Signal handler and longjmp question

Hi, all
    I read from some book that a signal handler can either return or call exit, abort or longjmp, it is permitted by ANSI C.
    However, I remember that lonjmp never returns, which in turn causes the signal handler can not return. In that case, the kernel will think the program is in signal handler forever, am I right? 
    IMHO, I think that is too bad...

Leo

--------------------------------------
code sample:

jmp_buf buf;
static void signal_handler(int signo)
{
    longjmp(buf);
}
int main()
{
  signal(SIGUSR1, signal_handler);
  ...
  setjmp(buf);
  ...
  return 0;
}

Suppose the program received SIGUSR1 after setjmp has been called, is the program still in signal handle context after longjmp?


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