timeout.c

 1// SPDX-License-Identifier: GPL-2.0-only
 2/* Timeout API for single-threaded programs that use blocking
 3 * syscalls (read/write/send/recv/connect/accept).
 4 *
 5 * Copyright (C) 2017 Red Hat, Inc.
 6 *
 7 * Author: Stefan Hajnoczi <stefanha@redhat.com>
 8 */
 9
10/* Use the following pattern:
11 *
12 *   timeout_begin(TIMEOUT);
13 *   do {
14 *       ret = accept(...);
15 *       timeout_check("accept");
16 *   } while (ret < 0 && ret == EINTR);
17 *   timeout_end();
18 */
19
20#include <stdlib.h>
21#include <stdbool.h>
22#include <unistd.h>
23#include <stdio.h>
24#include <time.h>
25#include "timeout.h"
26
27static volatile bool timeout;
28
29/* SIGALRM handler function.  Do not use sleep(2), alarm(2), or
30 * setitimer(2) while using this API - they may interfere with each
31 * other.
32 *
33 * If you need to sleep, please use timeout_sleep() provided by this API.
34 */
35void sigalrm(int signo)
36{
37	timeout = true;
38}
39
40/* Start a timeout.  Call timeout_check() to verify that the timeout hasn't
41 * expired.  timeout_end() must be called to stop the timeout.  Timeouts cannot
42 * be nested.
43 */
44void timeout_begin(unsigned int seconds)
45{
46	alarm(seconds);
47}
48
49/* Exit with an error message if the timeout has expired */
50void timeout_check(const char *operation)
51{
52	if (timeout) {
53		fprintf(stderr, "%s timed out\n", operation);
54		exit(EXIT_FAILURE);
55	}
56}
57
58/* Stop a timeout */
59void timeout_end(void)
60{
61	alarm(0);
62	timeout = false;
63}
64
65/* Sleep in a timeout section.
66 *
67 * nanosleep(2) can be used with this API since POSIX.1 explicitly
68 * specifies that it does not interact with signals.
69 */
70int timeout_usleep(useconds_t usec)
71{
72	struct timespec ts = {
73		.tv_sec = usec / 1000000,
74		.tv_nsec = (usec % 1000000) * 1000,
75	};
76
77	return nanosleep(&ts, NULL);
78}