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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/memory/weak_ptr.h" | |
13 #include "base/time/tick_clock.h" | |
14 #include "base/time/time.h" | |
15 #include "base/timer/timer.h" | |
16 #include "net/base/network_throttle_manager.h" | |
17 #include "net/base/percentile_estimator.h" | |
18 | |
19 namespace net { | |
20 | |
21 // The NetworkThrottleManagerImpl implements the following semantics: | |
22 // * All throttles of priority above THROTTLED are created unblocked. | |
23 // * Throttles of priority THROTTLED are created unblocked, unless | |
24 // there are |kActiveRequestThrottlingLimit| or more throttles active, | |
25 // in which case they are created blocked. | |
26 // When that condition is no longer true, throttles of priority | |
27 // THROTTLED are unblocked, in FIFO order. | |
28 // * Throttles that have been alive for more than |kMedianLifetimeMultiple| | |
29 // times the current estimate of the throttle median lifetime do | |
30 // not count against the |kActiveRequestThrottlingLimit| limit. | |
31 class NET_EXPORT NetworkThrottleManagerImpl : public NetworkThrottleManager { | |
32 public: | |
33 // Maximum number of active requests before new THROTTLED throttles | |
34 // are created blocked. Throttles are unblocked as the active requests | |
35 // fall below this limit. | |
36 static const size_t kActiveRequestThrottlingLimit; | |
37 | |
38 // Note that the following constants are implementation details exposed in the | |
39 // header file only for testing, and should not be relied on by consumers. | |
40 | |
41 // Constants used for the running estimate of the median lifetime | |
42 // for throttles created by this class. That estimate is used to detect | |
43 // throttles that are "unusually old" and hence may represent hanging GETs | |
44 // or long-running streams. Such throttles should not be considered | |
45 // "active" for the purposes of determining whether THROTTLED throttles | |
46 // should be created in a blocked state. | |
47 // Note that the precise details of this algorithm aren't very important; | |
48 // specifically, if it takes a while for the median estimate to reach the | |
49 // "actual" median of a request stream, the consequence is either a bit more | |
50 // of a delay in unblocking THROTTLED requests or more THROTTLED requests | |
51 // being unblocked than would be ideal (i.e. performance tweaks at | |
52 // the margins). | |
53 | |
54 // Multiple of the current median lifetime beyond which a throttle is | |
55 // considered "unusually old" and not considered in counting active | |
56 // requests. This is used instead of a percentile estimate because the goal | |
57 // is eliminating requests that are qualitatively different | |
58 // (e.g. hanging gets, streams), and the percentage of all requests | |
59 // that are in that category can vary greatly. | |
60 static const int kMedianLifetimeMultiple; | |
61 | |
62 // The median lifetime estimate starts at class creation at | |
63 // |kInitialMedianInMs|. | |
64 static const int kInitialMedianInMs; | |
65 | |
66 NetworkThrottleManagerImpl(); | |
67 ~NetworkThrottleManagerImpl() override; | |
68 | |
69 // NetworkThrottleManager: | |
70 std::unique_ptr<Throttle> CreateThrottle(ThrottleDelegate* delegate, | |
71 RequestPriority priority, | |
72 bool ignore_limits) override; | |
73 | |
74 void SetTickClockForTesting(std::unique_ptr<base::TickClock> tick_clock); | |
75 | |
76 // If the |NowTicks()| value of |tick_clock_| is greater than the | |
77 // time the outstanding_recomputation_timer_ has set to go off, Stop() | |
78 // the timer and manually run the associated user task. This is to allow | |
79 // "fast-forwarding" of the clock for testing by working around | |
80 // base::Timer's direct use of base::TimeTicks rather than a base::TickClock. | |
81 // | |
82 // Note specifically that base::Timer::Start takes a time delta into the | |
83 // future and adds it to base::TimeTicks::Now() to get | |
84 // base::Timer::desired_run_time(), which is what this method compares | |
85 // |tick_clock_->NowTicks()| against. So tests should be written so that | |
86 // the timer Start() routine whose callback should be run is called | |
87 // with |tick_clock_| in accord with wallclock time. This routine can then | |
88 // be called with |tick_clock_| set into the future. | |
89 // | |
90 // Returns true if there was a timer running and it was triggerred | |
91 // (|tick_clock_->NowTicks() > | |
92 // outstanding_recomputation_timer_.desired_run_time()|). | |
93 bool ConditionallyTriggerTimerForTesting(); | |
94 | |
95 private: | |
96 class ThrottleImpl; | |
97 using ThrottleList = std::list<ThrottleImpl*>; | |
98 | |
99 // Comparison function used to define the ordering relationship | |
100 // for |StartTimeOrderedSet| below. | |
101 static bool StartTimeSetCompare(ThrottleImpl* throttle1, | |
102 ThrottleImpl* throttle2); | |
103 | |
104 using StartTimeOrderedSet = | |
105 std::set<ThrottleImpl*, bool (*)(ThrottleImpl*, ThrottleImpl*)>; | |
106 | |
107 void OnThrottlePriorityChanged(ThrottleImpl* throttle, | |
108 RequestPriority old_priority, | |
109 RequestPriority new_priority); | |
110 void OnThrottleDestroyed(ThrottleImpl* throttle); | |
111 | |
112 // Recompute how many requests count as outstanding (i.e. | |
113 // are not older than kMedianLifetimeMultiple * MedianThrottleLifetime()). | |
114 // If outstanding_recomputation_timer_ is not set, it will be set | |
115 // to the earliest a throttle might "age out" of the outstanding list. | |
116 void RecomputeOutstanding(); | |
117 | |
118 // Unblock the specified throttle. May result in re-entrant calls | |
119 // into NetworkThrottleManagerImpl. | |
120 void UnblockThrottle(ThrottleImpl* throttle); | |
121 | |
122 // Recomputes how many requests count as outstanding, checks to see | |
123 // if any currently blocked throttles should be unblocked, | |
124 // and unblock them if so. Note that unblocking may result in | |
125 // re-entrant calls to this class, so no assumptions about state persistence | |
126 // should be made across this call. | |
127 void MaybeUnblockThrottles(); | |
128 | |
129 PercentileEstimator lifetime_median_estimate_; | |
130 | |
131 // base::Timer controlling outstanding request recomputation. | |
132 // | |
133 // This is started whenever it is not running and a new throttle is | |
134 // added to |outstanding_throttles_|, and is never cleared except by | |
135 // execution, which re-starts it if there are any | |
136 // outstanding_throttles_. So it should always be running if any | |
137 // throttles are outstanding. This guarantees that the class will | |
138 // eventually detect aging out of outstanding throttles and unblock | |
139 // throttles blocked on those outstanding throttles. | |
140 base::Timer outstanding_recomputation_timer_; | |
141 | |
142 // Contains only OUTSTANDING throttles. | |
143 StartTimeOrderedSet outstanding_throttles_; | |
mmenke
2016/10/12 15:39:12
Do we get anything from making this a set, and Thr
Randy Smith (Not in Mondays)
2016/10/18 21:41:05
Ah, good point; for historical reasons (shift of t
| |
144 | |
145 // FIFO list of BLOCKED throttles. This is a list so that the | |
146 // throttles can store iterators to themselves. | |
147 ThrottleList blocked_throttles_; | |
148 | |
149 // For testing. | |
150 std::unique_ptr<base::TickClock> tick_clock_; | |
151 | |
152 base::WeakPtrFactory<NetworkThrottleManagerImpl> weak_ptr_factory_; | |
153 | |
154 DISALLOW_COPY_AND_ASSIGN(NetworkThrottleManagerImpl); | |
155 }; | |
156 | |
157 } // namespace net | |
158 | |
159 #endif // NET_BASE_NETWORK_THROTTLE_MANAGER_IMPL_H_ | |
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