runtime: add threadprof tag for test that starts busy thread

The CgoExternalThreadSIGPROF test starts a thread at constructor time
that does a busy loop. That can throw off some other tests. So only
build that code if testprogcgo is built with the tag threadprof, and
adjust the tests that use that code to pass that build tag.

This revealed that the CgoPprofThread test was not testing what it
should have, as it never actually started the cpuHog thread. It was
passing because of the busy loop thread. Fix it to start the thread as
intended.

Change-Id: I087a9e4fc734a86be16a287456441afac5676beb
Reviewed-on: https://go-review.googlesource.com/30362
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/crash_cgo_test.go

@@ -100,9 +100,18 @@ func TestCgoExternalThreadSIGPROF(t *testing.T) {
 		// ppc64 (issue #8912)
 		t.Skipf("no external linking on ppc64")
 	}
-	got := runTestProg(t, "testprogcgo", "CgoExternalThreadSIGPROF")
-	want := "OK\n"
-	if got != want {
+
+	exe, err := buildTestProg(t, "testprogcgo", "-tags=threadprof")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := testEnv(exec.Command(exe, "CgoExternalThreadSIGPROF")).CombinedOutput()
+	if err != nil {
+		t.Fatalf("exit status: %v\n%s", err, got)
+	}
+
+	if want := "OK\n"; string(got) != want {
 		t.Fatalf("expected %q, but got:\n%s", want, got)
 	}
 }
@@ -113,9 +122,19 @@ func TestCgoExternalThreadSignal(t *testing.T) {
 	case "plan9", "windows":
 		t.Skipf("no pthreads on %s", runtime.GOOS)
 	}
-	got := runTestProg(t, "testprogcgo", "CgoExternalThreadSignal")
-	want := "OK\n"
-	if got != want {
+
+	exe, err := buildTestProg(t, "testprogcgo", "-tags=threadprof")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := testEnv(exec.Command(exe, "CgoExternalThreadSIGPROF")).CombinedOutput()
+	if err != nil {
+		t.Fatalf("exit status: %v\n%s", err, got)
+	}
+
+	want := []byte("OK\n")
+	if !bytes.Equal(got, want) {
 		t.Fatalf("expected %q, but got:\n%s", want, got)
 	}
 }

src/runtime/testdata/testprogcgo/threadpprof.go

@@ -53,6 +53,18 @@ void pprofCgoThreadTraceback(void* parg) {
 int getCPUHogThreadCount() {
 	return __sync_add_and_fetch(&cpuHogThreadCount, 0);
 }
+
+static void* cpuHogDriver(void* arg __attribute__ ((unused))) {
+	while (1) {
+		cpuHogThread();
+	}
+	return 0;
+}
+
+void runCPUHogThread() {
+	pthread_t tid;
+	pthread_create(&tid, 0, cpuHogDriver, 0);
+}
 */
 import "C"
 
@@ -84,6 +96,8 @@ func CgoPprofThread() {
 		os.Exit(2)
 	}
 
+	C.runCPUHogThread()
+
 	t0 := time.Now()
 	for C.getCPUHogThreadCount() < 2 && time.Since(t0) < time.Second {
 		time.Sleep(100 * time.Millisecond)

src/runtime/testdata/testprogcgo/threadprof.go

@@ -2,7 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// We only build this file with the tag "threadprof", since it starts
+// a thread running a busy loop at constructor time.
+
 // +build !plan9,!windows
+// +build threadprof
 
 package main
 
@@ -21,6 +25,7 @@ static void *thread1(void *p) {
 	spinlock = 0;
 	return NULL;
 }
+
 __attribute__((constructor)) void issue9456() {
 	pthread_t tid;
 	pthread_create(&tid, 0, thread1, NULL);