update_manager: Make Prefs Variable async.
The update_engine prefs, while stored in disk, are private daemon
values changed by the daemon only. There was a 5 minutes delay between
changing this value and the update policy checking it again, and there
was a log spam every 5 minutes due to policy re-evaluations.
This patch makes these Prefs-based variables async by implementing an
observer pattern in the PrefsInterface and makes these variables async.
Bug: chromium:367333
Test: Added uniittest. No more log spam every 5 minutes.
Change-Id: I8b3f7072cc87515972c9f5b1ddcc54b865ffe238
diff --git a/prefs_interface.h b/prefs_interface.h
index eedba4b..d409a1f 100644
--- a/prefs_interface.h
+++ b/prefs_interface.h
@@ -30,12 +30,24 @@
class PrefsInterface {
public:
- virtual ~PrefsInterface() {}
+ // Observer class to be notified about key value changes.
+ class ObserverInterface {
+ public:
+ virtual ~ObserverInterface() = default;
+
+ // Called when the value is set for the observed |key|.
+ virtual void OnPrefSet(const std::string& key) = 0;
+
+ // Called when the observed |key| is deleted.
+ virtual void OnPrefDeleted(const std::string& key) = 0;
+ };
+
+ virtual ~PrefsInterface() = default;
// Gets a string |value| associated with |key|. Returns true on
// success, false on failure (including when the |key| is not
// present in the store).
- virtual bool GetString(const std::string& key, std::string* value) = 0;
+ virtual bool GetString(const std::string& key, std::string* value) const = 0;
// Associates |key| with a string |value|. Returns true on success,
// false otherwise.
@@ -44,7 +56,7 @@
// Gets an int64_t |value| associated with |key|. Returns true on
// success, false on failure (including when the |key| is not
// present in the store).
- virtual bool GetInt64(const std::string& key, int64_t* value) = 0;
+ virtual bool GetInt64(const std::string& key, int64_t* value) const = 0;
// Associates |key| with an int64_t |value|. Returns true on success,
// false otherwise.
@@ -53,7 +65,7 @@
// Gets a boolean |value| associated with |key|. Returns true on
// success, false on failure (including when the |key| is not
// present in the store).
- virtual bool GetBoolean(const std::string& key, bool* value) = 0;
+ virtual bool GetBoolean(const std::string& key, bool* value) const = 0;
// Associates |key| with a boolean |value|. Returns true on success,
// false otherwise.
@@ -61,11 +73,23 @@
// Returns true if the setting exists (i.e. a file with the given key
// exists in the prefs directory)
- virtual bool Exists(const std::string& key) = 0;
+ virtual bool Exists(const std::string& key) const = 0;
// Returns true if successfully deleted the file corresponding to
// this key. Calling with non-existent keys does nothing.
virtual bool Delete(const std::string& key) = 0;
+
+ // Add an observer to watch whenever the given |key| is modified. The
+ // OnPrefSet() and OnPrefDelete() methods will be called whenever any of the
+ // Set*() methods or the Delete() method are called on the given key,
+ // respectively.
+ virtual void AddObserver(const std::string& key,
+ ObserverInterface* observer) = 0;
+
+ // Remove an observer added with AddObserver(). The observer won't be called
+ // anymore for future Set*() and Delete() method calls.
+ virtual void RemoveObserver(const std::string& key,
+ ObserverInterface* observer) = 0;
};
} // namespace chromeos_update_engine
