在 C 中每 x 秒执行一个方法 [英] Execute a method every x seconds in C

问题描述

是否有一个工作定时器的例子，它使用 C 每隔 x 秒执行一些函数.

Is there an example of a working timer that executes some function every x amount seconds using C.

如果有示例工作代码，我会很感激.

I'd appreciate an example working code.

推荐答案

您可以创建一个新线程:

You could spawn a new thread:

void *threadproc(void *arg)
{
    while(!done)
    {
        sleep(delay_in_seconds);
        call_function();
    }
    return 0;
}
...
pthread_t tid;
pthread_create(&tid, NULL, &threadproc, NULL);

或者，您可以使用 alarm(2) 或 setitimer(2):

Or, you could set an alarm with alarm(2) or setitimer(2):

void on_alarm(int signum)
{
    call_function();
    if(!done)
        alarm(delay_in_seconds);  // Reschedule alarm
}
...
// Setup on_alarm as a signal handler for the SIGALRM signal
struct sigaction act;
act.sa_handler = &on_alarm;
act.sa_mask = 0;
act.sa_flags = SA_RESTART;  // Restart interrupted system calls
sigaction(SIGALRM, &act, NULL);

alarm(delay_in_seconds);  // Setup initial alarm

当然，这两种方法都存在问题，即您定期调用的函数需要是线程安全的.

Of course, both of these methods have the problem that the function you're calling periodically needs to be thread-safe.

信号方法特别危险，因为它也必须是异步安全的，这很难做到——即使像printf这样简单的东西也是不安全的，因为printf可能会分配内存，如果 SIGALRM 中断了对 malloc 的调用，你就会遇到麻烦，因为 malloc 是不可重入的.所以我不推荐使用信号方法，除非你所做的只是在信号处理程序中设置一个标志，该标志稍后会被其他一些函数检查，这会让你回到与线程版本相同的位置.

The signal method is particularly dangerous because it must also be async-safe, which is very hard to do -- even something as simple as printf is unsafe because printf might allocate memory, and if the SIGALRM interrupted a call to malloc, you're in trouble because malloc is not reentrant. So I wouldn't recommend the signal method, unless all you do is set a flag in the signal handler which later gets checked by some other function, which puts you back in the same place as the threaded version.

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