blob: df5816a73a0f20c6b5c78115ad6cd9983d3ca4f1 [file] [log] [blame]
// Copyright (C) 2014 The Android Open Source Project
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include <map>
#include <memory>
#include <string>
#include <base/bind.h>
#include <base/callback.h>
#include <base/memory/ref_counted.h>
#include <base/memory/weak_ptr.h>
#include <base/time/time.h>
#include <brillo/message_loops/message_loop.h>
#include "update_engine/common/clock_interface.h"
#include "update_engine/update_manager/boxed_value.h"
#include "update_engine/update_manager/variable.h"
namespace chromeos_update_manager {
// The EvaluationContext class is the interface between a policy implementation
// and the state. The EvaluationContext tracks the variables used by a policy
// request and caches the returned values, owning those cached values.
// The same EvaluationContext should be re-used for all the evaluations of the
// same policy request (an AsyncPolicyRequest might involve several
// re-evaluations). Each evaluation of the EvaluationContext is run at a given
// point in time, which is used as a reference for the evaluation timeout and
// the time based queries of the policy, such as
// Is{Wallclock,Monotonic}TimeGreaterThan().
// Example:
// scoped_refptr<EvaluationContext> ec = new EvaluationContext(...);
// ...
// // The following call to ResetEvaluation() is optional. Use it to reset the
// // evaluation time if the EvaluationContext isn't used right after its
// // construction.
// ec->ResetEvaluation();
// EvalStatus status = policy->SomeMethod(ec, state, &result, args...);
// ...
// // Run a closure when any of the used async variables changes its value or
// // the timeout for re-query the values happens again.
// ec->RunOnValueChangeOrTimeout(closure);
// // If the provided |closure| wants to re-evaluate the policy, it should
// // call ec->ResetEvaluation() to start a new evaluation.
class EvaluationContext : public base::RefCounted<EvaluationContext>,
private BaseVariable::ObserverInterface {
chromeos_update_engine::ClockInterface* clock,
base::TimeDelta evaluation_timeout,
base::TimeDelta expiration_timeout,
std::unique_ptr<base::Callback<void(EvaluationContext*)>> unregister_cb);
EvaluationContext(chromeos_update_engine::ClockInterface* clock,
base::TimeDelta evaluation_timeout)
: EvaluationContext(
clock, evaluation_timeout, base::TimeDelta::Max(),
std::unique_ptr<base::Callback<void(EvaluationContext*)>>()) {}
// Returns a pointer to the value returned by the passed variable |var|. The
// EvaluationContext instance keeps the ownership of the returned object. The
// returned object is valid during the life of the evaluation, even if the
// passed Variable changes it.
// In case of error, a null value is returned.
template<typename T>
const T* GetValue(Variable<T>* var);
// Returns whether the evaluation time has surpassed |timestamp|, on either
// the ClockInterface::GetWallclockTime() or
// ClockInterface::GetMonotonicTime() scales, respectively.
bool IsWallclockTimeGreaterThan(base::Time timestamp);
bool IsMonotonicTimeGreaterThan(base::Time timestamp);
// Returns whether the evaluation context has expired.
bool is_expired() const { return is_expired_; }
// TODO(deymo): Move the following methods to an interface only visible by the
// UpdateManager class and not the policy implementations.
// Resets the EvaluationContext to its initial state removing all the
// non-const cached variables and re-setting the evaluation time. This should
// be called right before any new evaluation starts.
void ResetEvaluation();
// Clears the expiration status of the EvaluationContext and resets its
// expiration timeout based on |expiration_timeout_|. This should be called if
// expiration occurred, prior to re-evaluating the policy.
void ResetExpiration();
// Schedules the passed |callback| closure to be called when a cached
// variable changes its value, a polling interval passes, or the context
// expiration occurs. If none of these events can happen, for example if
// there's no cached variable, this method returns false.
// Right before the passed closure is called the EvaluationContext is
// reseted, removing all the non-const cached values.
bool RunOnValueChangeOrTimeout(base::Closure callback);
// Returns a textual representation of the evaluation context,
// including the variables and their values. This is intended only
// to help with debugging and the format may change in the future.
std::string DumpContext() const;
// Removes all the Observers callbacks and timeout events scheduled by
// RunOnValueChangeOrTimeout(). Also releases and returns the closure
// associated with these events. This method is idempotent.
std::unique_ptr<base::Closure> RemoveObserversAndTimeout();
friend class UmEvaluationContextTest;
// BaseVariable::ObserverInterface override.
void ValueChanged(BaseVariable* var) override;
// Called from the main loop when a scheduled timeout has passed.
void OnTimeout();
// Removes the observers from the used Variables and cancels the timeout,
// then executes the scheduled callback.
void OnValueChangedOrTimeout();
// If |monotonic_deadline| is not Time::Max(), returns the remaining time
// until it is reached, or zero if it has passed. Otherwise, returns
// TimeDelta::Max().
base::TimeDelta RemainingTime(base::Time monotonic_deadline) const;
// Returns a monotonic clock timestamp at which |timeout| will have elapsed
// since the current time.
base::Time MonotonicDeadline(base::TimeDelta timeout);
// A map to hold the cached values for every variable.
typedef std::map<BaseVariable*, BoxedValue> ValueCacheMap;
// The cached values of the called Variables.
ValueCacheMap value_cache_;
// A callback used for triggering re-evaluation upon a value change or poll
// timeout, or notifying about the evaluation context expiration. It is up to
// the caller to determine whether or not expiration occurred via
// is_expired().
std::unique_ptr<base::Closure> callback_;
// The TaskId returned by the message loop identifying the timeout callback.
// Used for canceling the timeout callback.
brillo::MessageLoop::TaskId timeout_event_ =
// Whether a timeout event firing marks the expiration of the evaluation
// context.
bool timeout_marks_expiration_;
// Whether the evaluation context has indeed expired.
bool is_expired_ = false;
// Pointer to the mockable clock interface;
chromeos_update_engine::ClockInterface* const clock_;
// The timestamps when the evaluation of this EvaluationContext started,
// corresponding to ClockInterface::GetWallclockTime() and
// ClockInterface::GetMonotonicTime(), respectively. These values are reset
// every time ResetEvaluation() is called.
base::Time evaluation_start_wallclock_;
base::Time evaluation_start_monotonic_;
// The timestamps when a reevaluation should be triggered due to various
// expected value changes, corresponding to ClockInterface::GetWallclockTime()
// and ClockInterface::GetMonotonicTIme(), respectively. These timestamps are
// greater or equal to corresponding |evaluation_start_{wallclock,monotonic}_|
// counterparts since they are in the future; however, they may be smaller
// than the current corresponding times during the course of evaluation.
base::Time reevaluation_time_wallclock_;
base::Time reevaluation_time_monotonic_;
// The timeout of an evaluation.
const base::TimeDelta evaluation_timeout_;
// The timestamp in the ClockInterface::GetMonotonicTime() scale at which the
// current evaluation should finish.
base::Time evaluation_monotonic_deadline_;
// The expiration timeout of the evaluation context.
const base::TimeDelta expiration_timeout_;
// The monotonic clock deadline at which expiration occurs.
base::Time expiration_monotonic_deadline_;
// A callback for unregistering the context upon destruction.
std::unique_ptr<base::Callback<void(EvaluationContext*)>> unregister_cb_;
base::WeakPtrFactory<EvaluationContext> weak_ptr_factory_;
} // namespace chromeos_update_manager
// Include the implementation of the template methods.
#include "update_engine/update_manager/evaluation_context-inl.h"