/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/calls/internal.h"
#include "libc/calls/struct/sigset.h"
#include "libc/errno.h"
#include "libc/sysv/consts/sig.h"

/**
 * Waits for signal.
 *
 * This suspends execution until an unmasked signal is delivered
 * and its callback function has been called. It's a better idea
 * to use sigsuspend() w/ sigprocmask() to avoid race conditions
 *
 * @return should always be -1 w/ EINTR
 * @see sigsuspend()
 */
int pause(void) {
  int rc, olderr;
  sigset_t oldmask;
  olderr = errno;
  if ((rc = sys_pause()) == -1 && errno == ENOSYS) {
    errno = olderr;
    if (sigprocmask(SIG_BLOCK, NULL, &oldmask) == -1) return -1;
    rc = sigsuspend(&oldmask);
  }
  return rc;
}