Use of sigaction

sigaction Structure definition

struct sigaction
{
    void (*sa_handler)(int);
    void (*sa_sigaction)(int, siginfo_t*, void*);
    sigset_t sa_mask;
    int sa_flags;
};

• sa_handler： Address of the signal processor function , Or constant SIG_IGN、SIG_DFL One of . Only when the sa_handler Is the address of the signal handler , or sa_handler The value is SIG_IGN and SIG_DFL outside , That's right sa_mask and sa_flags Fields are processed .
• sa_sigaction： If set SA_SIGINFO Sign a , Will use sa_sigaction Processing function , Otherwise use sa_handler Processing function .
• sa_mask： Define a set of signals , In the call by sa_handler The defined processor program will block this set of signals , They are not allowed to interrupt the execution of this processor program .
• sa_flags： Bitmask , Specify various options for controlling the signal processing process .
  • SA_NODEFER： When the signal is captured , This signal is not automatically added to the process mask when the processor program is executed .
  • SA_ONSTACK： When a processor function is called for this signal , Used by sigaltstack() Optional stack installed .
  • SA_RESETHAND： When the signal is captured , The signal handling is reset to the default value before calling the processor function ( namely SIG_IGN).
  • SA_SIGINFO： The signal processor program is called with additional parameters , It provides in-depth information about the signal

Use example 1 ( Use sa_handler)

void setupSignalHandlers(void)
{
    struct sigaction act;

    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
    act.sa_handler = sigtermHandler;
    sigaction(SIGTERM, &act, NULL);

    return;
}

static void sigtermHandler(int sig)
{
    // TODO
}

Use example 2 ( Use sa_sigaction)

//  Set up signal processing 
void setupSignalHandlers(void)
{
    struct sigaction act;

    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
    act.sa_sigaction = sigsegvHandler;
    sigaction(SIGSEGV, &act, NULL);

    return;
}

static void sigsegvHandler(int sig, siginfo_t *info, void *secret)
{
    // TODO
}

Processing of fatal signals such as segment errors

When a fatal signal such as a segment error is received , You can capture the signal first , Do something about it , For example, save call stack information , Then send the signal to the process , Make sure the program ends in a normal way , For example, set generation dump Documents, etc. .

struct sigaction act;
// TODO

sigemptyset (&act.sa_mask);
act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
act.sa_handler = SIG_DFL;
sigaction (sig, &act, NULL);
kill(getpid(),sig);

Reference resources

• 《Linux/UNIX System programming manual 》
• https://github.com/antirez/redis/tree/2.2