fring.c

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/*
 *   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 2 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, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/** Implementation of a circular buffer with fixed element size
 *
 * This offers similar functionality to ring_buffer.c, but uses a fixed
 * element size, and expects all elements to be talloced.
 *
 * @file src/lib/util/fring.c
 *
 * @copyright 2013 The FreeRADIUS server project
 * @copyright 2013 Arran Cudbard-Bell (a.cudbardb@freeradius.org)
 */
RCSID("$Id: acef49804e222a1e58c7d3539820dbd24a33bb8f $")
 
#include <freeradius-devel/util/fring.h>
 
#include <pthread.h>
 
/** Standard thread safe circular buffer
 *
 */
struct fr_fring_buffer {
        void const              *end;                   //!< End of allocated memory
 
        uint32_t                size;
        uint32_t                in;                     //!< Write index
        uint32_t                out;                    //!< Read index
 
        void                    **data;                 //!< Ring buffer data
 
        bool                    lock;                   //!< Perform thread synchronisation
 
        pthread_mutex_t         mutex;                  //!< Thread synchronisation mutex
};
 
/** Destroy mutex associated with ring buffer
 *
 * @param[in] fring being freed.
 * @return 0
 */
static int _fring_free(fr_fring_t *fring)
{
        void *next;
 
        /*
         *      Free any data left in the buffer
         */
        while ((next = fr_fring_next(fring))) talloc_free(next);
 
        if (fring->lock) pthread_mutex_destroy(&fring->mutex);
 
        return 0;
}
 
/** Initialise a ring buffer with fixed element size
 *
 * @param[in] ctx       to allocate the buffer in.
 * @param[in] size      of buffer to allocate.
 * @param[in] lock      If true, insert and next operations will lock the buffer.
 * @return
 *      - New fring.
 *      - NULL on error.
 */
fr_fring_t *fr_fring_alloc(TALLOC_CTX *ctx, uint32_t size, bool lock)
{
        fr_fring_t *fring;
 
        uint32_t pow;
 
        if (size == 0 || size > 0x80000000U) return NULL;
 
        /*
         *      Find the nearest power of 2 (rounding up)
         */
        for (pow = 0x00000001;
             pow < size;
             pow <<= 1);
        size = pow;
        size--;
 
        fring = talloc_zero(ctx, fr_fring_t);
        if (!fring) return NULL;
        talloc_set_destructor(fring, _fring_free);
 
        fring->data = talloc_zero_array(fring, void *, size);
        if (!fring->data) {
                talloc_free(fring);
                return NULL;
        }
        fring->size = size;
 
        if (lock) {
                fring->lock = true;
                pthread_mutex_init(&fring->mutex, NULL);
        }
 
        return fring;
}
 
/** Insert a new item into the circular buffer, freeing the tail if we hit it
 *
 * @param[in] fring     to insert item into
 * @param[in] in        item to insert (must have been allocated with talloc).
 * @return
 *      - 0 if we inserted the item without freeing existing items.
 *      - 1 if we inserted the item, but needed to free an existing item.
 */
int fr_fring_overwrite(fr_fring_t *fring, void *in)
{
        bool freed = false;
        if (fring->lock) pthread_mutex_lock(&fring->mutex);
 
        if (fring->data[fring->in]) {
                freed = true;
                talloc_free(fring->data[fring->in]);
        }
 
        fring->data[fring->in] = in;
        fring->in = (fring->in + 1) & fring->size;
 
        /* overwrite - out is advanced ahead of in */
        if (fring->in == fring->out) fring->out = (fring->out + 1) & fring->size;
 
        if (fring->lock) pthread_mutex_unlock(&fring->mutex);
 
        return freed ? 1 : 0;
}
 
/** Insert a new item into the circular buffer if the buffer is not full
 *
 * @param[in] fring     to insert item into.
 * @param[in] in        item to insert.
 * @return
 *      - 0 if we inserted the item.
 *      - -1 if there's no more space in the buffer to insert items
 */
int fr_fring_insert(fr_fring_t *fring, void *in)
{
        if (fring->lock) pthread_mutex_lock(&fring->mutex);
 
        if (fring->data[fring->in]) {
                if (fring->lock) pthread_mutex_unlock(&fring->mutex);
 
                return -1;
        }
 
        fring->data[fring->in] = in;
        fring->in = (fring->in + 1) & fring->size;
 
        /* overwrite - out is advanced ahead of in */
        if (fring->in == fring->out) fring->out = (fring->out + 1) & fring->size;
 
        if (fring->lock) pthread_mutex_unlock(&fring->mutex);
 
        return 0;
}
 
/** Remove an item from the buffer
 *
 * @param[in] fring     to drain data from.
 * @return
 *      - NULL if no dataents in the buffer.
 *      - An dataent from the buffer reparented to ctx.
 */
void *fr_fring_next(fr_fring_t *fring)
{
        void *out = NULL;
 
        if (fring->lock) pthread_mutex_lock(&fring->mutex);
 
        /* Buffer is empty */
        if (fring->out == fring->in) goto done;
 
        out = fring->data[fring->out];
        fring->data[fring->out] = NULL;
        fring->out = (fring->out + 1) & fring->size;
 
done:
        if (fring->lock) pthread_mutex_unlock(&fring->mutex);
 
        return out;
}