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 #pragma once 18 19 #include <sys/cdefs.h> 20 21 #include <chrono> 22 #include <limits> 23 #include <optional> 24 #include <string> 25 26 struct prop_info; 27 28 namespace android { 29 namespace base { 30 31 // Returns the current value of the system property `key`, 32 // or `default_value` if the property is empty or doesn't exist. 33 std::string GetProperty(const std::string& key, const std::string& default_value); 34 35 // Returns true if the system property `key` has the value "1", "y", "yes", "on", or "true", 36 // false for "0", "n", "no", "off", or "false", or `default_value` otherwise. 37 bool GetBoolProperty(const std::string& key, bool default_value); 38 39 // Returns the signed integer corresponding to the system property `key`. 40 // If the property is empty, doesn't exist, doesn't have an integer value, or is outside 41 // the optional bounds, returns `default_value`. 42 template <typename T> T GetIntProperty(const std::string& key, 43 T default_value, 44 T min = std::numeric_limits<T>::min(), 45 T max = std::numeric_limits<T>::max()); 46 47 // Returns the unsigned integer corresponding to the system property `key`. 48 // If the property is empty, doesn't exist, doesn't have an integer value, or is outside 49 // the optional bound, returns `default_value`. 50 template <typename T> T GetUintProperty(const std::string& key, 51 T default_value, 52 T max = std::numeric_limits<T>::max()); 53 54 // Sets the system property `key` to `value`. 55 bool SetProperty(const std::string& key, const std::string& value); 56 57 // Waits for the system property `key` to have the value `expected_value`. 58 // Times out after `relative_timeout`. 59 // Returns true on success, false on timeout. 60 #if defined(__BIONIC__) 61 bool WaitForProperty(const std::string& key, const std::string& expected_value, 62 std::chrono::milliseconds relative_timeout = std::chrono::milliseconds::max()); 63 #endif 64 65 // Waits for the system property `key` to be created. 66 // Times out after `relative_timeout`. 67 // Returns true on success, false on timeout. 68 #if defined(__BIONIC__) 69 bool WaitForPropertyCreation(const std::string& key, std::chrono::milliseconds relative_timeout = 70 std::chrono::milliseconds::max()); 71 #endif 72 73 #if defined(__BIONIC__) && __cplusplus >= 201703L 74 // Cached system property lookup. For code that needs to read the same property multiple times, 75 // this class helps optimize those lookups. 76 class CachedProperty { 77 public: 78 explicit CachedProperty(const char* property_name); 79 80 // Returns the current value of the underlying system property as cheaply as possible. 81 // The returned pointer is valid until the next call to Get. Because most callers are going 82 // to want to parse the string returned here and cached that as well, this function performs 83 // no locking, and is completely thread unsafe. It is the caller's responsibility to provide a 84 // lock for thread-safety. 85 // 86 // Note: *changed can be set to true even if the contents of the property remain the same. 87 const char* Get(bool* changed = nullptr); 88 89 private: 90 std::string property_name_; 91 const prop_info* prop_info_; 92 std::optional<uint32_t> cached_area_serial_; 93 std::optional<uint32_t> cached_property_serial_; 94 char cached_value_[92]; 95 bool is_read_only_; 96 const char* read_only_property_; 97 }; 98 #endif 99 100 } // namespace base 101 } // namespace android 102 103 #if !defined(__BIONIC__) 104 /** Implementation detail. */ 105 extern "C" int __system_property_set(const char*, const char*); 106 /** Implementation detail. */ 107 extern "C" int __system_property_get(const char*, char*); 108 #endif 109