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// Copyright (c) 2006-2008 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/referrer.h"
#include "base/logging.h"
namespace chrome_browser_net {
void Referrer::SuggestHost(const std::string& host) {
// Limit how large our list can get, in case we make mistakes about what
// hostnames are in sub-resources (example: Some advertisments have a link to
// the ad agency, and then provide a "surprising" redirect to the advertised
// entity, which then (mistakenly) appears to be a subresource on the page
// hosting the ad).
// TODO(jar): Do experiments to optimize the max count of suggestions.
static const size_t kMaxSuggestions = 8;
if (host.empty())
return;
if (kMaxSuggestions <= size()) {
DeleteLeastUseful();
DCHECK(kMaxSuggestions > size());
}
// Add in the new suggestion.
(*this)[host];
}
void Referrer::DeleteLeastUseful() {
std::string least_useful_name;
// We use longs for durations because we will use multiplication on them.
int64 least_useful_latency = 0; // Duration in milliseconds.
int64 least_useful_lifetime = 0; // Duration in milliseconds.
const base::Time kNow(base::Time::Now()); // Avoid multiple calls.
for (HostNameMap::iterator it = this->begin(); it != this->end(); ++it) {
int64 lifetime = (kNow - it->second.birth_time()).InMilliseconds();
int64 latency = it->second.latency().InMilliseconds();
if (!least_useful_name.empty()) {
if (!latency && !least_useful_latency) {
// Older name is less useful.
if (lifetime <= least_useful_lifetime)
continue;
} else {
// Compare the ratios latency/lifetime vs.
// least_useful_latency/least_useful_lifetime by cross multiplying (to
// avoid integer division hassles). Overflow's won't happen until
// both latency and lifetime pass about 49 days.
if (latency * least_useful_lifetime >=
least_useful_latency * lifetime) {
continue;
}
}
}
least_useful_name = it->first;
least_useful_latency = latency;
least_useful_lifetime = lifetime;
}
erase(least_useful_name);
// Note: there is a small chance that we will discard a least_useful_name
// that is currently being prefetched because it *was* in this referer list.
// In that case, when a benefit appears in AccrueValue() below, we are careful
// to check before accessing the member.
}
void Referrer::AccrueValue(const base::TimeDelta& delta,
const std::string host) {
HostNameMap::iterator it = this->find(host);
// Be careful that we weren't evicted from this referrer in DeleteLeastUseful.
if (it != this->end())
it->second.AccrueValue(delta);
}
} // namespace chrome_browser_net
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