1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
|
/*
* Copyright (C) 2017 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#pragma once
#include <string.h>
#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
#include <sys/_system_properties.h>
#include "private/bionic_lock.h"
class CachedProperty {
public:
CachedProperty(const char* property_name)
: property_name_(property_name),
prop_info_(nullptr),
cached_area_serial_(0),
cached_property_serial_(0) {
cached_value_[0] = '\0';
}
const char* Get() {
lock_.lock();
// Do we have a `struct prop_info` yet?
if (prop_info_ == nullptr) {
// `__system_property_find` is expensive, so only retry if a property
// has been created since last time we checked.
uint32_t property_area_serial = __system_property_area_serial();
if (property_area_serial != cached_area_serial_) {
prop_info_ = __system_property_find(property_name_);
cached_area_serial_ = property_area_serial;
}
}
if (prop_info_ != nullptr) {
// Only bother re-reading the property if it's actually changed since last time.
uint32_t property_serial = __system_property_serial(prop_info_);
if (property_serial != cached_property_serial_) {
__system_property_read_callback(prop_info_, &CachedProperty::Callback, this);
}
}
lock_.unlock();
return cached_value_;
}
private:
Lock lock_;
const char* property_name_;
const prop_info* prop_info_;
uint32_t cached_area_serial_;
uint32_t cached_property_serial_;
char cached_value_[PROP_VALUE_MAX];
static void Callback(void* data, const char*, const char* value, uint32_t serial) {
CachedProperty* instance = reinterpret_cast<CachedProperty*>(data);
instance->cached_property_serial_ = serial;
strcpy(instance->cached_value_, value);
}
};
|
