Linux中的计时器c

Question

可能重复:
C中的循环/计时器

我一直在读关于过去3天的计时器,我找不到任何有用的东西,我试图在实例中理解它,有人可以帮我弄清楚如何为下面的程序设置警报.

如何设置一个定时器,以便它发送2个a​​rgs,一个是数组名称,第二个是要删除的数字,我知道下面的安全无论如何,我只是想了解如何使用带有args的报警来调用一个函数.

请注意,环境是Linux,我也很欣赏与工作C示例的任何链接.

#include<stdio.h>
int delete_from_array(int arg) ;


    int main()
    {

    int a[10000], i, y ;
    //how to set timer here for to delete any number in array after half a second
    for (y=0; y < 100; y++) {


        for (i=0; i<sizeof(a) / sizeof(int); i++)
            a[i] = i;
    sleep(1);
    printf("wake\n");
    }

    }

    int delete_from_array(int arg) 
    {
    int i, a[1000], number_to_delete=0;

    //number_to_delete = arg->number;

    for (i=0; i<sizeof(a); i++)
        if (a[i] == number_to_delete)
            a[i] = 0;
    printf("deleted\n");

    }

我想要做的是我有一个哈希值,它在1秒后有值过期,所以在我将值插入哈希后,我需要创建一个计时器,以便在我们说之后删除该值1秒,如果我在该间隔(1秒)之前从服务器得到响应,那么我从哈希中删除值并删除定时器,几乎就像在tcp中重传一样

Answer 1

你想使用信号或线程吗？

首先,设置信号处理程序或准备合适的线程函数; 详情请见man 7 sigevent.

接下来,使用创建合适的计时器timer_create().有关详细信息,请参阅man 2 timer_create.

根据计时器触发时的操作,您可能希望将计时器设置为单次计时,或者在之后的短时间间隔内重复计时.你timer_settime()用来武装和解除计时器; 有关详细信息,请参阅man 2 timer_settime.

在实际应用中,您通常需要多路复用定时器.即使进程可以创建多个计时器,它们也是有限的资源.特别是超时定时器 - 无论是设置标志和/或向特定线程发送信号 - 都应使用单个定时器,该定时器在下一次超时时触发,设置相关的超时标志,并可选择发送信号(使用空体处理程序)到所需的线程,以确保它被中断.(对于单线程进程,原始信号传递将中断阻塞I/O调用.)考虑服务器,响应某些请求:请求本身可能在一分钟左右的时间内超时,同时处理请求可能需要连接超时,I/O超时等.

现在,最初的问题很有趣,因为定时器在有效使用时非常强大.但是,示例程序基本上是无意义的.为什么不创建一个设置一个或多个计时器的程序,例如每个计时器输出一些标准输出？请记住使用write()et al,unistd.h因为它们是异步信号安全的,而printf()等等stdio.h则不是.(如果你的信号处理程序使用非异步信号安全函数,结果是不确定的.它通常有效,但它根本不能保证;它也可能像工作一样崩溃.测试不会告诉,因为它是未定义的.)

编辑添加:这是多路复用超时的简单示例.

(在法律允许的范围内,我将以下所示的代码片段的所有版权及相关和相邻权利专用于全球公共领域;请参阅CC0 Public Domain Dedication.换句话说,请随时以任何方式使用以下代码希望,不要因为任何问题而责备我.)

我使用旧式GCC原子内置函数,所以它应该是线程安全的.添加一些内容后,它也适用于多线程代码.(你不能使用例如互斥体,因为pthread_mutex_lock()它不是异步信号安全的.原子操作超时状态应该有效,尽管如果你在它触发时禁用超时可能会有一些比赛.)

#define _POSIX_C_SOURCE 200809L
#include <unistd.h>
#include <signal.h>
#include <time.h>
#include <errno.h>

#define   TIMEOUTS       16
#define   TIMEOUT_SIGNAL (SIGRTMIN+0)

#define   TIMEOUT_USED   1
#define   TIMEOUT_ARMED  2
#define   TIMEOUT_PASSED 4

static timer_t               timeout_timer;
static volatile sig_atomic_t timeout_state[TIMEOUTS] = { 0 };
static struct timespec       timeout_time[TIMEOUTS];


/* Return the number of seconds between before and after, (after - before).
 * This must be async-signal safe, so it cannot use difftime().
*/
static inline double timespec_diff(const struct timespec after, const struct timespec before)
{
    return (double)(after.tv_sec - before.tv_sec)
         + (double)(after.tv_nsec - before.tv_nsec) / 1000000000.0;
}

/* Add positive seconds to a timespec, nothing if seconds is negative.
 * This must be async-signal safe.
*/
static inline void timespec_add(struct timespec *const to, const double seconds)
{
    if (to && seconds > 0.0) {
        long  s = (long)seconds;
        long  ns = (long)(0.5 + 1000000000.0 * (seconds - (double)s));

        /* Adjust for rounding errors. */
        if (ns < 0L)
            ns = 0L;
        else
        if (ns > 999999999L)
            ns = 999999999L;

        to->tv_sec += (time_t)s;
        to->tv_nsec += ns;

        if (to->tv_nsec >= 1000000000L) {
            to->tv_nsec -= 1000000000L;
            to->tv_sec++;
        }
    }
}

/* Set the timespec to the specified number of seconds, or zero if negative seconds.
*/
static inline void timespec_set(struct timespec *const to, const double seconds)
{
    if (to) {
        if (seconds > 0.0) {
            const long  s = (long)seconds;
            long       ns = (long)(0.5 + 1000000000.0 * (seconds - (double)s));

            if (ns < 0L)
                ns = 0L;
            else
            if (ns > 999999999L)
                ns = 999999999L;

            to->tv_sec = (time_t)s;
            to->tv_nsec = ns;

        } else {
            to->tv_sec = (time_t)0;
            to->tv_nsec = 0L;
        }
    }
}


/* Return nonzero if the timeout has occurred.
*/
static inline int timeout_passed(const int timeout)
{
    if (timeout >= 0 && timeout < TIMEOUTS) {
        const int  state = __sync_or_and_fetch(&timeout_state[timeout], 0);

        /* Refers to an unused timeout? */
        if (!(state & TIMEOUT_USED))
            return -1;

        /* Not armed? */
        if (!(state & TIMEOUT_ARMED))
            return -1;

        /* Return 1 if timeout passed, 0 otherwise. */
        return (state & TIMEOUT_PASSED) ? 1 : 0;

    } else {
        /* Invalid timeout number. */
        return -1;
    }
}

/* Release the timeout.
 * Returns 0 if the timeout had not fired yet, 1 if it had.
*/
static inline int timeout_unset(const int timeout)
{
    if (timeout >= 0 && timeout < TIMEOUTS) {
        /* Obtain the current timeout state to 'state',
         * then clear all but the TIMEOUT_PASSED flag
         * for the specified timeout.
         * Thanks to Bylos for catching this bug. */
        const int  state = __sync_fetch_and_and(&timeout_state[timeout], TIMEOUT_PASSED);

        /* Invalid timeout? */
        if (!(state & TIMEOUT_USED))
            return -1;

        /* Not armed? */
        if (!(state & TIMEOUT_ARMED))
            return -1;

        /* Return 1 if passed, 0 otherwise. */
        return (state & TIMEOUT_PASSED) ? 1 : 0;

    } else {
        /* Invalid timeout number. */
        return -1;
    }
}


int timeout_set(const double seconds)
{
    struct timespec   now, then;
    struct itimerspec when;
    double            next;
    int               timeout, i;

    /* Timeout must be in the future. */
    if (seconds <= 0.0)
        return -1;

    /* Get current time, */
    if (clock_gettime(CLOCK_REALTIME, &now))
        return -1;

    /* and calculate when the timeout should fire. */
    then = now;
    timespec_add(&then, seconds);

    /* Find an unused timeout. */
    for (timeout = 0; timeout < TIMEOUTS; timeout++)
        if (!(__sync_fetch_and_or(&timeout_state[timeout], TIMEOUT_USED) & TIMEOUT_USED))
            break;

    /* No unused timeouts? */
    if (timeout >= TIMEOUTS)
        return -1;

    /* Clear all but TIMEOUT_USED from the state, */
    __sync_and_and_fetch(&timeout_state[timeout], TIMEOUT_USED);

    /* update the timeout details, */
    timeout_time[timeout] = then;

    /* and mark the timeout armable. */
    __sync_or_and_fetch(&timeout_state[timeout], TIMEOUT_ARMED);

    /* How long till the next timeout? */
    next = seconds;
    for (i = 0; i < TIMEOUTS; i++)
        if ((__sync_fetch_and_or(&timeout_state[i], 0) & (TIMEOUT_USED | TIMEOUT_ARMED | TIMEOUT_PASSED)) == (TIMEOUT_USED | TIMEOUT_ARMED)) {
            const double secs = timespec_diff(timeout_time[i], now);
            if (secs >= 0.0 && secs < next)
                next = secs;
        }

    /* Calculate duration when to fire the timeout next, */
    timespec_set(&when.it_value, next);
    when.it_interval.tv_sec = 0;
    when.it_interval.tv_nsec = 0L;

    /* and arm the timer. */
    if (timer_settime(timeout_timer, 0, &when, NULL)) {
        /* Failed. */
        __sync_and_and_fetch(&timeout_state[timeout], 0);
        return -1;
    }

    /* Return the timeout number. */
    return timeout;
}


static void timeout_signal_handler(int signum __attribute__((unused)), siginfo_t *info, void *context __attribute__((unused)))
{
    struct timespec   now;
    struct itimerspec when;
    int               saved_errno, i;
    double            next;

    /* Not a timer signal? */
    if (!info || info->si_code != SI_TIMER)
        return;

    /* Save errno; some of the functions used may modify errno. */
    saved_errno = errno;

    if (clock_gettime(CLOCK_REALTIME, &now)) {
        errno = saved_errno;
        return;
    }

    /* Assume no next timeout. */
    next = -1.0;

    /* Check all timeouts that are used and armed, but not passed yet. */
    for (i = 0; i < TIMEOUTS; i++)
        if ((__sync_or_and_fetch(&timeout_state[i], 0) & (TIMEOUT_USED | TIMEOUT_ARMED | TIMEOUT_PASSED)) == (TIMEOUT_USED | TIMEOUT_ARMED)) {
            const double  seconds = timespec_diff(timeout_time[i], now);
            if (seconds <= 0.0) {
                /* timeout [i] fires! */
                __sync_or_and_fetch(&timeout_state[i], TIMEOUT_PASSED);

            } else
            if (next <= 0.0 || seconds < next) {
                /* This is the soonest timeout in the future. */
                next = seconds;
            }
        }

    /* Note: timespec_set() will set the time to zero if next <= 0.0,
     *       which in turn will disarm the timer.
     * The timer is one-shot; it_interval == 0.
    */
    timespec_set(&when.it_value, next);
    when.it_interval.tv_sec = 0;
    when.it_interval.tv_nsec = 0L;
    timer_settime(timeout_timer, 0, &when, NULL);

    /* Restore errno. */
    errno = saved_errno;
}


int timeout_init(void)
{
    struct sigaction  act;
    struct sigevent   evt;
    struct itimerspec arm;

    /* Install timeout_signal_handler. */
    sigemptyset(&act.sa_mask);
    act.sa_sigaction = timeout_signal_handler;
    act.sa_flags = SA_SIGINFO;
    if (sigaction(TIMEOUT_SIGNAL, &act, NULL))
        return errno;

    /* Create a timer that will signal to timeout_signal_handler. */
    evt.sigev_notify = SIGEV_SIGNAL;
    evt.sigev_signo = TIMEOUT_SIGNAL;
    evt.sigev_value.sival_ptr = NULL;
    if (timer_create(CLOCK_REALTIME, &evt, &timeout_timer))
        return errno;

    /* Disarm the timeout timer (for now). */
    arm.it_value.tv_sec = 0;
    arm.it_value.tv_nsec = 0L;
    arm.it_interval.tv_sec = 0;
    arm.it_interval.tv_nsec = 0L;
    if (timer_settime(timeout_timer, 0, &arm, NULL))
        return errno;

    return 0;
}

int timeout_done(void)
{
    struct sigaction  act;
    struct itimerspec arm;
    int               errors = 0;

    /* Ignore the timeout signals. */
    sigemptyset(&act.sa_mask);
    act.sa_handler = SIG_IGN;
    if (sigaction(TIMEOUT_SIGNAL, &act, NULL))
        if (!errors) errors = errno;

    /* Disarm any current timeouts. */
    arm.it_value.tv_sec = 0;
    arm.it_value.tv_nsec = 0L;
    arm.it_interval.tv_sec = 0;
    arm.it_interval.tv_nsec = 0;
    if (timer_settime(timeout_timer, 0, &arm, NULL))
        if (!errors) errors = errno;

    /* Destroy the timer itself. */
    if (timer_delete(timeout_timer))
        if (!errors) errors = errno;

    /* If any errors occurred, set errno. */
    if (errors)
        errno = errors;

    /* Return 0 if success, errno otherwise. */
    return errors;
}

记得rt在编译时包含库,即用于gcc -W -Wall *source*.c -lrt -o *binary*编译.

这个想法是主程序首先调用timeout_init()安装所有必要的处理程序等等,并且可以timeout_done()在退出之前(或者在子程序之后fork())调用它来取消它.

要设置超时,请致电timeout_set(seconds).返回值是超时描述符.目前只有一个可以使用的标志timeout_passed(),但是超时信号的传递也会中断任何阻塞的I/O调用.因此,您可以预期超时会中断任何阻塞I/O调用.

如果你想做更多的事情而不是在超时时设置一个标志,你就不能在信号处理程序中做到这一点; 请记住,在信号处理程序中,您只能使用异步信号安全功能.周围的最简单的方法是一种通过使用一个单独的线程具有无限循环sigwaitinfo(),与TIMEOUT_SIGNAL阻塞所有其他线程中的信号.这样,专用线程可以保证捕获信号,但同时不限于异步信号安全功能.例如,它可以做更多的工作,甚至可以使用发送信号到特定的线程pthread_kill().(只要该信号具有处理程序,即使是具有空体的处理程序,它的传递也会中断该线程中的任何阻塞I/O调用.)

这是一个main()使用超时的简单示例.这是愚蠢的,并且依赖于fgets()不重试(当被信号中断时),但它似乎有效.

#include <string.h>
#include <stdio.h>

int main(void)
{
    char    buffer[1024], *line;
    int t1, t2, warned1;

    if (timeout_init()) {
        fprintf(stderr, "timeout_init(): %s.\n", strerror(errno));
        return 1;
    }

    printf("You have five seconds to type something.\n");
    t1 = timeout_set(2.5); warned1 = 0;
    t2 = timeout_set(5.0);
    line = NULL;

    while (1) {

        if (timeout_passed(t1)) {
            /* Print only the first time we notice. */
            if (!warned1++)
                printf("\nTwo and a half seconds left, buddy.\n");
        }

        if (timeout_passed(t2)) {
            printf("\nAw, just forget it, then.\n");
            break;
        }

        line = fgets(buffer, sizeof buffer, stdin);
        if (line) {
            printf("\nOk, you typed: %s\n", line);
            break;
        }
    }

    /* The two timeouts are no longer needed. */
    timeout_unset(t1);
    timeout_unset(t2);

    /* Note: 'line' is non-NULL if the user did type a line. */

    if (timeout_done()) {
        fprintf(stderr, "timeout_done(): %s.\n", strerror(errno));
        return 1;
    }

    return 0;
}