pthread without static decelaration with class - c++

Question

Inside the class I declared the thread function. I used static keyword because with out static keyword it is not working with class.
But if the type of the function is static I could not able to access the member function and public variables of the class
#include <iostream>
#include <pthread.h>
using namespace std;
class Base{
private:
static void * fpga_read(void*); // Thread function
void foo_2();
public:
/* member variables */
void foo(void);
protected:
int b;
};
void Base::foo(void)
{
pthread_t id;
pthread_create(&id, NULL,fpga_read,NULL);
cout << "\nInside base class" << endl;
}
void * Base::fpga_read(void *p)
{
cout << "\nInside thread function " << endl;
// error: invalid use of member ‘Base::b’ in static member function
cout << "Value of B inside thread class" << b;
int b;
}
int main()
{
Base a;
a.foo();
pthread_exit(NULL);
return 0;
}
Any-body tell me how to use thread function with-out static keyword. so i can able to access all class variables.

Answer 1

You do not need any static member function. You can use the argument parameter of pthread_create and that stateless lambda functions decay to normal function pointers to make code which almost looks like what you actually wrote:
Godbolt link: https://godbolt.org/z/QIGNUX
#include <iostream>
#include <pthread.h>
class Base {
public:
Base(int state) noexcept : b{state} {}
void foo();
private:
int b;
void fpga_read() {
std::cout << "Value of B inside thread class" << b;
}
};
void Base::foo()
{
pthread_t thread;
pthread_create(&thread, nullptr, [](void* that) -> void* {
Base* this_ = static_cast<Base*>(that);
this_->fpga_read();
return nullptr;
}, static_cast<void*>(this));
pthread_join(thread, nullptr);
}

Answer 2

pthread_create, like all OS-specific thread creation APIs (CreateThread etc in Windows) has a "void*" parameter to pass to the thread function.
You can use this to pass a pointer to your class
class A
{
void ThreadToUse() {}
static void Thread2(void* p)
{
A* a = (A*)p;
p->ThreadToUse();
}
void foo()
{
pthread_create(&A::Thread2,(void*)this);
}
};
That said, you can use C++11 std::thread with the same functionality as well in a standard way:
void foo()
{
std::thread t(&A::Thread2,this);
}