chunk_queue.c

   1 /*
   2  * Copyright (C) 2007-2008 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 "para.h"
  10 #include "list.h"
  11 #include "afh.h"
  12 #include "vss.h"
  13 #include "string.h"
  14 #include "error.h"
  15
  16 /**
  17  * Senders may use the chunk queue facility to deal with laggy connections.  It
  18  * allows them to enqueue chunks if they can not be sent out immediately.
  19  *
  20  * Chunk queues are "cheap" in the sense that only reference to the audio file
  21  * data is stored, but not the data itself.
  22  */
  23 struct chunk_queue {
  24         /** The list of pending chunks for this client. */
  25         struct list_head q;
  26         /** The number of pending bytes for this client. */
  27         unsigned long num_pending;
  28         /** More than that many bytes in the queue is considered an error. */
  29         unsigned long max_pending;
  30 };
  31
  32 /** Describes one queued chunk in a chunk queue. */
  33 struct queued_chunk {
  34         /** Pointer to the data to be queued. */
  35         const char *buf;
  36         /** The number of bytes of this chunk. */
  37         size_t num_bytes;
  38         /** Position of the chunk in the chunk queue. */
  39         struct list_head node;
  40 };
  41
  42 /**
  43  * Add a chunk to the given queue.
  44  *
  45  * \param cq the queue to add the chunk to.
  46  * \param buf Pointer to the data to be queued.
  47  * \param num_bytes The size of \a buf.
  48  *
  49  * \return Standard.
  50  */
  51 int cq_enqueue(struct chunk_queue *cq, const char *buf, size_t num_bytes)
  52 {
  53         struct queued_chunk *qc;
  54
  55         if (cq->num_pending + num_bytes > cq->max_pending)
  56                 return -E_QUEUE;
  57         qc = para_malloc(sizeof(struct queued_chunk));
  58         cq->num_pending += num_bytes;
  59         qc->buf = buf;
  60         qc->num_bytes = num_bytes;
  61         list_add_tail(&qc->node, &cq->q);
  62         PARA_DEBUG_LOG("%lu bytes queued for %p\n", cq->num_pending, &cq->q);
  63         return 1;
  64 }
  65
  66 /**
  67  * Lookup the next chunk in the queue.
  68  *
  69  * \param cq The chunk queue.
  70  *
  71  * \return The next queued chunk, or \p NULL if there is no chunk available.
  72  */
  73 struct queued_chunk *cq_peek(struct chunk_queue *cq)
  74 {
  75         if (list_empty(&cq->q))
  76                 return NULL;
  77         return list_entry(cq->q.next, struct queued_chunk, node);
  78 }
  79
  80 /**
  81  * Remove the current chunk from the queue.
  82  *
  83  * \param cq The chunk to remove.
  84  */
  85 void cq_dequeue(struct chunk_queue *cq)
  86 {
  87         struct queued_chunk *qc = cq_peek(cq);
  88         assert(qc);
  89         list_del(&qc->node);
  90         free(qc);
  91 }
  92
  93 /**
  94  * Change the number of bytes sent for the current queued chunk.
  95  *
  96  * \param cq The chunk queue.
  97  * \param sent Number of bytes successfully sent.
  98  */
  99 void cq_update(struct chunk_queue *cq, size_t sent)
 100 {
 101         struct queued_chunk *qc = cq_peek(cq);
 102         assert(qc);
 103         qc->num_bytes -= sent;
 104         qc->buf += sent;
 105         cq->num_pending -= sent;
 106 }
 107
 108 /**
 109  * Get a pointer to the given queued chunk.
 110  *
 111  * \param qc The queued chunk.
 112  * \param buf Result pointer.
 113  * \param num_bytes Number of bytes of \a buf.
 114  *
 115  * \return Positive on success, negative on errors.
 116  */
 117 int cq_get(struct queued_chunk *qc, const char **buf, size_t *num_bytes)
 118 {
 119         *buf = qc->buf;
 120         *num_bytes = qc->num_bytes;
 121         return 1;
 122 }
 123
 124 /**
 125  * Allocate and initialize a chunk queue.
 126  *
 127  * \param max_pending Maximal number of bytes that will be queued.
 128  *
 129  * \return A pointer to the new queue.
 130  */
 131 struct chunk_queue *cq_new(size_t max_pending)
 132 {
 133         struct chunk_queue *cq = para_malloc(sizeof(*cq));
 134         INIT_LIST_HEAD(&cq->q);
 135         cq->max_pending = max_pending;
 136         cq->num_pending = 0;
 137         return cq;
 138 }
 139
 140 /**
 141  * Deallocate all resources of this queue.
 142  *
 143  * \param cq The chunk queue.
 144  */
 145 void cq_destroy(struct chunk_queue *cq)
 146 {
 147         struct queued_chunk *qc, *tmp;
 148         list_for_each_entry_safe(qc, tmp, &cq->q, node) {
 149                 list_del(&qc->node);
 150                 free(qc);
 151         }
 152         free(cq);
 153 }