Index: net/base/network_throttle_manager_impl.h |
diff --git a/net/base/network_throttle_manager_impl.h b/net/base/network_throttle_manager_impl.h |
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+++ b/net/base/network_throttle_manager_impl.h |
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+// 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(std::unique_ptr<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. |
+ 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. |
+ std::unique_ptr<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_ |