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