Here I have written a thread wrapper for c thread function pthread_create(). It will allow calling any method on any object and passing any number of arguments to that method. The API is:
template <typename T, typename R, typename... ATs>
pthread_t NewThread(T *obj, R (T::*mem)(ATs...), ATs... args);
Below is the template:
template<unsigned int i>
class TupleUnpack
{
public:
template<typename R, typename ...ATs, typename ...T_function_arguments>
inline static R unpack (R (*function) (ATs...),
std::tuple<ATs...> arguments_tuple,
T_function_arguments ...function_arguments)
{
return TupleUnpack<i-1>::unpack (function, arguments_tuple, std::get<i-1> (arguments_tuple), function_arguments...);
}
};
template<>
class TupleUnpack<0>
{
public:
template<typename R, typename ...ATs, typename ...T_function_arguments>
inline static R unpack (R (*function) (ATs...),
std::tuple<ATs...> arguments_tuple,
T_function_arguments ...function_arguments)
{
return function (function_arguments...);
}
};
class CallCaller
{
virtual bool dispatch (void)=0;
};
template<typename T,typename R,typename ...ATs>
class Call : public CallCaller
{
public:
Call (T *obj,R (*function) (ATs...),ATs... arguments) :obj(obj),function (function),tuplearg (arguments...) {}
~Call() {}
bool dispatch (void)
{
return TupleUnpack<sizeof ...(ATs)>::unpack (this->function, this->tuplearg);
}
private:
std::tuple<ATs...> tuplearg;
R (*function) (ATs...);
T *obj;
};
void *test(int d,double sf)
{
std::cout<<"yay my thread runs d="<<d<<" sf="<<sf<<std::endl;
}
template<typename T,typename R,typename ...ATs>
void* stub (void* vp)
{
Call<T,R,ATs...>* call = static_cast<Call<T,R,ATs...>*>(vp);
call->dispatch();
delete call;
pthread_exit (0);
}
template <typename T, typename R, typename... ATs>
pthread_t NewThread(T *ob, R (T::*mem)(ATs...), ATs... args)
{
pthread_t tid;
R (*func) (ATs...);
Call<T,R,ATs...> *task=new Call<T,R,ATs...>(ob,&test,args...);
pthread_create(&tid, nullptr, stub<T,R,ATs...>, task) ;
return tid;
}
Below is the CPP file:
#include <tr1/tuple>
#include <utility>
#include <iostream>
#include <pthread.h>
#include <tuple>
#include <type_traits>
#include <utility>
#include "NewThread.hpp"
class X
{
public:
void *method(int a, double x)
{
std::cout<<"yay my tread runs a="<<a<<" x="<<x<<std::endl;
}
};
int main()
{
X x;
int i;
pthread_t tid = NewThread(&x, &X::method, 1234, 3.14);
pthread_join(tid,NULL);
std::cout<<"Thread Ended "<<tid<<std::endl;
return 0;
}
I am trying to call the x::method() with the arguments. As you can see I have a test() function which is similar to x::method() just to demonstrate that my thread is working. But I want to be able to call the x::method(). Could anyone please guide me?
In Essence my current output is:
yay my thread runs d=1234 sf=3.14
Thread Ended 139766222432000
I want my output to be
yay my thread runs a=1234 x=3.14
Thread Ended 139766222432000
So this
R (*function) (ATs...);
is a function pointer, but you need a member function pointer
R (T::*function) (ATs...);
For calling a member function pointer you need an object and you have to call it with the following syntax:
self->*function(function_arguments...);
Note ->* syntax here.
So I added a T* self parameter to TupleUnpack<>::unpack and called it in Call<>::dispatch with the obj member. Now, I could replace the test function with the mem parameter in NewThread.
Here is a patch:
diff --git a/NewThread.hpp b/NewThread.hpp
index e121294..768f7d9 100644
--- a/NewThread.hpp
+++ b/NewThread.hpp
@@ -5,12 +5,12 @@ template<unsigned int i>
class TupleUnpack
{
public:
- template<typename R, typename ...ATs, typename ...T_function_arguments>
- inline static R unpack (R (*function) (ATs...),
+ template<typename T, typename R, typename ...ATs, typename ...T_function_arguments>
+ inline static R unpack (T* self, R (T::*function) (ATs...),
std::tuple<ATs...> arguments_tuple,
T_function_arguments ...function_arguments)
{
- return TupleUnpack<i-1>::unpack (function, arguments_tuple, std::get<i-1> (arguments_tuple), function_arguments...);
+ return TupleUnpack<i-1>::unpack (self, function, arguments_tuple, std::get<i-1> (arguments_tuple), function_arguments...);
}
};
@@ -18,12 +18,12 @@ template<>
class TupleUnpack<0>
{
public:
- template<typename R, typename ...ATs, typename ...T_function_arguments>
- inline static R unpack (R (*function) (ATs...),
+ template<typename T, typename R, typename ...ATs, typename ...T_function_arguments>
+ inline static R unpack (T* self, R (T::*function) (ATs...),
std::tuple<ATs...> arguments_tuple,
T_function_arguments ...function_arguments)
{
- return function (function_arguments...);
+ return (self->*function) (function_arguments...);
}
};
class CallCaller
@@ -35,19 +35,17 @@ template<typename T,typename R,typename ...ATs>
class Call : public CallCaller
{
public:
- Call (T *obj,R (*function) (ATs...),ATs... arguments) :obj(obj),function (function),tuplearg (arguments...) {}
+ Call (T *obj,R (T::*function) (ATs...),ATs... arguments) :obj(obj),function (function),tuplearg (arguments...) {}
~Call() {}
bool dispatch (void)
{
- return TupleUnpack<sizeof ...(ATs)>::unpack (this->function, this->tuplearg);
+ return TupleUnpack<sizeof ...(ATs)>::unpack(obj, this->function, this->tuplearg);
}
private:
std::tuple<ATs...> tuplearg;
- R (*function) (ATs...);
+ R (T::*function) (ATs...);
T *obj;
};
@@ -71,8 +69,7 @@ template <typename T, typename R, typename... ATs>
pthread_t NewThread(T *ob, R (T::*mem)(ATs...), ATs... args)
{
pthread_t tid;
- R (*func) (ATs...);
- Call<T,R,ATs...> *task=new Call<T,R,ATs...>(ob,&test,args...);
+ Call<T,R,ATs...> *task=new Call<T,R,ATs...>(ob,mem,args...);
pthread_create(&tid, nullptr, stub<T,R,ATs...>, task) ;