APUE信号-程序汇总

APUE信号-程序汇总

     近期重看APUE，发现对于非常多程序的要领还是没有全然理解。所以梳理下便于查看，并且有非常多值得思考的问题。

程序清单10- 1  捕获 SIGUSR1 和 SIGUSR2的简单程序

#include "util.h"

static void sig_usr(int);

int
main(void){
	if(signal(SIGUSR1,sig_usr) == SIG_ERR)
		err_sys("cannot catch SIGUSR1!");
	if(signal(SIGUSR2,sig_usr) == SIG_ERR)
		err_sys("cannot catch SIGUSR2!");
	for(;;)
		pause();
}

static void sig_usr(int signo){
	if(signo == SIGUSR1)
		printf("received SIGUSR1\n");
	else if(signo == SIGUSR2)
		printf("received SIGUSR2\n");
	else err_dump("received signal %d\n",signo);
}

程序清单10- 2  在信号处理程序中调用不可重入函数

#include "util.h"
#include <pwd.h>

static void
my_alarm(int signo){
    struct passwd*rootptr;
    printf("in signal handler\n");
    if ((rootptr = getpwnam("de15")) == NULL)
        err_sys("getpwnam(de15) error");
    alarm(1);
}

int
main(void){
    struct passwd*ptr;

    signal(SIGALRM, my_alarm);
    alarm(1);
    for ( ; ; ) {
        if ((ptr = getpwnam("vonzhou")) == NULL)
            err_sys("getpwnam error");
        if (strcmp(ptr->pw_name, "vonzhou") != 0)
            printf("return value corrupted!, pw_name = %s\n", ptr->pw_name);
    }
}

程序清单10- 3  SIGCLD处理程序（在Linux下等价于SIGCHLD）

#include"util.h"
#include<sys/wait.h>

static void sig_cld(int);

int
main()
{
        pid_t pid;
        if (signal(SIGCLD, sig_cld) == SIG_ERR)
            perror("signal error");
        if ((pid = fork()) < 0) {
            perror("fork error");
        } else if (pid == 0) {/* child */
            sleep(2);
            _exit(0);
        }

        pause();/* parent */
        exit(0);
}

static void
sig_cld(int signo)/* interrupts pause() */
{
    pid_t    pid;
    int status;

    printf("SIGCLD received\n");
    if (signal(SIGCLD, sig_cld) == SIG_ERR)/* reestablish handler */
        perror("signal error"   );
    if ((pid = wait(&status)) < 0)/* fetch child status */
        perror("wait error");
    printf("pid = %d\n", pid);
}

程序清单10- 4  sleep 的简单而不完整的实现

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

/**存在的问题是。可能在一个繁忙的系统中调用pause之前超时，
 * 直接调用信号处理程序。pause后假设没有捕捉到其它信号，
 * 该程序将永远被挂起
 */
static void
sig_alrm(int signo)
{
        /* nothing to d o, just return to wake up the pause */
}

unsigned int
sleep1(unsigned int nsecs)
{
    if (signal(SIGALRM, sig_alrm) == SIG_ERR)
        return(nsecs);
    alarm(nsecs);/*      start the timer */
    pause();/* next caught signal wakes us up */
    return(alarm(0));/* turn off timer, return unslept time */
}

程序清单10- 5  sleep 的还有一个（不完好）实现

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

static jmp_buf env_alrm;

static void
sig_alrm(int signo)
{
    longjmp(env_alrm, 1);
}

unsigned int
sleep2(unsigned int nsecs)
{
    if (signal(SIGALRM, sig_alrm) == SIG_ERR)
        return(nsecs);
    if(setjmp(env_alrm) == 0){
        alarm(nsecs);/*      start the timer */
        pause();/* next caught signal wakes us up */
    }

    return(alarm(0));/* turn off timer, return unslept time */
}

程序清单10- 6  在一个捕获其它信号的程序中调用sleep2

#include "util.h"

unsigned int sleep2(unsigned int);
static void sig_int(int);

int
main(void)
{
    unsigned int unslept;
    if (signal(SIGINT, sig_int) == SIG_ERR)
        err_sys("signal(SIGINT) error");
    unslept = sleep2(5);
    printf("sleep2 returned: %u\n", unslept);
    exit(0);
}

static void
sig_int(int signo)
{
    int i, j;
    volatile int k;
    /*
     * Tune these loops to run for more than 5 seconds
     * on whatever system this test program is run.
     */
    printf("\nsig_int starting\n");
    for (i = 0; i < 300000; i++)
        for (j = 0; j < 4000; j++)
            k += i * j;
    printf("sig_int finished\n");
}
/*
 vonzhou@de15:~/Coding/apue/signals$ ./a.out
 ^C
 sig_int starting
 sleep2 returned: 0
 vonzhou@de15:~/Coding/apue/signals$
 */

程序清单10- 7  具有超时限制的read调用

#include "util.h"

static void sig_alrm(int);

int
main(void)
{
    int n;
    char line[MAXLINE];
    if (signal(SIGALRM, sig_alrm) == SIG_ERR)
        err_sys("signal(SIGALRM) error");
    alarm(10);
    if ((n = read(STDIN_FILENO, line, MAXLINE)) < 0)
        err_sys("read error");
    alarm(0);
    write(STDOUT_FILENO, line, n);
    exit(0);
}

static void
sig_alrm(int signo)
{
        /* nothing to do, just return to interrupt the read */
}
/*
 vonzhou@de15:~/Coding/apue/signals$ ./a.out
 read error: Interrupted system call (假设长时间不输入，则发现系统调用被中断)
 vonzhou@de15:~/Coding/apue/signals$ ./a.out
 oewutjowerjtlewrt
 oewutjowerjtlewrt
 vonzhou@de15:~/Coding/apue/signals$
*/

程序清单10- 8  使用longjmp。带超时限制，调用read

#include "util.h"
#include <setjmp.h>

static void sig_alrm(int);
static jmp_buf env_alrm;

int
main(void)
{
    int n;
    char line[MAXLINE];
    if (signal(SIGALRM, sig_alrm) == SIG_ERR)
        err_sys("signal(SIGALRM) error");
    if (setjmp(env_alrm) != 0)
        err_quit("read timeout");

    alarm(10);
    if ((n = read(STDIN_FILENO, line, MAXLINE)) < 0)
        err_sys("read error");
    alarm(0);

    write(STDOUT_FILENO, line, n);
    exit(0);
}

static void
sig_alrm(int signo)
{
    longjmp(env_alrm, 1);
}

程序清单10- 9  sigaddset,sigdelset,sigismember的实现（假定信号集合是整型）

#include<signal.h>
#include<errno.h>
/**
 * 如果把 sigset_t 视为整数。各种位操作
 */
/* <signal.h> usually defines NSIG to include signa l number 0 */
#define SIGBAD(signo)((signo) <= 0 || (signo) >= NSIG)

int sigaddset(sigset_t *set, int signo)
{
    if (SIGBAD(signo)) { errno = EINVAL; return(-1); }

    *set |= 1 << (signo - 1);/* turn bit on */
    return(0);
}       

int
sigdelset(sigset_t *set, int signo)
{
    if (SIGBAD(signo)) { errno = EINVAL; return(-1); }
    *set &= ~(1 << (signo - 1));/* turn bit off */
    retur   n(0);
}

int
sigismember(const sigset_t *set, int signo)
{
    if (SIGBAD(signo)) { errno = EINVAL; return(-1); }
    return((*set & (1 << (signo - 1))) != 0);
}

程序清单10-10  为进程打印信号屏蔽字

#include "util.h"
#include<errno.h>

void
pr_mask(const char *str){
	sigset_t sigset;
	int errno_save;

	errno_save = errno;
	if(sigprocmask(0, NULL, &sigset) < 0)
		err_sys("sigpromask failed.");
	printf("%s",str);
	if(sigismember(&sigset, SIGINT))
        printf("SIGINT ");
	if(sigismember(&sigset, SIGQUIT))
        printf("SIGQUIT ");
	if(sigismember(&sigset, SIGUSR1))
        printf("SIGUSR1 ");
	if(sigismember(&sigset, SIGALRM))
        printf("SIGARM ");

	//remaining signals can get here.
	printf("\n");
	errno = errno_save;
}

程序清单10-11  信号设置和 sigpromask 实例

#include "util.h"

static void sig_quit(int);

int
main(void)
{
    sigset_t newmask, oldmask, pendmask;
    if (signal(SIGQUIT, sig_quit) == SIG_ERR)
        err_sys("can't catch SIGQUIT");
    /*
    * Block SIGQUIT and save current signal mask.
    */
    sigemptyset(&newmask);
    sigaddset(&newmask, SIGQUIT);
    if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
        err_sys("SIG_BLOCK error");

    sleep(5);/* SIGQUIT here will remain pending */

    if (sigpending(&pendmask) < 0)
        err_sys("sigpending error");
    if (sigismember(&pendmask, SIGQUIT))
        printf("\nSIGQUIT pending\n");

    /*
    * Reset signal mask which unblocks SIGQUIT.
    */
    if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
        err_sys("SIG_SETMASK error");
    printf("SIGQUIT unblocked\n");

    sleep(5);/* SIGQUIT here will terminate with core file */
    exit(0);
}

static void
sig_quit(int signo)
{
    printf("caught SIGQUIT\n");
    if (signal(SIGQUIT, SIG_DFL) == SIG_ERR)
        err_sys("can't reset SIGQUIT");
}

程序清单10-12  用 sigaction 实现的 signal 函数

#include "util.h"
// Reliable version of signal(),using POSIX sigaction;
Sigfunc *signal(int signo,Sigfunc *func){
	struct sigaction act,oact;

	act.sa_handler = func;
	sigemptyset(&act.sa_mask);
	act.sa_flags = 0;
	if(signo == SIGALRM){
		#ifdef SA_INTERRUPT
			act.sa_flags |= SA_INTERRUPT;
		#endif
	}else{
		#ifdef SA_RESTART
			act.sa_flags |= SA_RESTART;
		#endif
	}
	if(sigaction(signo,&act,&oact)<0)
		return(SIG_ERR);
	return(oact.sa_handler);
}

程序清单10-13  阻止不论什么被中断系统调用重新启动动的的 signal 函数

#include "util.h"

// will stop all the inttrupted signal,that is sigaction's
//default behavior ,so deal with the early aspects;
Sigfunc *
signal_intr(int signo, Sigfunc *func)
{
    struct sigaction    act, oact;
    act.sa_handler = func;
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;

#ifdef SA_INTERRUPT
    act.sa_flags |= SA_INTERRUPT;
#endif
    if (sigaction(signo, &act, &oact) < 0)
        return(SIG_ERR);
    return(oact.sa_handler);
}

程序清单10-14  信号屏蔽字，sigsetjmp。siglongjmp 实例

#include "util.h"
#include<setjmp.h>
#include<time.h>

static void sig_usr(int),sig_alrm(int);
static sigjmp_buf jmpbuf;
static volatile sig_atomic_t canjmp;

int
main(void){
	if(signal(SIGUSR1,sig_usr) == SIG_ERR)
		err_sys("register signal SIGUSR1 error");
	if(signal(SIGALRM,sig_alrm) == SIG_ERR)
		err_sys("register signal SIGALRM error");

	pr_mask("starting main:");

	if(sigsetjmp(jmpbuf,1)){
		pr_mask("ending main:");
		exit(0);
	}

	canjmp = 1;// now sigsetjmp is ok ,can jmp there
	for(;;)
		pause();
}

static void
sig_usr(int signo){
	time_t starttime;
	if(canjmp == 0)
		return;//not prepare well,so ignore it ;
	pr_mask("starting sig_usr:");
	alarm(3); // SIGALRM in 3 sec
	starttime = time(NULL);
	for(;;)
		if(time(NULL) > starttime + 5)
			break;
	pr_mask("ending sig_usr:");

	canjmp = 0;
	siglongjmp(jmpbuf,1);
}

static void
sig_alrm(int signo){
	pr_mask("in sig_alrm:");
}

程序清单10-15  保护临界区不被信号中断

#include "util.h"

static void sig_int(int);

int
main(void)
{
    sigset_t newmask, oldmask, waitmask;
    pr_mask("program start: ");
    if (signal(SIGINT, sig_int) == SIG_ERR)
        err_sys("signal(SIGINT) error");
    sigemptyset(&waitmask);
    sigaddset(&waitmask, SIGUSR1);
    sigemptyset(&newmask);
    sigaddset(&newmask, SIGINT);
    /*
     * Block SIGINT and save current signal mask.
     * */
    if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
        err_sys("SIG_BLOCK error");
    /*
     * Critical region of code.
     */
    pr_mask("in critical region: ");
    /*
     * * Pause, allowing all signals except SIGUSR1.
     */
    if (sigsuspend(&waitmask) != -1)
        err_sys("sigsuspend error");
    pr_mask("after return from sigsuspend: ");
    /*
     * Reset signal mask which unblocks SIGINT.
     */
    if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
        err_sys("SIG_SETMASK error");

    /*
     * And continue processing ...
     */
    pr_mask("program exit: ");

    exit(0);
}

static void
sig_int(int signo)
{
    pr_mask("\nin sig_int: ");
}

程序清单10-16  用sigsuspend等待一个全局变量被设置

#include "util.h"

volatile sig_atomic_t	quitflag;	/* set nonzero by signal handler */

static void
sig_int(int signo)	/* one signal handler for SIGINT and SIGQUIT */
{
	if (signo == SIGINT)
		printf("\ninterrupt\n");
	else if (signo == SIGQUIT)
		quitflag = 1;	/* set flag for main loop */
}

int
main(void)
{
	sigset_t	newmask, oldmask, zeromask;

	if (signal(SIGINT, sig_int) == SIG_ERR)
		err_sys("signal(SIGINT) error");
	if (signal(SIGQUIT, sig_int) == SIG_ERR)
		err_sys("signal(SIGQUIT) error");

	sigemptyset(&zeromask);
	sigemptyset(&newmask);
	sigaddset(&newmask, SIGQUIT);

	/*
	 * Block SIGQUIT and save current signal mask.
	 */
	if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
		err_sys("SIG_BLOCK error");

	while (quitflag == 0)
		sigsuspend(&zeromask);
	// suspend will use zeromask to replace the new mask , this is to say ,
	//here we temporarily change the signal mask, can catch any signal ;
	/*
	 * SIGQUIT has been caught and is now blocked; do whatever.
	 */
	quitflag = 0;

	/*
	 * Reset signal mask which unblocks SIGQUIT.
	 */
	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
		err_sys("SIG_SETMASK error");

	exit(0);
}

程序清单10-17  父子进程能够用来实现同步的例程（TELL_WAIT）

#include "util.h"

static volatile sig_atomic_t sigflag; 	/* set nonzero by sig handler */
static sigset_t newmask, oldmask, zeromask;

static void sig_usr(int signo)	/* one signal handler for SIGUSR1 and SIGUSR2 */
{
	sigflag = 1;
}

void TELL_WAIT(void)
{
	if (signal(SIGUSR1, sig_usr) == SIG_ERR)
		err_sys("signal(SIGUSR1) error");
	if (signal(SIGUSR2, sig_usr) == SIG_ERR)
		err_sys("signal(SIGUSR2) error");
	sigemptyset(&zeromask);
	sigemptyset(&newmask);
	sigaddset(&newmask, SIGUSR1);
	sigaddset(&newmask, SIGUSR2);

	/*
	 * Block SIGUSR1 and SIGUSR2, and save current signal mask.
	 */
	if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
		err_sys("SIG_BLOCK error");
}

void TELL_PARENT(pid_t pid)
{
	kill(pid, SIGUSR2);		/* tell parent we're done */
}

void WAIT_PARENT(void)
{
	while (sigflag == 0)
		sigsuspend(&zeromask);	/* and wait for parent */
	sigflag = 0;

	/*
	 * Reset signal mask to original value.
	 */
	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
		err_sys("SIG_SETMASK error");
}

void TELL_CHILD(pid_t pid)
{
	kill(pid, SIGUSR1);			/* tell child we're done */
}

void WAIT_CHILD(void)
{
	while (sigflag == 0)
		sigsuspend(&zeromask);	/* and wait for child */
	sigflag = 0;

	/*
	 * Reset signal mask to original value.
	 */
	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
		err_sys("SIG_SETMASK error");
}

程序清单10-18  abort 的 POSIX.1 实现

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

void
abort(void)         /* POSIX-style abort() function */
{
    sigset_t            mask;
    struct sigaction action;

    /*
     * * Caller can't ignore SIGABRT, i   f so reset to default.
     * *       */
    sigaction(SIGABRT, NULL, &action);
    if (action.sa_handler == SIG_IGN) {
        action.sa_handler = SIG_DFL;
        sigaction(SIGABRT, &action, NULL);
    }

    if (action.sa_handler == SIG_DFL)
        fflush(NULL);/* flush all open stdio streams */
    /*
     * *   * Caller can't block SIGA          BRT; make sure it's unblocked.
     * *       */
    sigfillset(&mask);
    igdelset(&mask, SIGABRT);/* mask has only SIGABRT turned off */
    sigprocmask(SIG_SETMASK, &mask, NULL);
    kill(getpid(), SIGABRT);/* send the signal */

    /*
     * *   * If we're here, p rocess caught SIGABRT and returned.
     * *       */
    fflush(NULL);/* flush all                open stdio streams */
    action.sa_handler = SIG_DFL;
    sigaction(SIGABRT, &action, NULL);/* reset to default */
    igprocmask(SIG_SETMASK, &mask, NU  LL);/* just in case ... */
    kill(getpid(), SIGABRT);/* and one mor                  e time */
    exit(1);/* this should never be executed ... */
}

程序清单10-19  用 system 调用 ed 编辑器  

#include "util.h"

static void sig_int(int signo){
    printf("Caught SIGINT \n");
}
static void sig_chld(int signo){
    printf("Caught SIGCHLD \n");
}
int main(){
 if(signal(SIGINT, sig_int)  == SIG_ERR)
     err_sys("signal(SIGINT) error");
 if(signal(SIGCHLD, sig_chld) == SIG_ERR)
     err_sys("signal(SIGCHLD) error");

 if(system("/bin/ed") < 0)
     err_sys("system(ed) error");

 exit(0);
}

程序清单10-20  system 函数的 POSIX.1 正确实现

#include<sys/wait.h>
#include<errno.h>
#include<signal.h>
#include<unistd.h>
#include <stdio.h>

int
system(  const char *cmdstring)/* with appropriate signal handling */
{
    pid_t                   pid;
    int status;
    struct sigaction ignore, saveintr, savequit;
    sigset_t chldmask, savemask;
    if (cmdstring == NULL)
        return(1);                  /* always a command processor with UNIX */

    ignore.sa_handler = SIG_IGN;/* ignore SIGINT and SIGQUIT */
    sigemptyset(&ignore.sa_mask);
    ignore.sa_flags = 0;
    if (sigaction(SIGINT, &ignore, &saveintr) < 0)
        return(-1);
    if (sigaction(SIGQUIT, &ignore, &savequit) < 0)
        return(-1);
    sigemptyset(&chldmask);/* now block SIGCHLD */
    sigaddset(&chldmask, SIGCHLD);
    if(sigprocmask(SIG_BLOCK, &chldmask, &savemask) < 0)
        return(-1);

    if ((pid = fork()) < 0) {
        status = -1;/* probably out of processes */
    } else if (pid == 0)     {/* child */
        /* restore previous signal actions & reset signal ma           sk */
        sigaction(SIGINT, &saveintr, NULL);
        sigaction(SIGQUIT, &savequit, NULL);
        sigprocmask(SIG_SETMASK, &savemask, NULL);

        execl("/bin/sh", "sh", "-c", cmdstring, (char *)0);
        _exit(127);/* exec error */
    } else {                                /* parent */
        while (waitpid(pid, &status, 0) < 0)
            if (errno != EINTR) {
                status = -1; /* error other than EINTR from waitpid() */
                break;
            }
    }

    /* restore previous signal actions & reset signal mask */
    if (sigaction(SIGINT, &saveintr, NULL) < 0)
        return(-1);
    if (sigaction(SIGQUIT, &savequit, NULL) < 0)
        return(-1);
    printf("before unblock SIGCHLD...\n");
    if (sigprocmask(SIG_SETMASK, &savemask, NULL) < 0)
        return(-1);

    return(status);
}

程序清单10-21  sleep 的可靠实现

#include "util.h"

static void
sig_alrm(int signo)
{
    /* nothing to do, just returning wakes up sigsuspend() */
}

unsigned int
sleep(unsigned int nsecs)
{
    struct sigaction newact, oldact;
    sigset_t                newmask, oldmask, suspmask;
    unsigned int unslept;

    /* set our handler, save previous information */
    newact.sa_handler = sig_alrm;
    sigemptyset(&newact.sa_mask);
    newact.sa_flags = 0;
    sigaction(SIGALRM, &newact, &oldact);

    /* block SIGALRM and save current signal mask */
    sigemptyset(&newmask);
    sigaddset(&newmask, SIGALRM);
    sigprocmask(SIG_BLOCK, &newmask, &oldmask);

    alarm(nsecs);

    suspmask = oldmask;
    sigdelset(&suspmask, SIGALRM);/* make sure SIGALRM isn't    blocked */
    sigsuspend(&suspmask);/* wait for any signal to be caught */

    /* some signal has been caught, SIGALRM is now blocked */

    unslept = alarm(0);
    sigaction(SIGALRM, &oldact, NULL);/* reset previous action */

    /* reset signal mask, which unblocks SIGALRM  */
        sigprocmask(SIG_SETMASK, &oldmask, NULL);
    return(unslept);
}