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1 // Copyright 2016 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #ifndef NET_BASE_NETWORK_THROTTLE_MANAGER_IMPL_H_ | |
6 #define NET_BASE_NETWORK_THROTTLE_MANAGER_IMPL_H_ | |
7 | |
8 #include <list> | |
9 #include <memory> | |
10 #include <set> | |
11 | |
12 #include "base/time/tick_clock.h" | |
13 #include "base/time/time.h" | |
14 #include "base/timer/timer.h" | |
15 #include "net/base/network_throttle_manager.h" | |
16 #include "net/base/quantile_estimator.h" | |
17 | |
18 namespace net { | |
19 | |
20 // The NetworkThrottleManagerImpl implements the following semantics: | |
21 // * All throttles of priority above THROTTLED are created unblocked. | |
22 // * Throttles of priority THROTTLED are created unblocked, unless | |
23 // there are |kActiveRequestThrottlingLimit| or more throttles active, | |
24 // in which case they are created blocked. | |
25 // When that condition is no longer true, throttles of priority | |
26 // THROTTLED are unblocked, in priority order. | |
27 // * Throttles that have been alive for more than |kMedianLifetimeMultiple| | |
28 // times the current estimate of the throttle median lifetime do | |
29 // not count against the |kActiveRequestThrottlingLimit| limit. | |
30 class NET_EXPORT NetworkThrottleManagerImpl : public NetworkThrottleManager { | |
31 public: | |
32 // Maximum number of active requests before new THROTTLED throttles | |
33 // are created blocked. Throttles are unblocked as the active requests | |
34 // fall below this limit. | |
35 static const size_t kActiveRequestThrottlingLimit; | |
36 | |
37 // Note that the following constants are implementation details exposed in the | |
38 // header file only for testing, and should not be relied on by consumers. | |
39 | |
40 // Constants used for the running estimate of the median lifetime | |
41 // for throttles created by this class. That estimate is used to detect | |
42 // throttles that are "unusually old" and hence may represent hanging GETs | |
43 // or long-running streams. Such throttles should not be considered | |
44 // "active" for the purposes of determining whether THROTTLED throttles | |
45 // should be created in a blocked state. | |
46 // Note that the precise details of this algorithm aren't very important; | |
47 // specifically, if it takes a while for the median estimate to reach the | |
48 // "actual" median of a request stream, the consequence is either a bit more | |
49 // of a delay in unblocking THROTTLED requests or more THROTTLED requests | |
50 // being unblocked than would be ideal (i.e. performance tweaks at | |
51 // the margins). | |
52 | |
53 // Multiple of the current median lifetime beyond which a throttle is | |
54 // considered "unusually old" and not considered in counting active | |
55 // requests. | |
56 static const int kMedianLifetimeMultiple; | |
Charlie Harrison
2016/09/01 18:17:52
Why not just implement the algorithm that calculat
Randy Smith (Not in Mondays)
2016/09/18 19:12:34
I want things that are qualitatively different to
| |
57 | |
58 // The median lifetime estimate starts at class creation at | |
59 // |kInitialMedianInMs|. | |
60 static const int kInitialMedianInMs; | |
61 | |
62 NetworkThrottleManagerImpl(); | |
63 ~NetworkThrottleManagerImpl() override; | |
64 | |
65 // NetworkThrottleManager: | |
66 std::unique_ptr<Throttle> CreateThrottle(ThrottleDelegate* delegate, | |
67 RequestPriority priority, | |
68 bool ignore_limits) override; | |
69 | |
70 void SetTickClockForTesting(std::unique_ptr<base::TickClock> tick_clock); | |
71 | |
72 // If the |NowTicks()| value of |tick_clock_| is greater than the | |
73 // time the outstanding_recomputation_timer_ has set to go off, Stop() | |
74 // the timer and manually run the associated user task. This is to allow | |
75 // "fast-forwarding" of the clock for testing by working around | |
76 // base::Timer's direct use of base::TimeTicks rather than a base::TickClock. | |
77 // | |
78 // Note specifically that base::Timer::Start takes a time delta into the | |
79 // future and adds it to base::TimeTicks::Now() to get | |
80 // base::Timer::desired_run_time(), which is what this method compares | |
81 // |tick_clock_->NowTicks()| against. So tests should be written so that | |
82 // the timer Start() routine whose callback should be run is called | |
83 // with |tick_clock_| in accord with wallclock time. This routine can then | |
84 // be called with |tick_clock_| set into the future. | |
85 void ConditionallyTriggerTimerForTesting(); | |
86 | |
87 private: | |
88 class ThrottleImpl : public NetworkThrottleManager::Throttle { | |
89 public: | |
90 using ThrottleList = std::list<ThrottleImpl*>; | |
91 using QueuePointer = ThrottleList::iterator; | |
92 | |
93 // Caller must arrange that |*delegate| and |*manager| outlive | |
94 // the ThrottleImpl class. | |
95 ThrottleImpl(bool blocked, | |
96 RequestPriority priority, | |
97 ThrottleDelegate* delegate, | |
98 NetworkThrottleManagerImpl* manager, | |
99 QueuePointer queue_pointer); | |
100 | |
101 ~ThrottleImpl() override; | |
102 | |
103 // Throttle: | |
104 bool IsBlocked() const override; | |
105 RequestPriority Priority() const override; | |
106 void SetPriority(RequestPriority priority) override; | |
107 | |
108 RequestPriority priority() const { return priority_; } | |
109 QueuePointer queue_pointer() const { return queue_pointer_; } | |
110 void set_queue_pointer(const QueuePointer& pointer) { | |
111 queue_pointer_ = pointer; | |
112 } | |
113 base::TimeTicks start_time() const { return start_time_; } | |
114 void set_start_time(base::TimeTicks start_time) { | |
115 start_time_ = start_time; | |
116 } | |
117 | |
118 // Note that this call calls the delegate, and hence | |
119 // may result in re-entrant calls into the manager or | |
120 // ThrottleImpl. The manager should not rely on | |
121 // any state other than its own existence being persistent | |
122 // across this call. | |
123 void NotifyUnblocked(); | |
124 | |
125 private: | |
126 bool blocked_; | |
127 RequestPriority priority_; | |
128 ThrottleDelegate* const delegate_; | |
129 NetworkThrottleManagerImpl* const manager_; | |
130 | |
131 base::TimeTicks start_time_; | |
132 | |
133 // For deletion from owning queue. | |
134 QueuePointer queue_pointer_; | |
135 | |
136 DISALLOW_COPY_AND_ASSIGN(ThrottleImpl); | |
137 }; | |
138 | |
139 // Comparison function used to define the ordering relationship | |
140 // for |CreationOrderingSet| below. | |
141 static bool CompareThrottlesForCreationTime(ThrottleImpl* throttle1, | |
142 ThrottleImpl* throttle2); | |
mmenke
2016/09/01 19:14:23
This does need to be in this file, right?
Randy Smith (Not in Mondays)
2016/09/18 19:12:34
It needs access to the start time of the throttles
| |
143 | |
144 using CreationOrderingSet = | |
mmenke
2016/09/01 19:14:23
CreationTimeOrderedSet? This it's better to name
Randy Smith (Not in Mondays)
2016/09/18 19:12:34
Done.
| |
145 std::set<ThrottleImpl*, bool (*)(ThrottleImpl*, ThrottleImpl*)>; | |
146 | |
147 void OnThrottlePriorityChanged(ThrottleImpl* throttle, | |
148 RequestPriority old_priority, | |
149 RequestPriority new_priority); | |
150 void OnThrottleDestroyed(ThrottleImpl* throttle); | |
151 | |
152 // Recompute how many requests "count" as outstanding (i.e. | |
153 // are not older than kMedianLifetimeMultiple * MedianThrottleLifetime()). | |
154 void RecomputeOutstanding(); | |
155 | |
156 // Unblock the specified throttle. May result in re-entrant calls | |
157 // into NetworkThrottleManagerImpl. | |
158 void UnblockThrottle(ThrottleImpl* throttle); | |
159 | |
160 // Recomputes how many requests count as outstanding, checks to see | |
161 // if any currently blocked throttles should be unblocked, | |
162 // and unblock them if so. Note that unblocking may result in | |
163 // re-entrant calls to this class, so no assumptions about state persistence | |
164 // should be made across this call. | |
165 void MaybeUnblockThrottles(); | |
166 | |
167 // Convenience functions to determine which of the ThrottleLists | |
168 // from {blocked,unblocked}_requests_ apply to a given | |
169 // throttle/(blocked, priority) pair. | |
170 ThrottleImpl::ThrottleList* ListForThrottle(bool blocked, | |
Charlie Harrison
2016/09/01 18:17:52
Technically not really the list for a throttle, bu
Randy Smith (Not in Mondays)
2016/09/18 19:12:34
Done.
| |
171 RequestPriority priority); | |
172 ThrottleImpl::ThrottleList* ListForThrottle(ThrottleImpl* throttle); | |
173 | |
174 // For DCHECK assertions: Could the number of blocked throttles. | |
175 size_t NumberBlockedThrottles() const; | |
176 | |
177 QuantileEstimator lifetime_median_estimate_; | |
178 | |
179 // Only contains unblocked throttles; blocked throttles haven't started | |
180 // and hence don't have a start time. | |
181 CreationOrderingSet start_time_ordering_set_; | |
182 | |
183 size_t num_throttles_blocked_; | |
184 | |
185 // Count of throttles that are considered as outstanding. Throttles that | |
186 // are too old or blocked are not counted. | |
187 size_t num_effective_outstanding_; | |
188 | |
189 // base::Timer controlling outstanding request recomputation. | |
190 base::Timer outstanding_recomputation_timer_; | |
191 | |
192 // Lists of blocked/unblocked request at each priority level. | |
193 // It is safe to store a raw pointer in these lists because the | |
194 // manager will be notified by OnThrottleDestroyed before a ThrottleImpl | |
195 // is destroyed, and will remove the pointer from the appropriate list | |
196 // at that point. | |
197 ThrottleImpl::ThrottleList blocked_requests_[NUM_PRIORITIES]; | |
198 ThrottleImpl::ThrottleList unblocked_requests_[NUM_PRIORITIES]; | |
199 | |
200 // For testing. | |
201 std::unique_ptr<base::TickClock> tick_clock_; | |
202 | |
203 DISALLOW_COPY_AND_ASSIGN(NetworkThrottleManagerImpl); | |
204 }; | |
205 | |
206 } // namespace net | |
207 | |
208 #endif // NET_BASE_NETWORK_THROTTLE_MANAGER_IMPL_H_ | |
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