| // Copyright 2016 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. |
| |
| #ifndef NET_BASE_NETWORK_THROTTLE_MANAGER_IMPL_H_ |
| #define NET_BASE_NETWORK_THROTTLE_MANAGER_IMPL_H_ |
| |
| #include <list> |
| #include <memory> |
| #include <set> |
| |
| #include "base/memory/weak_ptr.h" |
| #include "base/time/tick_clock.h" |
| #include "base/time/time.h" |
| #include "base/timer/timer.h" |
| #include "net/base/network_throttle_manager.h" |
| #include "net/base/percentile_estimator.h" |
| |
| namespace net { |
| |
| // The NetworkThrottleManagerImpl implements the following semantics: |
| // * All throttles of priority above THROTTLED are created unblocked. |
| // * Throttles of priority THROTTLED are created unblocked, unless |
| // there are |kActiveRequestThrottlingLimit| or more throttles active, |
| // in which case they are created blocked. |
| // When that condition is no longer true, throttles of priority |
| // THROTTLED are unblocked, in FIFO order. |
| // * Throttles that have been alive for more than |kMedianLifetimeMultiple| |
| // times the current estimate of the throttle median lifetime do |
| // not count against the |kActiveRequestThrottlingLimit| limit. |
| class NET_EXPORT NetworkThrottleManagerImpl : public NetworkThrottleManager { |
| public: |
| // Maximum number of active requests before new THROTTLED throttles |
| // are created blocked. Throttles are unblocked as the active requests |
| // fall below this limit. |
| static const size_t kActiveRequestThrottlingLimit; |
| |
| // Note that the following constants are implementation details exposed in the |
| // header file only for testing, and should not be relied on by consumers. |
| |
| // Constants used for the running estimate of the median lifetime |
| // for throttles created by this class. That estimate is used to detect |
| // throttles that are "unusually old" and hence may represent hanging GETs |
| // or long-running streams. Such throttles should not be considered |
| // "active" for the purposes of determining whether THROTTLED throttles |
| // should be created in a blocked state. |
| // Note that the precise details of this algorithm aren't very important; |
| // specifically, if it takes a while for the median estimate to reach the |
| // "actual" median of a request stream, the consequence is either a bit more |
| // of a delay in unblocking THROTTLED requests or more THROTTLED requests |
| // being unblocked than would be ideal (i.e. performance tweaks at |
| // the margins). |
| |
| // Multiple of the current median lifetime beyond which a throttle is |
| // considered "unusually old" and not considered in counting active |
| // requests. This is used instead of a percentile estimate because the goal |
| // is eliminating requests that are qualitatively different |
| // (e.g. hanging gets, streams), and the percentage of all requests |
| // that are in that category can vary greatly. |
| static const int kMedianLifetimeMultiple; |
| |
| // The median lifetime estimate starts at class creation at |
| // |kInitialMedianInMs|. |
| static const int kInitialMedianInMs; |
| |
| NetworkThrottleManagerImpl(); |
| ~NetworkThrottleManagerImpl() override; |
| |
| // NetworkThrottleManager: |
| std::unique_ptr<Throttle> CreateThrottle(ThrottleDelegate* delegate, |
| RequestPriority priority, |
| bool ignore_limits) override; |
| |
| void SetTickClockForTesting(const base::TickClock* tick_clock); |
| |
| // If the |NowTicks()| value of |tick_clock_| is greater than the |
| // time the outstanding_recomputation_timer_ has set to go off, Stop() |
| // the timer and manually run the associated user task. This is to allow |
| // "fast-forwarding" of the clock for testing by working around |
| // base::Timer's direct use of base::TimeTicks rather than a base::TickClock. |
| // |
| // Note specifically that base::Timer::Start takes a time delta into the |
| // future and adds it to base::TimeTicks::Now() to get |
| // base::Timer::desired_run_time(), which is what this method compares |
| // |tick_clock_->NowTicks()| against. So tests should be written so that |
| // the timer Start() routine whose callback should be run is called |
| // with |tick_clock_| in accord with wallclock time. This routine can then |
| // be called with |tick_clock_| set into the future. |
| // |
| // Returns true if there was a timer running and it was triggerred |
| // (|tick_clock_->NowTicks() > |
| // outstanding_recomputation_timer_.desired_run_time()|). |
| bool ConditionallyTriggerTimerForTesting(); |
| |
| private: |
| class ThrottleImpl; |
| using ThrottleList = std::list<ThrottleImpl*>; |
| |
| void OnThrottlePriorityChanged(ThrottleImpl* throttle, |
| RequestPriority old_priority, |
| RequestPriority new_priority); |
| void OnThrottleDestroyed(ThrottleImpl* throttle); |
| |
| // Recompute how many requests count as outstanding (i.e. |
| // are not older than kMedianLifetimeMultiple * MedianThrottleLifetime()). |
| // If outstanding_recomputation_timer_ is not set, it will be set |
| // to the earliest a throttle might "age out" of the outstanding list. |
| void RecomputeOutstanding(); |
| |
| // Unblock the specified throttle. May result in re-entrant calls |
| // into NetworkThrottleManagerImpl. |
| void UnblockThrottle(ThrottleImpl* throttle); |
| |
| // Recomputes how many requests count as outstanding, checks to see |
| // if any currently blocked throttles should be unblocked, |
| // and unblock them if so. Note that unblocking may result in |
| // re-entrant calls to this class, so no assumptions about state persistence |
| // should be made across this call. |
| void MaybeUnblockThrottles(); |
| |
| PercentileEstimator lifetime_median_estimate_; |
| |
| // base::Timer controlling outstanding request recomputation. |
| // |
| // This is started whenever it is not running and a new throttle is |
| // added to |outstanding_throttles_|, and is never cleared except by |
| // execution, which re-starts it if there are any |
| // outstanding_throttles_. So it should always be running if any |
| // throttles are outstanding. This guarantees that the class will |
| // eventually detect aging out of outstanding throttles and unblock |
| // throttles blocked on those outstanding throttles. |
| std::unique_ptr<base::Timer> outstanding_recomputation_timer_; |
| |
| // FIFO of OUTSTANDING throttles (ordered by time of entry into the |
| // OUTSTANDING state). |
| ThrottleList outstanding_throttles_; |
| |
| // FIFO list of BLOCKED throttles. This is a list so that the |
| // throttles can store iterators to themselves. |
| ThrottleList blocked_throttles_; |
| |
| // For testing. |
| const base::TickClock* tick_clock_; |
| |
| base::WeakPtrFactory<NetworkThrottleManagerImpl> weak_ptr_factory_; |
| |
| DISALLOW_COPY_AND_ASSIGN(NetworkThrottleManagerImpl); |
| }; |
| |
| } // namespace net |
| |
| #endif // NET_BASE_NETWORK_THROTTLE_MANAGER_IMPL_H_ |