1 /*
2  * Copyright (C) 2016 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 ANDROID_BASE_PROPERTIES_H
18 #define ANDROID_BASE_PROPERTIES_H
19 
20 #include <sys/cdefs.h>
21 
22 #if !defined(__BIONIC__)
23 #error Only bionic supports system properties.
24 #endif
25 
26 #include <chrono>
27 #include <limits>
28 #include <string>
29 
30 namespace android {
31 namespace base {
32 
33 // Returns the current value of the system property `key`,
34 // or `default_value` if the property is empty or doesn't exist.
35 std::string GetProperty(const std::string& key, const std::string& default_value);
36 
37 // Returns true if the system property `key` has the value "1", "y", "yes", "on", or "true",
38 // false for "0", "n", "no", "off", or "false", or `default_value` otherwise.
39 bool GetBoolProperty(const std::string& key, bool default_value);
40 
41 // Returns the signed integer corresponding to the system property `key`.
42 // If the property is empty, doesn't exist, doesn't have an integer value, or is outside
43 // the optional bounds, returns `default_value`.
44 template <typename T> T GetIntProperty(const std::string& key,
45                                        T default_value,
46                                        T min = std::numeric_limits<T>::min(),
47                                        T max = std::numeric_limits<T>::max());
48 
49 // Returns the unsigned integer corresponding to the system property `key`.
50 // If the property is empty, doesn't exist, doesn't have an integer value, or is outside
51 // the optional bound, returns `default_value`.
52 template <typename T> T GetUintProperty(const std::string& key,
53                                         T default_value,
54                                         T max = std::numeric_limits<T>::max());
55 
56 // Sets the system property `key` to `value`.
57 // Note that system property setting is inherently asynchronous so a return value of `true`
58 // isn't particularly meaningful, and immediately reading back the value won't necessarily
59 // tell you whether or not your call succeeded. A `false` return value definitely means failure.
60 bool SetProperty(const std::string& key, const std::string& value);
61 
62 // Waits for the system property `key` to have the value `expected_value`.
63 // Times out after `relative_timeout`.
64 // Returns true on success, false on timeout.
65 bool WaitForProperty(const std::string& key, const std::string& expected_value,
66                      std::chrono::milliseconds relative_timeout = std::chrono::milliseconds::max());
67 
68 // Waits for the system property `key` to be created.
69 // Times out after `relative_timeout`.
70 // Returns true on success, false on timeout.
71 bool WaitForPropertyCreation(const std::string& key, std::chrono::milliseconds relative_timeout =
72                                                          std::chrono::milliseconds::max());
73 
74 } // namespace base
75 } // namespace android
76 
77 #endif  // ANDROID_BASE_PROPERTIES_H
78