IABSD.fr/src/lib/librthread/synch.h

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• Author : kettenis
  Date : 2021-06-13 21:11:54
  Hash : 96f2311e
  Message : Save and restore errno around FUTEX_WAIT futex(2) operations. While there remove the unused _wait() function in librthread such that we don't have to add the save/restore sequence there. Fixed building Python as a race with another thread unlocking a futex(2) would make futex(2) set errno to EAGAIN which would confuse Python in beleiving that readdir(2) failed instead of reaching the end of the directory. Spotted and tested by tb@ ok bluhm@

• lib/librthread/synch.h

• /*	$OpenBSD: synch.h,v 1.8 2021/06/13 21:11:54 kettenis Exp $ */
  /*
   * Copyright (c) 2017 Martin Pieuchot
   *
   * Permission to use, copy, modify, and 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 <sys/atomic.h>
  #include <sys/time.h>
  #include <sys/futex.h>
  
  static inline int
  _wake(volatile uint32_t *p, int n)
  {
  	return futex(p, FUTEX_WAKE, n, NULL, NULL);
  }
  
  static inline int
  _twait(volatile uint32_t *p, int val, clockid_t clockid, const struct timespec *abs)
  {
  	struct timespec rel;
  	int saved_errno = errno;
  	int error;
  
  	if (abs == NULL) {
  		error = futex(p, FUTEX_WAIT, val, NULL, NULL);
  		if (error == -1) {
  			error = errno;
  			errno = saved_errno;
  		}
  		return error;
  	}
  
  	if (abs->tv_nsec >= 1000000000 || clock_gettime(clockid, &rel))
  		return EINVAL;
  
  	rel.tv_sec = abs->tv_sec - rel.tv_sec;
  	if ((rel.tv_nsec = abs->tv_nsec - rel.tv_nsec) < 0) {
  		rel.tv_sec--;
  		rel.tv_nsec += 1000000000;
  	}
  	if (rel.tv_sec < 0)
  		return ETIMEDOUT;
  
  	error = futex(p, FUTEX_WAIT, val, &rel, NULL);
  	if (error == -1) {
  		error = errno;
  		errno = saved_errno;
  	}
  	return error;
  }
  
  static inline int
  _requeue(volatile uint32_t *p, int n, int m, volatile uint32_t *q)
  {
  	return futex(p, FUTEX_REQUEUE, n, (void *)(long)m, q);
  }