Object initialization in C# thread - unexplained behaviour

Hello all,

I have a C# class (in this example, called A) that, in its
constructor, starts a thread with a method of its own. That thread
will be used to continuously check for one of its object's state and
generate classe's A events "Connected" and "Disconnect ed".

It looks something like this:

"
public class A
{
private AnotherObject an_obj;
private Thread thr;
...

public event System.EventHan dler Connected;
public event System.EventHan dler Disconnected;

public A()
{
thr = new Thread(new ThreadStart(thi s.DoThreadWork) );
thr.Start();
while (!thr.IsAlive);
thr.IsBackgroun d = true;
}

private void DoThreadWork()
{
an_obj = new AnotherObject() ;

while(true)
{
if (an_obj.IsPrese nt())
if (Connected != null)
Connected(this, EventArgs.Empty );
else
if (Disconnected != null)
Disconnected(th is, EventArgs.Empty );
}
}

public void DoSomethingX()
{
an_obj.CallXWor k();
}

public int DoSomethingY()
{
return an_obj.CallYWor k();
}
}
"

and a form that uses the previous class:

"
public class Form1: System.Windows. Forms.Form
{
private A objA;
...

public Form1()
{
objA = new SmartcardEVCont roller();

objA.Connected += new EventHandler(ob jA_Connected);
objA.Disconnect ed += new EventHandler(ob jA_Disconnected );
}

private void objA_Connected( object sender, EventArgs e)
{
objA.DoSomethin gX();
}

private void objA_Disconnect ed(object sender, EventArgs e)
{
int i = objA.DoSomethin gY();
MessageBox.Show ("Value: " + i);
}

private void button1_Click(o bject sender, System.EventArg s e)
{
objA.DoSomethin gX();
MessageBox.Show ("Done");
}
}
"
The problem is that although every call made to object "objA", inside
the "objA_Connected " or "objA_Disconnec ted" captured event works
perfectly fine, when a method is called on "objA" anywhere else it
just blocks the program execution. In this example, when button1 is
clicked, the instruction "MessageBox.Sho w("Done");" won't get called
and the program (Form1) will stop responding.

By the way, class AnotherObj is a .NET wrapper for a C dll that, in
turn, is a JNI wrapper for a Java class. All Java methods are
"synchroniz ed".

I thought that this could be a problem of the Java object but the fact
is that the cycle inside the thread keeps on executing when calls are
made inside "objA_Connected " or "objA_Disconnec ted" and those calls
execute successfully, no matter how many calls are made to object
"objA".
A strange thing that happens is that the call "objA.DoSomethi ngX();"
inside the click event makes the corresponding Java method start
executing (using log utilities in Java, I can check that the method
began execution but then stopped for no apparent reason).

The only thing I can now think of is that the thread that is spawned
in the A class has some kind of own memory space that the object that
was initialized inside the thread ("an_obj") can't be safely used
outside the thread. Being the thread that generates the events
"Connected" and "Disconnect ed", that could explain that calls to
object "objA", inside "objA_Connected " and "objA_Disconnec ted",
executed well. But that's only an hipothetical thought.

p.s.: I also tried initializing object "an_obj" outside the thread, in
classe's A contructor, but that way the call "an_obj.IsPrese nt())"
would also block in the C dll (that calls JNI code) for no apparent
reason.

If anyone could give me an explanation of why this is happening and
what I can do to avoid it, I would be grateful, as I can't figure it
out just by myself.

Thank you very much,
Ricardo Pereira

If anyone could give me an explanation of why this is happening and
what I can do to avoid it, I would be grateful, as I can't figure it
out just by myself.

Hello all,

I have a C# class (in this example, called A) that, in its
constructor, starts a thread with a method of its own. That thread
will be used to continuously check for one of its object's state and
generate classe's A events "Connected" and "Disconnect ed".

It looks something like this:

"
public class A
{
private AnotherObject an_obj;
private Thread thr;
...

public event System.EventHan dler Connected;
public event System.EventHan dler Disconnected;

public A()
{
thr = new Thread(new ThreadStart(thi s.DoThreadWork) );
thr.Start();
while (!thr.IsAlive);
thr.IsBackgroun d = true;
}

private void DoThreadWork()
{
an_obj = new AnotherObject() ;

while(true)
{
if (an_obj.IsPrese nt())
if (Connected != null)
Connected(this, EventArgs.Empty );
else
if (Disconnected != null)
Disconnected(th is, EventArgs.Empty );
}
}

public void DoSomethingX()
{
an_obj.CallXWor k();
}

public int DoSomethingY()
{
return an_obj.CallYWor k();
}
}
"

and a form that uses the previous class:

"
public class Form1: System.Windows. Forms.Form
{
private A objA;
...

public Form1()
{
objA = new SmartcardEVCont roller();

objA.Connected += new EventHandler(ob jA_Connected);
objA.Disconnect ed += new EventHandler(ob jA_Disconnected );
}

private void objA_Connected( object sender, EventArgs e)
{
objA.DoSomethin gX();
}

private void objA_Disconnect ed(object sender, EventArgs e)
{
int i = objA.DoSomethin gY();
MessageBox.Show ("Value: " + i);
}

private void button1_Click(o bject sender, System.EventArg s e)
{
objA.DoSomethin gX();
MessageBox.Show ("Done");
}
}
"
The problem is that although every call made to object "objA", inside
the "objA_Connected " or "objA_Disconnec ted" captured event works
perfectly fine, when a method is called on "objA" anywhere else it
just blocks the program execution. In this example, when button1 is
clicked, the instruction "MessageBox.Sho w("Done");" won't get called
and the program (Form1) will stop responding.

By the way, class AnotherObj is a .NET wrapper for a C dll that, in
turn, is a JNI wrapper for a Java class. All Java methods are
"synchronized" .

I thought that this could be a problem of the Java object but the fact
is that the cycle inside the thread keeps on executing when calls are
made inside "objA_Connected " or "objA_Disconnec ted" and those calls
execute successfully, no matter how many calls are made to object
"objA".
A strange thing that happens is that the call "objA.DoSomethi ngX();"
inside the click event makes the corresponding Java method start
executing (using log utilities in Java, I can check that the method
began execution but then stopped for no apparent reason).

The only thing I can now think of is that the thread that is spawned
in the A class has some kind of own memory space that the object that
was initialized inside the thread ("an_obj") can't be safely used
outside the thread. Being the thread that generates the events
"Connected" and "Disconnect ed", that could explain that calls to
object "objA", inside "objA_Connected " and "objA_Disconnec ted",
executed well. But that's only an hipothetical thought.

p.s.: I also tried initializing object "an_obj" outside the thread, in
classe's A contructor, but that way the call "an_obj.IsPrese nt())"
would also block in the C dll (that calls JNI code) for no apparent
reason.

If anyone could give me an explanation of why this is happening and
what I can do to avoid it, I would be grateful, as I can't figure it
out just by myself.

Thank you very much,
Ricardo Pereira

The following line of code in class A's constructor is putting the
calling thread into an infinite loop:

while (!thr.IsAlive);

Because the thread you are creating (thr) is also in an infinite
while(true) loop.

Hello all,

I have a C# class (in this example, called A) that, in its
constructor, starts a thread with a method of its own. That thread
will be used to continuously check for one of its object's state and
generate classe's A events "Connected" and "Disconnect ed".

It looks something like this:

"
public class A
{
private AnotherObject an_obj;
private Thread thr;
...

public event System.EventHan dler Connected;
public event System.EventHan dler Disconnected;

public A()
{
thr = new Thread(new ThreadStart(thi s.DoThreadWork) );
thr.Start();
while (!thr.IsAlive);
thr.IsBackgroun d = true;
}

private void DoThreadWork()
{
an_obj = new AnotherObject() ;

while(true)
{
if (an_obj.IsPrese nt())
if (Connected != null)
Connected(this, EventArgs.Empty );
else
if (Disconnected != null)
Disconnected(th is, EventArgs.Empty );
}
}

public void DoSomethingX()
{
an_obj.CallXWor k();
}

public int DoSomethingY()
{
return an_obj.CallYWor k();
}
}
"

and a form that uses the previous class:

"
public class Form1: System.Windows. Forms.Form
{
private A objA;
...

public Form1()
{
objA = new SmartcardEVCont roller();

objA.Connected += new EventHandler(ob jA_Connected);
objA.Disconnect ed += new EventHandler(ob jA_Disconnected );
}

private void objA_Connected( object sender, EventArgs e)
{
objA.DoSomethin gX();
}

private void objA_Disconnect ed(object sender, EventArgs e)
{
int i = objA.DoSomethin gY();
MessageBox.Show ("Value: " + i);
}

private void button1_Click(o bject sender, System.EventArg s e)
{
objA.DoSomethin gX();
MessageBox.Show ("Done");
}
}
"
The problem is that although every call made to object "objA", inside
the "objA_Connected " or "objA_Disconnec ted" captured event works
perfectly fine, when a method is called on "objA" anywhere else it
just blocks the program execution. In this example, when button1 is
clicked, the instruction "MessageBox.Sho w("Done");" won't get called
and the program (Form1) will stop responding.

By the way, class AnotherObj is a .NET wrapper for a C dll that, in
turn, is a JNI wrapper for a Java class. All Java methods are
"synchroniz ed".

I thought that this could be a problem of the Java object but the fact
is that the cycle inside the thread keeps on executing when calls are
made inside "objA_Connected " or "objA_Disconnec ted" and those calls
execute successfully, no matter how many calls are made to object
"objA".
A strange thing that happens is that the call "objA.DoSomethi ngX();"
inside the click event makes the corresponding Java method start
executing (using log utilities in Java, I can check that the method
began execution but then stopped for no apparent reason).

The only thing I can now think of is that the thread that is spawned
in the A class has some kind of own memory space that the object that
was initialized inside the thread ("an_obj") can't be safely used
outside the thread. Being the thread that generates the events
"Connected" and "Disconnect ed", that could explain that calls to
object "objA", inside "objA_Connected " and "objA_Disconnec ted",
executed well. But that's only an hipothetical thought.

p.s.: I also tried initializing object "an_obj" outside the thread, in
classe's A contructor, but that way the call "an_obj.IsPrese nt())"
would also block in the C dll (that calls JNI code) for no apparent
reason.

If anyone could give me an explanation of why this is happening and
what I can do to avoid it, I would be grateful, as I can't figure it
out just by myself.

Thank you very much,
Ricardo Pereira

Ricardo,

To me, it seems that the problem is arising from the fact that your
event is coming in on a separate thread, which then tries to access windows elements outside of the thread that they were created in. When you call the static Show method on the MessageBox class, it is not on the main UI thread. In order to marshal the call to the correct thread, you need to call the
Invoke method on a control that is created on the UI thread (your form would be fine). You then pass a delegate pointing to the method to be called on
the UI thread, along with any parameters that are needed.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

"Ricardo Pereira" <pe*********@ma il.telepac.pt> wrote in message
news:f1******** *************** **@posting.goog le.com...

Hello all,

I have a C# class (in this example, called A) that, in its
constructor, starts a thread with a method of its own. That thread
will be used to continuously check for one of its object's state and
generate classe's A events "Connected" and "Disconnect ed".

It looks something like this:

"
public class A
{
private AnotherObject an_obj;
private Thread thr;
...

public event System.EventHan dler Connected;
public event System.EventHan dler Disconnected;

public A()
{
thr = new Thread(new ThreadStart(thi s.DoThreadWork) );
thr.Start();
while (!thr.IsAlive);
thr.IsBackgroun d = true;
}

private void DoThreadWork()
{
an_obj = new AnotherObject() ;

while(true)
{
if (an_obj.IsPrese nt())
if (Connected != null)
Connected(this, EventArgs.Empty );
else
if (Disconnected != null)
Disconnected(th is, EventArgs.Empty );
}
}

public void DoSomethingX()
{
an_obj.CallXWor k();
}

public int DoSomethingY()
{
return an_obj.CallYWor k();
}
}
"

and a form that uses the previous class:

"
public class Form1: System.Windows. Forms.Form
{
private A objA;
...

public Form1()
{
objA = new SmartcardEVCont roller();

objA.Connected += new EventHandler(ob jA_Connected);
objA.Disconnect ed += new EventHandler(ob jA_Disconnected );
}

private void objA_Connected( object sender, EventArgs e)
{
objA.DoSomethin gX();
}

private void objA_Disconnect ed(object sender, EventArgs e)
{
int i = objA.DoSomethin gY();
MessageBox.Show ("Value: " + i);
}

private void button1_Click(o bject sender, System.EventArg s e)
{
objA.DoSomethin gX();
MessageBox.Show ("Done");
}
}
"
The problem is that although every call made to object "objA", inside
the "objA_Connected " or "objA_Disconnec ted" captured event works
perfectly fine, when a method is called on "objA" anywhere else it
just blocks the program execution. In this example, when button1 is
clicked, the instruction "MessageBox.Sho w("Done");" won't get called
and the program (Form1) will stop responding.

By the way, class AnotherObj is a .NET wrapper for a C dll that, in
turn, is a JNI wrapper for a Java class. All Java methods are
"synchroniz ed".

I thought that this could be a problem of the Java object but the fact
is that the cycle inside the thread keeps on executing when calls are
made inside "objA_Connected " or "objA_Disconnec ted" and those calls
execute successfully, no matter how many calls are made to object
"objA".
A strange thing that happens is that the call "objA.DoSomethi ngX();"
inside the click event makes the corresponding Java method start
executing (using log utilities in Java, I can check that the method
began execution but then stopped for no apparent reason).

The only thing I can now think of is that the thread that is spawned
in the A class has some kind of own memory space that the object that
was initialized inside the thread ("an_obj") can't be safely used
outside the thread. Being the thread that generates the events
"Connected" and "Disconnect ed", that could explain that calls to
object "objA", inside "objA_Connected " and "objA_Disconnec ted",
executed well. But that's only an hipothetical thought.

p.s.: I also tried initializing object "an_obj" outside the thread, in
classe's A contructor, but that way the call "an_obj.IsPrese nt())"
would also block in the C dll (that calls JNI code) for no apparent
reason.

If anyone could give me an explanation of why this is happening and
what I can do to avoid it, I would be grateful, as I can't figure it
out just by myself.

Thank you very much,
Ricardo Pereira

Scott Allen <bitmask@[nospam].fred.net> wrote:

The following line of code in class A's constructor is putting the
calling thread into an infinite loop:

while (!thr.IsAlive);

Because the thread you are creating (thr) is also in an infinite
while(true) loop.

Nope - while (!thr.IsAlive); is just waiting for the thread to actually
start. It's not a good idea, but it's not actually an infinite loop.

Hello all,

I have a C# class (in this example, called A) that, in its
constructor, starts a thread with a method of its own. That thread
will be used to continuously check for one of its object's state and
generate classe's A events "Connected" and "Disconnect ed".

It looks something like this: [...] public A()
{
thr = new Thread(new ThreadStart(thi s.DoThreadWork) );
thr.Start();
while (!thr.IsAlive);
thr.IsBackgroun d = true;
}