如果我使用 scanf 程序終止

Question

我正在嘗試在代碼中實現計時器，我發現的所有示例都使用while(1)或for(;;)但是當我嘗試使用scanf時，我的程序終止了。 它是否在stdin上獲得任何值，因為如果我使用scanf兩次，那么在退出程序之前會調用兩次計時器。 這是我的示例代碼：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <netinet/in.h>
#include <signal.h>
#include <time.h>

#include <linux/socket.h>
#include <time.h>


#define SIGTIMER (SIGRTMAX)
#define SIG SIGUSR1
static timer_t     tid;
static timer_t     tid2;

void SignalHandler(int, siginfo_t*, void* );
timer_t SetTimer(int, int);

int main(int argc, char *argv[]) {

    int t;

    printf("SIGRTMAX %d\n", SIGRTMAX);
        printf("SIGRTMIN %d\n", SIGRTMIN);

    struct sigaction sigact;
    sigemptyset(&sigact.sa_mask);
    sigact.sa_flags = SA_SIGINFO;
    sigact.sa_sigaction = SignalHandler;
    // set up sigaction to catch signal
    if (sigaction(SIGTIMER, &sigact, NULL) == -1) {
        perror("sigaction failed");
        exit( EXIT_FAILURE );
    }

    // Establish a handler to catch CTRL+c and use it for exiting.
    sigaction(SIGINT, &sigact, NULL);
    tid=SetTimer(SIGTIMER, 1000);

    struct sigaction sa;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_SIGINFO;
    sa.sa_sigaction = SignalHandler;
    // set up sigaction to catch signal
    if (sigaction(SIG, &sa, NULL) == -1) {
        perror("sa failed");
        exit( EXIT_FAILURE );
    }

    // Establish a handler to catch CTRL+c and use it for exiting.
    sigaction(SIGINT, &sa, NULL);
    tid2=SetTimer(SIG, 1000);

   // for(;;);  or while(1) Working properly

    scanf("%d", &t); /// Program terminates
    return 0;
}

void SignalHandler(int signo, siginfo_t* info, void* context)
{


    if (signo == SIGTIMER) {
        printf("Command Caller has ticked\n");

    }else if (signo == SIG) {
        printf("Data Caller has ticked\n");

    } else if (signo == SIGINT) {
        timer_delete(tid);
        perror("Crtl+c cached!");
        exit(1);  // exit if CRTL/C is issued
    }
}
timer_t SetTimer(int signo, int sec)
{
    static struct sigevent sigev;
    static timer_t tid;
    static struct itimerspec itval;
    static struct itimerspec oitval;

    // Create the POSIX timer to generate signo
    sigev.sigev_notify = SIGEV_SIGNAL;
    sigev.sigev_signo = signo;
    sigev.sigev_value.sival_ptr = &tid;

    if (timer_create(CLOCK_REALTIME, &sigev, &tid) == 0)
    {

        itval.it_value.tv_sec = sec / 1000;
        itval.it_value.tv_nsec = (long)(sec % 1000) * (1000000L);
        itval.it_interval.tv_sec = itval.it_value.tv_sec;
        itval.it_interval.tv_nsec = itval.it_value.tv_nsec;



        if (timer_settime(tid, 0, &itval, &oitval) != 0)
        {
            perror("time_settime error!");
        }
    }
    else
    {
        perror("timer_create error!");
        return NULL;
    }
    return tid;
}

那么，我該如何解決這個問題呢？ 任何幫助，將不勝感激。 謝謝，尤維

Answer 1

信號中斷 scanf。 如果在 scanf output 之后添加perror('scanf')將是：

SIGRTMAX 64
SIGRTMIN 34
Command Caller has ticked
Data Caller has ticked
scanf: Interrupted system call

如果將scanf替換為：

do {
    errno = 0;
    scanf("%d", &t);
} while(errno == EINTR);

當 scanf 因Interrupted system call而失敗時將重試。

Answer 2

您絕對不能在信號處理程序中使用printf和perror 。 它們不可重入。

此外，如果您的程序在其中接收到信號，則scanf可能會返回錯誤。 如果scanf返回 EOF，請檢查errno ，它可能是EINTR 。