media/capture/content/smooth_event_sampler.cc

// Copyright (c) 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "media/capture/content/smooth_event_sampler.h"

#include <stdint.h>

#include <algorithm>

#include "base/trace_event/trace_event.h"

namespace media {

SmoothEventSampler::SmoothEventSampler(base::TimeDelta min_capture_period)
    : token_bucket_(base::TimeDelta::Max()) {
  SetMinCapturePeriod(min_capture_period);
}

void SmoothEventSampler::SetMinCapturePeriod(base::TimeDelta period) {
  DCHECK_GT(period, base::TimeDelta());
  min_capture_period_ = period;
  token_bucket_capacity_ = period + period / 2;
  token_bucket_ = std::min(token_bucket_capacity_, token_bucket_);
}

void SmoothEventSampler::ConsiderPresentationEvent(base::TimeTicks event_time) {
  DCHECK(!event_time.is_null());

  // Add tokens to the bucket based on advancement in time.  Then, re-bound the
  // number of tokens in the bucket.  Overflow occurs when there is too much
  // time between events (a common case), or when RecordSample() is not being
  // called often enough (a bug).  On the other hand, if RecordSample() is being
  // called too often (e.g., as a reaction to IsOverdueForSamplingAt()), the
  // bucket will underflow.
  if (!current_event_.is_null()) {
    if (current_event_ < event_time) {
      token_bucket_ += event_time - current_event_;
      if (token_bucket_ > token_bucket_capacity_)
        token_bucket_ = token_bucket_capacity_;
    }
    TRACE_COUNTER1("gpu.capture", "MirroringTokenBucketUsec",
                   std::max<int64_t>(0, token_bucket_.InMicroseconds()));
  }
  current_event_ = event_time;
}

bool SmoothEventSampler::ShouldSample() const {
  return token_bucket_ >= min_capture_period_;
}

void SmoothEventSampler::RecordSample() {
  token_bucket_ -= min_capture_period_;
  if (token_bucket_ < base::TimeDelta())
    token_bucket_ = base::TimeDelta();
  TRACE_COUNTER1("gpu.capture", "MirroringTokenBucketUsec",
                 std::max<int64_t>(0, token_bucket_.InMicroseconds()));

  if (HasUnrecordedEvent())
    last_sample_ = current_event_;
}

bool SmoothEventSampler::HasUnrecordedEvent() const {
  return !current_event_.is_null() && current_event_ != last_sample_;
}

}  // namespace media