9

我正在寻找一个用 C 编写的开源计时器库。该库应该具有 Timer 回调函数等。

在搜索时，我看到POSIX 计时器或setitimer()，它们使用基于信号的方法，这可能会导致多线程代码出现问题。

假设我在线程代码中使用 POSIX 计时器，信号将不会到达正确的位置。如果我在一个进程中使用多个计时器，那么每个计时器都应该使用不同的信号。还有其他选择吗？

4

3 回答 3

11

由于您运行的是 Linux，我建议您使用内置的 POSIX 计时器 API。

int timer_create(clockid_t clockid, struct sigevent *sevp, timer_t *timerid);

这是一些文档的链接，展示了如何使用为回调函数提供支持的 POSIX 计时器。

关于一个进程中的多个计时器，文档是这样说的：

   A program may create multiple interval timers using timer_create().

   Timers are not inherited by the child of a fork(2), and are disarmed and
   deleted during an execve(2).

   The kernel preallocates a "queued real-time signal" for each timer created
   using timer_create().  Consequently, the number of timers is limited by the
   RLIMIT_SIGPENDING resource limit (see setrlimit(2)).

请注意，通过使用 SIGEV_THREAD_ID 设置通知，可以在线程应用程序中使用 POSIX 计时器，如下所示：

The sevp.sigev_notify field can have the following values:

       SIGEV_NONE
              Don't asynchronously notify when the timer expires.  Progress of the
              timer can be monitored using timer_gettime(2).

       SIGEV_SIGNAL
              Upon timer expiration, generate the signal sigev_signo for the process.
              See sigevent(7) for general details.  The si_code field of the
              siginfo_t structure will be set to SI_TIMER.  At any point in time, at
              most one signal is queued to the process for a given timer; see
              timer_getoverrun(2) for more details.

       SIGEV_THREAD
              Upon timer expiration, invoke sigev_notify_function as if it were the
              start function of a new thread.  See sigevent(7) for details.

       SIGEV_THREAD_ID (Linux-specific)
              As for SIGEV_SIGNAL, but the signal is targeted at the thread whose ID
              is given in sigev_notify_thread_id, which must be a thread in the same
              process as the caller.  The sigev_notify_thread_id field specifies a
              kernel thread ID, that is, the value returned by clone(2) or gettid(2).
              This flag is only intended for use by threading libraries.
于 2012-09-17T16:44:38.203 回答
7

Linux 的做法是通过timerfd_create与基于 epoll 的事件循环很好地集成（从而避免信号处理程序的限制）

于 2012-09-17T20:12:02.867 回答
-6

为其创建库非常简单。

例子： 

#include <time.h>
int main()
{
    time_t start,end;
    double dif;
    double duration=40f; //duration of timer
    bool loop=true;
    while(loop==true)
    {
        time(&start);
        if(dif==duration)
        {
            /*callback*/
            dif=0;
        }
        //do stuff
        time(&end);
        dif+=difftime(end,start);
    }
{

于 2012-09-17T16:53:38.837 回答