chrome/browser/net/url_info.cc

// Copyright (c) 2012 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 "chrome/browser/net/url_info.h"

#include <ctype.h>
#include <math.h>
#include <stddef.h>
#include <stdint.h>

#include <algorithm>
#include <limits>
#include <string>

#include "base/format_macros.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/metrics/histogram_macros.h"
#include "base/strings/stringprintf.h"

using base::TimeDelta;
using base::TimeTicks;

namespace chrome_browser_net {

namespace {

// The number of OS cache entries we can guarantee(?) before cache eviction
// might likely take place.
const int kMaxGuaranteedDnsCacheSize = 50;

// Common low end TTL for sites is 5 minutes.  However, DNS servers give us the
// remaining time, not the original 5 minutes.  Hence it doesn't much matter
// whether we found something in the local cache, or an ISP cache, it will on
// average be 2.5 minutes before it expires.  We could try to model this with
// 180 seconds, but simpler is just to do the lookups all the time (wasting OS
// calls(?)), and let that OS cache decide what to do (with TTL in hand).  We
// use a small time to help get some duplicate suppression, in case a page has
// a TON of copies of the same domain name, so that we don't thrash the OS to
// death.  Hopefully it is small enough that we're not hurting our cache hit
// rate (i.e., we could always ask the OS).
const int kDefaultCacheExpirationDuration = 5;

TimeDelta MaxNonNetworkDnsLookupDuration() {
  return TimeDelta::FromMilliseconds(15);
}

bool detailed_logging_enabled = false;

struct GlobalState {
  GlobalState() {
    cache_expiration_duration =
        TimeDelta::FromSeconds(kDefaultCacheExpirationDuration);
  }
  TimeDelta cache_expiration_duration;
};

base::LazyInstance<GlobalState>::Leaky global_state;

}  // anonymous namespace

// Use command line switch to enable detailed logging.
void EnablePredictorDetailedLog(bool enable) {
  detailed_logging_enabled = enable;
}

// static
int UrlInfo::sequence_counter = 1;

UrlInfo::UrlInfo()
    : state_(PENDING),
      old_prequeue_state_(state_),
      resolve_duration_(NullDuration()),
      queue_duration_(NullDuration()),
      sequence_number_(0),
      motivation_(NO_PREFETCH_MOTIVATION),
      was_linked_(false) {
}

UrlInfo::UrlInfo(UrlInfo&& other) = default;
UrlInfo& UrlInfo::operator=(UrlInfo&& other) = default;

UrlInfo::~UrlInfo() {}

bool UrlInfo::NeedsDnsUpdate() {
  switch (state_) {
    case PENDING:  // Just now created info.
      return true;

    case QUEUED:  // In queue.
    case ASSIGNED:  // It's being resolved.
    case ASSIGNED_BUT_MARKED:  // It's being resolved.
      return false;  // We're already working on it

    case NO_SUCH_NAME:  // Lookup failed.
    case FOUND:  // Lookup succeeded.
      return !IsStillCached();  // See if DNS cache expired.

    default:
      NOTREACHED();
      return false;
  }
}

// Used by test ONLY. The value is otherwise constant.
// static
void UrlInfo::set_cache_expiration(TimeDelta time) {
  global_state.Pointer()->cache_expiration_duration = time;
}

// static
TimeDelta UrlInfo::get_cache_expiration() {
  return global_state.Get().cache_expiration_duration;
}

void UrlInfo::SetQueuedState(ResolutionMotivation motivation) {
  DCHECK(PENDING == state_ || FOUND == state_ || NO_SUCH_NAME == state_);
  old_prequeue_state_ = state_;
  state_ = QUEUED;
  queue_duration_ = resolve_duration_ = NullDuration();
  SetMotivation(motivation);
  GetDuration();  // Set time_
  DLogResultsStats("DNS Prefetch in queue");
}

void UrlInfo::SetAssignedState() {
  DCHECK(QUEUED == state_);
  state_ = ASSIGNED;
  queue_duration_ = GetDuration();
  DLogResultsStats("DNS Prefetch assigned");
}

void UrlInfo::RemoveFromQueue() {
  DCHECK(ASSIGNED == state_);
  state_ = old_prequeue_state_;
  DLogResultsStats("DNS Prefetch reset to prequeue");
}

void UrlInfo::SetPendingDeleteState() {
  DCHECK(ASSIGNED == state_  || ASSIGNED_BUT_MARKED == state_);
  state_ = ASSIGNED_BUT_MARKED;
}

void UrlInfo::SetFoundState() {
  DCHECK(ASSIGNED == state_ || ASSIGNED_BUT_MARKED == state_);
  state_ = FOUND;
  resolve_duration_ = GetDuration();
  const TimeDelta max_duration = MaxNonNetworkDnsLookupDuration();
  if (max_duration <= resolve_duration_) {
    UMA_HISTOGRAM_CUSTOM_TIMES("DNS.PrefetchResolution", resolve_duration_,
        max_duration, TimeDelta::FromMinutes(15), 100);
  }
  sequence_number_ = sequence_counter++;
  DLogResultsStats("DNS PrefetchFound");
}

void UrlInfo::SetNoSuchNameState() {
  DCHECK(ASSIGNED == state_ || ASSIGNED_BUT_MARKED == state_);
  state_ = NO_SUCH_NAME;
  resolve_duration_ = GetDuration();
#ifndef NDEBUG
  if (MaxNonNetworkDnsLookupDuration() <= resolve_duration_) {
    LOCAL_HISTOGRAM_TIMES("DNS.PrefetchNotFoundName", resolve_duration_);
  }
#endif
  sequence_number_ = sequence_counter++;
  DLogResultsStats("DNS PrefetchNotFound");
}

void UrlInfo::SetUrl(const GURL& url) {
  if (url_.is_empty())  // Not yet initialized.
    url_ = url;
  else
    DCHECK_EQ(url_, url);
}

// IsStillCached() guesses if the DNS cache still has IP data,
// or at least remembers results about "not finding host."
bool UrlInfo::IsStillCached() const {
  DCHECK(FOUND == state_ || NO_SUCH_NAME == state_);

  // Default MS OS does not cache failures. Hence we could return false almost
  // all the time for that case.  However, we'd never try again to prefetch
  // the value if we returned false that way.  Hence we'll just let the lookup
  // time out the same way as FOUND case.

  if (sequence_counter - sequence_number_ > kMaxGuaranteedDnsCacheSize)
    return false;

  TimeDelta time_since_resolution = TimeTicks::Now() - time_;
  return time_since_resolution < global_state.Get().cache_expiration_duration;
}

void UrlInfo::DLogResultsStats(const char* message) const {
  if (!detailed_logging_enabled)
    return;
  DVLOG(1) << "\t" << message << "\tq=" << queue_duration().InMilliseconds()
           << "ms,\tr=" << resolve_duration().InMilliseconds()
           << "ms,\tp=" << sequence_number_ << "\t" << url_.spec();
}

void UrlInfo::SetMotivation(ResolutionMotivation motivation) {
  motivation_ = motivation;
  if (motivation < LINKED_MAX_MOTIVATED)
    was_linked_ = true;
}

}  // namespace chrome_browser_net