Anonymous Delegate

[Stefan Hoffmann]

hi @all,

is there something like an anonymous delegate?

This is the original code:

--
private delegate void DelegateSetFormCaption(string text);
private void SetFormCaption(string text)
{
if (this.InvokeRequired)
{
DelegateSetFormCaption d = new
DelegateSetFormCaption(SetFormCaption);
this.Invoke(d, new object[] { text });
}
else { this.Text = text; }
}
--

I'd like to avoid the delegate declaration, e.g.:

--
private void SetFormCaption(string text)
{
if (this.InvokeRequired)
{
this.Invoke(
new delegate(string text)(SetFormCaption), new object[] { text }
);
}
else { this.Text = text; }
}
--

Is this possible?
mfG
--stefan <--

[Barry Kelly]

Stefan Hoffmann wrote:

private void SetFormCaption(string text)
{
if (this.InvokeRequired)
{
this.Invoke(
new delegate(string text)(SetFormCaption), new object[] { text }
);
}
else { this.Text = text; }
}

If you're using C# 3.0:

this.Invoke((Action) () =this.Text = text);

Action delegate type is in the System namespace in System.Core assembly.

If you're using C# 2.0:

delegate void Action(); // a single delegate type will do for all
// ...
this.Invoke((Action) delegate { this.Text = text; });

The reference to 'text' in the C# 3.0 syntax (lambda syntax) and in the
C# 2.0 anonymous delegate syntax is ok, because the parameter will be
captured and thus made available to the delegate when the control
invokes it on the UI thread.

-- Barry

--
http://barrkel.blogspot.com/

[Stefan Hoffmann]

hi Barry,

thanks for your answer.
mfG
--stefan <--

[Ben Voigt [C++ MVP]]

If you're using C# 2.0:

>
delegate void Action(); // a single delegate type will do for all
// ...
this.Invoke((Action) delegate { this.Text = text; });

Use MethodInvoker instead of defining your own. The CLR recognizes
MethodInvoker and executes a specialized fast-path implementation of Invoke.

[Peter Duniho]

On Thu, 28 Aug 2008 12:52:47 -0700, Ben Voigt [C++ MVP]
<rb*@nospam.nospamwrote:

>If you're using C# 2.0:

delegate void Action(); // a single delegate type will do for all
// ...
this.Invoke((Action) delegate { this.Text = text; });

Use MethodInvoker instead of defining your own. The CLR recognizes
MethodInvoker and executes a specialized fast-path implementation of
Invoke.

Can you elaborate? I can see in Reflector that the framework (the Control
class, not the CLR) special-cases delegates of type EventHandler,
MethodInvoker, and WaitCallback. For those types, it casts directly
rather than calling Delegate.DynamicInvoke().

But do most people really care? Just what kind of performance difference
are we talking about here? Especially given all the other overhead
involved in calling Invoke() (after all, for the true cross-thread case it
involves a full context switch, which is surely at least as costly as any
of the extra work in DynamicInvoke()?).

Seems like a premature optimization to me. Is there some specific reason
to believe otherwise (especially given that the framework-defined Action
delegate type could be considered more expressive)?

Pete

[Ben Voigt [C++ MVP]]

"Peter Duniho" <Np*********@nnowslpianmk.comwrote in message
news:op***************@petes-computer.local...

On Thu, 28 Aug 2008 12:52:47 -0700, Ben Voigt [C++ MVP]
<rb*@nospam.nospamwrote:

>>If you're using C# 2.0:

delegate void Action(); // a single delegate type will do for all
// ...
this.Invoke((Action) delegate { this.Text = text; });

Use MethodInvoker instead of defining your own. The CLR recognizes
MethodInvoker and executes a specialized fast-path implementation of
Invoke.

Can you elaborate? I can see in Reflector that the framework (the Control
class, not the CLR) special-cases delegates of type EventHandler,

Ok, didn't check whether that was MSIL or internalcall. Doesn't much
matter, does it?

MethodInvoker, and WaitCallback. For those types, it casts directly
rather than calling Delegate.DynamicInvoke().

But do most people really care? Just what kind of performance difference
are we talking about here? Especially given all the other overhead
involved in calling Invoke() (after all, for the true cross-thread case it
involves a full context switch, which is surely at least as costly as any
of the extra work in DynamicInvoke()?).

Posting a message to another thread waits for the next context switch, it
doesn't insert an extra context switch.

Plus, DynamicInvoke is a very expensive operation.

>
Seems like a premature optimization to me. Is there some specific reason
to believe otherwise (especially given that the framework-defined Action
delegate type could be considered more expressive)?

The documentation (http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx)
says:
The delegate can be an instance of EventHandler, in which case the sender
parameter will contain this control, and the event parameter will contain
EventArgs..::.Empty. The delegate can also be an instance of MethodInvoker,
or any other delegate that takes a void parameter list. A call to an
EventHandler or MethodInvoker delegate will be faster than a call to another
type of delegate.

Also "premature optimization" assumes that there's a cost to the
optimization. Here, there's effectively no cost at all.

>
Pete

[Peter Duniho]

On Thu, 28 Aug 2008 16:08:09 -0700, Ben Voigt [C++ MVP]
<rb*@nospam.nospamwrote:

Ok, didn't check whether that was MSIL or internalcall. Doesn't much
matter, does it?

No, not really. I just like being precise.

Posting a message to another thread waits for the next context switch,
it doesn't insert an extra context switch.

I suppose that depends on how you look at it. Calling Invoke() blocks the
calling thread, which will prematurely relinquish the current timeslice.
If you've got a CPU bound thread, with the usual 50ms timeslice, but it's
calling Invoke() every 5ms, I'd say that's adding 9 context switches for
every context switch that would have happened otherwise.

I'll acknowledge that you may have some other way of looking at it in
which you come to a different conclusion. But by my reckoning, Invoke()
does in fact wind up forcing a context switch that wouldn't otherwise
happen.

Maybe you're thinking of BeginInvoke() instead? I'd agree that that
method doesn't add context switches to the execution of the code.

Plus, DynamicInvoke is a very expensive operation.

The whole process of invoking is a very expensive operation. That
DynamicInvoke is "very expensive" isn't necessarily important.

In particular, by my measurements it doesn't look like it's expensive
enough to cause a significant difference in performance. I ran a little
test, calling Invoke() 100,000 times in a row with a do-nothing method,
once with a type of MethodInvoker and once with a type of Action.

The timing was more sensitive to which test ran first than to the actual
type. That is, the first test always was slower, regardless of which type
was being used for the call. Changing the test so that it did a "warm-up"
first, I found more consistent results showing that 100,000 calls took
about 3.3 seconds for MethodInvoker and 4.2 seconds for Action.

If I changed the test so that the method actually did something useful --
for example, setting the Text property of a control to the formatted value
of my loop index -- the execution time dropped precipitously. Almost 40
seconds in either case, a 10x slowdown.

So, yes it's faster to call MethodInvoker, but putting that into context
it means you really don't want to be calling Invoke() _either_ way too
often, assuming the delegate is actually doing to be doing something
interesting, and in any case the overhead of the call is very tiny as
compared to the cost of whatever code might actually be executed by the
delegate (10% at the most).

The documentation
(http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx) says:
The delegate can be an instance of EventHandler, in which case the
sender parameter will contain this control, and the event parameter will
contain EventArgs..::.Empty. The delegate can also be an instance of
MethodInvoker, or any other delegate that takes a void parameter list. A
call to an EventHandler or MethodInvoker delegate will be faster than a
call to another type of delegate.

Well, I can't say the documentation is wrong. My own tests prove it
correct. But that's only because the docs don't quantify how much
faster. I wouldn't call the difference significant.

Also "premature optimization" assumes that there's a cost to the
optimization. Here, there's effectively no cost at all.

Eye of the beholder. Personally, I find the newer generic delegate types
more expressive. But sure...if you don't personally see any difference
between "MethodInvoker" and "Action" semantically, the only cost involved
is that of remembering which is faster and of typing the extra
characters. Obviously neither costs is significant.

However, I still find it misleading to imply that the optimization is
worth doing. I saw no practical difference in performance, even if there
was a tiny measurable difference. No real world application is going to
find it matters which delegate type you use.

Pete

[Barry Kelly]

Ben Voigt [C++ MVP] wrote:

Also "premature optimization" assumes that there's a cost to the
optimization. Here, there's effectively no cost at all.

Knowing a piece of trivia is a cost :)

-- Barry

--
http://barrkel.blogspot.com/