使用sigaction实现ctr

Question

我试图使用sigaction来忽略ctrl。当我按下ctrl，^Cctrl而不是^C，它不会立即打印下一个提示符。只有在我点击输入之前，它才开始打印提示符。如下所示：

> // run the program sigAction
$./sigAction
sigAction>^Cctrl-C
// it is waiting,waiting . Nothing happens until I hit Enter, next prompt comes up.

sigAction>

我正在寻找的结果是，当我点击ctrl而没有按回车时，下一个提示应该立即出现。问题如下：

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <signal.h>
  4 #include <string.h>
  5 // implement ignoring ctrl-C
  6 void sigIntHandler(int signum) {
  7     fprintf(stderr, "ctrl-C\n" );
  8   
  9 }
 10
 11 main()
 12 {
 13
 14     struct sigaction signalAction;
 15     signalAction.sa_handler = sigIntHandler;
 16     sigemptyset(&signalAction.sa_mask);
 17     signalAction.sa_flags = SA_RESTART;
 18     sigaction(SIGINT, &signalAction, NULL);
 19     while(1) {
 20
 21         char block[4096];
 22
 23         printf("sigAction>");
 24         fflush(stdout);
 25
 26         fgets(block, 4096, stdin);
 27        
 28         if (!strcmp(block, "exit\n")) {
 29            exit(1);
 30         }
 31     } 
 32 }       

当我使用gdb查看内部时，它提供了以下信息：

  (gdb) n
Single stepping until exit from function main,
which has no line number information.
sigAction>^C
Program received signal SIGINT, Interrupt.
0x00007ffff7b15d10 in __read_nocancel () from /lib64/libc.so.6
(gdb) n
Single stepping until exit from function __read_nocancel,
which has no line number information

任何想法都有帮助！提前感谢！

Answer 1

正如我在评论中指出的那样，您并不真正想使用SA_RESTART。这意味着当read()收到一个中断时，在中断后继续读取，这就排除了主程序打印新提示符的机会。

这段代码很可能接近您想要的内容：

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static void sigIntHandler(int signum)
{
    fprintf(stderr, "Ctrl-C (%d)\n", signum);
}

int main(void)
{
    struct sigaction signalAction;
    signalAction.sa_handler = sigIntHandler;
    sigemptyset(&signalAction.sa_mask);
    signalAction.sa_flags = 0;      // SA_RESTART;
    sigaction(SIGINT, &signalAction, NULL);

    while (1)
    {
        char block[4096];

        printf("sigAction>");
        fflush(stdout);

        if (fgets(block, 4096, stdin) == 0)
        {
            if (errno == EINTR)
            {
                errno = 0;
                clearerr(stdin);
                fprintf(stderr, "Interrupted!\n");
                continue;
            }
            else
            {
                fprintf(stderr, "EOF spotted\n");
                break;
            }
        }

        if (!strcmp(block, "exit\n"))
        {
            fprintf(stderr, "Exiting\n");
            exit(1);
        }
        printf("Read: [%.*s]\n", (int)(strlen(block) - 1), block);
    }
}

注意，在官方上，您不应该在信号处理程序中使用printf()系列函数--参见 in a signal handler?

示例运行(名为sigact的程序)：

$ ./sigact
sigAction>Ordinary input
Read: [Ordinary input]
sigAction>Some typing, then an interrupt! ^CCtrl-C (2)
Interrupted!
sigAction>More input?
Read: [More input?]
sigAction>Yes, more input.
Read: [Yes, more input.]
sigAction>And why you type control-D?
Read: [And why you type control-D?]
sigAction>EOF spotted
$ ./sigact
sigAction>Also typing exit works, of course.
Read: [Also typing exit works, of course.]
sigAction>exit
Exiting
$

^C来自终端驱动程序(在MacOSX10.11.6上)。echoctl在lflags的第一行末尾执行以下操作：

$ stty -a
speed 9600 baud; 50 rows; 141 columns;
lflags: icanon isig iexten echo echoe -echok echoke -echonl echoctl
    -echoprt -altwerase -noflsh -tostop -flusho pendin -nokerninfo
    -extproc
iflags: -istrip icrnl -inlcr -igncr ixon -ixoff ixany imaxbel iutf8
    -ignbrk brkint -inpck -ignpar -parmrk
oflags: opost onlcr -oxtabs -onocr -onlret
cflags: cread cs8 -parenb -parodd hupcl -clocal -cstopb -crtscts -dsrflow
    -dtrflow -mdmbuf
cchars: discard = ^O; dsusp = ^Y; eof = ^D; eol = <undef>;
    eol2 = <undef>; erase = ^?; intr = ^C; kill = ^X; lnext = ^V;
    min = 1; quit = ^\; reprint = ^R; start = ^Q; status = ^T;
    stop = ^S; susp = ^Z; time = 0; werase = ^W;
$

Answer 2

如果您想忽略，那么使用SIG_IGN作为操作，如果不是，则不是忽略而是捕捉。

当您使用SA_RESTART时，中断的系统调用将是restard而不是中断。然后，fgets可能会在某些内部系统调用中被阻塞，然后指定重新启动它。我不记得fgets在被中断时的行为，但是它可能会返回一个NULL值。您还可以使用read和控制errno来实现EINTR。