C语言 pause() 是如何工作的？
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How does pause() work?
提问by Luis Quesado
I'm completely noob in c. I have to write a function mypause()that should have a functionality similar to the pause()system call, and test the mypause()function in a program that repeatedly blocks waiting for a signal.
How does te pause()function works?? Can't I just do a mypause()like this:
我完全是 c 的菜鸟。我必须编写一个函数mypause()，该函数应该具有类似于pause()系统调用的mypause()功能，并在重复阻塞等待信号的程序中测试该函数。tepause()函数是如何工作的？？我不能这样做mypause()：
fprintf( stderr, "press any key to continue\n" );
in order for the program to block and wait for an signal?
为了让程序阻塞并等待信号？
Have in mind that I can't ever use pause()or sigpause().
请记住，我永远不能使用pause()或sigpause()。
采纳答案by Halim Qarroum
The pause()function blocks until a signal arrives. User inputs are not signals. A signal can be emitted by another process or the system itself.
该pause()功能会阻塞，直到信号到达。用户输入不是信号。信号可以由另一个进程或系统本身发出。
Pressing Ctrl-Cfor instance, causes your shell to send a SIGINTsignal to the current running process, which in normalcases causes the process to be killed.
Ctrl-C例如，按下会使您的 shell 向SIGINT当前正在运行的进程发送信号，这在正常情况下会导致该进程被终止。
In order to emulate the behaviour of pausein ISO C99 you could write something like the following. The code is commented, if you have a question about this implementation, please ask.
为了模拟pauseISO C99 中的行为，您可以编写如下内容。代码已注释，如果您对此实现有疑问，请提问。
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
/**
* The type sig_atomic_t is used in C99 to guarantee
* that a variable can be accessed/modified in an atomic way
* in the case an interruption (reception of a signal for example) happens.
*/
static volatile sig_atomic_t done_waiting = 0;
static void handler()
{
printf("Signal caught\n");
done_waiting = 1;
}
void my_pause()
{
/**
* In ISO C, the signal system call is used
* to call a specific handler when a specified
* signal is received by the current process.
* In POSIX.1, it is encouraged to use the sigaction APIs.
**/
signal(SIGINT, handler);
done_waiting = 0;
while ( !done_waiting )
;
}
int main()
{
my_pause();
printf("Hey ! The first call to my_pause returned !\n");
my_pause();
printf("The second call to my_pause returned !\n");
return (0);
}
Note this example only works with the SIGINTsignal. To handle an additional set of signals, you can use other calls to signal()with different signal numbers or use sigaction()with a mask referencing all the desired signals.
请注意，此示例仅适用于SIGINT信号。要处理一组额外的信号，您可以使用signal()具有不同信号编号的其他调用，或sigaction()与引用所有所需信号的掩码一起使用。
A complete list of the signals availables on your system can be found in you <signal.h>include.
您可以在<signal.h>包含中找到系统上可用信号的完整列表。
