I'm facing a deadlock, my code structure is similar to this:
private delegate void UpdateControlDelegate(string value);
public void UpdateControl(string value)
{
if (txtAddress.InvokeRequired)
{
txtAddress.Invoke(new UpdateControlDelegate(UpdateControl), value);
}
else
{
txtAddress.Text = value; // This is in GroupBox1
txtValue.Text = value; // This is in GroupBox2
}
}
class ThreadHandler
{
List<string> _list = new List<string>();
object _criticalSection = new object();
public ThreadHandler()
{
new Thread(new ThreadStart(Run)).Start();
}
public static ThreadHandler _threadHandler = null;
public static ThreadHandler GetThreadHandler()
{
if (_threadHandler == null)
{
_threadHandler = new ThreadHandler();
}
return _threadHandler;
}
public void Run()
{
while (true)
{
// some code
lock (_criticalSection)
{
foreach (string str in _list)
{
// some Code
}
}
// some code
Thread.Sleep(SomeTime);
}
}
public void AddItem(string item)
{
lock (_criticalSection)
{
_list.Add(item);
}
}
public void RemoveItem(string item)
{
lock (_criticalSection)
{
_list.Remove(item);
}
}
}
But using the same code, I just modified the UpdateControl method like this:
private delegate void UpdateControlDelegate(string value);
public void UpdateControl(string value)
{
if (InvokeRequired)
{
BeginInvoke(new UpdateControlDelegate(UpdateControl), value);
}
else
{
txtAddress.Text = value; // This is in GroupBox1
txtValue.Text = value; // This is in GroupBox2
}
}
This is working fine. What is the problem?
The problem is almost certainly that you're acquiring the lock within a background thread, then calling Control.Invoke, and invoking a delegate (on the UI thread) which tries to acquire the same lock. It can't do that, because the other thread holds the lock - and will keep holding the lock while it waits for the UI operation to complete.
Admittedly there's no locking within the UpdateControl method you've posted, but I suspect that's not the complete code - and you haven't shown where you're using AddItem or RemoveItem.
I note that GetThreadHandler() isn't thread-safe, by the way - that looks like a bug to me...
Are you calling AddItem and RemoveItem from the main thread while calling UpdateControl from the worker thread? That will cause deadlocks.
Here is my code,
public class ValueReader
{
List<IDataReader> _list = new List<IDataReader>();
object _criticalSection = new object();
public ValueReader()
{
//Nothign here
}
public void Attach(IDataReader reader)
{
lock(_criticalSection)
{
_list.Add(reader);
}
}
public void Detach(IDataReader reader)
{
lock(_criticalSection)
{
_list.Remove(reader);
}
}
public void Notify(string value)
{
lock(_criticalSection)
{
foreach(IDataReader reader in _list)
{
reader.Update(value);
}
}
}
public void Start()
{
new Thread(new ThreadStart(Run)).Start();
}
private void Run()
{
while(true)
{
//generate value
Notify(value);
Thread.Sleep(5000);
}
}
}
public interface IDataReader
{
void UpdateControls(string value);
}
public class FirstClass : IDataReader
{
....
......
ValueReader _reader = null;
public FirstClass()
{
_reader = new ValueReader();
_reader.Start();
_reader.Attach(this);
}
private void AddToSmartClient()
{
// _reader has added to SmartClient's WorkItem
}
private delegate void UpdateControlDelegate(string value);
public void UpdateControl(string value)
{
if(txtAddress.InvokeRequired)
{
txtAddress.Invoke(new UpdateControlDelegate(UpdateControl), value);
}
else
{
txtAddress.Text = value;
txtValue.Text = value;
}
}
}
public class SecondClass : IDataReader
{
....
......
ValueReader _reader = null;
public void SecondClass()
{
_reader = ReadFromSmartClient();
_reader.Attach(this);
}
private ValueReader ReadFromSmartClient()
{
reader = //Get from SmartClient's Workitem.
return reader
}
private delegate void UpdateControlDelegate(string value);
public void UpdateControl(string value)
{
if(InvokeRequired)
{
BeginInvoke(new UpdateControlDelegate(UpdateControl), value);
}
else
{
control1.Text = value;
control2.Text = value;
}
}
}
I invokes only FirstClass for some time. In this case its working fine. After some time i invoked the Second class, at this time while calling Attach from secondClass the application is hanging.(i monitered that its comming until Attach methods's lock(_criticalSection).
After some time i converter the Update control in the Frist Class as follow
public void UpdateControl(string value)
{
if(InvokeRequired)
{
BeginInvoke(new UpdateControlDelegate(UpdateControl), value);
}
else
{
txtAddress.Text = value;
txtValue.Text = value;
}
}
This is working well after invoking the SecondClass also. Why its happening?
