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/*
* Copyright (c) 2012 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/>.
*
*
* Spin lock.
*
* This implementation relies on the availability of hardware compare-and-swap
* support. In addition, spin locks are reserved for the special cases where
* a critical section must work in every context (thread, interrupt, or even
* during early boot). As a result, interrupts are disabled when a spin lock
* is acquired.
*/
#ifndef _KERN_SPINLOCK_H
#define _KERN_SPINLOCK_H
#include <machine/atomic.h>
#include <machine/cpu.h>
struct spinlock {
unsigned long locked;
};
/*
* Static spin lock initializer.
*/
#define SPINLOCK_INITIALIZER { 0 }
/*
* Initialize a spin lock.
*/
static inline void
spinlock_init(struct spinlock *lock)
{
lock->locked = 0;
}
/*
* Attempt to acquire a spin lock.
*
* Return false if acquired, true if busy.
*/
static inline int
spinlock_trylock(struct spinlock *lock, unsigned long *flagsp)
{
unsigned long flags, locked;
flags = cpu_intr_save();
locked = atomic_cas(&lock->locked, 0, 1);
if (locked)
cpu_intr_restore(flags);
else
*flagsp = flags;
return locked;
}
/*
* Acquire a spin lock.
*/
static inline unsigned long
spinlock_lock(struct spinlock *lock)
{
unsigned long flags;
flags = cpu_intr_save();
while (atomic_cas(&lock->locked, 0, 1))
cpu_pause();
return flags;
}
/*
* Release a spin lock.
*/
static inline void
spinlock_unlock(struct spinlock *lock, unsigned long flags)
{
atomic_swap(&lock->locked, 0);
cpu_intr_restore(flags);
}
#endif /* _KERN_SPINLOCK_H */
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