Program fails when using my thread implementation? - c++

Question

This is my first post on your forum, but I'm not quite sure if I'm asking the right place? - Can I post C++ questions in this section, or is this just like a general programming section?
Anyway, enough of my noobish doubts, let's get to my problem :).
In my .h file (thread.h) I have a struct (RUNNABLE) and a class (thread).
'RUNNABLE' is like the interface you implement and override, or at least you override its virtual 'run()' void. You then create a 'thread' instance and call its 'start(void* ptr)' function, to start the thread. You pass in an object instance which has RUNNABLE as the base class as the parameter for the 'start' function.
This all seems great, but my implementation crashes my program.
Here's thread.h:
#include <process.h>
struct RUNNABLE{
virtual void run() = 0;
};
class thread{
public:
void start(void *ptr){
DWORD thr_id;
HANDLE thr_handl = (HANDLE)_beginthreadex(NULL, 0, thread_proc, ptr, 0, (unsigned int*)&thr_id);
}
private:
static unsigned int __stdcall thread_proc(void *param){
((RUNNABLE*)param)->run();
ExitThread(0);
return 0;
}
};
And this is my example implementation:
class test : RUNNABLE{
virtual void run(){
while(true){
dbText(0, 0, "hej");
}
}
};
test *obj = new test();
thread th;
th.start(obj);
And the program simply just crashes when I open it.
Help is appreciated :).
Best regards,
Benjamin.

Answer 1

test *obj = new test();
This is a memory management problem. When does obj get deleted? It can take a while for the thread to actually start running, the object needs to stay around long enough. I'm guessing you've got some code that's not in the snippet that is deleting that object again. Too soon.
The only code that can safely and accurately delete the object is the thread itself.

Answer 2

I tested it and it runs just fine, probably your dbText thingy there that crashes, I replaced it with printf("hejdå").

Answer 3

This runs fine for me:
#include <iostream>
#include <process.h>
#include <windows.h>
struct RUNNABLE{
virtual void run() = 0;
};
class thread{
public:
void start(void *ptr){
DWORD thr_id;
HANDLE thr_handl = (HANDLE)_beginthreadex(NULL, 0, thread_proc, ptr,
0, (unsigned int*)&thr_id);
}
private:
static unsigned int __stdcall thread_proc(void *param){
((RUNNABLE*)param)->run();
std::cout << "ending thread\n";
::ExitThread(0);
return 0;
}
};
class test : RUNNABLE{
virtual void run(){
for(unsigned int u=0; u<10; ++u){
std::cout << "thread\n";
}
}
};
int main()
{
test *obj = new test();
thread th;
th.start(obj);
std::cout << "giving thread some time\n";
::Sleep(5000);
std::cout << "ending process\n";
return 0;
}
However, you should probably call _endthreadex() (instead of EndThread()) to end the thread.