libgo/go/runtime/trace/trace_test.go - gofrontend - Git at Google

 // Copyright 2014 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 trace_test

 import (
 	"bytes"
 	"flag"
 	"internal/race"
 	"internal/trace"
 	"io"
 	"io/ioutil"
 	"net"
 	"os"
 	"runtime"
 	. "runtime/trace"
 	"strconv"
 	"sync"
 	"testing"
 	"time"
 )

 var (
 	saveTraces = flag.Bool("savetraces", false, "save traces collected by tests")
 )

 // TestEventBatch tests Flush calls that happen during Start
 // don't produce corrupted traces.
 func TestEventBatch(t *testing.T) {
 	if race.Enabled {
 		t.Skip("skipping in race mode")
 	}
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
 	if testing.Short() {
 		t.Skip("skipping in short mode")
 	}
 	// During Start, bunch of records are written to reflect the current
 	// snapshot of the program, including state of each goroutines.
 	// And some string constants are written to the trace to aid trace
 	// parsing. This test checks Flush of the buffer occurred during
 	// this process doesn't cause corrupted traces.
 	// When a Flush is called during Start is complicated
 	// so we test with a range of number of goroutines hoping that one
 	// of them triggers Flush.
 	// This range was chosen to fill up a ~64KB buffer with traceEvGoCreate
 	// and traceEvGoWaiting events (12~13bytes per goroutine).
 	for g := 4950; g < 5050; g++ {
 		n := g
 		t.Run("G="+strconv.Itoa(n), func(t *testing.T) {
 			var wg sync.WaitGroup
 			wg.Add(n)

 			in := make(chan bool, 1000)
 			for i := 0; i < n; i++ {
 				go func() {
 					<-in
 					wg.Done()
 				}()
 			}
 			buf := new(bytes.Buffer)
 			if err := Start(buf); err != nil {
 				t.Fatalf("failed to start tracing: %v", err)
 			}

 			for i := 0; i < n; i++ {
 				in <- true
 			}
 			wg.Wait()
 			Stop()

 			_, err := trace.Parse(buf, "")
 			if err == trace.ErrTimeOrder {
 				t.Skipf("skipping trace: %v", err)
 			}

 			if err != nil {
 				t.Fatalf("failed to parse trace: %v", err)
 			}
 		})
 	}
 }

 func TestTraceStartStop(t *testing.T) {
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
 	buf := new(bytes.Buffer)
 	if err := Start(buf); err != nil {
 		t.Fatalf("failed to start tracing: %v", err)
 	}
 	Stop()
 	size := buf.Len()
 	if size == 0 {
 		t.Fatalf("trace is empty")
 	}
 	time.Sleep(100 * time.Millisecond)
 	if size != buf.Len() {
 		t.Fatalf("trace writes after stop: %v -> %v", size, buf.Len())
 	}
 	saveTrace(t, buf, "TestTraceStartStop")
 }

 func TestTraceDoubleStart(t *testing.T) {
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
 	Stop()
 	buf := new(bytes.Buffer)
 	if err := Start(buf); err != nil {
 		t.Fatalf("failed to start tracing: %v", err)
 	}
 	if err := Start(buf); err == nil {
 		t.Fatalf("succeed to start tracing second time")
 	}
 	Stop()
 	Stop()
 }

 func TestTrace(t *testing.T) {
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
 	buf := new(bytes.Buffer)
 	if err := Start(buf); err != nil {
 		t.Fatalf("failed to start tracing: %v", err)
 	}
 	Stop()
 	saveTrace(t, buf, "TestTrace")
 	_, err := trace.Parse(buf, "")
 	if err == trace.ErrTimeOrder {
 		t.Skipf("skipping trace: %v", err)
 	}
 	if err != nil {
 		t.Fatalf("failed to parse trace: %v", err)
 	}
 }

 func parseTrace(t *testing.T, r io.Reader) ([]*trace.Event, map[uint64]*trace.GDesc) {
 	res, err := trace.Parse(r, "")
 	if err == trace.ErrTimeOrder {
 		t.Skipf("skipping trace: %v", err)
 	}
 	if err != nil {
 		t.Fatalf("failed to parse trace: %v", err)
 	}
 	gs := trace.GoroutineStats(res.Events)
 	for goid := range gs {
 		// We don't do any particular checks on the result at the moment.
 		// But still check that RelatedGoroutines does not crash, hang, etc.
 		_ = trace.RelatedGoroutines(res.Events, goid)
 	}
 	return res.Events, gs
 }

 func testBrokenTimestamps(t *testing.T, data []byte) {
 	// On some processors cputicks (used to generate trace timestamps)
 	// produce non-monotonic timestamps. It is important that the parser
 	// distinguishes logically inconsistent traces (e.g. missing, excessive
 	// or misordered events) from broken timestamps. The former is a bug
 	// in tracer, the latter is a machine issue.
 	// So now that we have a consistent trace, test that (1) parser does
 	// not return a logical error in case of broken timestamps
 	// and (2) broken timestamps are eventually detected and reported.
 	trace.BreakTimestampsForTesting = true
 	defer func() {
 		trace.BreakTimestampsForTesting = false
 	}()
 	for i := 0; i < 1e4; i++ {
 		_, err := trace.Parse(bytes.NewReader(data), "")
 		if err == trace.ErrTimeOrder {
 			return
 		}
 		if err != nil {
 			t.Fatalf("failed to parse trace: %v", err)
 		}
 	}
 }

 func TestTraceStress(t *testing.T) {
 	if runtime.GOOS == "js" {
 		t.Skip("no os.Pipe on js")
 	}
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
 	if testing.Short() {
 		t.Skip("skipping in -short mode")
 	}

 	var wg sync.WaitGroup
 	done := make(chan bool)

 	// Create a goroutine blocked before tracing.
 	wg.Add(1)
 	go func() {
 		<-done
 		wg.Done()
 	}()

 	// Create a goroutine blocked in syscall before tracing.
 	rp, wp, err := os.Pipe()
 	if err != nil {
 		t.Fatalf("failed to create pipe: %v", err)
 	}
 	defer func() {
 		rp.Close()
 		wp.Close()
 	}()
 	wg.Add(1)
 	go func() {
 		var tmp [1]byte
 		rp.Read(tmp[:])
 		<-done
 		wg.Done()
 	}()
 	time.Sleep(time.Millisecond) // give the goroutine above time to block

 	buf := new(bytes.Buffer)
 	if err := Start(buf); err != nil {
 		t.Fatalf("failed to start tracing: %v", err)
 	}

 	procs := runtime.GOMAXPROCS(10)
 	time.Sleep(50 * time.Millisecond) // test proc stop/start events

 	go func() {
 		runtime.LockOSThread()
 		for {
 			select {
 			case <-done:
 				return
 			default:
 				runtime.Gosched()
 			}
 		}
 	}()

 	runtime.GC()
 	// Trigger GC from malloc.
 	n := int(1e3)
 	if isMemoryConstrained() {
 		// Reduce allocation to avoid running out of
 		// memory on the builder - see issue/12032.
 		n = 512
 	}
 	for i := 0; i < n; i++ {
 		_ = make([]byte, 1<<20)
 	}

 	// Create a bunch of busy goroutines to load all Ps.
 	for p := 0; p < 10; p++ {
 		wg.Add(1)
 		go func() {
 			// Do something useful.
 			tmp := make([]byte, 1<<16)
 			for i := range tmp {
 				tmp[i]++
 			}
 			_ = tmp
 			<-done
 			wg.Done()
 		}()
 	}

 	// Block in syscall.
 	wg.Add(1)
 	go func() {
 		var tmp [1]byte
 		rp.Read(tmp[:])
 		<-done
 		wg.Done()
 	}()

 	// Test timers.
 	timerDone := make(chan bool)
 	go func() {
 		time.Sleep(time.Millisecond)
 		timerDone <- true
 	}()
 	<-timerDone

 	// A bit of network.
 	ln, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatalf("listen failed: %v", err)
 	}
 	defer ln.Close()
 	go func() {
 		c, err := ln.Accept()
 		if err != nil {
 			return
 		}
 		time.Sleep(time.Millisecond)
 		var buf [1]byte
 		c.Write(buf[:])
 		c.Close()
 	}()
 	c, err := net.Dial("tcp", ln.Addr().String())
 	if err != nil {
 		t.Fatalf("dial failed: %v", err)
 	}
 	var tmp [1]byte
 	c.Read(tmp[:])
 	c.Close()

 	go func() {
 		runtime.Gosched()
 		select {}
 	}()

 	// Unblock helper goroutines and wait them to finish.
 	wp.Write(tmp[:])
 	wp.Write(tmp[:])
 	close(done)
 	wg.Wait()

 	runtime.GOMAXPROCS(procs)

 	Stop()
 	saveTrace(t, buf, "TestTraceStress")
 	trace := buf.Bytes()
 	parseTrace(t, buf)
 	testBrokenTimestamps(t, trace)
 }

 // isMemoryConstrained reports whether the current machine is likely
 // to be memory constrained.
 // This was originally for the openbsd/arm builder (Issue 12032).
 // TODO: move this to testenv? Make this look at memory? Look at GO_BUILDER_NAME?
 func isMemoryConstrained() bool {
 	if runtime.GOOS == "plan9" {
 		return true
 	}
 	switch runtime.GOARCH {
 	case "arm", "mips", "mipsle":
 		return true
 	}
 	return false
 }

 // Do a bunch of various stuff (timers, GC, network, etc) in a separate goroutine.
 // And concurrently with all that start/stop trace 3 times.
 func TestTraceStressStartStop(t *testing.T) {
 	if runtime.GOOS == "js" {
 		t.Skip("no os.Pipe on js")
 	}
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(8))
 	outerDone := make(chan bool)

 	go func() {
 		defer func() {
 			outerDone <- true
 		}()

 		var wg sync.WaitGroup
 		done := make(chan bool)

 		wg.Add(1)
 		go func() {
 			<-done
 			wg.Done()
 		}()

 		rp, wp, err := os.Pipe()
 		if err != nil {
 			t.Errorf("failed to create pipe: %v", err)
 			return
 		}
 		defer func() {
 			rp.Close()
 			wp.Close()
 		}()
 		wg.Add(1)
 		go func() {
 			var tmp [1]byte
 			rp.Read(tmp[:])
 			<-done
 			wg.Done()
 		}()
 		time.Sleep(time.Millisecond)

 		go func() {
 			runtime.LockOSThread()
 			for {
 				select {
 				case <-done:
 					return
 				default:
 					runtime.Gosched()
 				}
 			}
 		}()

 		runtime.GC()
 		// Trigger GC from malloc.
 		n := int(1e3)
 		if isMemoryConstrained() {
 			// Reduce allocation to avoid running out of
 			// memory on the builder.
 			n = 512
 		}
 		for i := 0; i < n; i++ {
 			_ = make([]byte, 1<<20)
 		}

 		// Create a bunch of busy goroutines to load all Ps.
 		for p := 0; p < 10; p++ {
 			wg.Add(1)
 			go func() {
 				// Do something useful.
 				tmp := make([]byte, 1<<16)
 				for i := range tmp {
 					tmp[i]++
 				}
 				_ = tmp
 				<-done
 				wg.Done()
 			}()
 		}

 		// Block in syscall.
 		wg.Add(1)
 		go func() {
 			var tmp [1]byte
 			rp.Read(tmp[:])
 			<-done
 			wg.Done()
 		}()

 		runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))

 		// Test timers.
 		timerDone := make(chan bool)
 		go func() {
 			time.Sleep(time.Millisecond)
 			timerDone <- true
 		}()
 		<-timerDone

 		// A bit of network.
 		ln, err := net.Listen("tcp", "127.0.0.1:0")
 		if err != nil {
 			t.Errorf("listen failed: %v", err)
 			return
 		}
 		defer ln.Close()
 		go func() {
 			c, err := ln.Accept()
 			if err != nil {
 				return
 			}
 			time.Sleep(time.Millisecond)
 			var buf [1]byte
 			c.Write(buf[:])
 			c.Close()
 		}()
 		c, err := net.Dial("tcp", ln.Addr().String())
 		if err != nil {
 			t.Errorf("dial failed: %v", err)
 			return
 		}
 		var tmp [1]byte
 		c.Read(tmp[:])
 		c.Close()

 		go func() {
 			runtime.Gosched()
 			select {}
 		}()

 		// Unblock helper goroutines and wait them to finish.
 		wp.Write(tmp[:])
 		wp.Write(tmp[:])
 		close(done)
 		wg.Wait()
 	}()

 	for i := 0; i < 3; i++ {
 		buf := new(bytes.Buffer)
 		if err := Start(buf); err != nil {
 			t.Fatalf("failed to start tracing: %v", err)
 		}
 		time.Sleep(time.Millisecond)
 		Stop()
 		saveTrace(t, buf, "TestTraceStressStartStop")
 		trace := buf.Bytes()
 		parseTrace(t, buf)
 		testBrokenTimestamps(t, trace)
 	}
 	<-outerDone
 }

 func TestTraceFutileWakeup(t *testing.T) {
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
 	buf := new(bytes.Buffer)
 	if err := Start(buf); err != nil {
 		t.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() {
 			for i := 0; i < iters; i++ {
 				runtime.Gosched()
 				c0 <- 0
 			}
 			done.Done()
 		}()
 		go func() {
 			for i := 0; i < iters; i++ {
 				runtime.Gosched()
 				<-c0
 			}
 			done.Done()
 		}()
 		go func() {
 			for i := 0; i < iters; i++ {
 				runtime.Gosched()
 				select {
 				case c1 <- 0:
 				case c2 <- 0:
 				}
 			}
 			done.Done()
 		}()
 		go func() {
 			for i := 0; i < iters; i++ {
 				runtime.Gosched()
 				select {
 				case <-c1:
 				case <-c2:
 				}
 			}
 			done.Done()
 		}()
 	}
 	done.Wait()

 	Stop()
 	saveTrace(t, buf, "TestTraceFutileWakeup")
 	events, _ := parseTrace(t, buf)
 	// Check that (1) trace does not contain EvFutileWakeup events and
 	// (2) there are no consecutive EvGoBlock/EvGCStart/EvGoBlock events
 	// (we call runtime.Gosched between all operations, so these would be futile wakeups).
 	gs := make(map[uint64]int)
 	for _, ev := range events {
 		switch ev.Type {
 		case trace.EvFutileWakeup:
 			t.Fatalf("found EvFutileWakeup event")
 		case trace.EvGoBlockSend, trace.EvGoBlockRecv, trace.EvGoBlockSelect:
 			if gs[ev.G] == 2 {
 				t.Fatalf("goroutine %v blocked on %v at %v right after start",
 					ev.G, trace.EventDescriptions[ev.Type].Name, ev.Ts)
 			}
 			if gs[ev.G] == 1 {
 				t.Fatalf("goroutine %v blocked on %v at %v while blocked",
 					ev.G, trace.EventDescriptions[ev.Type].Name, ev.Ts)
 			}
 			gs[ev.G] = 1
 		case trace.EvGoStart:
 			if gs[ev.G] == 1 {
 				gs[ev.G] = 2
 			}
 		default:
 			delete(gs, ev.G)
 		}
 	}
 }

 func saveTrace(t *testing.T, buf *bytes.Buffer, name string) {
 	if !*saveTraces {
 		return
 	}
 	if err := ioutil.WriteFile(name+".trace", buf.Bytes(), 0600); err != nil {
 		t.Errorf("failed to write trace file: %s", err)
 	}
 }
	// Copyright 2014 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 trace_test

	import (
	"bytes"
	"flag"
	"internal/race"
	"internal/trace"
	"io"
	"io/ioutil"
	"net"
	"os"
	"runtime"
	. "runtime/trace"
	"strconv"
	"sync"
	"testing"
	"time"
	)

	var (
	saveTraces = flag.Bool("savetraces", false, "save traces collected by tests")
	)

	// TestEventBatch tests Flush calls that happen during Start
	// don't produce corrupted traces.
	func TestEventBatch(t *testing.T) {
	if race.Enabled {
	t.Skip("skipping in race mode")
	}
	if IsEnabled() {
	t.Skip("skipping because -test.trace is set")
	}
	if testing.Short() {
	t.Skip("skipping in short mode")
	}
	// During Start, bunch of records are written to reflect the current
	// snapshot of the program, including state of each goroutines.
	// And some string constants are written to the trace to aid trace
	// parsing. This test checks Flush of the buffer occurred during
	// this process doesn't cause corrupted traces.
	// When a Flush is called during Start is complicated
	// so we test with a range of number of goroutines hoping that one
	// of them triggers Flush.
	// This range was chosen to fill up a ~64KB buffer with traceEvGoCreate
	// and traceEvGoWaiting events (12~13bytes per goroutine).
	for g := 4950; g < 5050; g++ {
	n := g
	t.Run("G="+strconv.Itoa(n), func(t *testing.T) {
	var wg sync.WaitGroup
	wg.Add(n)

	in := make(chan bool, 1000)
	for i := 0; i < n; i++ {
	go func() {
	<-in
	wg.Done()
	}()
	}
	buf := new(bytes.Buffer)
	if err := Start(buf); err != nil {
	t.Fatalf("failed to start tracing: %v", err)
	}

	for i := 0; i < n; i++ {
	in <- true
	}
	wg.Wait()
	Stop()

	_, err := trace.Parse(buf, "")
	if err == trace.ErrTimeOrder {
	t.Skipf("skipping trace: %v", err)
	}

	if err != nil {
	t.Fatalf("failed to parse trace: %v", err)
	}
	})
	}
	}

	func TestTraceStartStop(t *testing.T) {
	if IsEnabled() {
	t.Skip("skipping because -test.trace is set")
	}
	buf := new(bytes.Buffer)
	if err := Start(buf); err != nil {
	t.Fatalf("failed to start tracing: %v", err)
	}
	Stop()
	size := buf.Len()
	if size == 0 {
	t.Fatalf("trace is empty")
	}
	time.Sleep(100 * time.Millisecond)
	if size != buf.Len() {
	t.Fatalf("trace writes after stop: %v -> %v", size, buf.Len())
	}
	saveTrace(t, buf, "TestTraceStartStop")
	}

	func TestTraceDoubleStart(t *testing.T) {
	if IsEnabled() {
	t.Skip("skipping because -test.trace is set")
	}
	Stop()
	buf := new(bytes.Buffer)
	if err := Start(buf); err != nil {
	t.Fatalf("failed to start tracing: %v", err)
	}
	if err := Start(buf); err == nil {
	t.Fatalf("succeed to start tracing second time")
	}
	Stop()
	Stop()
	}

	func TestTrace(t *testing.T) {
	if IsEnabled() {
	t.Skip("skipping because -test.trace is set")
	}
	buf := new(bytes.Buffer)
	if err := Start(buf); err != nil {
	t.Fatalf("failed to start tracing: %v", err)
	}
	Stop()
	saveTrace(t, buf, "TestTrace")
	_, err := trace.Parse(buf, "")
	if err == trace.ErrTimeOrder {
	t.Skipf("skipping trace: %v", err)
	}
	if err != nil {
	t.Fatalf("failed to parse trace: %v", err)
	}
	}

	func parseTrace(t testing.T, r io.Reader) ([]trace.Event, map[uint64]*trace.GDesc) {
	res, err := trace.Parse(r, "")
	if err == trace.ErrTimeOrder {
	t.Skipf("skipping trace: %v", err)
	}
	if err != nil {
	t.Fatalf("failed to parse trace: %v", err)
	}
	gs := trace.GoroutineStats(res.Events)
	for goid := range gs {
	// We don't do any particular checks on the result at the moment.
	// But still check that RelatedGoroutines does not crash, hang, etc.
	_ = trace.RelatedGoroutines(res.Events, goid)
	}
	return res.Events, gs
	}

	func testBrokenTimestamps(t *testing.T, data []byte) {
	// On some processors cputicks (used to generate trace timestamps)
	// produce non-monotonic timestamps. It is important that the parser
	// distinguishes logically inconsistent traces (e.g. missing, excessive
	// or misordered events) from broken timestamps. The former is a bug
	// in tracer, the latter is a machine issue.
	// So now that we have a consistent trace, test that (1) parser does
	// not return a logical error in case of broken timestamps
	// and (2) broken timestamps are eventually detected and reported.
	trace.BreakTimestampsForTesting = true
	defer func() {
	trace.BreakTimestampsForTesting = false
	}()
	for i := 0; i < 1e4; i++ {
	_, err := trace.Parse(bytes.NewReader(data), "")
	if err == trace.ErrTimeOrder {
	return
	}
	if err != nil {
	t.Fatalf("failed to parse trace: %v", err)
	}
	}
	}

	func TestTraceStress(t *testing.T) {
	if runtime.GOOS == "js" {
	t.Skip("no os.Pipe on js")
	}
	if IsEnabled() {
	t.Skip("skipping because -test.trace is set")
	}
	if testing.Short() {
	t.Skip("skipping in -short mode")
	}

	var wg sync.WaitGroup
	done := make(chan bool)

	// Create a goroutine blocked before tracing.
	wg.Add(1)
	go func() {
	<-done
	wg.Done()
	}()

	// Create a goroutine blocked in syscall before tracing.
	rp, wp, err := os.Pipe()
	if err != nil {
	t.Fatalf("failed to create pipe: %v", err)
	}
	defer func() {
	rp.Close()
	wp.Close()
	}()
	wg.Add(1)
	go func() {
	var tmp [1]byte
	rp.Read(tmp[:])
	<-done
	wg.Done()
	}()
	time.Sleep(time.Millisecond) // give the goroutine above time to block

	buf := new(bytes.Buffer)
	if err := Start(buf); err != nil {
	t.Fatalf("failed to start tracing: %v", err)
	}

	procs := runtime.GOMAXPROCS(10)
	time.Sleep(50 * time.Millisecond) // test proc stop/start events

	go func() {
	runtime.LockOSThread()
	for {
	select {
	case <-done:
	return
	default:
	runtime.Gosched()
	}
	}
	}()

	runtime.GC()
	// Trigger GC from malloc.
	n := int(1e3)
	if isMemoryConstrained() {
	// Reduce allocation to avoid running out of
	// memory on the builder - see issue/12032.
	n = 512
	}
	for i := 0; i < n; i++ {
	_ = make([]byte, 1<<20)
	}

	// Create a bunch of busy goroutines to load all Ps.
	for p := 0; p < 10; p++ {
	wg.Add(1)
	go func() {
	// Do something useful.
	tmp := make([]byte, 1<<16)
	for i := range tmp {
	tmp[i]++
	}
	_ = tmp
	<-done
	wg.Done()
	}()
	}

	// Block in syscall.
	wg.Add(1)
	go func() {
	var tmp [1]byte
	rp.Read(tmp[:])
	<-done
	wg.Done()
	}()

	// Test timers.
	timerDone := make(chan bool)
	go func() {
	time.Sleep(time.Millisecond)
	timerDone <- true
	}()
	<-timerDone

	// A bit of network.
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
	t.Fatalf("listen failed: %v", err)
	}
	defer ln.Close()
	go func() {
	c, err := ln.Accept()
	if err != nil {
	return
	}
	time.Sleep(time.Millisecond)
	var buf [1]byte
	c.Write(buf[:])
	c.Close()
	}()
	c, err := net.Dial("tcp", ln.Addr().String())
	if err != nil {
	t.Fatalf("dial failed: %v", err)
	}
	var tmp [1]byte
	c.Read(tmp[:])
	c.Close()

	go func() {
	runtime.Gosched()
	select {}
	}()

	// Unblock helper goroutines and wait them to finish.
	wp.Write(tmp[:])
	wp.Write(tmp[:])
	close(done)
	wg.Wait()

	runtime.GOMAXPROCS(procs)

	Stop()
	saveTrace(t, buf, "TestTraceStress")
	trace := buf.Bytes()
	parseTrace(t, buf)
	testBrokenTimestamps(t, trace)
	}

	// isMemoryConstrained reports whether the current machine is likely
	// to be memory constrained.
	// This was originally for the openbsd/arm builder (Issue 12032).
	// TODO: move this to testenv? Make this look at memory? Look at GO_BUILDER_NAME?
	func isMemoryConstrained() bool {
	if runtime.GOOS == "plan9" {
	return true
	}
	switch runtime.GOARCH {
	case "arm", "mips", "mipsle":
	return true
	}
	return false
	}

	// Do a bunch of various stuff (timers, GC, network, etc) in a separate goroutine.
	// And concurrently with all that start/stop trace 3 times.
	func TestTraceStressStartStop(t *testing.T) {
	if runtime.GOOS == "js" {
	t.Skip("no os.Pipe on js")
	}
	if IsEnabled() {
	t.Skip("skipping because -test.trace is set")
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(8))
	outerDone := make(chan bool)

	go func() {
	defer func() {
	outerDone <- true
	}()

	var wg sync.WaitGroup
	done := make(chan bool)

	wg.Add(1)
	go func() {
	<-done
	wg.Done()
	}()

	rp, wp, err := os.Pipe()
	if err != nil {
	t.Errorf("failed to create pipe: %v", err)
	return
	}
	defer func() {
	rp.Close()
	wp.Close()
	}()
	wg.Add(1)
	go func() {
	var tmp [1]byte
	rp.Read(tmp[:])
	<-done
	wg.Done()
	}()
	time.Sleep(time.Millisecond)

	go func() {
	runtime.LockOSThread()
	for {
	select {
	case <-done:
	return
	default:
	runtime.Gosched()
	}
	}
	}()

	runtime.GC()
	// Trigger GC from malloc.
	n := int(1e3)
	if isMemoryConstrained() {
	// Reduce allocation to avoid running out of
	// memory on the builder.
	n = 512
	}
	for i := 0; i < n; i++ {
	_ = make([]byte, 1<<20)
	}

	// Create a bunch of busy goroutines to load all Ps.
	for p := 0; p < 10; p++ {
	wg.Add(1)
	go func() {
	// Do something useful.
	tmp := make([]byte, 1<<16)
	for i := range tmp {
	tmp[i]++
	}
	_ = tmp
	<-done
	wg.Done()
	}()
	}

	// Block in syscall.
	wg.Add(1)
	go func() {
	var tmp [1]byte
	rp.Read(tmp[:])
	<-done
	wg.Done()
	}()

	runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))

	// Test timers.
	timerDone := make(chan bool)
	go func() {
	time.Sleep(time.Millisecond)
	timerDone <- true
	}()
	<-timerDone

	// A bit of network.
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
	t.Errorf("listen failed: %v", err)
	return
	}
	defer ln.Close()
	go func() {
	c, err := ln.Accept()
	if err != nil {
	return
	}
	time.Sleep(time.Millisecond)
	var buf [1]byte
	c.Write(buf[:])
	c.Close()
	}()
	c, err := net.Dial("tcp", ln.Addr().String())
	if err != nil {
	t.Errorf("dial failed: %v", err)
	return
	}
	var tmp [1]byte
	c.Read(tmp[:])
	c.Close()

	go func() {
	runtime.Gosched()
	select {}
	}()

	// Unblock helper goroutines and wait them to finish.
	wp.Write(tmp[:])
	wp.Write(tmp[:])
	close(done)
	wg.Wait()
	}()

	for i := 0; i < 3; i++ {
	buf := new(bytes.Buffer)
	if err := Start(buf); err != nil {
	t.Fatalf("failed to start tracing: %v", err)
	}
	time.Sleep(time.Millisecond)
	Stop()
	saveTrace(t, buf, "TestTraceStressStartStop")
	trace := buf.Bytes()
	parseTrace(t, buf)
	testBrokenTimestamps(t, trace)
	}
	<-outerDone
	}

	func TestTraceFutileWakeup(t *testing.T) {
	if IsEnabled() {
	t.Skip("skipping because -test.trace is set")
	}
	buf := new(bytes.Buffer)
	if err := Start(buf); err != nil {
	t.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() {
	for i := 0; i < iters; i++ {
	runtime.Gosched()
	c0 <- 0
	}
	done.Done()
	}()
	go func() {
	for i := 0; i < iters; i++ {
	runtime.Gosched()
	<-c0
	}
	done.Done()
	}()
	go func() {
	for i := 0; i < iters; i++ {
	runtime.Gosched()
	select {
	case c1 <- 0:
	case c2 <- 0:
	}
	}
	done.Done()
	}()
	go func() {
	for i := 0; i < iters; i++ {
	runtime.Gosched()
	select {
	case <-c1:
	case <-c2:
	}
	}
	done.Done()
	}()
	}
	done.Wait()

	Stop()
	saveTrace(t, buf, "TestTraceFutileWakeup")
	events, _ := parseTrace(t, buf)
	// Check that (1) trace does not contain EvFutileWakeup events and
	// (2) there are no consecutive EvGoBlock/EvGCStart/EvGoBlock events
	// (we call runtime.Gosched between all operations, so these would be futile wakeups).
	gs := make(map[uint64]int)
	for _, ev := range events {
	switch ev.Type {
	case trace.EvFutileWakeup:
	t.Fatalf("found EvFutileWakeup event")
	case trace.EvGoBlockSend, trace.EvGoBlockRecv, trace.EvGoBlockSelect:
	if gs[ev.G] == 2 {
	t.Fatalf("goroutine %v blocked on %v at %v right after start",
	ev.G, trace.EventDescriptions[ev.Type].Name, ev.Ts)
	}
	if gs[ev.G] == 1 {
	t.Fatalf("goroutine %v blocked on %v at %v while blocked",
	ev.G, trace.EventDescriptions[ev.Type].Name, ev.Ts)
	}
	gs[ev.G] = 1
	case trace.EvGoStart:
	if gs[ev.G] == 1 {
	gs[ev.G] = 2
	}
	default:
	delete(gs, ev.G)
	}
	}
	}

	func saveTrace(t testing.T, buf bytes.Buffer, name string) {
	if !*saveTraces {
	return
	}
	if err := ioutil.WriteFile(name+".trace", buf.Bytes(), 0600); err != nil {
	t.Errorf("failed to write trace file: %s", err)
	}
	}