C# threading & events

[Aidal]

Hi NG.

I'm creating a little app. that has to use a 3rd party API.
The functions in this API has no return value but trigger events like OK
or NOT OK with event args.

Where I need to use this API I must have a synchrone modul so I need to
force a synchrone look to this asynchrone model of the API.

I was thinking this would call for some waiting for events and since I
don't wanna make a loop eat all the cpu power I was thinking of using a
few threads to accomplish this.

It's giving me some trouble though I'm aware it's a pretty common and
simple scenario.

I was hoping maybe somone here could lend me a hand.

What I need is as said, to make some code that uses the API but my code
has to be synchrone while the API is not.

So I can do somthing like:
--------------------------
public MyClass
{
private bool InProcess;
private bool ItWentWell;

public bool Function1()
{
InProcess = true;

APIClass apic = new APIClass();

apic.FunctionAP I1_Success += EventHandler(Fu nctionOK);
apic.FunctionAP I1_Failed += EventHandler(Fu nctionERROR);

apic.FunctionAP I1();

...
Wait for InProcess to change from TRUE to FALSE.
Once this happens, return ItWentWell.
}

public void FunctionOK()
{
Inprocess = false;

ItWentWell = true;
}

public void FunctionERROR()
{
InProcess = false;

ItWentWell = false;
}
}

//--- somwhere like the Main of a console app. ---
MyClass mc = new MyClass();

if(mc.Function1 ())
{
Consile.WriteLi ne("API call went well.");
}
else
{
Consile.WriteLi ne("API call went bad.")
}
--------------------------

I'm aware that the above doesn't work, it's only to give a picture of
what I'm trying to accomplish. Somwhere around the part with the waiting
for the event to occur should most likely be using a new thread not to
eat all the cpu power, but I can't get the things I've tried to work.

Any help would be much appreciated, thanks :)

/Aidal

[Ben Voigt]

"Aidal" <[e-mail] wrote in message
news:45******** *************@d reader2.cyberci ty.dk...

Hi NG.

I'm creating a little app. that has to use a 3rd party API.
The functions in this API has no return value but trigger events like OK
or NOT OK with event args.

Where I need to use this API I must have a synchrone modul so I need to
force a synchrone look to this asynchrone model of the API.

I was thinking this would call for some waiting for events and since I
don't wanna make a loop eat all the cpu power I was thinking of using a
few threads to accomplish this.

Use the EventWaitHandle class built in to .NET. Or convert your algorithm
to a state machine.

[Aidal]

Aidal skrev:

Hi NG.

I'm creating a little app. that has to use a 3rd party API.
The functions in this API has no return value but trigger events like OK
or NOT OK with event args.

Where I need to use this API I must have a synchrone modul so I need to
force a synchrone look to this asynchrone model of the API.

I was thinking this would call for some waiting for events and since I
don't wanna make a loop eat all the cpu power I was thinking of using a
few threads to accomplish this.

It's giving me some trouble though I'm aware it's a pretty common and
simple scenario.

I was hoping maybe somone here could lend me a hand.

What I need is as said, to make some code that uses the API but my code
has to be synchrone while the API is not.

So I can do somthing like:
--------------------------
public MyClass
{
private bool InProcess;
private bool ItWentWell;

public bool Function1()
{
InProcess = true;

APIClass apic = new APIClass();

apic.FunctionAP I1_Success += EventHandler(Fu nctionOK);
apic.FunctionAP I1_Failed += EventHandler(Fu nctionERROR);

apic.FunctionAP I1();

...
Wait for InProcess to change from TRUE to FALSE.
Once this happens, return ItWentWell.
}

public void FunctionOK()
{
Inprocess = false;

ItWentWell = true;
}

public void FunctionERROR()
{
InProcess = false;

ItWentWell = false;
}
}

//--- somwhere like the Main of a console app. ---
MyClass mc = new MyClass();

if(mc.Function1 ())
{
Consile.WriteLi ne("API call went well.");
}
else
{
Consile.WriteLi ne("API call went bad.")
}
--------------------------

I'm aware that the above doesn't work, it's only to give a picture of
what I'm trying to accomplish. Somwhere around the part with the waiting
for the event to occur should most likely be using a new thread not to
eat all the cpu power, but I can't get the things I've tried to work.

Any help would be much appreciated, thanks :)

/Aidal

Anyone have an actual code example or a link to one where:

Class1.Function A calls Class2.Function B which will (at some point)
trigger an event.
Class1.Function A must not return before the event occuers because it
needs to base its return value on what the event "said" like true/false.

Aka Class1.Function A must wait for the event triggered by
Class2.Function B to occuer before it knows what to return.

As mentioned above I assume some threading should be used but I'm not sure.

/Aidal

[Marc Gravell]

Like so?

using System;
using System.Threadin g;

static class Program
{
static void Main()
{
new ClassA().Method A();
}
}
class ClassA
{
public void MethodA()
{
ClassB b = new ClassB();
string theSomething = "";
ManualResetEven t evt = new ManualResetEven t(false);
b.SomethingHapp ened += delegate
{
theSomething = b.TheSomething;
evt.Set();
};
ThreadPool.Queu eUserWorkItem(d elegate {
b.MethodB();
});
evt.WaitOne();
Console.WriteLi ne(theSomething );
}
}
class ClassB
{
public event EventHandler SomethingHappen ed;
private string _theSomething;
public string TheSomething {get {return _theSomething;} }
protected void OnSomethingHapp ened()
{
EventHandler handler = SomethingHappen ed;
if (handler != null) handler(this, EventArgs.Empty );
}
public void MethodB()
{
_theSomething = Console.ReadLin e();
OnSomethingHapp ened();
}
}

[Marc Gravell]

Note: for brevity, in my example I didn't bother putting the "what
happened" into an event-arg subclass - but this would work identically
to the property approach; you may also wish to be "using" the
ManualResetEven t (since it is IDisposable).

As an alternative, note that you can also do this using locks to avoid
the (marginally more expensive) ManualResetEven t - but unless you are
high volume it might not be worth it; note to follow the logic here
requires a good understanding of "lock" (Monitor.Enter, Monitor.Exit),
Monitor.Wait and Monitor.Pulse.. .

public void MethodA() {
ClassB b = new ClassB();
string theSomething = "";
object sync = new object();
b.SomethingHapp ened += delegate {
theSomething = b.TheSomething;
lock (sync) {
Monitor.Pulse(s ync);
}
};
lock (sync) {
ThreadPool.Queu eUserWorkItem(d elegate {
b.MethodB();
});
Monitor.Wait(sy nc);
}
Console.WriteLi ne(theSomething );
}

[Aidal]

Marc Gravell skrev:

Like so?

using System;
using System.Threadin g;

static class Program
{
static void Main()
{
new ClassA().Method A();
}
}
class ClassA
{
public void MethodA()
{
ClassB b = new ClassB();
string theSomething = "";
ManualResetEven t evt = new ManualResetEven t(false);
b.SomethingHapp ened += delegate
{
theSomething = b.TheSomething;
evt.Set();
};
ThreadPool.Queu eUserWorkItem(d elegate {
b.MethodB();
});
evt.WaitOne();
Console.WriteLi ne(theSomething );
}
}
class ClassB
{
public event EventHandler SomethingHappen ed;
private string _theSomething;
public string TheSomething {get {return _theSomething;} }
protected void OnSomethingHapp ened()
{
EventHandler handler = SomethingHappen ed;
if (handler != null) handler(this, EventArgs.Empty );
}
public void MethodB()
{
_theSomething = Console.ReadLin e();
OnSomethingHapp ened();
}
}

I've tried to create your example but it appears to have syntax errors
around "b.SomthingHapp ened += delegate". :(

/Aidal

[Aidal]

Marc Gravell skrev:

Like so?

using System;
using System.Threadin g;

static class Program
{
static void Main()
{
new ClassA().Method A();
}
}
class ClassA
{
public void MethodA()
{
ClassB b = new ClassB();
string theSomething = "";
ManualResetEven t evt = new ManualResetEven t(false);
b.SomethingHapp ened += delegate
{
theSomething = b.TheSomething;
evt.Set();
};
ThreadPool.Queu eUserWorkItem(d elegate {
b.MethodB();
});
evt.WaitOne();
Console.WriteLi ne(theSomething );
}
}
class ClassB
{
public event EventHandler SomethingHappen ed;
private string _theSomething;
public string TheSomething {get {return _theSomething;} }
protected void OnSomethingHapp ened()
{
EventHandler handler = SomethingHappen ed;
if (handler != null) handler(this, EventArgs.Empty );
}
public void MethodB()
{
_theSomething = Console.ReadLin e();
OnSomethingHapp ened();
}
}

The actual scenario is:
=============== ========
ClassAPI has a function
- void SendFile()
and the two events
- FileSendOK
and
- FileSendError

MyClass has the function
- bool SendFile()
which is to use the function ClassAPI.SendFi le()

What I want to be able to do is:
--------------------------------
MyClass mc = new MyClass();

if(mc.SendFile( ))
{
do somthing when sending file is successful...
}
else
{
do somthing else when sending file fails...
}
---------------------------------

Which means MyClass.SendFil e() must wait for one of the two events in
ClassAPI to occuer (due to the ClassAPI.SendFi le call) before it returns.

/Aidal

[Marc Gravell]

Ah... 1.1... I was heavily using the "captured variable" feature of
anonymous methods as a means to share state between threads. Never
mind... it can be done the other way - it just takes more code. Note:
I hanve't tested this in 1.1, so it may need tweaking, but it should
be fairly close (may also need to lose "static" from "static class
Program"):

class ClassA
{
internal class MethodAState
{
private readonly ClassB B;
private readonly object Sync = new object();
private string _theSomething;
public MethodAState()
{
B = new ClassB();
B.SomethingHapp ened += new
EventHandler(B_ SomethingHappen ed);
}
public string StartAndWaitMet hodB()
{
lock (Sync)
{
ThreadPool.Queu eUserWorkItem(n ew
WaitCallback(B_ StartB));
Monitor.Wait(Sy nc);
return _theSomething;
}
}
void B_StartB(object state)
{
B.MethodB();
}

void B_SomethingHapp ened(object sender, EventArgs e)
{
lock (Sync)
{
_theSomething = B.TheSomething;
Monitor.Pulse(S ync);
}
}

}
public void MethodA()
{
MethodAState state = new MethodAState();
string value = state.StartAndW aitMethodB();
Console.WriteLi ne(value);
}
}

[Marc Gravell]

Previous post re-worked to handle two different events with differing
signatures (pretend that TheSomething is in the event-args <g>). Type
"boom" to get the new behaviour; the string could likewise be a
success bool:

using System;
using System.Threadin g;

class Program
{
static void Main()
{
new ClassA().Method A();
}
}
class ClassA
{
internal class MethodAState
{
private readonly ClassB B;
private readonly object Sync = new object();
private string _theSomething;
public MethodAState()
{
B = new ClassB();
B.SomethingHapp ened += new
EventHandler(B_ SomethingHappen ed);
B.SomethingElse Happened +=new
EventHandler(B_ SomethingElseHa ppened);
}
public string StartAndWaitMet hodB()
{
lock (Sync)
{
ThreadPool.Queu eUserWorkItem(n ew
WaitCallback(B_ StartB));
Monitor.Wait(Sy nc);
return _theSomething;
}
}
void B_StartB(object state)
{
B.MethodB();
}

void B_SomethingHapp ened(object sender, EventArgs e)
{
ReleaseCaller(B .TheSomething);
}
void B_SomethingElse Happened(object sender, EventArgs e)
{
ReleaseCaller(" PANIC PANIC PANIC");
}
private void ReleaseCaller(s tring result)
{
lock (Sync)
{
_theSomething = result;
Monitor.Pulse(S ync);
}
}

}
public void MethodA()
{
MethodAState state = new MethodAState();
string value = state.StartAndW aitMethodB();
Console.WriteLi ne(value);
}
}
class ClassB
{
public event EventHandler SomethingHappen ed,
SomethingElseHa ppened;
private string _theSomething;
public string TheSomething { get { return _theSomething; } }
private void OnEvent(EventHa ndler handler)
{
if (handler != null) handler(this, EventArgs.Empty );
}
public void MethodB()
{
string value = Console.ReadLin e();
if (value == "boom")
{
OnEvent(Somethi ngElseHappened) ;
}
else
{
_theSomething = value;
OnEvent(Somethi ngHappened);
}
}
}

[Aidal]

Marc Gravell skrev:

Previous post re-worked to handle two different events with differing
signatures (pretend that TheSomething is in the event-args <g>). Type
"boom" to get the new behaviour; the string could likewise be a
success bool:

using System;
using System.Threadin g;

class Program
{
static void Main()
{
new ClassA().Method A();
}
}
class ClassA
{
internal class MethodAState
{
private readonly ClassB B;
private readonly object Sync = new object();
private string _theSomething;
public MethodAState()
{
B = new ClassB();
B.SomethingHapp ened += new
EventHandler(B_ SomethingHappen ed);
B.SomethingElse Happened +=new
EventHandler(B_ SomethingElseHa ppened);
}
public string StartAndWaitMet hodB()
{
lock (Sync)
{
ThreadPool.Queu eUserWorkItem(n ew
WaitCallback(B_ StartB));
Monitor.Wait(Sy nc);
return _theSomething;
}
}
void B_StartB(object state)
{
B.MethodB();
}

void B_SomethingHapp ened(object sender, EventArgs e)
{
ReleaseCaller(B .TheSomething);
}
void B_SomethingElse Happened(object sender, EventArgs e)
{
ReleaseCaller(" PANIC PANIC PANIC");
}
private void ReleaseCaller(s tring result)
{
lock (Sync)
{
_theSomething = result;
Monitor.Pulse(S ync);
}
}

}
public void MethodA()
{
MethodAState state = new MethodAState();
string value = state.StartAndW aitMethodB();
Console.WriteLi ne(value);
}
}
class ClassB
{
public event EventHandler SomethingHappen ed,
SomethingElseHa ppened;
private string _theSomething;
public string TheSomething { get { return _theSomething; } }
private void OnEvent(EventHa ndler handler)
{
if (handler != null) handler(this, EventArgs.Empty );
}
public void MethodB()
{
string value = Console.ReadLin e();
if (value == "boom")
{
OnEvent(Somethi ngElseHappened) ;
}
else
{
_theSomething = value;
OnEvent(Somethi ngHappened);
}
}
}

Thanks Marc :)

This example looks very interesting, I will try to apply the idea to my
code as soon as I get a free moment from other stuff.

/Aidal