ch6信号学习笔记

知识点归纳

Unix/Linux支持31种不同的信号，每种信号在signal.h文件中都有定义。

#define  	SIGHUP  	1
#define  	SIGINT  	2
#define  	SIGQUIT  	3
#define  	SIGILL  	4
#define  	SIGTRAP  	5
#define  	SIGABRT  	6
#define  	SIGIOT  	6
#define  	SIGBUS  	7
#define  	SIGFPE  	8
#define  	SIGKILL  	9
#define  	SIGUSR1  	10
#define  	SIGSEGV  	11
#define  	SIGUSR2  	12
#define  	SIGPIPE  	13
#define  	SIGALRM  	14
#define  	SIGTERM	        15
#define  	SIGSTKFLT	16
#define  	SIGCHLD    	17
#define  	SIGCONT	        18
#define  	SIGSTOP      	19
#define  	SIGTSTP	        20
#dpfine  	STGTTTN	        21
#define  	SIGTTOU	        22
#define  	SIGURG	        23
#define  	SIGXCPU	        24
#define  	SIGXFSZ    	25
#define  	SIGVTALRM	26
#define  	SIGPROF  	27
#define  	SIGWINCH	28
#define  	SIGPOLL  	29
#define  	SIGPWR	        30
#define  	SIGSYS	        31

问题与解决思路

实践内容

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <setjmp.h>
#include <string.h>
jmp_buf env;
int count = 0;
void handler(int sig, siginfo_t *siginfo, void *context)
{
    printf("handler: sig=%d from PID=%d UID=%d count=%d
",
           sig, siginfo->si_pid, siginfo->si_uid, ++count);
    if (count >= 4) // let it occur up to 4 times
        longjmp(env, 1234);
}
int BAD()
{
    int *ip = 0;
    printf("in BAD(): try to dereference NULL pointer
");
    *ip = 123; // dereference a NULL pointer
    printf("should not see this line
");
}
int main(int argc, char *argv[])
{
    int r;
    struct sigaction act;
    memset(&act, 0, sizeof(act));
    act.sa_sigaction = &handler;
    act.sa_flags = SA_SIGINFO;
    sigaction(SIGSEGV, &act, NULL);
    if ((r = setjmp(env)) == 0)
        BAD();
    else
        printf("proc %d survived SEGMENTATION FAULT: r=%d
", getpid(), r);

    printf("proc %d looping
", getpid());
    while (1)
        ;
}

  1 #include <stdio.h>
  2 #include <signal.h>
  3 #include <fcntl.h>
  4 #include <string.h>
  5 #include <unistd.h>
  6 
  7 #define LEN 64
  8 int ppipe[2]; // pipe descriptors
  9 int pid; // child pid
 10 char line[LEN];
 11 
 12 int parent()
 13 {
 14     printf("parent %d running
", getpid());
 15     close(ppipe[0]); // parent = pipe writer
 16     while(1){
 17         printf("parent %d: input a line : 
", getpid());
 18         fgets(line, LEN, stdin);
 19         line[strlen(line)-1] = 0; // kill 
 at end
 20         printf("parent %d write to pipe
", getpid());
 21         write(ppipe[1], line, LEN); // write to pipe
 22         printf("parent %d send signal 10 to %d
", getpid(), pid);
 23         kill(pid, SIGUSR1); // send signal to child process
 24     } }
 25 void chandler(int sig)
 26 {
 27     printf("
child %d got an interrupt sig=%d
", getpid(), sig);
 28     read(ppipe[0], line, LEN); // read pipe
 29     printf("child %d get a message = %s
", getpid(), line);
 30 }
 31 int child()
 32 {
 33     char msg[LEN];
 34     int parent = getppid();
 35     printf("child %d running
", getpid());
 36     close(ppipe[1]); // child is pipe reader
 37     signal(SIGUSR1, chandler); // install signal catcher
 38     while(1);
 39 }
 40 int main()
 41 {
 42     pipe(ppipe); // create a pipe
 43     pid = fork(); // fork a child process
 44     if (pid) // parent
 45       parent();
 46     else
 47       child();
 48 }