[C/C++] Unix Signal Handle－我要回家想一想~

註冊 signal 的 handler function        ---> signal(SIGALRM, helloHandler);
2秒後發送一次 SIGALRM signal      ---> alarm(2);
注意！
連續呼叫 alarm
例：
alarm(1);
alarm(2);
alarm(3);
會以最後的數值為主

另外 alarm 不設定 handler 的話
alarm 發生預設處理是結束 process
You should establish a handler for the appropriate alarm signal using signal or sigaction before issuing a call to setitimer or alarm. Otherwise, an unusual chain of events could cause the timer to expire before your program establishes the handler. In this case it would be terminated, since termination is the default action for the alarm signals.
by GNU C Library

Unix Signal Wiki

程式範例：
#include < unistd.h >
#include < signal.h >
#include < stdio.h >
#include < stdlib.h >

static int is_exit = 0;

void terminateHandler(int sig)
{
   is_exit = 1;
   printf("sig = %d\n", sig);
}
void helloHandler()
{
   is_exit = 1;
   printf("helloHandler\n");
}

int main(void) {
    int i;
   // asign alarm signal handler
   signal(SIGALRM, helloHandler);
   // terminate singal handler
   // when console type #>kill alarmT PID(process ID)
   signal(SIGTERM, terminateHandler);

   while(!is_exit){
        if (1){
            alarm(1);
            printf("if 1\n");
            for (i = 0; i < 3; i++){
                printf("sleep %d\n", i);
                sleep(3);
            }
        }
        if (1){
            alarm(1);
            printf("if 2\n");
            sleep(3);
        }
        if (1){
            alarm(1);
            printf("if 3\n");
            sleep(3);
        }
   }
   printf("jump while\n");
   return EXIT_SUCCESS;
}