linux,在Linux上显式调用SIG"/>
生成.sig linux,在Linux上显式调用SIG
提问
我已阻止,然后通过以下代码等待信号:
sigset_t set;
sigfillset(&set); // all signals
sigprocmask(SIG_SETMASK, &set, NULL); // block all signals
siginfo_t info;
int signum = sigwaitinfo(&set, &info); // wait for next signal
struct sigaction act;
sigaction(signum, NULL, &act); // get the current handler for the signal
act.sa_handler(signum); // invoke it
最后一行生成分段错误,因为处理程序设置为SIG_DFL(定义为0).如果设置为SIG_DFL或SIG_IGN,如何手动调用默认处理程序?另请注意,SIG_IGN定义为1.
最佳答案
正如您所发现的那样,您本身无法调用SIG_DFL和SIG_IGN.但是,您可以或多或少地模仿他们的行为.
简而言之,模仿正常的信号配置将是:
>用户定义的sa_handler非常容易
>对于SIG_IGN来说已经足够了,需要注意的是在CHLD的情况下你需要waitpid()
>直截了当但令人不愉快的SIG_DFL,重新提升让内核发挥其魔力.
这样做你想要的吗?
#include
#include
/* Manually dispose of a signal, mimicking the behavior of current
* signal dispositions as best we can. We won't cause EINTR, for
* instance.
*
* FIXME: save and restore errno around the SIG_DFL logic and
* SIG_IGN/CHLD logic.
*/
void dispatch_signal(const int signo) {
int stop = 0;
sigset_t oset;
struct sigaction curact;
sigaction(signo, NULL, &curact);
/* SIG_IGN => noop or soak up child term/stop signals (for CHLD) */
if (SIG_IGN == curact.sa_handler) {
if (SIGCHLD == signo) {
int status;
while (waitpid(-1, &status, WNOHANG|WUNTRACED) > 0) {;}
}
return;
}
/* user defined => invoke it */
if (SIG_DFL != curact.sa_handler) {
curact.sa_handler(signo);
return;
}
/* SIG_DFL => let kernel handle it (mostly).
*
* We handle noop signals ourselves -- "Ign" and "Cont", which we
* can never intercept while stopped.
*/
if (SIGURG == signo || SIGWINCH == signo || SIGCONT == signo) return;
/* Unblock CONT if this is a "Stop" signal, so that we may later be
* woken up.
*/
stop = (SIGTSTP == signo || SIGTTIN == signo || SIGTTOU == signo);
if (stop) {
sigset_t sig_cont;
sigemptyset(&sig_cont);
sigaddset(&sig_cont, SIGCONT);
sigprocmask(SIG_UNBLOCK, &sig_cont, &oset);
}
/* Re-raise, letting the kernel do the work:
* - Set exit codes and corefiles for "Term" and "Core"
* - Halt us and signal WUNTRACED'ing parents for "Stop"
* - Do the right thing if we forgot to handle any special
* signals or signals yet to be introduced
*/
kill(getpid(), signo);
/* Re-block CONT, if needed */
if (stop) sigprocmask(SIG_SETMASK, &oset, NULL);
}
UPDATE
(回应OP的优秀问题)
1: does this slot in after the sigwaitinfo?
是.就像是:
... block signals ...
signo = sigwaitinfo(&set, &info);
dispatch_signal(signo);
2: Why not raise those signals handled by SIG_IGN, they’ll be ignored anyway
用户空间中的noop比三个系统调用(重新提升,取消屏蔽,重新屏蔽)更有效.此外,CHLD在SIG_IGNored时具有特殊的语义.
3: Why treat SIGCHLD specially?
但是,因为“natural” CHLD signals carry information about
the terminated process(至少是PID,状态和真实的UID)我改变了它.
用户生成的CHLD信号不具有相同的语义,在我的测试中,
IGNoring它们不会导致2.6自动恢复其SIGCHLD的排队僵尸
被“错过了”.所以,我自己做.
4: Why are “stop” related signals unblocking CONT. Will not invoking the default handler for CONT unstop the process?
如果我们停止(不执行)并且CONT被阻止,我们将永远不会收到
发信号唤醒我们!
5: Why not call raise instead of the kill line you’ve given?
个人喜好; raise()也会起作用.
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