我有一个
select()
每秒更新我的 UI,并处理来自 X11 的用户操作。这是此源代码的片段:
XEvent e;
/* Input file descriptor */
fd_set in_fd;
/* Get the file descriptor of the link with X11 */
int dpy_fd = ConnectionNumber(disp->dpy);
while (!finish) {
FD_ZERO(&in_fd);
FD_SET(dpy_fd, &in_fd);
if (select(dpy_fd+1, &in_fd, 0, 0, &tv)) {
printf("Event Received!\n");
XNextEvent(disp->dpy, &e);
/* do something */
}
else {
printf("Timer Fired!\n");
/* do something else*/
}
}
到目前为止,一切都还好。
同时,我需要使用警报每 500 毫秒执行另一件事,所以我实现了这个:
static void timer_handler(int sig)
{
signal(SIGALRM, SIG_IGN); /* ignore this signal */
printf("timer_handler\n");
signal(SIGALRM, timer_handler); /* reinstall the handler */
}
int test_timer()
{
printf("test_timer\n");
signal(SIGALRM, timer_handler);
ualarm(1, 500000); /* every 500 ms */
return 0;
}
我每 500 毫秒就会在控制台中收到 timer_handler,但这就像它消耗了
select()
中的事件,因为我不再有 Timer Fired!(不再更新 UI)。如果我按下某个键或将鼠标移到 UI 上,我会在控制台中收到Event Received!,并且警报仍在响应。
select()
是否使用了SIGALRM信号?我做错了什么?我只想使用select()
来处理UI和警报以每500毫秒调用一个方法(此方法复用硬件性能计数器)。
SIGALRM
在 EINTR
调用中触发 select(2)
错误。您必须检查系统调用是否返回超时、文件描述符事件或错误(以及哪种错误):
while (!finish) {
int s;
FD_ZERO(&in_fd);
FD_SET(dpy_fd, &in_fd);
s = select(dpy_fd+1, &in_fd, 0, 0, &tv)
if (s > 0) {
printf("Event Received!\n");
XNextEvent(disp->dpy, &e);
/* do something */
} else if (s == 0) {
/* This is probably where we should break the loop or reset the
* select(2) timeout, so... I chose to break it. If you don't
* do something about it you're gonna end up in a busy wait. */
break;
} else {
if (errno == EINTR) {
/* We've been interrupted by another signal, and it might be
* because of the alarm(3) (using the SIGALRM) or any other
* signal we have received externally. */
continue;
}
perror("Select failed");
/* Handle the error properly. */
}
}