一些关于sigsetjmp的错误

Question

我正在阅读APUE，第10章。下面是我的代码。

#include "apue.h" 
#include <unistd.h> 
#include <setjmp.h> 
#include <time.h> 
#include <errno.h> 

static void sig_usr1(int), sig_alrm(int); 
static sigjmp_buf jmpbuf; 
static volatile sig_atomic_t canjmp; 

int 
main(void) 
{ 
    if(signal(SIGUSR1, sig_usr1) == SIG_ERR) 
     err_sys("signal(SIGUSR1) error"); 
    if(signal(SIGALRM, sig_alrm) == SIG_ERR) 
     err_sys("signal(SIGALRM) error"); 
    //print signal. 
    pr_mask("Starting main: "); 
    if(sigsetjmp(jmpbuf, 1)) { 
     pr_mask("End main: "); 
     exit(0); 
    } 
    canjmp = 1; 
    for(;;) 
     pause(); 
} 

static void 
sig_usr1(int signo) 
{ 
    time_t starttime; 

    if(canjmp == 0) { 
     return; 
    } 

    pr_mask("starting sig_usr1: "); 
    alarm(3); 
    starttime = time(NULL); 
    for(;;) 
     if(time(NULL) > starttime + 5) 
      break; 
    pr_mask("finishing sig_usr1: "); 
    canjmp = 0; 
    siglongjmp(jmpbuf, 1); 
} 

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

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

    errno_save = errno;  /* we can be called by signal handlers */ 
    if (sigprocmask(0, NULL, &sigset) < 0) 
     err_sys("sigprocmask error"); 

    printf("%s", str); 
    if (sigismember(&sigset, SIGUSR1)) printf("SIGUSR1 "); 
    if (sigismember(&sigset, SIGALRM)) printf("SIGALRM "); 
    /* remaining signals can go here */ 

    printf("\n"); 
    errno = errno_save; 
} 

我想输出会是这样的：

Starting main: 
starting sig_usr1: SIGUSR1 
in sig_alrm: SIGUSR1 SIGALRM 
finishing sig_usr1: SIGUSR1 
End main: 

但似乎有些不对劲，这是我其实输出：

Starting main: 
starting sig_usr1: 
in sig_alrm: 
finishing sig_usr1: 
End main: 

就是没有信号。请帮帮我。

Answer 1

我觉得麻烦可能是您使用的是signal()而不是sigaction()来设置信号处理。并且signal()不会屏蔽任何其他信号 - 因此没有信号显示为被阻止。我修改了您的代码，如下所示，根据是否有任何参数使用signal()和sigaction()。

#include <signal.h> 
#include <unistd.h> 
#include <setjmp.h> 
#include <time.h> 
#include <errno.h> 
#include <string.h> 
#include <stdio.h> 
#include <stdlib.h> 

typedef void (*Handler)(int); 
static void sig_usr1(int), sig_alrm(int); 
static sigjmp_buf jmpbuf; 
static volatile sig_atomic_t canjmp; 
static void pr_mask(const char *str); 

static void err_sys(const char *str) 
{ 
    int errnum = errno; 
    fprintf(stderr, "%s (%d: %s)\n", str, errnum, strerror(errnum)); 
    exit(1); 
} 

static void set_sigaction(int signum, Handler handler) 
{ 
    struct sigaction nact; 
    nact.sa_handler = handler; 
    sigfillset(&nact.sa_mask); 
    //sigemptyset(&nact.sa_mask); 
    nact.sa_flags = 0; 
    if (sigaction(signum, &nact, 0) != 0) 
     err_sys("Failed to set signal handling"); 
} 

int 
main(int argc, char **argv) 
{ 
    printf("PID = %u\n", (unsigned)getpid()); 
    if (argc > 1) 
    { 
     if (signal(SIGUSR1, sig_usr1) == SIG_ERR) 
      err_sys("signal(SIGUSR1) error"); 
     if (signal(SIGALRM, sig_alrm) == SIG_ERR) 
      err_sys("signal(SIGALRM) error"); 
    } 
    else 
    { 
     set_sigaction(SIGUSR1, sig_usr1); 
     set_sigaction(SIGALRM, sig_alrm); 
    } 
    //print signal. 
    pr_mask("Starting main: "); 
    if (sigsetjmp(jmpbuf, 1)) { 
     pr_mask("End main: "); 
     exit(0); 
    } 
    canjmp = 1; 
    for (;;) 
     pause(); 
} 

static void 
sig_usr1(int signo) 
{ 
    time_t starttime; 

    if (canjmp == 0) { 
     return; 
    } 

    pr_mask("starting sig_usr1: "); 
    alarm(3); 
    starttime = time(NULL); 
    for (;;) 
     if (time(NULL) > starttime + 5) 
      break; 
    pr_mask("finishing sig_usr1: "); 
    canjmp = 0; 
    siglongjmp(jmpbuf, 1); 
} 

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

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

    errno_save = errno;  /* we can be called by signal handlers */ 
    if (sigprocmask(0, NULL, &sigset) < 0) 
     err_sys("sigprocmask error"); 

    printf("%s", str); 
    if (sigismember(&sigset, SIGUSR1)) printf("SIGUSR1 "); 
    if (sigismember(&sigset, SIGALRM)) printf("SIGALRM "); 
    /* remaining signals can go here */ 

    printf("\n"); 
    errno = errno_save; 
} 

运行在Mac OS X 10.7.2与当前的XCode（？4.2），我得到（例如）：

$ ./sigtest 
PID = 11066 
Starting main: 
starting sig_usr1: SIGUSR1 SIGALRM 
finishing sig_usr1: SIGUSR1 SIGALRM 
in sig_arlm: SIGUSR1 SIGALRM 
End main: 
$ ./sigtest 1 
PID = 11067 
Starting main: 
starting sig_usr1: SIGUSR1 
in sig_arlm: SIGUSR1 SIGALRM 
finishing sig_usr1: SIGUSR1 
End main: 
$