1// Copyright 2018 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5//go:build !plan9 && !windows && !js && !wasip1
6
7package runtime_test
8
9import (
10	"io"
11	"os/exec"
12	"syscall"
13	"testing"
14	"time"
15)
16
17// Issue #27250. Spurious wakeups to pthread_cond_timedwait_relative_np
18// shouldn't cause semasleep to retry with the same timeout which would
19// cause indefinite spinning.
20func TestSpuriousWakeupsNeverHangSemasleep(t *testing.T) {
21	if *flagQuick {
22		t.Skip("-quick")
23	}
24	t.Parallel() // Waits for a program to sleep for 1s.
25
26	exe, err := buildTestProg(t, "testprog")
27	if err != nil {
28		t.Fatal(err)
29	}
30
31	cmd := exec.Command(exe, "After1")
32	stdout, err := cmd.StdoutPipe()
33	if err != nil {
34		t.Fatalf("StdoutPipe: %v", err)
35	}
36	beforeStart := time.Now()
37	if err := cmd.Start(); err != nil {
38		t.Fatalf("Failed to start command: %v", err)
39	}
40
41	waiting := false
42	doneCh := make(chan error, 1)
43	t.Cleanup(func() {
44		cmd.Process.Kill()
45		if waiting {
46			<-doneCh
47		} else {
48			cmd.Wait()
49		}
50	})
51
52	// Wait for After1 to close its stdout so that we know the runtime's SIGIO
53	// handler is registered.
54	b, err := io.ReadAll(stdout)
55	if len(b) > 0 {
56		t.Logf("read from testprog stdout: %s", b)
57	}
58	if err != nil {
59		t.Fatalf("error reading from testprog: %v", err)
60	}
61
62	// Wait for child exit.
63	//
64	// Note that we must do this after waiting for the write/child end of
65	// stdout to close. Wait closes the read/parent end of stdout, so
66	// starting this goroutine prior to io.ReadAll introduces a race
67	// condition where ReadAll may get fs.ErrClosed if the child exits too
68	// quickly.
69	waiting = true
70	go func() {
71		doneCh <- cmd.Wait()
72		close(doneCh)
73	}()
74
75	// Wait for an arbitrary timeout longer than one second. The subprocess itself
76	// attempts to sleep for one second, but if the machine running the test is
77	// heavily loaded that subprocess may not schedule very quickly even if the
78	// bug remains fixed. (This is fine, because if the bug really is unfixed we
79	// can keep the process hung indefinitely, as long as we signal it often
80	// enough.)
81	timeout := 10 * time.Second
82
83	// The subprocess begins sleeping for 1s after it writes to stdout, so measure
84	// the timeout from here (not from when we started creating the process).
85	// That should reduce noise from process startup overhead.
86	ready := time.Now()
87
88	// With the repro running, we can continuously send to it
89	// a signal that the runtime considers non-terminal,
90	// such as SIGIO, to spuriously wake up
91	// pthread_cond_timedwait_relative_np.
92	ticker := time.NewTicker(200 * time.Millisecond)
93	defer ticker.Stop()
94	for {
95		select {
96		case now := <-ticker.C:
97			if now.Sub(ready) > timeout {
98				t.Error("Program failed to return on time and has to be killed, issue #27520 still exists")
99				// Send SIGQUIT to get a goroutine dump.
100				// Stop sending SIGIO so that the program can clean up and actually terminate.
101				cmd.Process.Signal(syscall.SIGQUIT)
102				return
103			}
104
105			// Send the pesky signal that toggles spinning
106			// indefinitely if #27520 is not fixed.
107			cmd.Process.Signal(syscall.SIGIO)
108
109		case err := <-doneCh:
110			if err != nil {
111				t.Fatalf("The program returned but unfortunately with an error: %v", err)
112			}
113			if time.Since(beforeStart) < 1*time.Second {
114				// The program was supposed to sleep for a full (monotonic) second;
115				// it should not return before that has elapsed.
116				t.Fatalf("The program stopped too quickly.")
117			}
118			return
119		}
120	}
121}
122