upload android base code part6

android/system/update_engine/update_manager/generic_variables.h

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+//
+// 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
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// Generic and provider-independent Variable subclasses. These variables can be
+// used by any state provider to implement simple variables to avoid repeat the
+// same common code on different state providers.
+
+#ifndef UPDATE_ENGINE_UPDATE_MANAGER_GENERIC_VARIABLES_H_
+#define UPDATE_ENGINE_UPDATE_MANAGER_GENERIC_VARIABLES_H_
+
+#include <string>
+
+#include <base/callback.h>
+
+#include "update_engine/update_manager/variable.h"
+
+namespace chromeos_update_manager {
+
+// Variable class returning a copy of a given object using the copy constructor.
+// This template class can be used to define variables that expose as a variable
+// any fixed object, such as the a provider's private member. The variable will
+// create copies of the provided object using the copy constructor of that
+// class.
+//
+// For example, a state provider exposing a private member as a variable can
+// implement this as follows:
+//
+//   class SomethingProvider {
+//    public:
+//      SomethingProvider(...) {
+//        var_something_foo = new PollCopyVariable<MyType>(foo_);
+//      }
+//      ...
+//    private:
+//     MyType foo_;
+//   };
+template<typename T>
+class PollCopyVariable : public Variable<T> {
+ public:
+  // Creates the variable returning copies of the passed |ref|. The reference to
+  // this object is kept and it should be available whenever the GetValue()
+  // method is called. If |is_set_p| is not null, then this flag will be
+  // consulted prior to returning the value, and an |errmsg| will be returned if
+  // it is not set.
+  PollCopyVariable(const std::string& name, const T& ref, const bool* is_set_p,
+                   const std::string& errmsg)
+      : Variable<T>(name, kVariableModePoll), ref_(ref), is_set_p_(is_set_p),
+        errmsg_(errmsg) {}
+  PollCopyVariable(const std::string& name, const T& ref, const bool* is_set_p)
+      : PollCopyVariable(name, ref, is_set_p, std::string()) {}
+  PollCopyVariable(const std::string& name, const T& ref)
+      : PollCopyVariable(name, ref, nullptr) {}
+
+  PollCopyVariable(const std::string& name, const base::TimeDelta poll_interval,
+                   const T& ref, const bool* is_set_p,
+                   const std::string& errmsg)
+      : Variable<T>(name, poll_interval), ref_(ref), is_set_p_(is_set_p),
+        errmsg_(errmsg) {}
+  PollCopyVariable(const std::string& name, const base::TimeDelta poll_interval,
+                   const T& ref, const bool* is_set_p)
+      : PollCopyVariable(name, poll_interval, ref, is_set_p, std::string()) {}
+  PollCopyVariable(const std::string& name, const base::TimeDelta poll_interval,
+                   const T& ref)
+      : PollCopyVariable(name, poll_interval, ref, nullptr) {}
+
+ protected:
+  FRIEND_TEST(UmPollCopyVariableTest, SimpleTest);
+  FRIEND_TEST(UmPollCopyVariableTest, UseCopyConstructorTest);
+
+  // Variable override.
+  inline const T* GetValue(base::TimeDelta /* timeout */,
+                           std::string* errmsg) override {
+    if (is_set_p_ && !(*is_set_p_)) {
+      if (errmsg) {
+        if (errmsg_.empty())
+          *errmsg = "No value set for " + this->GetName();
+        else
+          *errmsg = errmsg_;
+      }
+      return nullptr;
+    }
+    return new T(ref_);
+  }
+
+ private:
+  // Reference to the object to be copied by GetValue().
+  const T& ref_;
+
+  // A pointer to a flag indicating whether the value is set. If null, then the
+  // value is assumed to be set.
+  const bool* const is_set_p_;
+
+  // An error message to be returned when attempting to get an unset value.
+  const std::string errmsg_;
+};
+
+// Variable class returning a constant value that is cached on the variable when
+// it is created.
+template<typename T>
+class ConstCopyVariable : public Variable<T> {
+ public:
+  // Creates the variable returning copies of the passed |obj|. The value passed
+  // is copied in this variable, and new copies of it will be returned by
+  // GetValue().
+  ConstCopyVariable(const std::string& name, const T& obj)
+      : Variable<T>(name, kVariableModeConst), obj_(obj) {}
+
+ protected:
+  // Variable override.
+  const T* GetValue(base::TimeDelta /* timeout */,
+                    std::string* /* errmsg */) override {
+    return new T(obj_);
+  }
+
+ private:
+  // Value to be copied by GetValue().
+  const T obj_;
+};
+
+// Variable class returning a copy of a value returned by a given function. The
+// function is called every time the variable is being polled.
+template<typename T>
+class CallCopyVariable : public Variable<T> {
+ public:
+  CallCopyVariable(const std::string& name, base::Callback<T(void)> func)
+      : Variable<T>(name, kVariableModePoll), func_(func) {}
+  CallCopyVariable(const std::string& name,
+                   const base::TimeDelta poll_interval,
+                   base::Callback<T(void)> func)
+      : Variable<T>(name, poll_interval), func_(func) {}
+
+ protected:
+  // Variable override.
+  const T* GetValue(base::TimeDelta /* timeout */,
+                    std::string* /* errmsg */) override {
+    if (func_.is_null())
+      return nullptr;
+    return new T(func_.Run());
+  }
+
+ private:
+  FRIEND_TEST(UmCallCopyVariableTest, SimpleTest);
+
+  // The function to be called, stored as a base::Callback.
+  base::Callback<T(void)> func_;
+
+  DISALLOW_COPY_AND_ASSIGN(CallCopyVariable);
+};
+
+
+// A Variable class to implement simple Async variables. It provides two methods
+// SetValue and UnsetValue to modify the current value of the variable and
+// notify the registered observers whenever the value changed.
+//
+// The type T needs to be copy-constructible, default-constructible and have an
+// operator== (to determine if the value changed), which makes this class
+// suitable for basic types.
+template<typename T>
+class AsyncCopyVariable : public Variable<T> {
+ public:
+  explicit AsyncCopyVariable(const std::string& name)
+      : Variable<T>(name, kVariableModeAsync), has_value_(false) {}
+
+  AsyncCopyVariable(const std::string& name, const T value)
+      : Variable<T>(name, kVariableModeAsync),
+        has_value_(true), value_(value) {}
+
+  void SetValue(const T& new_value) {
+    bool should_notify = !(has_value_ && new_value == value_);
+    value_ = new_value;
+    has_value_ = true;
+    if (should_notify)
+      this->NotifyValueChanged();
+  }
+
+  void UnsetValue() {
+    if (has_value_) {
+      has_value_ = false;
+      this->NotifyValueChanged();
+    }
+  }
+
+ protected:
+  // Variable override.
+  const T* GetValue(base::TimeDelta /* timeout */,
+                    std::string* errmsg) override {
+    if (!has_value_) {
+      if (errmsg)
+        *errmsg = "No value set for " + this->GetName();
+      return nullptr;
+    }
+    return new T(value_);
+  }
+
+ private:
+  // Whether the variable has a value set.
+  bool has_value_;
+
+  // Copy of the object to be returned by GetValue().
+  T value_;
+};
+
+}  // namespace chromeos_update_manager
+
+#endif  // UPDATE_ENGINE_UPDATE_MANAGER_GENERIC_VARIABLES_H_