media/mtransport/simpletokenbucket.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* Original author: bcampen@mozilla.com */
   8
   9 #include "simpletokenbucket.h"
  10
  11 #include <stdint.h>
  12
  13 #include "prinrval.h"
  14
  15 namespace mozilla {
  16
  17 SimpleTokenBucket::SimpleTokenBucket(size_t bucket_size,
  18                                      size_t tokens_per_second) :
  19   max_tokens_(bucket_size),
  20   num_tokens_(bucket_size),
  21   tokens_per_second_(tokens_per_second),
  22   last_time_tokens_added_(PR_IntervalNow()) {
  23 }
  24
  25 size_t SimpleTokenBucket::getTokens(size_t num_requested_tokens) {
  26   // Only fill if there isn't enough to satisfy the request.
  27   // If we get tokens so seldomly that we are able to roll the timer all
  28   // the way around its range, then we lose that entire range of time
  29   // for token accumulation. Probably not the end of the world.
  30   if (num_requested_tokens > num_tokens_) {
  31     PRIntervalTime now = PR_IntervalNow();
  32
  33     // If we roll over the max, since everything in this calculation is the same
  34     // unsigned type, this will still yield the elapsed time (unless we've
  35     // wrapped more than once).
  36     PRIntervalTime elapsed_ticks = now - last_time_tokens_added_;
  37
  38     uint32_t elapsed_milli_sec = PR_IntervalToMilliseconds(elapsed_ticks);
  39     size_t tokens_to_add = (elapsed_milli_sec * tokens_per_second_)/1000;
  40
  41     // Only update our timestamp if we added some tokens
  42     // TODO:(bcampen@mozilla.com) Should we attempt to "save" leftover time?
  43     if (tokens_to_add) {
  44       num_tokens_ += tokens_to_add;
  45       if (num_tokens_ > max_tokens_) {
  46         num_tokens_ = max_tokens_;
  47       }
  48
  49       last_time_tokens_added_ = now;
  50     }
  51
  52     if (num_requested_tokens > num_tokens_) {
  53       return num_tokens_;
  54     }
  55   }
  56
  57   num_tokens_ -= num_requested_tokens;
  58   return num_requested_tokens;
  59 }
  60
  61 } // namespace mozilla
  62