A := makeMatrix(n)
+	B := makeMatrix(n)
+	C := makeMatrix(n)
+	b.StartTimer()
+	matmult(nil, A, B, C, 0, n, 0, n, 0, n, 8)
+}
+
+func makeMatrix(n int) Matrix {
+	m := make(Matrix, n)
+	for i := 0; i < n; i++ {
+		m[i] = make([]float64, n)
+		for j := 0; j < n; j++ {
+			m[i][j] = float64(i*n + j)
+		}
+	}
+	return m
+}
+
+func matmult(done chan<- struct{}, A, B, C Matrix, i0, i1, j0, j1, k0, k1, threshold int) {
+	di := i1 - i0
+	dj := j1 - j0
+	dk := k1 - k0
+	if di >= dj && di >= dk && di >= threshold {
+		// divide in two by y axis
+		mi := i0 + di/2
+		done1 := make(chan struct{}, 1)
+		go matmult(done1, A, B, C, i0, mi, j0, j1, k0, k1, threshold)
+		matmult(nil, A, B, C, mi, i1, j0, j1, k0, k1, threshold)
+		<-done1
+	} else if dj >= dk && dj >= threshold {
+		// divide in two by x axis
+		mj := j0 + dj/2
+		done1 := make(chan struct{}, 1)
+		go matmult(done1, A, B, C, i0, i1, j0, mj, k0, k1, threshold)
+		matmult(nil, A, B, C, i0, i1, mj, j1, k0, k1, threshold)
+		<-done1
+	} else if dk >= threshold {
+		// divide in two by "k" axis
+		// deliberately not parallel because of data races
+		mk := k0 + dk/2
+		matmult(nil, A, B, C, i0, i1, j0, j1, k0, mk, threshold)
+		matmult(nil, A, B, C, i0, i1, j0, j1, mk, k1, threshold)
+	} else {
+		// the matrices are small enough, compute directly
+		for i := i0; i < i1; i++ {
+			for j := j0; j < j1; j++ {
+				for k := k0; k < k1; k++ {
+					C[i][j] += A[i][k] * B[k][j]
+				}
+			}
+		}
+	}
+	if done != nil {
+		done <- struct{}{}
+	}
+}
+
+func TestStealOrder(t *testing.T) {
+	runtime.RunStealOrderTest()
+}
+
+func TestLockOSThreadNesting(t *testing.T) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no threads on wasm yet")
+	}
+
+	go func() {
+		e, i := runtime.LockOSCounts()
+		if e != 0 || i != 0 {
+			t.Errorf("want locked counts 0, 0; got %d, %d", e, i)
+			return
+		}
+		runtime.LockOSThread()
+		runtime.LockOSThread()
+		runtime.UnlockOSThread()
+		e, i = runtime.LockOSCounts()
+		if e != 1 || i != 0 {
+			t.Errorf("want locked counts 1, 0; got %d, %d", e, i)
+			return
+		}
+		runtime.UnlockOSThread()
+		e, i = runtime.LockOSCounts()
+		if e != 0 || i != 0 {
+			t.Errorf("want locked counts 0, 0; got %d, %d", e, i)
+			return
+		}
+	}()
+}
+
+func TestLockOSThreadExit(t *testing.T) {
+	testLockOSThreadExit(t, "testprog")
+}
+
+func testLockOSThreadExit(t *testing.T, prog string) {
+	output := runTestProg(t, prog, "LockOSThreadMain", "GOMAXPROCS=1")
+	want := "OK\n"
+	if output != want {
+		t.Errorf("want %q, got %q", want, output)
+	}
+
+	output = runTestProg(t, prog, "LockOSThreadAlt")
+	if output != want {
+		t.Errorf("want %q, got %q", want, output)
+	}
+}
+
+func TestLockOSThreadAvoidsStatePropagation(t *testing.T) {
+	want := "OK\n"
+	skip := "unshare not permitted\n"
+	output := runTestProg(t, "testprog", "LockOSThreadAvoidsStatePropagation", "GOMAXPROCS=1")
+	if output == skip {
+		t.Skip("unshare syscall not permitted on this system")
+	} else if output != want {
+		t.Errorf("want %q, got %q", want, output)
+	}
+}
+
+func TestLockOSThreadTemplateThreadRace(t *testing.T) {
+	testenv.MustHaveGoRun(t)
+
+	exe, err := buildTestProg(t, "testprog")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	iterations := 100
+	if testing.Short() {
+		// Reduce run time to ~100ms, with much lower probability of
+		// catching issues.
+		iterations = 5
+	}
+	for i := 0; i < iterations; i++ {
+		want := "OK\n"
+		output := runBuiltTestProg(t, exe, "LockOSThreadTemplateThreadRace")
+		if output != want {
+			t.Fatalf("run %d: want %q, got %q", i, want, output)
+		}
+	}
+}
+
+// fakeSyscall emulates a system call.
+//go:nosplit
+func fakeSyscall(duration time.Duration) {
+	runtime.Entersyscall()
+	for start := runtime.Nanotime(); runtime.Nanotime()-start < int64(duration); {
+	}
+	runtime.Exitsyscall()
+}
+
+// Check that a goroutine will be preempted if it is calling short system calls.
+func testPreemptionAfterSyscall(t *testing.T, syscallDuration time.Duration) {
+	if runtime.GOARCH == "wasm" {
+		t.Skip("no preemption on wasm yet")
+	}
+
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+
+	interations := 10
+	if testing.Short() {
+		interations = 1
+	}
+	const (
+		maxDuration = 3 * time.Second
+		nroutines   = 8
+	)
+
+	for i := 0; i < interations; i++ {
+		c := make(chan bool, nroutines)
+		stop := uint32(0)
+
+		start := time.Now()
+		for g := 0; g < nroutines; g++ {
+			go func(stop *uint32) {
+				c <- true
+				for atomic.LoadUint32(stop) == 0 {
+					fakeSyscall(syscallDuration)
+				}
+				c <- true
+			}(&stop)
+		}
+		// wait until all goroutines have started.
+		for g := 0; g < nroutines; g++ {
+			<-c
+		}
+		atomic.StoreUint32(&stop, 1)
+		// wait until all goroutines have finished.
+		for g := 0; g < nroutines; g++ {
+			<-c
+		}
+		duration := time.Since(start)
+
+		if duration > maxDuration {
+			t.Errorf("timeout exceeded: %v (%v)", duration, maxDuration)
+		}
+	}
+}
+
+func TestPreemptionAfterSyscall(t *testing.T) {
+	for _, i := range []time.Duration{10, 100, 1000} {
+		d := i * time.Microsecond
+		t.Run(fmt.Sprint(d), func(t *testing.T) {
+			testPreemptionAfterSyscall(t, d)
+		})
+	}
+}
+
+func TestGetgThreadSwitch(t *testing.T) {
+	runtime.RunGetgThreadSwitchTest()
+}
+
+// TestNetpollBreak tests that netpollBreak can break a netpoll.
+// This test is not particularly safe since the call to netpoll
+// will pick up any stray files that are ready, but it should work
+// OK as long it is not run in parallel.
+func TestNetpollBreak(t *testing.T) {
+	if runtime.GOMAXPROCS(0) == 1 {
+		t.Skip("skipping: GOMAXPROCS=1")
+	}
+
+	// Make sure that netpoll is initialized.
+	runtime.NetpollGenericInit()
+
+	start := time.Now()
+	c := make(chan bool, 2)
+	go func() {
+		c <- true
+		runtime.Netpoll(10 * time.Second.Nanoseconds())
+		c <- true
+	}()
+	<-c
+	// Loop because the break might get eaten by the scheduler.
+	// Break twice to break both the netpoll we started and the
+	// scheduler netpoll.
+loop:
+	for {
+		runtime.Usleep(100)
+		runtime.NetpollBreak()
+		runtime.NetpollBreak()
+		select {
+		case <-c:
+			break loop
+		default:
+		}
+	}
+	if dur := time.Since(start); dur > 5*time.Second {
+		t.Errorf("netpollBreak did not interrupt netpoll: slept for: %v", dur)
+	}
+}
+
+// TestBigGOMAXPROCS tests that setting GOMAXPROCS to a large value
+// doesn't cause a crash at startup. See issue 38474.
+func TestBigGOMAXPROCS(t *testing.T) {
+	t.Parallel()
+	output := runTestProg(t, "testprog", "NonexistentTest", "GOMAXPROCS=1024")
+	// Ignore error conditions on small machines.
+	for _, errstr := range []string{
+		"failed to create new OS thread",
+		"cannot allocate memory",
+	} {
+		if strings.Contains(output, errstr) {
+			t.Skipf("failed to create 1024 threads")
+		}
+	}
+	if !strings.Contains(output, "unknown function: NonexistentTest") {
+		t.Errorf("output:\n%s\nwanted:\nunknown function: NonexistentTest", output)
+	}
+}