嵌入式linux学习笔记-- 记录一种dlopen 打开的动态库无法被卸载的情形，情形分析以及对应的解决方法

项目中使用了rapidjson 的库函数，然后将这个库分别编译进入了不同的动态库中，然后产品的动态库设计上要能实现动态的卸载和装载然后就遇到了问题。
具体的表现就是打开的动态库无法被卸载。
工程的获取地址如下：

https://gitee.com/jeasonb/dlclose

建议实际运行一下工程体验一下
工程框图如下

解决方法

# 编译选项中 加入 -fno-gnu-unique
# set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} "-fno-gnu-unique" )
# set(CMAKE_C_FLAGS   ${CMAKE_C_FLAGS}   "-fno-gnu-unique" )

以上截图的语句中的 -fno-gnu-unique 语句是解决问题的关键
详细的解释可以参考这里

https://www.shuzhiduo.com/A/A7zgRmxld4/

引发问题的关键点就是

STB_GNU_UNIQUE属性的符号，在链接时只会有一份，即使这些符号分布在不同的so之间。就算由于模板函数中的静态变量是STB_GNU_UNIQUE属性，导致改模板函数即使在不同的so中各实例化了一份代码，也要使用同一个静态变量。

效果演示

前后两次运行工程的主要差异就是这里加了编译选项可以正常卸载，不加编译选项不能卸载！！！！！

1. 无法卸载的情形

[xxx@xxx:~/rapidjsonTest/build → master]$ ./app
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1236
p1 = 0x1d89030
p2 = 0x1d89670
func1 = 0x7f7abbdfda25
func2 = 0x7f7abbbfba25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib2.so unloaded  .....
liblib2.so loaded ...
testFun ... a= 1237
p1 = 0x1d89030
p2 = 0x1d89670
func1 = 0x7f7abbdfda25
func2 = 0x7f7abbbfba25
this is 1 ... a = 8
this is 1 ... a = 9
this is 1 ... a = 10
this is 1 ... a = 11
this is 1 ... a = 12
this is 1 ... a = 13
this is 1 ... a = 14
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib2.so unloaded  .....
liblib2.so loaded ...
testFun ... a= 1238
p1 = 0x1d89030
p2 = 0x1d89670
func1 = 0x7f7abbdfda25
func2 = 0x7f7abbbfba25
this is 1 ... a = 15
this is 1 ... a = 16
this is 1 ... a = 17
this is 1 ... a = 18
this is 1 ... a = 19
this is 1 ... a = 20
this is 1 ... a = 21
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib2.so unloaded  .....
liblib2.so loaded ...
testFun ... a= 1239
p1 = 0x1d89030
p2 = 0x1d89670
func1 = 0x7f7abbdfda25
func2 = 0x7f7abbbfba25
this is 1 ... a = 22
this is 1 ... a = 23
this is 1 ... a = 24
this is 1 ... a = 25
this is 1 ... a = 26
this is 1 ... a = 27
this is 1 ... a = 28
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib2.so unloaded  .....
liblib2.so loaded ...
testFun ... a= 1240
p1 = 0x1d89030
p2 = 0x1d89670
func1 = 0x7f7abbdfda25
func2 = 0x7f7abbbfba25
this is 1 ... a = 29
this is 1 ... a = 30
this is 1 ... a = 31
this is 1 ... a = 32
this is 1 ... a = 33
this is 1 ... a = 34
this is 1 ... a = 35
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib2.so unloaded  .....
liblib2.so loaded ...
testFun ... a= 1241
p1 = 0x1d89030
p2 = 0x1d89670
func1 = 0x7f7abbdfda25
func2 = 0x7f7abbbfba25
this is 1 ... a = 36
this is 1 ... a = 37
this is 1 ... a = 38
this is 1 ... a = 39
this is 1 ... a = 40
this is 1 ... a = 41
this is 1 ... a = 42
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib2.so unloaded  .....
liblib2.so loaded ...
testFun ... a= 1242
p1 = 0x1d89030
p2 = 0x1d89670
func1 = 0x7f7abbdfda25
func2 = 0x7f7abbbfba25
this is 1 ... a = 43
this is 1 ... a = 44
this is 1 ... a = 45
this is 1 ... a = 46
this is 1 ... a = 47
this is 1 ... a = 48
this is 1 ... a = 49
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib2.so unloaded  .....

2. 可以卸载的情形

[xxx@xxxx:~/rapidjsonTest/build → master]$ ^C
[xxx@xxx:~/rapidjsonTest/build → master]$ make
-- Configuring done
-- Generating done
-- Build files have been written to: /home/xxx/rapidjsonTest/build
Scanning dependencies of target lib2
[ 16%] Building CXX object CMakeFiles/lib2.dir/2.cpp.o
[ 33%] Linking CXX shared library liblib2.so
[ 33%] Built target lib2
Scanning dependencies of target lib1
[ 50%] Building CXX object CMakeFiles/lib1.dir/1.cpp.o
[ 66%] Linking CXX shared library liblib1.so
[ 66%] Built target lib1
[ 83%] Building CXX object CMakeFiles/app.dir/main.cpp.o
[100%] Linking CXX executable app
[100%] Built target app
[xxx@xxxx:~/rapidjsonTest/build → master]$ ./app
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9030
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9010
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9010
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9010
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9010
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9010
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9010
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
liblib1.so loaded ...
testFun ... a= 1235
liblib2.so loaded ...
testFun ... a= 1235
p1 = 0x12c9010
p2 = 0x12c9670
func1 = 0x7f6018b52a25
func2 = 0x7f6018950a25
this is 1 ... a = 1
this is 1 ... a = 2
this is 1 ... a = 3
this is 1 ... a = 4
this is 1 ... a = 5
this is 1 ... a = 6
this is 1 ... a = 7
this is 2 ... a = 1
this is 2 ... a = 2
this is 2 ... a = 3
this is 2 ... a = 4
this is 2 ... a = 5
this is 2 ... a = 6
liblib1.so unloaded  .....
liblib2.so unloaded  .....
^C
[xxx@xxxx:~/rapidjsonTest/build → master]$

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