unix: add timeout tests for Select and Pselect on Linux

Test for correct timeout behavior of Select and Pselect

Updates golang/go#22246

Change-Id: I86d1804c6ddf5072e93f3ef4f359198e732fae94
Reviewed-on: https://go-review.googlesource.com/84955
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/syscall_linux_test.go

@@ -182,6 +182,39 @@ func TestSelect(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Select: %v", err)
 	}
+
+	dur := 150 * time.Millisecond
+	tv := unix.NsecToTimeval(int64(dur))
+	start := time.Now()
+	_, err = unix.Select(0, nil, nil, nil, &tv)
+	took := time.Since(start)
+	if err != nil {
+		t.Fatalf("Select: %v", err)
+	}
+
+	if took < dur {
+		t.Errorf("Select: timeout should have been at least %v, got %v", dur, took)
+	}
+}
+
+func TestPselect(t *testing.T) {
+	_, err := unix.Pselect(0, nil, nil, nil, &unix.Timespec{Sec: 0, Nsec: 0}, nil)
+	if err != nil {
+		t.Fatalf("Pselect: %v", err)
+	}
+
+	dur := 2500 * time.Microsecond
+	ts := unix.NsecToTimespec(int64(dur))
+	start := time.Now()
+	_, err = unix.Pselect(0, nil, nil, nil, &ts, nil)
+	took := time.Since(start)
+	if err != nil {
+		t.Fatalf("Pselect: %v", err)
+	}
+
+	if took < dur {
+		t.Errorf("Pselect: timeout should have been at least %v, got %v", dur, took)
+	}
 }
 
 func TestFstatat(t *testing.T) {