Bug 931186 - Dirt simple token bucket class. r=ekr

media/mtransport/build/moz.build

@@ -15,6 +15,7 @@ EXPORTS.mtransport += [
     '../runnable_utils.h',
     '../runnable_utils_generated.h',
     '../sigslot.h',
+    '../simpletokenbucket.h',
     '../transportflow.h',
     '../transportlayer.h',
     '../transportlayerdtls.h',

media/mtransport/objs.mozbuild

@@ -13,6 +13,7 @@ mtransport_lcppsrcs = [
     'nriceresolver.cpp',
     'nriceresolverfake.cpp',
     'nrinterfaceprioritizer.cpp',
+    'simpletokenbucket.cpp',
     'transportflow.cpp',
     'transportlayer.cpp',
     'transportlayerdtls.cpp',

media/mtransport/simpletokenbucket.cpp

@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Original author: bcampen@mozilla.com */
+
+#include "simpletokenbucket.h"
+
+#include <stdint.h>
+
+#include "prinrval.h"
+
+namespace mozilla {
+
+SimpleTokenBucket::SimpleTokenBucket(size_t bucket_size,
+                                     size_t tokens_per_second) :
+  max_tokens_(bucket_size),
+  num_tokens_(bucket_size),
+  tokens_per_second_(tokens_per_second),
+  last_time_tokens_added_(PR_IntervalNow()) {
+}
+
+size_t SimpleTokenBucket::getTokens(size_t num_requested_tokens) {
+  // Only fill if there isn't enough to satisfy the request.
+  // If we get tokens so seldomly that we are able to roll the timer all
+  // the way around its range, then we lose that entire range of time
+  // for token accumulation. Probably not the end of the world.
+  if (num_requested_tokens > num_tokens_) {
+    PRIntervalTime now = PR_IntervalNow();
+
+    // If we roll over the max, since everything in this calculation is the same
+    // unsigned type, this will still yield the elapsed time (unless we've
+    // wrapped more than once).
+    PRIntervalTime elapsed_ticks = now - last_time_tokens_added_;
+
+    uint32_t elapsed_milli_sec = PR_IntervalToMilliseconds(elapsed_ticks);
+    size_t tokens_to_add = (elapsed_milli_sec * tokens_per_second_)/1000;
+
+    // Only update our timestamp if we added some tokens
+    // TODO:(bcampen@mozilla.com) Should we attempt to "save" leftover time?
+    if (tokens_to_add) {
+      num_tokens_ += tokens_to_add;
+      if (num_tokens_ > max_tokens_) {
+        num_tokens_ = max_tokens_;
+      }
+
+      last_time_tokens_added_ = now;
+    }
+
+    if (num_requested_tokens > num_tokens_) {
+      return num_tokens_;
+    }
+  }
+
+  num_tokens_ -= num_requested_tokens;
+  return num_requested_tokens;
+}
+
+} // namespace mozilla
+

media/mtransport/simpletokenbucket.h

@@ -0,0 +1,54 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Original author: bcampen@mozilla.com */
+
+/*
+ *  This file defines a dirt-simple token bucket class.
+ */
+
+#ifndef simpletokenbucket_h__
+#define simpletokenbucket_h__
+
+#include <stdint.h>
+
+#include "prinrval.h"
+
+#include "m_cpp_utils.h"
+
+namespace mozilla {
+
+class SimpleTokenBucket {
+  public:
+    /*
+     *  Create a SimpleTokenBucket with a given maximum size and
+     *  token replenishment rate.
+     *  (eg; if you want a maximum rate of 5 per second over a 7 second
+     *  period, call SimpleTokenBucket b(5*7, 5);)
+     */
+    SimpleTokenBucket(size_t bucket_size, size_t tokens_per_second);
+
+    /*
+     *  Attempt to acquire a number of tokens. If successful, returns
+     *  |num_tokens|, otherwise returns the number of tokens currently
+     *  in the bucket.
+     *  Note: To get the number of tokens in the bucket, pass something
+     *  like UINT32_MAX.
+     */
+    size_t getTokens(size_t num_tokens);
+
+  protected: // Allow testing to touch these.
+    uint64_t max_tokens_;
+    uint64_t num_tokens_;
+    size_t tokens_per_second_;
+    PRIntervalTime last_time_tokens_added_;
+
+    DISALLOW_COPY_ASSIGN(SimpleTokenBucket);
+};
+} // namespace mozilla
+
+#endif // simpletokenbucket_h__
+

media/mtransport/test/moz.build

@@ -11,6 +11,7 @@ if CONFIG['OS_TARGET'] != 'WINNT' and CONFIG['MOZ_WIDGET_TOOLKIT'] != 'gonk':
         'ice_unittest.cpp',
         'nrappkit_unittest.cpp',
         'runnable_utils_unittest.cpp',
+        'simpletokenbucket_unittest.cpp',
         'sockettransportservice_unittest.cpp',
         'TestSyncRunnable.cpp',
         'transport_unittests.cpp',

media/mtransport/test/simpletokenbucket_unittest.cpp

@@ -0,0 +1,115 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Original author: bcampen@mozilla.com */
+
+#include "simpletokenbucket.h"
+
+#define GTEST_HAS_RTTI 0
+#include "gtest/gtest.h"
+#include "gtest_utils.h"
+
+using mozilla::SimpleTokenBucket;
+
+class TestSimpleTokenBucket : public SimpleTokenBucket {
+  public:
+    TestSimpleTokenBucket(size_t bucketSize, size_t tokensPerSecond) :
+      SimpleTokenBucket(bucketSize, tokensPerSecond) {
+    }
+
+    void fastForward(int32_t timeMilliSeconds) {
+      if (timeMilliSeconds >= 0) {
+        last_time_tokens_added_ -= PR_MillisecondsToInterval(timeMilliSeconds);
+      } else {
+        last_time_tokens_added_ += PR_MillisecondsToInterval(-timeMilliSeconds);
+      }
+    }
+};
+
+TEST(SimpleTokenBucketTest, TestConstruct) {
+  TestSimpleTokenBucket b(10, 1);
+}
+
+TEST(SimpleTokenBucketTest, TestGet) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(5U, b.getTokens(5));
+}
+
+TEST(SimpleTokenBucketTest, TestGetAll) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(10U, b.getTokens(10));
+}
+
+TEST(SimpleTokenBucketTest, TestGetInsufficient) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(5U, b.getTokens(5));
+  ASSERT_EQ(5U, b.getTokens(6));
+}
+
+TEST(SimpleTokenBucketTest, TestGetBucketCount) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(10U, b.getTokens(UINT32_MAX));
+  ASSERT_EQ(5U, b.getTokens(5));
+  ASSERT_EQ(5U, b.getTokens(UINT32_MAX));
+}
+
+TEST(SimpleTokenBucketTest, TestTokenRefill) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(5U, b.getTokens(5));
+  b.fastForward(1000);
+  ASSERT_EQ(6U, b.getTokens(6));
+}
+
+TEST(SimpleTokenBucketTest, TestNoTimeWasted) {
+  // Makes sure that when the time elapsed is insufficient to add any
+  // tokens to the bucket, the internal timestamp that is used in this
+  // calculation is not updated (ie; two subsequent 0.5 second elapsed times
+  // counts as a full second)
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(5U, b.getTokens(5));
+  b.fastForward(500);
+  ASSERT_EQ(5U, b.getTokens(6));
+  b.fastForward(500);
+  ASSERT_EQ(6U, b.getTokens(6));
+}
+
+TEST(SimpleTokenBucketTest, TestNegativeTime) {
+  TestSimpleTokenBucket b(10, 1);
+  b.fastForward(-1000);
+  // Make sure we don't end up with an invalid number of tokens, but otherwise
+  // permit anything.
+  ASSERT_GT(11U, b.getTokens(100));
+}
+
+TEST(SimpleTokenBucketTest, TestEmptyBucket) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(10U, b.getTokens(10));
+  ASSERT_EQ(0U, b.getTokens(10));
+}
+
+TEST(SimpleTokenBucketTest, TestEmptyThenFillBucket) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(10U, b.getTokens(10));
+  ASSERT_EQ(0U, b.getTokens(1));
+  b.fastForward(50000);
+  ASSERT_EQ(10U, b.getTokens(10));
+}
+
+TEST(SimpleTokenBucketTest, TestNoOverflow) {
+  TestSimpleTokenBucket b(10, 1);
+  ASSERT_EQ(10U, b.getTokens(10));
+  ASSERT_EQ(0U, b.getTokens(1));
+  b.fastForward(50000);
+  ASSERT_EQ(10U, b.getTokens(11));
+}
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+
+  int rv = RUN_ALL_TESTS();
+  return rv;
+}
+