使用静态单例class实例导致动态加载失败

Question

我正在创建一个共享库，它导出一个使用静态 class 实例的函数。共享库旨在动态加载。但是，出于某种原因，使用静态 class 实例会导致动态加载失败。我正在使用 Poco 加载库。

//my_library.h
#ifndef MY_LIB_H
#define MY_LIB_H

#define DUMMY_MSG 1;

class SendClass
{
  public:
    SendClass() = default;
    SendClass( const SendClass &other ) = delete;
    SendClass &operator=( const SendClass &other ) = delete;

    static SendClass *get_instance(){ return &singleton_instance; };

    int send(){ return DUMMY_MSG; };

  private:
    static SendClass singleton_instance;
};

extern "C" __attribute__ ((visibility ("default"))) int send();//this is the function to be exported

inline int send()
{
  return SendClass::get_instance()->send();
}

#endif // MY_LIB_H

我用下面的命令将上面的头文件编译成共享库，并把库放在/tmp/下

g++ -shared -fPIC -o libexp.so my_library.h

然后我尝试在我的主程序中加载库

//main.cpp
#include "Poco/SharedLibrary.h"

using namespace std;

typedef int(*SENDFUNC)();

int main
(
  int argc,
  char **argv
)
{
    Poco::SharedLibrary lib;
    lib.load( "/tmp/libexp.so" );    //crashes here!
    SENDFUNC send_func = (SENDFUNC)lib.getSymbol("send");
    int msg = send_func();
    return 0;
}

程序在第 "lib.load( "/tmp/libexp.so" );" 行崩溃带有以下消息：

terminate called after throwing an instance of
'Poco::LibraryLoadException' what(): Cannot load library

但是，如果我把SendClass::get_instance的body改成下面这样，动态加载就成功完成了

//if SendClass::get_instance is implemented as follows, dynamic loading succeeds    
static SendClass *get_instance(){ return new SendClass; };

那么为什么使用静态实例会导致动态加载失败呢？

Answer 1

根据@ALX23z 的建议，我通过添加以下 cpp 文件解决了这个问题

//my_library.cpp
#include "my_library.h"

SendClass SendClass::singleton_instance;

使用静态单例class实例导致动态加载失败

Using static singleton class instance causes dynamic loading to fail

c++

singleton

shared-libraries

poco-libraries

dynamic-loading