atomic_queue.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
 */
 
/**
 * $Id: 4c9b7eac8aec45848041939320b3ab29e966ff9f $
 *
 * @brief Thread-safe queues.
 * @file io/atomic_queue.c
 *
 * @copyright 2016 Alan DeKok (aland@freeradius.org)
 * @copyright 2016 Alister Winfield
 */
RCSID("$Id: 4c9b7eac8aec45848041939320b3ab29e966ff9f $")
 
#include <stdint.h>
#include <stdalign.h>
#include <inttypes.h>
 
#include <freeradius-devel/autoconf.h>
#include <freeradius-devel/io/atomic_queue.h>
#include <freeradius-devel/util/talloc.h>
 
#define CACHE_LINE_SIZE 64
 
/** Entry in the queue
 *
 * @note This structure is cache line aligned for modern AMD/Intel CPUs.
 * This is to avoid contention when the producer and consumer are executing
 * on different CPU cores.
 */
typedef struct CC_HINT(packed, aligned(CACHE_LINE_SIZE)) {
        atomic_int64_t                                  seq;            //!< Must be seq then data to ensure
                                                                        ///< seq is 64bit aligned for 32bit address
                                                                        ///< spaces.
        void                                            *data;
} fr_atomic_queue_entry_t;
 
/** Structure to hold the atomic queue
 *
 */
struct fr_atomic_queue_s {
        alignas(CACHE_LINE_SIZE) atomic_int64_t         head;           //!< Head, aligned bytes to ensure
                                                                        ///< it's in a different cache line to tail
                                                                        ///< to reduce memory contention.
        atomic_int64_t                                  tail;
 
        size_t                                          size;
 
        void                                            *chunk;         //!< To pass to free. The non-aligned address.
 
        alignas(CACHE_LINE_SIZE) fr_atomic_queue_entry_t entry[];       //!< The entry array, also aligned
                                                                        ///< to ensure it's not in the same cache
                                                                        ///< line as tail and size.
};
 
/** Create fixed-size atomic queue
 *
 * @note the queue must be freed explicitly by the ctx being freed, or by using
 * the #fr_atomic_queue_free function.
 *
 * @param[in] ctx       The talloc ctx to allocate the queue in.
 * @param[in] size      The number of entries in the queue.
 * @return
 *     - NULL on error.
 *     - fr_atomic_queue_t *, a pointer to the allocated and initialized queue.
 */
fr_atomic_queue_t *fr_atomic_queue_alloc(TALLOC_CTX *ctx, size_t size)
{
        size_t                  i;
        int64_t                 seq;
        fr_atomic_queue_t       *aq;
        TALLOC_CTX              *chunk;
 
        if (size == 0) return NULL;
 
        /*
         *      Allocate a contiguous blob for the header and queue.
         *      This helps with memory locality.
         *
         *      Since we're allocating a blob, we should also set the
         *      name of the data, too.
         */
        chunk = talloc_aligned_array(ctx, (void **)&aq, CACHE_LINE_SIZE,
                                     sizeof(*aq) + (size) * sizeof(aq->entry[0]));
        if (!chunk) return NULL;
        aq->chunk = chunk;
 
        talloc_set_name_const(chunk, "fr_atomic_queue_t");
 
        /*
         *      Initialize the array.  Data is NULL, and indexes are
         *      the array entry number.
         */
        for (i = 0; i < size; i++) {
                seq = i;
 
                aq->entry[i].data = NULL;
                store(aq->entry[i].seq, seq);
        }
 
        aq->size = size;
 
        /*
         *      Set the head / tail indexes, and force other CPUs to
         *      see the writes.
         */
        store(aq->head, 0);
        store(aq->tail, 0);
        atomic_thread_fence(memory_order_seq_cst);
 
        return aq;
}
 
/** Free an atomic queue if it's not freed by ctx
 *
 * This function is needed because the atomic queue memory
 * must be cache line aligned.
 */
void fr_atomic_queue_free(fr_atomic_queue_t **aq)
{
        if (!*aq) return;
 
        talloc_free((*aq)->chunk);
        *aq = NULL;
}
 
/** Push a pointer into the atomic queue
 *
 * @param[in] aq        The atomic queue to add data to.
 * @param[in] data      to push.
 * @return
 *      - true on successful push
 *      - false on queue full
 */
bool fr_atomic_queue_push(fr_atomic_queue_t *aq, void *data)
{
        int64_t head;
        fr_atomic_queue_entry_t *entry;
 
        if (!data) return false;
 
        head = load(aq->head);
 
        /*
         *      Try to find the current head.
         */
        for (;;) {
                int64_t seq, diff;
 
                entry = &aq->entry[ head % aq->size ];
                seq = aquire(entry->seq);
                diff = (seq - head);
 
                /*
                 *      head is larger than the current entry, the queue is full.
                 */
                if (diff < 0) {
#if 0
                        fr_atomic_queue_debug(aq, stderr);
#endif
                        return false;
                }
 
                /*
                 *      Someone else has already written to this entry.  Get the new head pointer, and continue.
                 */
                if (diff > 0) {
                        head = load(aq->head);
                        continue;
                }
 
                /*
                 *      We have the possibility that we can write to
                 *      this entry.  Try it.  If the write succeeds,
                 *      we're done.  If the write fails, re-load the
                 *      current head entry, and continue.
                 */
                if (cas_incr(aq->head, head)) {
                        break;
                }
        }
 
        /*
         *      Store the data in the queue, and increment the entry
         *      with the new index, and make the write visible to
         *      other CPUs.
         */
        entry->data = data;
        store(entry->seq, head + 1);
        return true;
}
 
 
/** Pop a pointer from the atomic queue
 *
 * @param[in] aq        the atomic queue to retrieve data from.
 * @param[out] p_data   where to write the data.
 * @return
 *      - true on successful pop
 *      - false on queue empty
 */
bool fr_atomic_queue_pop(fr_atomic_queue_t *aq, void **p_data)
{
        int64_t                 tail, seq;
        fr_atomic_queue_entry_t *entry;
 
        if (!p_data) return false;
 
        tail = load(aq->tail);
 
        for (;;) {
                int64_t diff;
 
                entry = &aq->entry[ tail % aq->size ];
                seq = aquire(entry->seq);
 
                diff = (seq - (tail + 1));
 
                /*
                 *      tail is smaller than the current entry, the queue is full.
                 */
                if (diff < 0) {
                        return false;
                }
 
                if (diff > 0) {
                        tail = load(aq->tail);
                        continue;
                }
 
                if (cas_incr(aq->tail, tail)) {
                        break;
                }
        }
 
        /*
         *      Copy the pointer to the caller BEFORE updating the
         *      queue entry.
         */
        *p_data = entry->data;
 
        /*
         *      Set the current entry to past the end of the queue.
         *      i.e. it's unused.
         */
        seq = tail + aq->size;
        store(entry->seq, seq);
 
        return true;
}
 
size_t fr_atomic_queue_size(fr_atomic_queue_t *aq)
{
        return aq->size;
}
 
#ifdef WITH_VERIFY_PTR
/** Check the talloc chunk is still valid
 *
 */
void fr_atomic_queue_verify(fr_atomic_queue_t *aq)
{
        (void)talloc_get_type_abort(aq->chunk, fr_atomic_queue_t);
}
#endif
 
#ifndef NDEBUG
 
#if 0
typedef struct {
        int                     status;         //!< status of this message
        size_t                  data_size;      //!< size of the data we're sending
 
        int                     signal;         //!< the signal to send
        uint64_t                ack;            //!< or the endpoint..
        void                    *ch;            //!< the channel
} fr_control_message_t;
#endif
 
 
/**  Dump an atomic queue.
 *
 * Absolutely NOT thread-safe.
 *
 * @param[in] aq        The atomic queue to debug.
 * @param[in] fp        where the debugging information will be printed.
 */
void fr_atomic_queue_debug(fr_atomic_queue_t *aq, FILE *fp)
{
        size_t i;
        int64_t head, tail;
 
        head = load(aq->head);
        tail = load(aq->head);
 
        fprintf(fp, "AQ %p size %zu, head %" PRId64 ", tail %" PRId64 "\n",
                aq, aq->size, head, tail);
 
        for (i = 0; i < aq->size; i++) {
                fr_atomic_queue_entry_t *entry;
 
                entry = &aq->entry[i];
 
                fprintf(fp, "\t[%zu] = { %p, %" PRId64 " }",
                        i, entry->data, load(entry->seq));
#if 0
                if (entry->data) {
                        fr_control_message_t *c;
 
                        c = entry->data;
 
                        fprintf(fp, "\tstatus %d, data_size %zd, signal %d, ack %zd, ch %p",
                                c->status, c->data_size, c->signal, c->ack, c->ch);
                }
#endif
                fprintf(fp, "\n");
        }
}
#endif