chunk_queue.c

   1 /*
   2  * Copyright (C) 2007-2010 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file chunk_queue.c Queuing functions for paraslash senders. */
   8
   9 #include <regex.h>
  10
  11 #include "para.h"
  12 #include "list.h"
  13 #include "afh.h"
  14 #include "string.h"
  15 #include "error.h"
  16
  17 /**
  18  * Senders may use the chunk queue facility to deal with laggy connections.  It
  19  * allows them to enqueue chunks if they can not be sent out immediately.
  20  *
  21  * Chunk queues are "cheap" in the sense that only reference to the audio file
  22  * data is stored, but not the data itself.
  23  */
  24 struct chunk_queue {
  25         /** The list of pending chunks for this client. */
  26         struct list_head q;
  27         /** The number of pending bytes for this client. */
  28         unsigned long num_pending;
  29         /** More than that many bytes in the queue is considered an error. */
  30         unsigned long max_pending;
  31 };
  32
  33 /** Describes one queued chunk in a chunk queue. */
  34 struct queued_chunk {
  35         /** Pointer to the data to be queued. */
  36         const char *buf;
  37         /** The number of bytes of this chunk. */
  38         size_t num_bytes;
  39         /** Position of the chunk in the chunk queue. */
  40         struct list_head node;
  41 };
  42
  43 /**
  44  * Add a chunk to the given queue.
  45  *
  46  * \param cq the queue to add the chunk to.
  47  * \param buf Pointer to the data to be queued.
  48  * \param num_bytes The size of \a buf.
  49  *
  50  * \return Standard.
  51  */
  52 int cq_enqueue(struct chunk_queue *cq, const char *buf, size_t num_bytes)
  53 {
  54         struct queued_chunk *qc;
  55
  56         if (cq->num_pending + num_bytes > cq->max_pending)
  57                 return -E_QUEUE;
  58         qc = para_malloc(sizeof(struct queued_chunk));
  59         cq->num_pending += num_bytes;
  60         qc->buf = buf;
  61         qc->num_bytes = num_bytes;
  62         list_add_tail(&qc->node, &cq->q);
  63         PARA_DEBUG_LOG("%lu bytes queued for %p\n", cq->num_pending, &cq->q);
  64         return 1;
  65 }
  66
  67 /**
  68  * Lookup the next chunk in the queue.
  69  *
  70  * \param cq The chunk queue.
  71  *
  72  * \return The next queued chunk, or \p NULL if there is no chunk available.
  73  */
  74 struct queued_chunk *cq_peek(struct chunk_queue *cq)
  75 {
  76         if (list_empty(&cq->q))
  77                 return NULL;
  78         return list_entry(cq->q.next, struct queued_chunk, node);
  79 }
  80
  81 /**
  82  * Remove the current chunk from the queue.
  83  *
  84  * \param cq The queue to remove from.
  85  */
  86 void cq_dequeue(struct chunk_queue *cq)
  87 {
  88         struct queued_chunk *qc = cq_peek(cq);
  89         assert(qc);
  90         assert(cq->num_pending >= qc->num_bytes);
  91         cq->num_pending -= qc->num_bytes;
  92         list_del(&qc->node);
  93         free(qc);
  94 }
  95
  96 /**
  97  * Force to add a chunk to the given queue.
  98  *
  99  * \param cq See \ref cq_enqueue.
 100  * \param buf See \ref cq_enqueue.
 101  * \param num_bytes See \ref cq_enqueue.
 102  *
 103  * If queuing the given buffer would result in exceeding the maximal queue
 104  * size, buffers are dropped from the beginning of the queue. Note that this
 105  * function still might fail.
 106  *
 107  * \return Standard.
 108  */
 109 int cq_force_enqueue(struct chunk_queue *cq, const char *buf, size_t num_bytes)
 110 {
 111         int ret;
 112
 113         if (num_bytes > cq->max_pending)
 114                 return -E_QUEUE;
 115         for (;;) {
 116                 ret = cq_enqueue(cq, buf, num_bytes);
 117                 if (ret >= 0)
 118                         return ret;
 119                 cq_dequeue(cq);
 120         }
 121         /* never reached */
 122 }
 123
 124 /**
 125  * Change the number of bytes sent for the current queued chunk.
 126  *
 127  * \param cq The chunk queue.
 128  * \param sent Number of bytes successfully sent.
 129  */
 130 void cq_update(struct chunk_queue *cq, size_t sent)
 131 {
 132         struct queued_chunk *qc = cq_peek(cq);
 133         assert(qc);
 134         qc->num_bytes -= sent;
 135         qc->buf += sent;
 136         cq->num_pending -= sent;
 137 }
 138
 139 /**
 140  * Get a pointer to the given queued chunk.
 141  *
 142  * \param qc The queued chunk.
 143  * \param buf Result pointer.
 144  * \param num_bytes Number of bytes of \a buf.
 145  *
 146  * \return Positive on success, negative on errors.
 147  */
 148 int cq_get(struct queued_chunk *qc, const char **buf, size_t *num_bytes)
 149 {
 150         *buf = qc->buf;
 151         *num_bytes = qc->num_bytes;
 152         return 1;
 153 }
 154
 155 /**
 156  * Allocate and initialize a chunk queue.
 157  *
 158  * \param max_pending Maximal number of bytes that will be queued.
 159  *
 160  * \return A pointer to the new queue.
 161  */
 162 struct chunk_queue *cq_new(size_t max_pending)
 163 {
 164         struct chunk_queue *cq = para_malloc(sizeof(*cq));
 165         INIT_LIST_HEAD(&cq->q);
 166         cq->max_pending = max_pending;
 167         cq->num_pending = 0;
 168         return cq;
 169 }
 170
 171 /**
 172  * Deallocate all resources of this queue.
 173  *
 174  * \param cq The chunk queue.
 175  */
 176 void cq_destroy(struct chunk_queue *cq)
 177 {
 178         struct queued_chunk *qc, *tmp;
 179         list_for_each_entry_safe(qc, tmp, &cq->q, node) {
 180                 list_del(&qc->node);
 181                 free(qc);
 182         }
 183         free(cq);
 184 }