/*
<:copyright-BRCM:2016:DUAL/GPL:standard

   Broadcom Proprietary and Confidential.(c) 2016 Broadcom
   All Rights Reserved

Unless you and Broadcom execute a separate written software license
agreement governing use of this software, this software is licensed
to you under the terms of the GNU General Public License version 2
(the "GPL"), available at http://www.broadcom.com/licenses/GPLv2.php,
with the following added to such license:

   As a special exception, the copyright holders of this software give
   you permission to link this software with independent modules, and
   to copy and distribute the resulting executable under terms of your
   choice, provided that you also meet, for each linked independent
   module, the terms and conditions of the license of that module.
   An independent module is a module which is not derived from this
   software.  The special exception does not apply to any modifications
   of the software.

Not withstanding the above, under no circumstances may you combine
this software in any way with any other Broadcom software provided
under a license other than the GPL, without Broadcom's express prior
written consent.

:>
 */
#include "bcmos_rw_lock.h"

struct bcmos_rw_lock
{
    /* the actual lock, held by the writer, used by the reader to safely obtain a read lock, but not held to allow
     * multiple readers */
    bcmos_mutex lock;
    /* used by the writer to prevent new readers from obtaining read locks while a writer is waiting */
    bcmos_mutex read_lock;
    /* used by readers to signal waiting writers that they have finished reading */
    bcmos_sem write_lock;
    /* current number of readers */
    uint32_t readers;
};

bcmos_errno bcmos_rw_lock_create(bcmos_rw_lock **lock)
{
    bcmos_errno err;
    *lock = (bcmos_rw_lock*)bcmos_calloc(sizeof(bcmos_rw_lock));
    if (*lock == NULL)
    {
        BUG();
        return BCM_ERR_NOMEM;
    }
    if (BCM_ERR_OK != (err = bcmos_mutex_create(&(*lock)->lock, 0, "bcmos_rw_lock_create_lock")))
    {
        BUG();
        return err;
    }
    if (BCM_ERR_OK != (err = bcmos_mutex_create(&(*lock)->read_lock, 0, "bcmos_rw_lock_create_rw_lock")))
    {
        BUG();
        return err;
    }
    (*lock)->readers = 0;
    if (BCM_ERR_OK != (err = bcmos_sem_create(&(*lock)->write_lock, 1, 0, "bcmos_rw_lock_create_write_lock")))
    {
        BUG();
        return err;
    }
    return err;
}

/*lint -e{455} suppress "thread mutex has not been locked" */
void bcmos_rw_write_lock(bcmos_rw_lock* lock)
{
    /* prevent any new readers from trying to obtain a read lock */
    bcmos_mutex_lock(&lock->read_lock);
    /* lock the actual lock */
    bcmos_mutex_lock(&lock->lock);
    while (lock->readers != 0)
    {
        /* there are still readers holding read locks, release the lock */
        bcmos_mutex_unlock(&lock->lock);
        /* wait for the signal from the last reader before trying again */
        bcmos_sem_wait(&lock->write_lock, BCMOS_WAIT_FOREVER);
        /* lock the actual lock and check for readers again */
        bcmos_mutex_lock(&lock->lock);
    }
    /* no more readers, allow new readers to wait on the lock */
    bcmos_mutex_unlock(&lock->read_lock);
}
/*lint +e{454} suppress "thread mutex has not been locked" */

void bcmos_rw_write_release(bcmos_rw_lock* lock)
{
    /*lint --e{455} suppress "thread mutex has not been locked" */
    bcmos_mutex_unlock(&lock->lock);
}

void bcmos_rw_read_lock(bcmos_rw_lock* lock)
{
    /* wait for anyone trying to get a write lock */
    bcmos_mutex_lock(&lock->read_lock);
    /* wait for the lock to be released */
    bcmos_mutex_lock(&lock->lock);
    lock->readers++;
    /* reset the signal to the writers */
    bcmos_sem_wait(&lock->write_lock, BCMOS_NO_WAIT);
    /* all done, release everything so other readers can get a read lock */
    bcmos_mutex_unlock(&lock->lock);
    bcmos_mutex_unlock(&lock->read_lock);
}

void bcmos_rw_read_release(bcmos_rw_lock* lock)
{
    /* get a lock to prevent interruptions */
    bcmos_mutex_lock(&lock->lock);
    if (--lock->readers == 0)
    {
        /* if we're the last reader, signal that the lock is available for a writer */
        bcmos_sem_post(&lock->write_lock);
    }
    bcmos_mutex_unlock(&lock->lock);
}