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args,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
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。
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。
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 。)
write()
unistd.h
printf()
stdio.h
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。)
pthread_mutex_lock()
#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。
rt
gcc -W -Wall *source*.c -lrt -o *binary*
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 。
timeout_init()
timeout_done()
fork()
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。
timeout_set(seconds)
timeout_passed()
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。)
sigwaitinfo()
TIMEOUT_SIGNAL
pthread_kill()
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。
main()
fgets()
#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; }