1 // 2 // Copyright (C) 2014 The Android Open Source Project 3 // 4 // Licensed under the Apache License, Version 2.0 (the "License"); 5 // you may not use this file except in compliance with the License. 6 // You may obtain a copy of the License at 7 // 8 // http://www.apache.org/licenses/LICENSE-2.0 9 // 10 // Unless required by applicable law or agreed to in writing, software 11 // distributed under the License is distributed on an "AS IS" BASIS, 12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 // See the License for the specific language governing permissions and 14 // limitations under the License. 15 // 16 17 #ifndef UPDATE_ENGINE_UPDATE_MANAGER_EVALUATION_CONTEXT_H_ 18 #define UPDATE_ENGINE_UPDATE_MANAGER_EVALUATION_CONTEXT_H_ 19 20 #include <map> 21 #include <memory> 22 #include <string> 23 24 #include <base/bind.h> 25 #include <base/callback.h> 26 #include <base/memory/ref_counted.h> 27 #include <base/memory/weak_ptr.h> 28 #include <base/time/time.h> 29 #include <brillo/message_loops/message_loop.h> 30 31 #include "update_engine/common/clock_interface.h" 32 #include "update_engine/update_manager/boxed_value.h" 33 #include "update_engine/update_manager/variable.h" 34 35 namespace chromeos_update_manager { 36 37 // The EvaluationContext class is the interface between a policy implementation 38 // and the state. The EvaluationContext tracks the variables used by a policy 39 // request and caches the returned values, owning those cached values. 40 // The same EvaluationContext should be re-used for all the evaluations of the 41 // same policy request (an AsyncPolicyRequest might involve several 42 // re-evaluations). Each evaluation of the EvaluationContext is run at a given 43 // point in time, which is used as a reference for the evaluation timeout and 44 // the time based queries of the policy, such as 45 // Is{Wallclock,Monotonic}TimeGreaterThan(). 46 // 47 // Example: 48 // 49 // scoped_refptr<EvaluationContext> ec = new EvaluationContext(...); 50 // 51 // ... 52 // // The following call to ResetEvaluation() is optional. Use it to reset the 53 // // evaluation time if the EvaluationContext isn't used right after its 54 // // construction. 55 // ec->ResetEvaluation(); 56 // EvalStatus status = policy->SomeMethod(ec, state, &result, args...); 57 // 58 // ... 59 // // Run a closure when any of the used async variables changes its value or 60 // // the timeout for re-query the values happens again. 61 // ec->RunOnValueChangeOrTimeout(closure); 62 // // If the provided |closure| wants to re-evaluate the policy, it should 63 // // call ec->ResetEvaluation() to start a new evaluation. 64 // 65 class EvaluationContext : public base::RefCounted<EvaluationContext>, 66 private BaseVariable::ObserverInterface { 67 public: 68 EvaluationContext( 69 chromeos_update_engine::ClockInterface* clock, 70 base::TimeDelta evaluation_timeout, 71 base::TimeDelta expiration_timeout, 72 std::unique_ptr<base::Callback<void(EvaluationContext*)>> unregister_cb); 73 EvaluationContext(chromeos_update_engine::ClockInterface* clock, 74 base::TimeDelta evaluation_timeout) 75 : EvaluationContext( 76 clock, 77 evaluation_timeout, 78 base::TimeDelta::Max(), 79 std::unique_ptr<base::Callback<void(EvaluationContext*)>>()) {} 80 ~EvaluationContext(); 81 82 // Returns a pointer to the value returned by the passed variable |var|. The 83 // EvaluationContext instance keeps the ownership of the returned object. The 84 // returned object is valid during the life of the evaluation, even if the 85 // passed Variable changes it. 86 // 87 // In case of error, a null value is returned. 88 template <typename T> 89 const T* GetValue(Variable<T>* var); 90 91 // Returns whether the evaluation time has surpassed |timestamp|, on either 92 // the ClockInterface::GetWallclockTime() or 93 // ClockInterface::GetMonotonicTime() scales, respectively. 94 bool IsWallclockTimeGreaterThan(base::Time timestamp); 95 bool IsMonotonicTimeGreaterThan(base::Time timestamp); 96 97 // Returns whether the evaluation context has expired. 98 bool is_expired() const { return is_expired_; } 99 100 // TODO(deymo): Move the following methods to an interface only visible by the 101 // UpdateManager class and not the policy implementations. 102 103 // Resets the EvaluationContext to its initial state removing all the 104 // non-const cached variables and re-setting the evaluation time. This should 105 // be called right before any new evaluation starts. 106 void ResetEvaluation(); 107 108 // Clears the expiration status of the EvaluationContext and resets its 109 // expiration timeout based on |expiration_timeout_|. This should be called if 110 // expiration occurred, prior to re-evaluating the policy. 111 void ResetExpiration(); 112 113 // Schedules the passed |callback| closure to be called when a cached 114 // variable changes its value, a polling interval passes, or the context 115 // expiration occurs. If none of these events can happen, for example if 116 // there's no cached variable, this method returns false. 117 // 118 // Right before the passed closure is called the EvaluationContext is 119 // reset, removing all the non-const cached values. 120 bool RunOnValueChangeOrTimeout(base::Closure callback); 121 122 // Returns a textual representation of the evaluation context, 123 // including the variables and their values. This is intended only 124 // to help with debugging and the format may change in the future. 125 std::string DumpContext() const; 126 127 // Removes all the Observers callbacks and timeout events scheduled by 128 // RunOnValueChangeOrTimeout(). Also releases and returns the closure 129 // associated with these events. This method is idempotent. 130 std::unique_ptr<base::Closure> RemoveObserversAndTimeout(); 131 132 private: 133 friend class UmEvaluationContextTest; 134 135 // BaseVariable::ObserverInterface override. 136 void ValueChanged(BaseVariable* var) override; 137 138 // Called from the main loop when a scheduled timeout has passed. 139 void OnTimeout(); 140 141 // Removes the observers from the used Variables and cancels the timeout, 142 // then executes the scheduled callback. 143 void OnValueChangedOrTimeout(); 144 145 // If |monotonic_deadline| is not Time::Max(), returns the remaining time 146 // until it is reached, or zero if it has passed. Otherwise, returns 147 // TimeDelta::Max(). 148 base::TimeDelta RemainingTime(base::Time monotonic_deadline) const; 149 150 // Returns a monotonic clock timestamp at which |timeout| will have elapsed 151 // since the current time. 152 base::Time MonotonicDeadline(base::TimeDelta timeout); 153 154 // A map to hold the cached values for every variable. 155 typedef std::map<BaseVariable*, BoxedValue> ValueCacheMap; 156 157 // The cached values of the called Variables. 158 ValueCacheMap value_cache_; 159 160 // A callback used for triggering re-evaluation upon a value change or poll 161 // timeout, or notifying about the evaluation context expiration. It is up to 162 // the caller to determine whether or not expiration occurred via 163 // is_expired(). 164 std::unique_ptr<base::Closure> callback_; 165 166 // The TaskId returned by the message loop identifying the timeout callback. 167 // Used for canceling the timeout callback. 168 brillo::MessageLoop::TaskId timeout_event_ = brillo::MessageLoop::kTaskIdNull; 169 170 // Whether a timeout event firing marks the expiration of the evaluation 171 // context. 172 bool timeout_marks_expiration_; 173 174 // Whether the evaluation context has indeed expired. 175 bool is_expired_ = false; 176 177 // Pointer to the mockable clock interface; 178 chromeos_update_engine::ClockInterface* const clock_; 179 180 // The timestamps when the evaluation of this EvaluationContext started, 181 // corresponding to ClockInterface::GetWallclockTime() and 182 // ClockInterface::GetMonotonicTime(), respectively. These values are reset 183 // every time ResetEvaluation() is called. 184 base::Time evaluation_start_wallclock_; 185 base::Time evaluation_start_monotonic_; 186 187 // The timestamps when a reevaluation should be triggered due to various 188 // expected value changes, corresponding to ClockInterface::GetWallclockTime() 189 // and ClockInterface::GetMonotonicTIme(), respectively. These timestamps are 190 // greater or equal to corresponding |evaluation_start_{wallclock,monotonic}_| 191 // counterparts since they are in the future; however, they may be smaller 192 // than the current corresponding times during the course of evaluation. 193 base::Time reevaluation_time_wallclock_; 194 base::Time reevaluation_time_monotonic_; 195 196 // The timeout of an evaluation. 197 const base::TimeDelta evaluation_timeout_; 198 199 // The timestamp in the ClockInterface::GetMonotonicTime() scale at which the 200 // current evaluation should finish. 201 base::Time evaluation_monotonic_deadline_; 202 203 // The expiration timeout of the evaluation context. 204 const base::TimeDelta expiration_timeout_; 205 206 // The monotonic clock deadline at which expiration occurs. 207 base::Time expiration_monotonic_deadline_; 208 209 // A callback for unregistering the context upon destruction. 210 std::unique_ptr<base::Callback<void(EvaluationContext*)>> unregister_cb_; 211 212 base::WeakPtrFactory<EvaluationContext> weak_ptr_factory_; 213 214 DISALLOW_COPY_AND_ASSIGN(EvaluationContext); 215 }; 216 217 } // namespace chromeos_update_manager 218 219 // Include the implementation of the template methods. 220 #include "update_engine/update_manager/evaluation_context-inl.h" 221 222 #endif // UPDATE_ENGINE_UPDATE_MANAGER_EVALUATION_CONTEXT_H_ 223