Threads in C++

[Seabra]

Hi,

In the constructor of my class Scene I call a thread "CreateThread" that not recognized the attributes of my class... By any chance, is it a property on the use of threads???

Scene::Scene()
{
	HANDLE hThreadTest;
	unsigned long iID; 
                spnavi = new Device();
	spnavi -> initDevice();
	hThreadTest = CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)ThreadTest,NULL,0,&iID);
}

DWORD WINAPI Scene::ThreadTest (void) {
	while (true) {
		spnavi -> loop();
	}
}

The message error is:
1>.\Class Scene.cpp(33) : error C2227: left of '->loop' must point to class/struct/union/generic type.

Does anyone have any idea?

Thanks.

[medievalelks]

What is spnavi?

[Seabra]

Is an attribute of the class (Scene) that represents an interaction physical device. Is an object of the other class (Device).

[medievalelks]

How is it defined?

[CornedBee]

You cannot pass a member function as the thread start routine. It must be a static or non-member function.

Better, just use Boost.Thread for this stuff. Then you can use Boost.Bind to pass a member function.

[Seabra]

How is it defined?

The class Device is defined how:

#include "dispositivo.h"

using namespace std;

Device::Device() {
...
}

void Device::initDevice() {
...
}

void Device::loop() {
... //get coordinates of device...
}

[Elysia]

hThreadTest = CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)ThreadTest,NULL,0,&iID);

Do NOT cast the address of a function unless you really, really, really, REALLY know what you're doing (hint: you don't).
If you remove it, the compiler will complain. As it should, because you cannot pass a pointer to a class function where a pointer to a global or static function is expected.
This is a good thing to remember. Casting the address will mask your error for the compiler.

[cpjust]

Also, a thread function should take a void* pointer parameter, not void.

[Elysia]

Another subtle and easily identified bug if you would just not cast the function address.

[Seabra]

Hi,

Finally, I compiled and executed the program. The function is:

HANDLE WINAPI Scene::ThreadTest (Device* spnavi) {
	while (true) {
		spnavi -> loop();
	}
}

The function above gets the coordinates (translation and rotation) of the user interaction device, however, seems to me that the thread is centralizing the execution of the application, as the main window of 3D application does not appear! I need to read the coordinates of the device in parallel to execution of 3D application...

By definition, this could not happen... anyone have any idea?

Thanks.

[Elysia]

Well, first, your loop is endless, which is bad. You should loop on a variable so that you can break the loop later.
Second, it will eat up 100% CPU (or 50% on dual core) unless you have some sleeps somewhere (most likely), so make sure you do that. The best bet is just make it wait until it has work to do, otherwise it's just waste of CPU cycles which games seem to be really good at.

And if you don't mind, what's the code for creating that thread?

[brewbuck]

Well, first, your loop is endless, which is bad. You should loop on a variable so that you can break the loop later.

It could be broken by an exception.

[Elysia]

Right, but I don't see any catch handlers.
So either throw/catch or flag.

[brewbuck]

Right, but I don't see any catch handlers.
So either throw/catch or flag.

This is really too speculative. But the lack of a catch would be exactly how the loop gets broken -- the exception propagates past it.

[CornedBee]

Into the threading infrastructure? Not a good idea.