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Linux中的定时器在C [重复]

linux

我一直在阅读有关过去三天的计时器的信息,但找不到任何有用的信息,我试图通过实际示例进行了解,有人可以帮助我弄清楚如何为以下程序设置警报。

我如何设置一个计时器,以便它将发送2个a​​rgs,一个是数组名称,第二个是要删除的数字,我知道下面无论如何都不安全,我只是想了解如何使用用args报警以调用函数。

请注意,该环境是Linux,并且我也非常感谢与有效的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");

    }

我要做的是,我有一个哈希值,该哈希值的值将在1秒后过期,因此,将值插入哈希值后,我需要创建一个计时器,以便在我们说完之后删除该值1秒,如果我在该间隔(1秒)之前收到服务器的响应,则从哈希中删除值并删除计时器,就像在tcp中重新传输一样


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2020-06-03

共1个答案

小编典典

您要使用信号还是线程?

首先,设置信号处理程序或准备合适的线程函数;有关详细信息,请参见man 7
sigevent

接下来,使用创建一个合适的计时器timer_create()。有关详细信息,请参见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一次触发,或稍后再重复一次。您timer_settime()可以同时使用计时器和撤防计时器。有关详细信息,请参见man
2 timer_settime

在实际应用中,通常需要复用计时器。即使一个进程可以创建多个计时器,它们也是有限的资源。特别是超时计时器-这很简单-设置标志和/或向特定线程发送信号-
应该使用单个计时器,该计时器在下一次超时时触发,设置相关的超时标志,并可选地发送信号(使用空体处理程序)到所需线程以确保其被中断。(对于单线程进程,原始信号传递将中断阻止I
/ O调用。)考虑服务器,它对某些请求做出响应:在处理请求时,请求本身可能会有一分钟左右的超时时间可能需要连接超时,I / O超时等等。

现在,最初的问题很有趣,因为计时器在有效使用时功能强大。但是,示例程序基本上是胡说八道。您为什么不创建一个程序,该程序设置一个或多个计时器,每个计时器例如将一些内容输出到标准输出?请记住使用write()from等,unistd.h因为它们是异步信号安全的,而printf()from等stdio.h则不是。(如果信号处理程序使用非异步信号安全函数,则结果是不确定的。它通常可以工作,但完全不能保证;它和工作一样崩溃。测试是
不明确的 ,因为它是 不确定的 。)


编辑添加:这是复用超时的准系统示例。

(在法律允许的范围内,我将以下所示代码段的所有版权,相关权和邻接权专用于全球公共领域;请参阅CC0公共领域专用。换句话说,请随时以任何方式使用以下代码希望,只是不要怪我有任何问题。)

我使用了旧式的GCC原子内置函数,因此它应该是线程安全的。除了一些补充,它也应该适用于多线程代码。(您不能使用例如互斥锁,因为pthread_mutex_lock()这不是异步信号安全的方法。以原子方式操作超时状态应该可以工作,尽管如果在触发时禁用超时可能会留下一些竞争。)

#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;
}

记住rt在编译时包括库,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()以安装所有必需的处理程序等,然后可以timeout_done()在退出之前(或在进入之后的子进程中fork())调用deistall

要设置超时,请致电timeout_set(seconds)。返回值是超时描述符。当前,您可以使用来检查一个标志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,您可以期望超时会中断任何阻塞的I / O调用。

如果您想要做的只是设置超时标志,则不能在信号处理程序中进行;请记住,在信号处理程序中,您仅限于异步信号安全功能。最简单的方法是使用一个单独的线程,该线程具有无限循环sigwaitinfo()TIMEOUT_SIGNAL信号在所有其他线程中均被阻塞。这样,可以确保专用线程捕获信号,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,甚至可以使用将信号发送到特定线程pthread_kill()。(只要该信号具有一个处理程序,即使是一个带有空主体的处理程序,它的传递都会中断该线程中任何阻塞的I
/ O调用。)

这是一个main()使用超时的简单示例。它很愚蠢,并且依赖于fgets()不重试(被信号中断时),但是它似乎可以工作。

#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;
}
2020-06-03