为什么我在采取行动之前执行了sigemptyset，但是有时SIGALRM被阻止了

Question

I had executed 'sigemptyset' before 'sigaction', but the SIGALRM is blocked.

But if I execute 'sigprocmask' to unblock SIGALRM, the SIGALRM is not blocked.

the part of codes as follow:

struct sigaction sa;
memset( & sa, 0, sizeof(sa));
sa.sa_handler = sigpipe_handler;
if (sigemptyset( & sa.sa_mask) < 0) {
  printf("sigemptyset fail! errno=%d, error info<%s>.\n", errno, strerror(errno));
}#
ifdef SA_INTERRUPT sa.sa_flags |= SA_INTERRUPT;#
endif
if (sigaction(signum, & sa, NULL) < 0) {
  printf("sigaction fail! errno=%d, error info<%s>.\n", errno, strerror(errno));
}–

Answer 1

似乎SIGALRM默认被屏蔽了？