cosmopolitan/libc/calls/clock_nanosleep.c

/*-*- 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 2022 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/asan.internal.h"
#include "libc/calls/struct/timespec.h"
#include "libc/calls/struct/timespec.internal.h"
#include "libc/calls/struct/timeval.h"
#include "libc/calls/struct/timeval.internal.h"
#include "libc/dce.h"
#include "libc/intrin/describeflags.internal.h"
#include "libc/intrin/strace.internal.h"
#include "libc/sysv/consts/clock.h"
#include "libc/sysv/consts/timer.h"
#include "libc/sysv/errfuns.h"

/**
 * Sleeps for particular amount of time.
 *
 * Here's how you could sleep for one second:
 *
 *     clock_nanosleep(0, 0, &(struct timespec){1}, 0);
 *
 * Your sleep will be interrupted automatically if you do something like
 * press ctrl-c during the wait. That's an `EINTR` error and it lets you
 * immediately react to status changes. This is always the case, even if
 * you're using `SA_RESTART` since this is a `@norestart` system call.
 *
 *     void OnCtrlC(int sig) {} // EINTR only happens after delivery
 *     signal(SIGINT, OnCtrlC); // do delivery rather than kill proc
 *     printf("save me from sleeping forever by pressing ctrl-c\n");
 *     clock_nanosleep(0, 0, &(struct timespec){INT_MAX}, 0);
 *     printf("you're my hero\n");
 *
 * If you want to perform an uninterruptible sleep without having to use
 * sigprocmask() to block all signals then this function provides a good
 * solution to that problem. For example:
 *
 *     struct timespec rel, now, abs;
 *     clock_gettime(CLOCK_REALTIME, &now);
 *     rel = _timespec_frommillis(100);
 *     abs = _timespec_add(now, rel);
 *     while (clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &abs, 0));
 *
 * will accurately spin on `EINTR` errors. That way you're not impeding
 * signal delivery and you're not losing precision on your wait timeout.
 * This function has first-class support on Linux, FreeBSD, and NetBSD;
 * on OpenBSD it's good; on XNU it's bad; and on Windows it's ugly.
 *
 * @param clock should be `CLOCK_REALTIME` and you may consult the docs
 *     of your preferred platforms to see what other clocks might work
 * @param flags can be 0 for relative and `TIMER_ABSTIME` for absolute
 * @param req can be a relative or absolute time, depending on `flags`
 * @param rem will be updated with the unslept time only when `flags`
 *     is zero, otherwise `rem` is ignored; when this call completes,
 *     that means `rem` will be set to `{0, 0}`, and shall only have
 *     something else when -1 is returned with `EINTR`, which means
 *     there was a signal delivery that happened mid-sleep and `rem`
 *     reflects (poorly) how much remaining time was left over, in
 *     case the caller wishes to retry the sleep operation, noting
 *     this isn't recommended since relative timestamps can drift
 * @return 0 on success, or -1 w/ errno
 * @raise EINTR when a signal got delivered while we were waiting
 * @raise ENOTSUP if `clock` is known but we can't use it here
 * @raise EINVAL if `clock` is unknown to current platform
 * @raise EINVAL if `flags` has an unrecognized value
 * @raise EINVAL if `req->tv_nsec ∉ [0,1000000000)`
 * @raise EFAULT if bad memory was passed
 * @raise ENOSYS on bare metal
 * @norestart
 */
int clock_nanosleep(int clock, int flags, const struct timespec *req,
                    struct timespec *rem) {
  int rc;

  if (!req || (IsAsan() && (!__asan_is_valid_timespec(req) ||
                            (rem && !__asan_is_valid_timespec(rem))))) {
    rc = efault();
  } else if (clock == 127 ||              //
             (flags & ~TIMER_ABSTIME) ||  //
             req->tv_sec < 0 ||           //
             !(0 <= req->tv_nsec && req->tv_nsec <= 999999999)) {
    rc = einval();
  } else if (IsLinux() || IsFreebsd() || IsNetbsd()) {
    rc = sys_clock_nanosleep(clock, flags, req, rem);
  } else if (IsXnu()) {
    rc = sys_clock_nanosleep_xnu(clock, flags, req, rem);
  } else if (IsOpenbsd()) {
    rc = sys_clock_nanosleep_openbsd(clock, flags, req, rem);
  } else if (IsMetal()) {
    rc = enosys();
  } else {
    rc = sys_clock_nanosleep_nt(clock, flags, req, rem);
  }

  // Linux Kernel doesn't change the remainder value on success, but
  // some kernels like OpenBSD will. POSIX doesn't specify the Linux
  // behavior. So we polyfill it here.
  if (!rc && !flags && rem) {
    rem->tv_sec = 0;
    rem->tv_nsec = 0;
  }

  STRACE("clock_nanosleep(%s, %s, %s, [%s]) → %d% m", DescribeClockName(clock),
         DescribeSleepFlags(flags), flags, DescribeTimespec(0, req),
         DescribeTimespec(rc, rem), rc);

  return rc;
}