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// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/download/public/common/rate_estimator.h"
#include "base/check.h"
#include "base/time/time.h"
using base::TimeTicks;
namespace download {
namespace {
static const int kDefaultBucketTimeSeconds = 1;
static const size_t kDefaultNumBuckets = 10;
} // namespace
RateEstimator::RateEstimator()
: history_(kDefaultNumBuckets),
bucket_time_(base::Seconds(kDefaultBucketTimeSeconds)),
oldest_index_(0),
bucket_count_(1) {
ResetBuckets(TimeTicks::Now());
}
RateEstimator::RateEstimator(base::TimeDelta bucket_time,
size_t num_buckets,
TimeTicks now)
: history_(num_buckets),
bucket_time_(bucket_time),
oldest_index_(0),
bucket_count_(1) {
DCHECK(bucket_time_.InSeconds() > 0);
ResetBuckets(now);
}
RateEstimator::~RateEstimator() = default;
void RateEstimator::Increment(uint32_t count) {
Increment(count, TimeTicks::Now());
}
void RateEstimator::Increment(uint32_t count, TimeTicks now) {
ClearOldBuckets(now);
int64_t seconds_since_oldest = (now - oldest_time_).InSeconds();
DCHECK(seconds_since_oldest >= 0);
int64_t delta_buckets = seconds_since_oldest / bucket_time_.InSeconds();
DCHECK(delta_buckets >= 0);
size_t index_offset = static_cast<size_t>(delta_buckets);
DCHECK(index_offset <= history_.size());
size_t current_index = (oldest_index_ + delta_buckets) % history_.size();
history_[current_index] += count;
}
uint64_t RateEstimator::GetCountPerSecond() const {
return GetCountPerSecond(TimeTicks::Now());
}
uint64_t RateEstimator::GetCountPerSecond(TimeTicks now) const {
const_cast<RateEstimator*>(this)->ClearOldBuckets(now);
// TODO(cbentzel): Support fractional seconds for active bucket?
// We explicitly don't check for overflow here. If it happens, unsigned
// arithmetic at least guarantees behavior by wrapping around. The estimate
// will be off, but the code will still be valid.
uint64_t total_count = 0;
for (size_t i = 0; i < bucket_count_; ++i) {
size_t index = (oldest_index_ + i) % history_.size();
total_count += history_[index];
}
return total_count / (bucket_count_ * bucket_time_.InSeconds());
}
void RateEstimator::ClearOldBuckets(TimeTicks now) {
int64_t seconds_since_oldest = (now - oldest_time_).InSeconds();
int64_t delta_buckets = seconds_since_oldest / bucket_time_.InSeconds();
// It's possible (although unlikely) for there to be rollover with TimeTicks.
// If that's the case, just reset the history.
if (delta_buckets < 0) {
ResetBuckets(now);
return;
}
size_t delta_index = static_cast<size_t>(delta_buckets);
// If we are within the current window, keep the existing data.
if (delta_index < history_.size()) {
bucket_count_ = delta_index + 1;
return;
}
// If it's been long enough that all history data is too stale, just
// clear all the buckets.
size_t extra_buckets = delta_index - history_.size() + 1;
if (extra_buckets > history_.size()) {
ResetBuckets(now);
return;
}
// Clear out stale buckets in the history.
bucket_count_ = history_.size();
for (size_t i = 0; i < extra_buckets; ++i) {
history_[oldest_index_] = 0;
oldest_index_ = (oldest_index_ + 1) % history_.size();
oldest_time_ = oldest_time_ + bucket_time_;
}
}
void RateEstimator::ResetBuckets(TimeTicks now) {
for (size_t i = 0; i < history_.size(); ++i) {
history_[i] = 0;
}
oldest_index_ = 0;
bucket_count_ = 1;
oldest_time_ = now;
}
} // namespace download
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