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/*
* Copyright (c) 2017 Richard Braun.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef KERN_RTMUTEX_I_H
#define KERN_RTMUTEX_I_H
#include <assert.h>
#include <stdbool.h>
#include <stdint.h>
#include <kern/atomic.h>
#include <kern/rtmutex_types.h>
#include <kern/thread.h>
/*
* Real-time mutex flags.
*
* The "contended" flag indicates that threads are waiting for the mutex
* to be unlocked. It forces threads trying to lock the mutex as well as
* the owner to take the slow path.
*
* The "force-wait" flag prevents "stealing" a mutex. When a contended
* mutex is unlocked, a thread may concurrently try to lock it. Without
* this flag, it may succeed, and in doing so, it would prevent a
* potentially higher priority thread from locking the mutex. The flag
* forces all threads to not only take the slow path, but to also call
* the turnstile wait function so that only the highest priority thread
* may lock the mutex.
*/
#define RTMUTEX_CONTENDED ((uintptr_t)0x1)
#define RTMUTEX_FORCE_WAIT ((uintptr_t)0x2)
#define RTMUTEX_OWNER_MASK (~((uintptr_t)(RTMUTEX_FORCE_WAIT \
| RTMUTEX_CONTENDED)))
#define rtmutex_assert_owner_aligned(owner) \
assert(((owner) & ~RTMUTEX_OWNER_MASK) == 0)
static inline uintptr_t
rtmutex_lock_fast(struct rtmutex *rtmutex)
{
uintptr_t owner;
owner = (uintptr_t)thread_self();
rtmutex_assert_owner_aligned(owner);
return atomic_cas(&rtmutex->owner, 0, owner, ATOMIC_ACQUIRE);
}
static inline uintptr_t
rtmutex_unlock_fast(struct rtmutex *rtmutex)
{
uintptr_t owner, prev_owner;
owner = (uintptr_t)thread_self();
rtmutex_assert_owner_aligned(owner);
prev_owner = atomic_cas(&rtmutex->owner, owner, 0, ATOMIC_RELEASE);
assert((prev_owner & RTMUTEX_OWNER_MASK) == owner);
return prev_owner;
}
void rtmutex_lock_slow(struct rtmutex *rtmutex);
int rtmutex_timedlock_slow(struct rtmutex *rtmutex, uint64_t ticks);
void rtmutex_unlock_slow(struct rtmutex *rtmutex);
#endif /* KERN_RTMUTEX_I_H */
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