source: trunk/kernel/libk/spinlock.c @ 51

/*
 * spinlock.c - kernel spinlock synchronization
 * 
 * Authors   Ghassan Almaless  (2008,2009,2010,2011,2012)
 *           Alain Greiner     (2016}
 *
 * Copyright (c) UPMC Sorbonne Universites
 *
 * This file is part of ALMOS-MKH.
 *
 * ALMOS-MKH 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; version 2.0 of the License.
 *
 * ALMOS-MKH 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 ALMOS-MKH; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <kernel_config.h>
#include <hal_types.h>
#include <hal_atomic.h>
#include <hal_special.h>
#include <hal_irqmask.h>
#include <thread.h>
#include <scheduler.h>
#include <printk.h>
#include <spinlock.h>

//////////////////////////////////////////////
inline void spinlock_init( spinlock_t * lock )
{  
        lock->taken = 0;
        lock->owner = NULL;
    list_entry_init( &lock->list );
}

///////////////////////////////////////////
void spinlock_lock_busy( spinlock_t * lock, 
                         uint32_t   * irq_state )
{
        uint32_t            mode;
        volatile uint32_t   taken;
        thread_t          * this     = CURRENT_THREAD;
        bool_t              isAtomic = false;

    // disable interrupts
        hal_disable_irq( &mode );
  
    // loop until success
        while( isAtomic == false )
        {
                taken = lock->taken;

        // try to take the lock if not already taken
                if( taken == 0 )
        {
                    isAtomic = hal_atomic_cas( &lock->taken , 0 , 1 );
        }
        }

        this->local_locks++;
    lock->owner = this;
    list_add_first( &this->locks_root , &lock->list );

    // irq_state must be restored when lock is released 
    *irq_state = mode;
}

//////////////////////////////////////////////
void spinlock_unlock_busy( spinlock_t * lock,
                           uint32_t     irq_state )
{
        thread_t * this = CURRENT_THREAD;;
  
    lock->owner = NULL;
    lock->taken = 0;
    this->local_locks--;
    list_unlink( &lock->list );
 
        hal_restore_irq( irq_state );
}
   
///////////////////////////////////////
void spinlock_lock( spinlock_t * lock )
{
        uint32_t          mode;
        thread_t        * this     = CURRENT_THREAD;
        bool_t            isAtomic = false;
        volatile uint32_t taken;
    
    // disable interrupts
        hal_disable_irq( &mode );
  
    // loop until success
        while( isAtomic == false )
        {
        taken = lock->taken;

        // deschedule without blocking when lock already taken
                if( taken != 0 )
        {
            hal_restore_irq( mode );
            if( thread_can_yield() ) sched_yield();
            hal_disable_irq( &mode );
            continue;
        }

        // try to atomically take the lock if not already taken
            isAtomic = hal_atomic_cas( &lock->taken , 0 , 1 );
    }

        this->local_locks++;
    lock->owner = this;
    list_add_first( &this->locks_root , &lock->list );

    // enable interrupts
    hal_restore_irq( mode );
}

/////////////////////////////////////////////
error_t spinlock_trylock( spinlock_t * lock )
{ 
        uint32_t   mode;
        bool_t     isAtomic = false;
        thread_t * this     = CURRENT_THREAD;

        hal_disable_irq( &mode );

        if( lock->taken == 0)
                isAtomic = hal_atomic_cas( &lock->taken , 0 , 1);
  
        if(isAtomic == false)
        {
                hal_restore_irq(mode);
                return 1;
        }
    else
    {
            this->local_locks++;
            lock->owner = this;
        list_add_first( &this->locks_root , &lock->list );
            hal_restore_irq(mode);  
            return 0;
    }
}

/////////////////////////////////////////
void spinlock_unlock( spinlock_t * lock )
{
        thread_t * this = CURRENT_THREAD;
  
    lock->owner = NULL;
    lock->taken = 0;
    this->local_locks--;
    list_unlink( &lock->list );
}