sigaction函数

sigaction函数是设置信号处理的接口。比signal函数更健壮

       #include <signal.h>

       int sigaction(int signum, const struct sigaction *act,
                     struct sigaction *oldact);

signum指除了SIGKILL 和 SIGSTOP之外，要捕获的信号。struct sigaction *act是要安装的信号。结构题定义为：

/* Structure describing the action to be taken when a signal arrives.  */
struct sigaction
  {
    /* Signal handler.  */
#if defined __USE_POSIX199309 || defined __USE_XOPEN_EXTENDED
    union
      {
    /* Used if SA_SIGINFO is not set.  */
    __sighandler_t sa_handler;
    /* Used if SA_SIGINFO is set.  */
    void (*sa_sigaction) (int, siginfo_t *, void *);
      }
    __sigaction_handler;
# define sa_handler __sigaction_handler.sa_handler
# define sa_sigaction   __sigaction_handler.sa_sigaction
#else
    __sighandler_t sa_handler;
#endif

    /* Additional set of signals to be blocked.  */
    __sigset_t sa_mask;

    /* Special flags.  */
    int sa_flags;

    /* Restore handler.  */
    void (*sa_restorer) (void);
  };　　

其中，sa_handler为信号的处理函数。sa_mask设置在进程原有信号掩码基础上增加信号掩码，来过滤信号，指定哪些信号不能发送给本进程。sa_mask是信号集sigset_t类型，定义在x86_64-linux-gnu/bits/types/__sigset_t.h文件：

#define _SIGSET_NWORDS (1024 / (8 * sizeof (unsigned long int)))
typedef struct
{
  unsigned long int __val[_SIGSET_NWORDS];
} __sigset_t;

sa_flags用来设置程序收到信号时的行为，和struct sigaction一样，在x86_64-linux-gnu/bits/sigaction.h文件中定义

关于信号集sigset_t类型，signal.h文件中定义了一些函数来操作信号集，包括：

       #include <signal.h>

       int sigemptyset(sigset_t *set);

       int sigfillset(sigset_t *set);

       int sigaddset(sigset_t *set, int signum);

       int sigdelset(sigset_t *set, int signum);

       int sigismember(const sigset_t *set, int signum);

　　

拿来《linux高性能服务器编程》中的捕捉信号函数：

void addsig(int sig, void (*sig_handler)(int))
{
    struct sigaction sa;
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = sig_handler;
    sa.sa_flags |= SA_RESTART;
    sigfillset(&sa.sa_mask);
    assert(sigaction(sig, &sa, NULL) != -1);
}