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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/check_op.h"
- #include "base/numerics/clamped_math.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,
- const base::TickClock* clock)
- : policy_(policy), clock_(clock) {
- DCHECK(policy_);
- Reset();
- }
- BackoffEntry::~BackoffEntry() {
- // TODO(joi): Enable this once our clients (e.g. URLRequestThrottlerManager)
- // always destroy from the I/O thread.
- // DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
- }
- 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::Milliseconds(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_t 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::GetTimeTicksNow() const {
- return clock_ ? clock_->NowTicks() : base::TimeTicks::Now();
- }
- base::TimeTicks BackoffEntry::CalculateReleaseTime() const {
- base::ClampedNumeric<int> effective_failure_count =
- base::ClampSub(failure_count_, policy_->num_errors_to_ignore).Max(0);
- // 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_t> 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_t> backoff_duration_us = delay_ms + 0.5;
- backoff_duration_us *= base::Time::kMicrosecondsPerMillisecond;
- base::TimeDelta backoff_duration = base::Microseconds(int64_t{
- backoff_duration_us.ValueOrDefault(std::numeric_limits<int64_t>::max())});
- 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_t kTimeTicksNowUs =
- (GetTimeTicksNow() - base::TimeTicks()).InMicroseconds();
- // Do overflow checking in microseconds, the internal unit of TimeTicks.
- base::internal::CheckedNumeric<int64_t> calculated_release_time_us =
- backoff_duration.InMicroseconds();
- calculated_release_time_us += kTimeTicksNowUs;
- base::internal::CheckedNumeric<int64_t> maximum_release_time_us =
- std::numeric_limits<int64_t>::max();
- 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_t release_time_us = std::min(calculated_release_time_us.ValueOrDefault(
- std::numeric_limits<int64_t>::max()),
- maximum_release_time_us.ValueOrDefault(
- std::numeric_limits<int64_t>::max()));
- return base::TimeTicks() + base::Microseconds(release_time_us);
- }
- } // namespace net
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