C#•2mo ago

WPF possible threading issue?

I am creating a application to update a bunch of usb devices at the same time. I have figured out the usb communication with devices just fine but somehow someway I get a threading issue. I am just getting into threading so I just need someone with personal experience on how they would handle this situation. I have a System.Management object to watch for usb events. When usb connect/disconnect event fires off then check all devices connected by specific usb protocol and look at device paths for PID/VID (specific to manufacturer).

public MainWindow()
        {
            InitializeComponent();
            StartDeviceDetection();
        }

public void StartDeviceDetection()//start device detection through USB
        {
            ManagementEventWatcher watcher = new ManagementEventWatcher();
            WqlEventQuery query = new WqlEventQuery("SELECT * FROM __InstanceOperationEvent WITHIN 1 WHERE TargetInstance ISA 'Win32_USBControllerDevice'"); //Querey for specific device standard
            watcher.EventArrived += USBEvents; //subscribe to events it should querey for
            watcher.Query = query; //Set Query
            watcher.Start();//start watch
        }

 private void USBEvents(object sender, EventArrivedEventArgs e)//detects when device is removed from computer
        {
ManagementBaseObject instance = (ManagementBaseObject)e.NewEvent["TargetInstance"];
                eventType = e.NewEvent.ClassPath.ClassName;
            //scanning for device arrival
            if (eventType.Equals("__InstanceCreationEvent"))
            {
                aDeviceArrived();
            }
        }

private void aDeviceArrive(){
        List<string> allPaths = {list of all paths with specific}
        foreach(string path in allPaths){
             if(path.Contains(VID) && path.Contains(PID)){
                  Device device = new Device();
                  device.path = path;
                  gridWithDevices.add(device);
             }
}

public MainWindow()
        {
            InitializeComponent();
            StartDeviceDetection();
        }

public void StartDeviceDetection()//start device detection through USB
        {
            ManagementEventWatcher watcher = new ManagementEventWatcher();
            WqlEventQuery query = new WqlEventQuery("SELECT * FROM __InstanceOperationEvent WITHIN 1 WHERE TargetInstance ISA 'Win32_USBControllerDevice'"); //Querey for specific device standard
            watcher.EventArrived += USBEvents; //subscribe to events it should querey for
            watcher.Query = query; //Set Query
            watcher.Start();//start watch
        }

 private void USBEvents(object sender, EventArrivedEventArgs e)//detects when device is removed from computer
        {
ManagementBaseObject instance = (ManagementBaseObject)e.NewEvent["TargetInstance"];
                eventType = e.NewEvent.ClassPath.ClassName;
            //scanning for device arrival
            if (eventType.Equals("__InstanceCreationEvent"))
            {
                aDeviceArrived();
            }
        }

private void aDeviceArrive(){
        List<string> allPaths = {list of all paths with specific}
        foreach(string path in allPaths){
             if(path.Contains(VID) && path.Contains(PID)){
                  Device device = new Device();
                  device.path = path;
                  gridWithDevices.add(device);
             }
}

4 Replies

Dingus•2mo ago

The issue starts when I press button in datagrid that is beside objects listed usb path

Public BackgroundWorker worker
private void updateDevice(object sender, RoutedEventArgs e){
    Device device = (sender as Button).DataContext as Device;
    worker = new BackgroundWorker();
    worker.DoWork += updateDeviceWithFiles;
    worker.RunWrokerAsync(argument: device);
    worker.dispose();
}

Public BackgroundWorker worker
private void updateDevice(object sender, RoutedEventArgs e){
    Device device = (sender as Button).DataContext as Device;
    worker = new BackgroundWorker();
    worker.DoWork += updateDeviceWithFiles;
    worker.RunWrokerAsync(argument: device);
    worker.dispose();
}

Right now the device communication works wonderfully and all files are sent to the device. The application doesn't freeze up since I am using the new thread to actually send the files. HOWEVER I update a ton of devices. (4 at once usually). When all files are sent a the device I have device removed from datagrid so I assume it does not exist anymore and Garbage collecter reclaims the memory. It always happens at the 6th device when I press its update button debugger in visual studio says System.OutofMemoryException and points to threading method of claiming thread. What I think is happening is that after worker finishes sending files to device the thread is not actually disposed and Visual Studio thinks I am just infinitely trying to claim threads so visual studio yells at me. If I am not implementing threading right please tell me a more proper way to do it! This program has been months in the making by myself trying to figure out USB protocol and file handling. I just want to be able to update all my devices at once!

sibber•2mo ago

i dont think you want to dispose the worker immediately after starting the work also io is inherently async you probably dont need a seperate thread for that and nowadays we use the TPL can you show updateDeviceWithFiles?

cap5lut•2mo ago

can u also give the exact exception, including the stack trace? reason is OOMEs are not only thrown for the lack of memory (eg System.Drawing stuff throws them for invalid/unsupported image formats)

Dingus•2mo ago

The updateDeviceWithFiles gets into the weeds of the program. I actually discovered I was missing an important method of the class I am using with all the dll imports from setupapi.dll in windows. updateDeviceWithFiles goes essentially like this though. I am testing right now with the new function and seeing how it works then will report back here if I still have the same issue

 async void updateDeviceWithFiles(motorollaDevice device)
{
    // Check handle on specific device
     Intpntr deviceHandle = DeviceManager.CreateFile(device.devicePath); 

    bool success = deviceHandle != IntPtr.Zero && deviceHandle != new IntPtr(-1);
    IntPtr fileHandle = 0;

    if (success)
    {
        List<string> filesForSelectedDevice = deviceFiles(); //here I grab files from database

        while (x < fileCount)
        {
            currentFileCount(device, x, fileCount);
            Thread.SpinWait(500);
            deviceHandle = DeviceManager.CreateFile(device.devicePath); 
            //make sure device exists

            success = deviceHandle != IntPtr.Zero && deviceHandle != new IntPtr(-1);
            if (success)
            {
                fileHandle = DeviceManager.CreateFile(filesForSelectedDevice[x]);
                //make sure file exists

                ProcessSelectedFileAsync(deviceHandle, fileHandle, device);
                

                DeviceManager.CloseHandle(fileHandle);
                x++;
            }
            if (x == fileCount)
            {
                DeviceManager.CloseHandle(deviceHandle); //dispose handle on device
                DeviceManager.SetupDiDestroyDeviceInfoList(deviceHandle); 
                //this is the function I was missing to release memory related to device                        causing my thread to be held

                removeFinishedDevice(device);
                break;
            }
        }

 async void updateDeviceWithFiles(motorollaDevice device)
{
    // Check handle on specific device
     Intpntr deviceHandle = DeviceManager.CreateFile(device.devicePath); 

    bool success = deviceHandle != IntPtr.Zero && deviceHandle != new IntPtr(-1);
    IntPtr fileHandle = 0;

    if (success)
    {
        List<string> filesForSelectedDevice = deviceFiles(); //here I grab files from database

        while (x < fileCount)
        {
            currentFileCount(device, x, fileCount);
            Thread.SpinWait(500);
            deviceHandle = DeviceManager.CreateFile(device.devicePath); 
            //make sure device exists

            success = deviceHandle != IntPtr.Zero && deviceHandle != new IntPtr(-1);
            if (success)
            {
                fileHandle = DeviceManager.CreateFile(filesForSelectedDevice[x]);
                //make sure file exists

                ProcessSelectedFileAsync(deviceHandle, fileHandle, device);
                

                DeviceManager.CloseHandle(fileHandle);
                x++;
            }
            if (x == fileCount)
            {
                DeviceManager.CloseHandle(deviceHandle); //dispose handle on device
                DeviceManager.SetupDiDestroyDeviceInfoList(deviceHandle); 
                //this is the function I was missing to release memory related to device                        causing my thread to be held

                removeFinishedDevice(device);
                break;
            }
        }

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WPF possible threading issue?