1 // Copyright 2015 The Chromium OS 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 LIBBRILLO_BRILLO_BACKOFF_ENTRY_H_ 6 #define LIBBRILLO_BRILLO_BACKOFF_ENTRY_H_ 7 8 #include <base/time/time.h> 9 #include <brillo/brillo_export.h> 10 11 namespace brillo { 12 13 // Provides the core logic needed for randomized exponential back-off 14 // on requests to a given resource, given a back-off policy. 15 // 16 // This class is largely taken from net/base/backoff_entry.h from Chromium. 17 // TODO(avakulenko): Consider packaging portions of Chrome's //net functionality 18 // into the current libchrome library. 19 class BRILLO_EXPORT BackoffEntry { 20 public: 21 // The set of parameters that define a back-off policy. 22 struct Policy { 23 // Number of initial errors (in sequence) to ignore before applying 24 // exponential back-off rules. 25 int num_errors_to_ignore; 26 27 // Initial delay. The interpretation of this value depends on 28 // always_use_initial_delay. It's either how long we wait between 29 // requests before backoff starts, or how much we delay the first request 30 // after backoff starts. 31 int initial_delay_ms; 32 33 // Factor by which the waiting time will be multiplied. 34 double multiply_factor; 35 36 // Fuzzing percentage. ex: 10% will spread requests randomly 37 // between 90%-100% of the calculated time. 38 double jitter_factor; 39 40 // Maximum amount of time we are willing to delay our request, -1 41 // for no maximum. 42 int64_t maximum_backoff_ms; 43 44 // Time to keep an entry from being discarded even when it 45 // has no significant state, -1 to never discard. 46 int64_t entry_lifetime_ms; 47 48 // If true, we always use a delay of initial_delay_ms, even before 49 // we've seen num_errors_to_ignore errors. Otherwise, initial_delay_ms 50 // is the first delay once we start exponential backoff. 51 // 52 // So if we're ignoring 1 error, we'll see (N, N, Nm, Nm^2, ...) if true, 53 // and (0, 0, N, Nm, ...) when false, where N is initial_backoff_ms and 54 // m is multiply_factor, assuming we've already seen one success. 55 bool always_use_initial_delay; 56 }; 57 58 // Lifetime of policy must enclose lifetime of BackoffEntry. The 59 // pointer must be valid but is not dereferenced during construction. 60 explicit BackoffEntry(const Policy* const policy); 61 virtual ~BackoffEntry() = default; 62 63 // Inform this item that a request for the network resource it is 64 // tracking was made, and whether it failed or succeeded. 65 void InformOfRequest(bool succeeded); 66 67 // Returns true if a request for the resource this item tracks should 68 // be rejected at the present time due to exponential back-off policy. 69 bool ShouldRejectRequest() const; 70 71 // Returns the absolute time after which this entry (given its present 72 // state) will no longer reject requests. 73 base::TimeTicks GetReleaseTime() const; 74 75 // Returns the time until a request can be sent. 76 base::TimeDelta GetTimeUntilRelease() const; 77 78 // Causes this object reject requests until the specified absolute time. 79 // This can be used to e.g. implement support for a Retry-After header. 80 void SetCustomReleaseTime(const base::TimeTicks& release_time); 81 82 // Returns true if this object has no significant state (i.e. you could 83 // just as well start with a fresh BackoffEntry object), and hasn't 84 // had for Policy::entry_lifetime_ms. 85 bool CanDiscard() const; 86 87 // Resets this entry to a fresh (as if just constructed) state. 88 void Reset(); 89 90 // Returns the failure count for this entry. failure_count()91 int failure_count() const { return failure_count_; } 92 93 protected: 94 // Equivalent to TimeTicks::Now(), virtual so unit tests can override. 95 virtual base::TimeTicks ImplGetTimeNow() const; 96 97 private: 98 // Calculates when requests should again be allowed through. 99 base::TimeTicks CalculateReleaseTime() const; 100 101 // Timestamp calculated by the exponential back-off algorithm at which we are 102 // allowed to start sending requests again. 103 base::TimeTicks exponential_backoff_release_time_; 104 105 // Counts request errors; decremented on success. 106 int failure_count_; 107 108 const Policy* const policy_; 109 110 DISALLOW_COPY_AND_ASSIGN(BackoffEntry); 111 }; 112 113 } // namespace brillo 114 115 #endif // LIBBRILLO_BRILLO_BACKOFF_ENTRY_H_ 116