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IABSD.fr/src/lib/librthread/rthread_rwlock.c
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- lib/librthread/rthread_rwlock.c
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/* $OpenBSD: rthread_rwlock.c,v 1.13 2019/03/03 18:39:10 visa Exp $ */ /* * Copyright (c) 2019 Martin Pieuchot <mpi@openbsd.org> * Copyright (c) 2012 Philip Guenther <guenther@openbsd.org> * * 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 <stdlib.h> #include <unistd.h> #include <errno.h> #include <pthread.h> #include "rthread.h" #include "synch.h" #define UNLOCKED 0 #define MAXREADER 0x7ffffffe #define WRITER 0x7fffffff #define WAITING 0x80000000 #define COUNT(v) ((v) & WRITER) #define SPIN_COUNT 128 #if defined(__i386__) || defined(__amd64__) #define SPIN_WAIT() asm volatile("pause": : : "memory") #else #define SPIN_WAIT() do { } while (0) #endif static _atomic_lock_t rwlock_init_lock = _SPINLOCK_UNLOCKED; int pthread_rwlock_init(pthread_rwlock_t *lockp, const pthread_rwlockattr_t *attrp __unused) { pthread_rwlock_t rwlock; rwlock = calloc(1, sizeof(*rwlock)); if (!rwlock) return (errno); *lockp = rwlock; return (0); } DEF_STD(pthread_rwlock_init); int pthread_rwlock_destroy(pthread_rwlock_t *lockp) { pthread_rwlock_t rwlock; rwlock = *lockp; if (rwlock) { if (rwlock->value != UNLOCKED) { #define MSG "pthread_rwlock_destroy on rwlock with waiters!\n" write(2, MSG, sizeof(MSG) - 1); #undef MSG return (EBUSY); } free((void *)rwlock); *lockp = NULL; } return (0); } static int _rthread_rwlock_ensure_init(pthread_rwlock_t *rwlockp) { int ret = 0; /* * If the rwlock is statically initialized, perform the dynamic * initialization. */ if (*rwlockp == NULL) { _spinlock(&rwlock_init_lock); if (*rwlockp == NULL) ret = pthread_rwlock_init(rwlockp, NULL); _spinunlock(&rwlock_init_lock); } return (ret); } static int _rthread_rwlock_tryrdlock(pthread_rwlock_t rwlock) { unsigned int val; do { val = rwlock->value; if (COUNT(val) == WRITER) return (EBUSY); if (COUNT(val) == MAXREADER) return (EAGAIN); } while (atomic_cas_uint(&rwlock->value, val, val + 1) != val); membar_enter_after_atomic(); return (0); } static int _rthread_rwlock_timedrdlock(pthread_rwlock_t *rwlockp, int trywait, const struct timespec *abs, int timed) { pthread_t self = pthread_self(); pthread_rwlock_t rwlock; unsigned int val, new; int i, error; if ((error = _rthread_rwlock_ensure_init(rwlockp))) return (error); rwlock = *rwlockp; _rthread_debug(5, "%p: rwlock_%srdlock %p (%u)\n", self, (timed ? "timed" : (trywait ? "try" : "")), (void *)rwlock, rwlock->value); error = _rthread_rwlock_tryrdlock(rwlock); if (error != EBUSY || trywait) return (error); /* Try hard to not enter the kernel. */ for (i = 0; i < SPIN_COUNT; i++) { val = rwlock->value; if (val == UNLOCKED || (val & WAITING)) break; SPIN_WAIT(); } while ((error = _rthread_rwlock_tryrdlock(rwlock)) == EBUSY) { val = rwlock->value; if (val == UNLOCKED || (COUNT(val)) != WRITER) continue; new = val | WAITING; if (atomic_cas_uint(&rwlock->value, val, new) == val) { error = _twait(&rwlock->value, new, CLOCK_REALTIME, abs); } if (error == ETIMEDOUT) break; } return (error); } int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlockp) { return (_rthread_rwlock_timedrdlock(rwlockp, 1, NULL, 0)); } int pthread_rwlock_timedrdlock(pthread_rwlock_t *rwlockp, const struct timespec *abs) { return (_rthread_rwlock_timedrdlock(rwlockp, 0, abs, 1)); } int pthread_rwlock_rdlock(pthread_rwlock_t *rwlockp) { return (_rthread_rwlock_timedrdlock(rwlockp, 0, NULL, 0)); } static int _rthread_rwlock_tryrwlock(pthread_rwlock_t rwlock) { if (atomic_cas_uint(&rwlock->value, UNLOCKED, WRITER) != UNLOCKED) return (EBUSY); membar_enter_after_atomic(); return (0); } static int _rthread_rwlock_timedwrlock(pthread_rwlock_t *rwlockp, int trywait, const struct timespec *abs, int timed) { pthread_t self = pthread_self(); pthread_rwlock_t rwlock; unsigned int val, new; int i, error; if ((error = _rthread_rwlock_ensure_init(rwlockp))) return (error); rwlock = *rwlockp; _rthread_debug(5, "%p: rwlock_%swrlock %p (%u)\n", self, (timed ? "timed" : (trywait ? "try" : "")), (void *)rwlock, rwlock->value); error = _rthread_rwlock_tryrwlock(rwlock); if (error != EBUSY || trywait) return (error); /* Try hard to not enter the kernel. */ for (i = 0; i < SPIN_COUNT; i++) { val = rwlock->value; if (val == UNLOCKED || (val & WAITING)) break; SPIN_WAIT(); } while ((error = _rthread_rwlock_tryrwlock(rwlock)) == EBUSY) { val = rwlock->value; if (val == UNLOCKED) continue; new = val | WAITING; if (atomic_cas_uint(&rwlock->value, val, new) == val) { error = _twait(&rwlock->value, new, CLOCK_REALTIME, abs); } if (error == ETIMEDOUT) break; } return (error); } int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlockp) { return (_rthread_rwlock_timedwrlock(rwlockp, 1, NULL, 0)); } int pthread_rwlock_timedwrlock(pthread_rwlock_t *rwlockp, const struct timespec *abs) { return (_rthread_rwlock_timedwrlock(rwlockp, 0, abs, 1)); } int pthread_rwlock_wrlock(pthread_rwlock_t *rwlockp) { return (_rthread_rwlock_timedwrlock(rwlockp, 0, NULL, 0)); } int pthread_rwlock_unlock(pthread_rwlock_t *rwlockp) { pthread_t self = pthread_self(); pthread_rwlock_t rwlock; unsigned int val, new; rwlock = *rwlockp; _rthread_debug(5, "%p: rwlock_unlock %p\n", self, (void *)rwlock); membar_exit_before_atomic(); do { val = rwlock->value; if (COUNT(val) == WRITER || COUNT(val) == 1) new = UNLOCKED; else new = val - 1; } while (atomic_cas_uint(&rwlock->value, val, new) != val); if (new == UNLOCKED && (val & WAITING)) _wake(&rwlock->value, INT_MAX); return (0); }