PeekMessage, DispatchMessage in C# ??

[Jozsef Bekes]

Hi All,

I am trying to implement a general threading approach in C#, and I have
faced this problem:
I have the function f_main running in thread th1. I want to invoke two
functions f1 and f2 in th_2. From f_main I want to do two distinct function
calls, the first results only in invoking f1 in the context of th_2, the
second function call would invoke only f2 in the context of th_2. f1 and f2
must run in the same thread context.
My approach in C++ would be to start a thread, put the usual while loop with
PeekMessage and DispatchMessage and trigger the function invokations via
PostThreadMessage. I cannot find such an opportunity in C# except for using
the windows API and implementing the stuff as if I was using C++ (that is I
guess not a good approach). Could someone please give me a suggestion how I
should proceed?

Thank you for your help.

Best Regards,
Jozsi

[Alex Passos]

Have you thought about the following:

Create an object X that performs the work required by T1 or T2 (in a
non-threaded manner, i.e. forget about threads for the time being while you
design X).

Then make X a static member of your main class.

Launch T1 and T2.

In T1 when you have a method call into X

Enter Critical Section
Perform work with X
Leave Critical Section

In T2 when you have a method call into X

Enter Critical Section
Perform work with X
Leave Critical Section

This will take care of any concurrency issues you might have. But to
address the main problem is when do you signal T2 to perform some work in T2
context, well you can create an object Y which will hold a queue of requests
for T2. Lets say that object Y has to boolean variables for example:

doWorkInMethod1 = false;
doWorkInMethod2 = true;

You will declare object Y as static on your main and then use the same
approach with critical section, except that in T2 will periodically check
object Y and "if doWorkInMethod1 == true then call method1 in current
context". T1 will periodically set the values of object Y to signal what
work must be done in T2. As long as T1 and T2 are not into Y at the same
time (thread concurrency control) you should be ok.

Does it make any sense? I suppose that would depend on wether I understood
your problem correctly.

Alex

When T1 needs work performed by T2, T1
"Jozsef Bekes" <bj****@hotmail.com> wrote in message
news:uP**************@tk2msftngp13.phx.gbl...

Hi Alex,

thank you for your answer. My problem with this approach is that it does
not ensure that f1 and f2 run in the same thread. There are two approaches
in the article, one is said to use ThreadPool, the other is said to use
Thread. Since I have found no hints about how to determine which thread
the ThreadPool should select for the desired execution, I guess using
ThreadPool I cannot ensure that f1 and f2 run in the same thread.
Moreover, the simple Thread approach also uses ThreadPool:

MSDN: "If the BeginInvoke method is called, the common language runtime
will queue the request and return immediately to the caller. The target
method will be called on a thread from the thread pool."

Regards,
Jozsi

"Alex Passos" <[e-mail]> wrote in message
news:%2****************@TK2MSFTNGP09.phx.gbl...

Take a look at this article, it might help you get started:

http://www.codeproject.com/csharp/winformthreading.asp

Alex

"Jozsef Bekes" <bj****@hotmail.com> wrote in message
news:%2****************@tk2msftngp13.phx.gbl...

Hi All,

I am trying to implement a general threading approach in C#, and I have
faced this problem:
I have the function f_main running in thread th1. I want to invoke two
functions f1 and f2 in th_2. From f_main I want to do two distinct
function calls, the first results only in invoking f1 in the context of
th_2, the second function call would invoke only f2 in the context of
th_2. f1 and f2 must run in the same thread context.
My approach in C++ would be to start a thread, put the usual while loop
with PeekMessage and DispatchMessage and trigger the function
invokations via PostThreadMessage. I cannot find such an opportunity in
C# except for using the windows API and implementing the stuff as if I
was using C++ (that is I guess not a good approach). Could someone
please give me a suggestion how I should proceed?

Thank you for your help.

Best Regards,
Jozsi

[Jozsef Bekes]

Hi Alex,

thank you for your answer. Actually, I have already implemented the concept
in a different way, but it seems strange to me that this is so complicated
in C#, the framework gave much better support in VC6 for this problem. What
I did is the following:
I have a queue q. I enter whatever I want in th1 into the q. I have a
working function running in th2 that has a loop, that checks the content of
q, if there is something to process, I process it, otherwise suspend the
thread. When I enter something to q from th1, I check the state of th2, if
it is suspended, I resume it. Of course there is cleanup code and variable
multithread access protection for q. Actually I had to rewrite the whole
messaging concept in C# - not complicated, but seems pure rework.
I also noticed yesterday that controls do not have message queues either, it
is a simple callback mechanism that is described as messaging. Well, I have
been into C# only since Monday, so I might face other surprises as well :-))

Thanks for your help,
Jozsi

"Alex Passos" <[e-mail]> wrote in message
news:Ow**************@TK2MSFTNGP15.phx.gbl...

Have you thought about the following:

Create an object X that performs the work required by T1 or T2 (in a
non-threaded manner, i.e. forget about threads for the time being while
you design X).

Then make X a static member of your main class.

Launch T1 and T2.

In T1 when you have a method call into X

Enter Critical Section
Perform work with X
Leave Critical Section

In T2 when you have a method call into X

Enter Critical Section
Perform work with X
Leave Critical Section

This will take care of any concurrency issues you might have. But to
address the main problem is when do you signal T2 to perform some work in
T2 context, well you can create an object Y which will hold a queue of
requests for T2. Lets say that object Y has to boolean variables for
example:

doWorkInMethod1 = false;
doWorkInMethod2 = true;

You will declare object Y as static on your main and then use the same
approach with critical section, except that in T2 will periodically check
object Y and "if doWorkInMethod1 == true then call method1 in current
context". T1 will periodically set the values of object Y to signal what
work must be done in T2. As long as T1 and T2 are not into Y at the same
time (thread concurrency control) you should be ok.

Does it make any sense? I suppose that would depend on wether I understood
your problem correctly.

Alex

When T1 needs work performed by T2, T1
"Jozsef Bekes" <bj****@hotmail.com> wrote in message
news:uP**************@tk2msftngp13.phx.gbl...

Hi Alex,

thank you for your answer. My problem with this approach is that it does
not ensure that f1 and f2 run in the same thread. There are two
approaches in the article, one is said to use ThreadPool, the other is
said to use Thread. Since I have found no hints about how to determine
which thread the ThreadPool should select for the desired execution, I
guess using ThreadPool I cannot ensure that f1 and f2 run in the same
thread. Moreover, the simple Thread approach also uses ThreadPool:

MSDN: "If the BeginInvoke method is called, the common language runtime
will queue the request and return immediately to the caller. The target
method will be called on a thread from the thread pool."

Regards,
Jozsi

"Alex Passos" <[e-mail]> wrote in message
news:%2****************@TK2MSFTNGP09.phx.gbl...

Take a look at this article, it might help you get started:

http://www.codeproject.com/csharp/winformthreading.asp

Alex

"Jozsef Bekes" <bj****@hotmail.com> wrote in message
news:%2****************@tk2msftngp13.phx.gbl...
Hi All,

I am trying to implement a general threading approach in C#, and I have
faced this problem:
I have the function f_main running in thread th1. I want to invoke two
functions f1 and f2 in th_2. From f_main I want to do two distinct
function calls, the first results only in invoking f1 in the context of
th_2, the second function call would invoke only f2 in the context of
th_2. f1 and f2 must run in the same thread context.
My approach in C++ would be to start a thread, put the usual while loop
with PeekMessage and DispatchMessage and trigger the function
invokations via PostThreadMessage. I cannot find such an opportunity in
C# except for using the windows API and implementing the stuff as if I
was using C++ (that is I guess not a good approach). Could someone
please give me a suggestion how I should proceed?

Thank you for your help.

Best Regards,
Jozsi