WIN API - Programm getting stuck while a button is selected - c++

Question

I am creating a simple software using WINAPI that reads the data from a sensor connected to a computer via USB.
In this software, I am implementing some functions like read mode, test mode, etc.
The problem that I am facing is that I am getting stuck while I select the button for continuous reading, the code follows below:
case WM_COMMAND:
switch (wp)
{
case START_BUTTON:
printf("START_BUTTON");
while(SendDlgItemMessage(hWnd,START_BUTTON,BM_GETCHECK ,TRUE,0)== BST_CHECKED)
{
char* var = USB_Read(); //Get data from the sensor
SetWindowText(hLux, var); //Display the data
if (SendDlgItemMessage(hWnd,START_BUTTON,BM_GETCHECK ,TRUE,0)!= BST_CHECKED) //Check if the botton is no longer selected
break;
}
break;
}
break;
I know that the problem is in the while-loop, when I press it all the program gets stuck, only the data is being displayed correctly, the other controls get like frozen.
The question is: How could I display the data continuously and have access to the other controls at the same time?

Answer 1

You have to create a thread of execution that reads the usb while the start is checked.
So we create a thread that is started in the program initialization, which run continuosly and reads usb each time it founds the button checked.
Now in the message loop you simply check or uncheck the button.
DWORD WINAPI ThreadFunction( LPVOID lpParam )
{
(void)lpParam; //make happy compiler for unused variable
while (TRUE) //Once created the thread runs always
{
//If checked reads usb for each iteration
if(SendDlgItemMessage(hWnd,START_BUTTON,BM_GETCHECK ,0,0)== BST_CHECKED)
{
char* var = USB_Read(); //Get data from the sensor
SetWindowText(hLux, var); //Display the data
Sleep(1); //Why this? to don't have a furious CPU usage
}
}
}
.....
//Winmain
DWORD dwThreadId; //thread ID in case you'll need it
//Create and start the thread
CreateThread(
NULL, // default security attributes
0, // use default stack size
ThreadFunction, // thread function name
NULL, // argument to thread function
0, // use default creation flags
&dwThreadId); // returns the thread identifier
......
case WM_COMMAND:
switch (wp)
{
case START_BUTTON:
printf("START_BUTTON");
if(SendDlgItemMessage(hWnd,START_BUTTON,BM_GETCHECK ,0,0)== BST_CHECKED)
SendDlgItemMessage(hWnd,START_BUTTON,BM_SETCHECK ,BST_UNCHECKED, 0);
else
SendDlgItemMessage(hWnd,START_BUTTON,BM_SETCHECK ,BST_CHECKED, 0);
break;
}
break;
EDIT: I modified the program to check/uncheck the radio button.
Please note the usage of the Sleep function with a minimal value of 1ms. It is used to give back control to the OS to smooth the CPU usage. If in the function that reads the usb there are enough OS synch primitives it can be omitted (check cpu usage).