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// 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 "net/base/backoff_entry.h"
#include <algorithm>
#include <cmath>
#include <limits>
#include "base/basictypes.h"
#include "base/logging.h"
#include "base/numerics/safe_math.h"
#include "base/rand_util.h"
#include "base/time/tick_clock.h"
namespace net {
BackoffEntry::BackoffEntry(const BackoffEntry::Policy* policy)
: BackoffEntry(policy, nullptr) {}
BackoffEntry::BackoffEntry(const BackoffEntry::Policy* policy,
base::TickClock* clock)
: policy_(policy), clock_(clock) {
DCHECK(policy_);
Reset();
}
BackoffEntry::~BackoffEntry() {
// TODO(joi): Remove this once our clients (e.g. URLRequestThrottlerManager)
// always destroy from the I/O thread.
DetachFromThread();
}
void BackoffEntry::InformOfRequest(bool succeeded) {
if (!succeeded) {
++failure_count_;
exponential_backoff_release_time_ = CalculateReleaseTime();
} else {
// We slowly decay the number of times delayed instead of
// resetting it to 0 in order to stay stable if we receive
// successes interleaved between lots of failures. Note that in
// the normal case, the calculated release time (in the next
// statement) will be in the past once the method returns.
if (failure_count_ > 0)
--failure_count_;
// The reason why we are not just cutting the release time to
// GetTimeTicksNow() is on the one hand, it would unset a release
// time set by SetCustomReleaseTime and on the other we would like
// to push every request up to our "horizon" when dealing with
// multiple in-flight requests. Ex: If we send three requests and
// we receive 2 failures and 1 success. The success that follows
// those failures will not reset the release time, further
// requests will then need to wait the delay caused by the 2
// failures.
base::TimeDelta delay;
if (policy_->always_use_initial_delay)
delay = base::TimeDelta::FromMilliseconds(policy_->initial_delay_ms);
exponential_backoff_release_time_ = std::max(
GetTimeTicksNow() + delay, exponential_backoff_release_time_);
}
}
bool BackoffEntry::ShouldRejectRequest() const {
return exponential_backoff_release_time_ > GetTimeTicksNow();
}
base::TimeDelta BackoffEntry::GetTimeUntilRelease() const {
base::TimeTicks now = GetTimeTicksNow();
if (exponential_backoff_release_time_ <= now)
return base::TimeDelta();
return exponential_backoff_release_time_ - now;
}
base::TimeTicks BackoffEntry::GetReleaseTime() const {
return exponential_backoff_release_time_;
}
void BackoffEntry::SetCustomReleaseTime(const base::TimeTicks& release_time) {
exponential_backoff_release_time_ = release_time;
}
bool BackoffEntry::CanDiscard() const {
if (policy_->entry_lifetime_ms == -1)
return false;
base::TimeTicks now = GetTimeTicksNow();
int64 unused_since_ms =
(now - exponential_backoff_release_time_).InMilliseconds();
// Release time is further than now, we are managing it.
if (unused_since_ms < 0)
return false;
if (failure_count_ > 0) {
// Need to keep track of failures until maximum back-off period
// has passed (since further failures can add to back-off).
return unused_since_ms >= std::max(policy_->maximum_backoff_ms,
policy_->entry_lifetime_ms);
}
// Otherwise, consider the entry is outdated if it hasn't been used for the
// specified lifetime period.
return unused_since_ms >= policy_->entry_lifetime_ms;
}
void BackoffEntry::Reset() {
failure_count_ = 0;
// For legacy reasons, we reset exponential_backoff_release_time_ to the
// uninitialized state. It would also be reasonable to reset it to
// GetTimeTicksNow(). The effects are the same, i.e. ShouldRejectRequest()
// will return false right after Reset().
exponential_backoff_release_time_ = base::TimeTicks();
}
base::TimeTicks BackoffEntry::CalculateReleaseTime() const {
int effective_failure_count =
std::max(0, failure_count_ - policy_->num_errors_to_ignore);
// If always_use_initial_delay is true, it's equivalent to
// the effective_failure_count always being one greater than when it's false.
if (policy_->always_use_initial_delay)
++effective_failure_count;
if (effective_failure_count == 0) {
// Never reduce previously set release horizon, e.g. due to Retry-After
// header.
return std::max(GetTimeTicksNow(), exponential_backoff_release_time_);
}
// The delay is calculated with this formula:
// delay = initial_backoff * multiply_factor^(
// effective_failure_count - 1) * Uniform(1 - jitter_factor, 1]
// Note: if the failure count is too high, |delay_ms| will become infinity
// after the exponential calculation, and then NaN after the jitter is
// accounted for. Both cases are handled by using CheckedNumeric<int64> to
// perform the conversion to integers.
double delay_ms = policy_->initial_delay_ms;
delay_ms *= pow(policy_->multiply_factor, effective_failure_count - 1);
delay_ms -= base::RandDouble() * policy_->jitter_factor * delay_ms;
// Do overflow checking in microseconds, the internal unit of TimeTicks.
base::internal::CheckedNumeric<int64> backoff_duration_us = delay_ms + 0.5;
backoff_duration_us *= base::Time::kMicrosecondsPerMillisecond;
base::TimeDelta backoff_duration = base::TimeDelta::FromMicroseconds(
backoff_duration_us.ValueOrDefault(kint64max));
base::TimeTicks release_time = BackoffDurationToReleaseTime(backoff_duration);
// Never reduce previously set release horizon, e.g. due to Retry-After
// header.
return std::max(release_time, exponential_backoff_release_time_);
}
base::TimeTicks BackoffEntry::BackoffDurationToReleaseTime(
base::TimeDelta backoff_duration) const {
const int64 kTimeTicksNowUs =
(GetTimeTicksNow() - base::TimeTicks()).InMicroseconds();
// Do overflow checking in microseconds, the internal unit of TimeTicks.
base::internal::CheckedNumeric<int64> calculated_release_time_us =
backoff_duration.InMicroseconds();
calculated_release_time_us += kTimeTicksNowUs;
base::internal::CheckedNumeric<int64> maximum_release_time_us = kint64max;
if (policy_->maximum_backoff_ms >= 0) {
maximum_release_time_us = policy_->maximum_backoff_ms;
maximum_release_time_us *= base::Time::kMicrosecondsPerMillisecond;
maximum_release_time_us += kTimeTicksNowUs;
}
// Decide between maximum release time and calculated release time, accounting
// for overflow with both.
int64 release_time_us = std::min(
calculated_release_time_us.ValueOrDefault(kint64max),
maximum_release_time_us.ValueOrDefault(kint64max));
return base::TimeTicks() + base::TimeDelta::FromMicroseconds(release_time_us);
}
base::TimeTicks BackoffEntry::GetTimeTicksNow() const {
return clock_ ? clock_->NowTicks() : base::TimeTicks::Now();
}
} // namespace net
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