mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-02-07 15:03:34 +00:00
2d43d400c6
Cosmo now has a non-nsync implementation of POSIX read-write locks. It's possible to call pthread_rwlockattr_setpshared in PTHREAD_PROCESS_SHARED mode. Furthermore, if cosmo is built with PTHREAD_USE_NSYNC set to zero, then Cosmo shouldn't use nsync at all. That's helpful if you want to not link any Apache 2.0 licensed code.
55 lines
2.8 KiB
C
55 lines
2.8 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
|
|
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
|
|
╞══════════════════════════════════════════════════════════════════════════════╡
|
|
│ Copyright 2023 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/errno.h"
|
|
#include "libc/intrin/atomic.h"
|
|
#include "libc/thread/thread.h"
|
|
#include "third_party/nsync/mu.h"
|
|
|
|
/**
|
|
* Attempts acquiring read lock on read-write lock.
|
|
*
|
|
* @return 0 if lock was acquired, otherwise an errno
|
|
* @raise EBUSY if lock is currently held in write mode
|
|
* @raise EAGAIN if maximum number of read locks are held
|
|
* @raise EINVAL if `rwlock` doesn't refer to an initialized r/w lock
|
|
*/
|
|
errno_t pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock) {
|
|
|
|
#if PTHREAD_USE_NSYNC
|
|
// use nsync if possible
|
|
if (!rwlock->_pshared) {
|
|
if (nsync_mu_rtrylock((nsync_mu *)rwlock->_nsync)) {
|
|
return 0;
|
|
} else {
|
|
return EBUSY;
|
|
}
|
|
}
|
|
#endif
|
|
|
|
// naive implementation
|
|
uint32_t word = 0;
|
|
for (;;) {
|
|
if (word & 1)
|
|
return EBUSY;
|
|
if (atomic_compare_exchange_weak_explicit(&rwlock->_word, &word, word + 2,
|
|
memory_order_acquire,
|
|
memory_order_relaxed))
|
|
return 0;
|
|
}
|
|
}
|