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// Copyright (c) 2011 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 "base/logging.h"
#include "base/rand_util.h"
namespace net {
BackoffEntry::BackoffEntry(const BackoffEntry::Policy* const policy)
: failure_count_(0),
policy_(policy) {
DCHECK(policy_);
// Can't use GetTimeNow() as it's virtual.
exponential_backoff_release_time_ = base::TimeTicks::Now();
}
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.
//
// TODO(joi): Revisit this; it might be most correct to go to zero
// but have a way to go back to "old error count +1" if there is
// another error soon after.
if (failure_count_ > 0)
--failure_count_;
// The reason why we are not just cutting the release time to GetTimeNow()
// 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.
exponential_backoff_release_time_ = std::max(
GetTimeNow(), exponential_backoff_release_time_);
}
}
bool BackoffEntry::ShouldRejectRequest() const {
return exponential_backoff_release_time_ > GetTimeNow();
}
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 = GetTimeNow();
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;
}
base::TimeTicks BackoffEntry::GetTimeNow() const {
return base::TimeTicks::Now();
}
base::TimeTicks BackoffEntry::CalculateReleaseTime() const {
int effective_failure_count =
std::max(0, failure_count_ - policy_->num_errors_to_ignore);
if (effective_failure_count == 0) {
// Never reduce previously set release horizon, e.g. due to Retry-After
// header.
return std::max(GetTimeNow(), 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]
double delay = policy_->initial_backoff_ms;
delay *= pow(policy_->multiply_factor, effective_failure_count - 1);
delay -= base::RandDouble() * policy_->jitter_factor * delay;
// Ensure that we do not exceed maximum delay.
int64 delay_int = static_cast<int64>(delay + 0.5);
delay_int = std::min(delay_int,
static_cast<int64>(policy_->maximum_backoff_ms));
// Never reduce previously set release horizon, e.g. due to Retry-After
// header.
return std::max(GetTimeNow() + base::TimeDelta::FromMilliseconds(delay_int),
exponential_backoff_release_time_);
}
} // namespace net
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