得到“用户信号1”以终止我的进程，在C中为UNIX

Question

void printToScreen(){
    write(1, boardString, strlen(boardString)) == -1 ? writeError() : 1;
    write(1, "\n", 1) == -1 ? writeError() : 1;

    int i = 0;
    char * pch;
    pch = strtok (boardString, ",");
    int len = strlen(pch);
    int count=0;
    // insert the number and pads it with zeros, '|' and spaces
    while (pch != NULL){
        printf("\niteration %d\n", count++);

        switch(len){
        case 1:
            if(*pch == '0'){
                write(1, "|      ", 7) == -1 ? writeError() : 1;
                break;
            }
            write(1, "| 000", 5) == -1 ? writeError() : 1;
            write(1, pch, 1) == -1 ? writeError() : 1;
            write(1, " ", 1) == -1 ? writeError() : 1;      
            break;
        case 2:
            write(1, "| 00", 4) == -1 ? writeError() : 1;
            write(1, pch, 2) == -1 ? writeError() : 1;
            write(1, " ", 1) == -1 ? writeError() : 1;  
            break;          
        case 3:
            write(1, "| 0", 3) == -1 ? writeError() : 1;
            write(1, pch, 3) == -1 ? writeError() : 1;
            write(1, " ", 1) == -1 ? writeError() : 1;  
            break;              
        case 4:
            write(1, "| ", 2) == -1 ? writeError() : 1;
            write(1, pch, 3) == -1 ? writeError() : 1;
            write(1, " ", 1) == -1 ? writeError() : 1;  
            break;
        default:
            break;
        }

        // update pch, len
        pch = strtok (NULL, ",");
        len = strlen(pch);
        i++;    
        // move to next line
        if (i % 4 == 0)
            write(1, "|\n", 2) == -1 ? writeError() : 1;    
    }
}

    void sig_hand(int sig){
    printf("got signal\n");
    read(STDIN, boardString, STRING_SIZE) == -1 ? readError() : 1;
    printToScreen();
}

I have this signal handler that handles SIGUSR1 signals.
boardString is an array of 16 ints in string format, with ',' as delimiters.
The printToScreen() just prints it in a 4X4 matrix format
I have a second process that sends SIGUSR1 to this process after each update in the boardString.
My problem is that the printToScreen function doesn't end. it prints the first iteration just fine and then I get this msg "User signal 1" and that's when my program terminates.
I can't understand why it terminates and what "User signal 1" means.

Answer 1

From the description, it sounds like you're setting up the signal handler as a single-use handler (so it is called the first time the signal is received, and is then reset to the default action, which is to kill the process; the shell will then generally print the "User signal 1" message).

How are you setting the signal handler? If you are using signal and are using a SysV-derived unix variant, the default will be single use. Use sigaction instead, and make sure the SA_RESETHAND flags is not set.

Answer 2

to start, there are other error return codes besides -1
and write() normally returns the number of chars written
and "\n" can be (depending on OS) more than one char
so the first two lines would be better written as:

(write(1, boardString, strlen(boardString)) < 0) ? writeError() : strlen(boardString);
(write(1, "\n", sizeof("\n") ) < 0) ? writeError() : sizeof("\n");

The follow is an example for handling a signal (note: kill and stop cannot be handled)
caveat: I have not run the following, so it may have keypunch errors.

#include<stdio.h>
#include<signal.h>
#include<unistd.h>

// handle the signal
void sig_handler(int signo)
{
    if (signo == SIGUSR1)  printToScreen();
}

// register the signal handler
typedef void sigfunc(int)

sigfunc* = signal(SIGUSR1, (sigfunc*)sig_handler(int));