Expressions in C#...

[Atmapuri]

Hi!

I noticed a very funny behaviour when overloading operators
on objects in C#:

MyOjbects a,b,c,d;
....
//objects are created and initalized here...
....
b.Length = 100;
c.Length = 100;

for (i = 0; i < 10000; i++)
{
a = MyFun(2*c)*b;
}

Inside the overladed multiplication operator, I check:

if (Op1.Length == Op2.Length) throw....

And the exception triggers after about 100 iterations...!! ?
Somehow the internal objects of the temporary variable
created by 2*c passed to MyFun are being
garbage collected (nullified) before the temporary variable is used for
the first time...

Are there some known issues with this?

Thanks!
Atmapuri

[Atmapuri]

Re: Expressions in C#...

Hi!

The fix for the problem is to write the expression as:

d = 2*c;
a = MyFun(d)*b;

That is to explicitely allocate the temporary variable....
But of course, that is not really a fix, it just points to
the problem...

Thanks!
Atmapuri




"Atmapuri" <dip@community. nospamwrote in message
news:ejuMK1B0GH A.4044@TK2MSFTN GP04.phx.gbl...

Hi!
>
I noticed a very funny behaviour when overloading operators
on objects in C#:
>
MyOjbects a,b,c,d;
...
//objects are created and initalized here...
...
b.Length = 100;
c.Length = 100;
>
for (i = 0; i < 10000; i++)
{
a = MyFun(2*c)*b;
}
>
Inside the overladed multiplication operator, I check:
>
if (Op1.Length == Op2.Length) throw....
>
And the exception triggers after about 100 iterations...!! ?
Somehow the internal objects of the temporary variable
created by 2*c passed to MyFun are being
garbage collected (nullified) before the temporary variable is used for
the first time...
>
Are there some known issues with this?
>
Thanks!
Atmapuri
>

[Marc Gravell]

Re: Expressions in C#...

Sounds curious; can you reproduce this in simple (yet complete), postable
code?

Is it possible that MyFun is return an MyOjbects [sic] instance that
genuinely has the same length as b (100)? Equally, depending on whether
these are structs or classes, it might be that you are (in the non-shown
code) accidentally changing properties of the operands, and this behaviour
is a side-effect?

Marc

[Nicholas Paldino [.NET/C# MVP]]

Re: Expressions in C#...

That's actually very, very wrong. Something else is going on here. The
temporary variable that is created as a result of calling 2 * c isn't being
GC'ed because the reference is held on the stack (through the parameter)
when you pass it to MyFun.

It is most definitely something else. Without seeing the code for the
class where the operator is overloaded, as well as the code for MyFun, it's
impossible to say.


--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Atmapuri" <dip@community. nospamwrote in message
news:ejuMK1B0GH A.4044@TK2MSFTN GP04.phx.gbl...

Hi!
>
I noticed a very funny behaviour when overloading operators
on objects in C#:
>
MyOjbects a,b,c,d;
...
//objects are created and initalized here...
...
b.Length = 100;
c.Length = 100;
>
for (i = 0; i < 10000; i++)
{
a = MyFun(2*c)*b;
}
>
Inside the overladed multiplication operator, I check:
>
if (Op1.Length == Op2.Length) throw....
>
And the exception triggers after about 100 iterations...!! ?
Somehow the internal objects of the temporary variable
created by 2*c passed to MyFun are being
garbage collected (nullified) before the temporary variable is used for
the first time...
>
Are there some known issues with this?
>
Thanks!
Atmapuri
>

[Atmapuri]

Re: Expressions in C#...

Hi!

Sounds curious; can you reproduce this in simple (yet complete), postable
code?

Could be a tough job. The garbage collector is not deterministic.. ..

Is it possible that MyFun is return an MyOjbects [sic] instance that
genuinely has the same length as b (100)? Equally, depending on whether
these are structs or classes, it might be that you are (in the non-shown
code) accidentally changing properties of the operands, and this behaviour
is a side-effect?

The code inside the loop works for 100 iterations and than fails?
This is C#. It should be impossible especially because the next
iteration does not depend upon the previous...

Struct works fine and classes fail...

Regards!
Atmapuri

[Atmapuri]

Re: Expressions in C#...

Hi!

It would be very difficult for me to post the code.
Can you think of anything why this would occur
considering that:

It works with struct but not with classes. I noticed
that the compiler copies the struct before passing it
to the function.

MyObjects has a finalizer declared. And the only
way I can imagine for the Length to be set to zero
is if that finalizer has been called on the temporary
object created by 2*c, before the object was used.

Thanks!
Atmapuri



"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c omwrote in
message news:%23M7SAaC0 GHA.1568@TK2MSF TNGP03.phx.gbl. ..

That's actually very, very wrong. Something else is going on here.
The temporary variable that is created as a result of calling 2 * c isn't
being GC'ed because the reference is held on the stack (through the
parameter) when you pass it to MyFun.
>
It is most definitely something else. Without seeing the code for the
class where the operator is overloaded, as well as the code for MyFun,
it's impossible to say.
>
>
--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m
>
"Atmapuri" <dip@community. nospamwrote in message
news:ejuMK1B0GH A.4044@TK2MSFTN GP04.phx.gbl...

>Hi!
>>
>I noticed a very funny behaviour when overloading operators
>on objects in C#:
>>
>MyOjbects a,b,c,d;
>...
>//objects are created and initalized here...
>...
>b.Length = 100;
>c.Length = 100;
>>
>for (i = 0; i < 10000; i++)
>{
> a = MyFun(2*c)*b;
>}
>>
>Inside the overladed multiplication operator, I check:
>>
>if (Op1.Length == Op2.Length) throw....
>>
>And the exception triggers after about 100 iterations...!! ?
>Somehow the internal objects of the temporary variable
>created by 2*c passed to MyFun are being
>garbage collected (nullified) before the temporary variable is used for
>the first time...
>>
>Are there some known issues with this?
>>
>Thanks!
>Atmapuri
>>

>
>

[Marc Gravell]

Re: Expressions in C#...

It should be impossible especially because the next

iteration does not depend upon the previous...

In your example, with classes, it really, really *does*; the variables b & c
are declared and initialised *outside* of the loop, so if you are causing
side-effects in the objects then it will persist between iterations, and can
(when some critical condition [determined by the exact foobar] is met) cause
it to bomb. *Especially* for classes. For structs (without "ref" usage), the
memory contents will be cloned when passing between stack contexts, so any
side effect in the memory will only live as long as that stack - which
probably explains why structs appear to work. You just "get lucky" with
structs, in that they don't propegate bugs as readily. But the bug may still
be there. I reckon that at some point you are monkeying with the contents of
the class without cloning it first. As an example of a possible foobar
(operator with operand side-effects):

SomeClass operator *(SomeClass lhs, SomeClass rhs) {
lhs.Length *= rhs;
return lhs
}

This should be:

SomeClass operator *(SomeClass lhs, SomeClass rhs) {
SomeClass result = lhs.Clone();
result.Length *= rhs;
return result;
}

Marc

[Christof Nordiek]

Re: Expressions in C#...

Why do you think, the result depends on garbage collection?
The result of an operator shouldn't depent on instances ont referenced
(directly or inderectly)
by the operands. So it shouldn't depend on the existence of objetcs eligable
for collection.

"Atmapuri" <dip@community. nospamschrieb im Newsbeitrag
news:e1rcmeC0GH A.1292@TK2MSFTN GP03.phx.gbl...

Hi!
>

>Sounds curious; can you reproduce this in simple (yet complete), postable
>code?

>
Could be a tough job. The garbage collector is not deterministic.. ..
>

>Is it possible that MyFun is return an MyOjbects [sic] instance that
>genuinely has the same length as b (100)? Equally, depending on whether
>these are structs or classes, it might be that you are (in the non-shown
>code) accidentally changing properties of the operands, and this
>behaviour
>is a side-effect?

>
The code inside the loop works for 100 iterations and than fails?
This is C#. It should be impossible especially because the next
iteration does not depend upon the previous...
>
Struct works fine and classes fail...
>
Regards!
Atmapuri
>
>
>

[Atmapuri]

Re: Expressions in C#...

Hi!

In your example, with classes, it really, really *does*; the variables b &
c

b and c are not modified inside of the loop and also not inside
of the operator. That is certain. This also does not account for
undeterministic
nature of the problem. If I debug the stuff, it works fine... It only
fails when being run free... only after about 100 iterations...
and only if the temporary variable is not assigned explicitely, but
the expression is passed directly to the function as a parameter.
(I double tested that...)

SomeClass operator *(SomeClass lhs, SomeClass rhs) {
lhs.Length *= rhs;
return lhs
}
>
This should be:
>
SomeClass operator *(SomeClass lhs, SomeClass rhs) {
SomeClass result = lhs.Clone();
result.Length *= rhs;
return result;
}

That is a deterministic case.. that will fail in the first loop.

Thanks!
Atmapuri

[Atmapuri]

Re: Expressions in C#...

Hi!

Why do you think, the result depends on garbage collection?
The result of an operator shouldn't depent on instances ont referenced
(directly or inderectly)
by the operands. So it shouldn't depend on the existence of objetcs
eligable for collection.

The iteration count at which the error happens is not fixed...
The loop will execute fine 100x and fail on 101 for example.
That points to the garbage collector, because the time at which
the garbage collector is run is determined by the CLR.

And it is a predictive pattern. Whenever you have a expression
passed directly to the function without assigning its result first to the
local variable. (which should not matter).

Thanks!
Atmapuri

[Nicholas Paldino [.NET/C# MVP]]

Re: Expressions in C#...

Without seeing the code for the things I mentioned, it's nearly
impossible. You might as well post it, otherwise, no one will be able to do
much but offer conjecture at this point.

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Atmapuri" <dip@community. nospamwrote in message
news:%235y5boC0 GHA.1256@TK2MSF TNGP02.phx.gbl. ..

Hi!
>
It would be very difficult for me to post the code.
Can you think of anything why this would occur
considering that:
>
It works with struct but not with classes. I noticed
that the compiler copies the struct before passing it
to the function.
>
MyObjects has a finalizer declared. And the only
way I can imagine for the Length to be set to zero
is if that finalizer has been called on the temporary
object created by 2*c, before the object was used.
>
Thanks!
Atmapuri
>
>
>
"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c omwrote
in message news:%23M7SAaC0 GHA.1568@TK2MSF TNGP03.phx.gbl. ..

> That's actually very, very wrong. Something else is going on here.
>The temporary variable that is created as a result of calling 2 * c isn't
>being GC'ed because the reference is held on the stack (through the
>parameter) when you pass it to MyFun.
>>
> It is most definitely something else. Without seeing the code for the
>class where the operator is overloaded, as well as the code for MyFun,
>it's impossible to say.
>>
>>
>--
> - Nicholas Paldino [.NET/C# MVP]
> - mvp@spam.guard. caspershouse.co m
>>
>"Atmapuri" <dip@community. nospamwrote in message
>news:ejuMK1B0G HA.4044@TK2MSFT NGP04.phx.gbl.. .

>>Hi!
>>>
>>I noticed a very funny behaviour when overloading operators
>>on objects in C#:
>>>
>>MyOjbects a,b,c,d;
>>...
>>//objects are created and initalized here...
>>...
>>b.Length = 100;
>>c.Length = 100;
>>>
>>for (i = 0; i < 10000; i++)
>>{
>> a = MyFun(2*c)*b;
>>}
>>>
>>Inside the overladed multiplication operator, I check:
>>>
>>if (Op1.Length == Op2.Length) throw....
>>>
>>And the exception triggers after about 100 iterations...!! ?
>>Somehow the internal objects of the temporary variable
>>created by 2*c passed to MyFun are being
>>garbage collected (nullified) before the temporary variable is used for
>>the first time...
>>>
>>Are there some known issues with this?
>>>
>>Thanks!
>>Atmapuri
>>>

>>
>>

>
>

[Christof Nordiek]

Re: Expressions in C#...

Hi,

if your class has a finalizer and you supose the problem is because of
GC-timing you could try to debug when the finalizer ist called.

If the problem doesn't occur with structsit could be a problem
with sides effects. You should never change the operands inside
a operator. Also MyFunc looks like a Method that computes a
new value and shouldn't change the argument in any way.

BTW, why are you using a finalizer at all?
Finalizer should only clean up unmanaged resources. Managed
resources will be finalized themselves if they are referenced only by
objects eligable for finalization.
Maybe you try to clean smoething up wich shouldn't be and thereby
destroy something.

hth

"Atmapuri" <dip@community. nospamschrieb im Newsbeitrag
news:%235y5boC0 GHA.1256@TK2MSF TNGP02.phx.gbl. ..

Hi!
>
It would be very difficult for me to post the code.
Can you think of anything why this would occur
considering that:
>
It works with struct but not with classes. I noticed
that the compiler copies the struct before passing it
to the function.
>
MyObjects has a finalizer declared. And the only
way I can imagine for the Length to be set to zero
is if that finalizer has been called on the temporary
object created by 2*c, before the object was used.
>
Thanks!
Atmapuri
>
>
>
"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c omwrote
in message news:%23M7SAaC0 GHA.1568@TK2MSF TNGP03.phx.gbl. ..

> That's actually very, very wrong. Something else is going on here.
>The temporary variable that is created as a result of calling 2 * c isn't
>being GC'ed because the reference is held on the stack (through the
>parameter) when you pass it to MyFun.
>>
> It is most definitely something else. Without seeing the code for the
>class where the operator is overloaded, as well as the code for MyFun,
>it's impossible to say.
>>
>>
>--
> - Nicholas Paldino [.NET/C# MVP]
> - mvp@spam.guard. caspershouse.co m
>>
>"Atmapuri" <dip@community. nospamwrote in message
>news:ejuMK1B0G HA.4044@TK2MSFT NGP04.phx.gbl.. .

>>Hi!
>>>
>>I noticed a very funny behaviour when overloading operators
>>on objects in C#:
>>>
>>MyOjbects a,b,c,d;
>>...
>>//objects are created and initalized here...
>>...
>>b.Length = 100;
>>c.Length = 100;
>>>
>>for (i = 0; i < 10000; i++)
>>{
>> a = MyFun(2*c)*b;
>>}
>>>
>>Inside the overladed multiplication operator, I check:
>>>
>>if (Op1.Length == Op2.Length) throw....
>>>
>>And the exception triggers after about 100 iterations...!! ?
>>Somehow the internal objects of the temporary variable
>>created by 2*c passed to MyFun are being
>>garbage collected (nullified) before the temporary variable is used for
>>the first time...
>>>
>>Are there some known issues with this?
>>>
>>Thanks!
>>Atmapuri
>>>

>>
>>

>
>

[Atmapuri]

Re: Expressions in C#...

Hi!

Could it be a problem if I call GC.Collect from inside a
class constructor?

Thanks!
Atmapuri

"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c omwrote in
message news:%23M7SAaC0 GHA.1568@TK2MSF TNGP03.phx.gbl. ..

That's actually very, very wrong. Something else is going on here.
The temporary variable that is created as a result of calling 2 * c isn't
being GC'ed because the reference is held on the stack (through the
parameter) when you pass it to MyFun.
>
It is most definitely something else. Without seeing the code for the
class where the operator is overloaded, as well as the code for MyFun,
it's impossible to say.
>
>
--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m
>
"Atmapuri" <dip@community. nospamwrote in message
news:ejuMK1B0GH A.4044@TK2MSFTN GP04.phx.gbl...

>Hi!
>>
>I noticed a very funny behaviour when overloading operators
>on objects in C#:
>>
>MyOjbects a,b,c,d;
>...
>//objects are created and initalized here...
>...
>b.Length = 100;
>c.Length = 100;
>>
>for (i = 0; i < 10000; i++)
>{
> a = MyFun(2*c)*b;
>}
>>
>Inside the overladed multiplication operator, I check:
>>
>if (Op1.Length == Op2.Length) throw....
>>
>And the exception triggers after about 100 iterations...!! ?
>Somehow the internal objects of the temporary variable
>created by 2*c passed to MyFun are being
>garbage collected (nullified) before the temporary variable is used for
>the first time...
>>
>Are there some known issues with this?
>>
>Thanks!
>Atmapuri
>>

>
>

[Marc Gravell]

Re: Expressions in C#...

That is a deterministic case.. that will fail in the first loop.

My example was for demonstration only, to illustrate what I meant be
side-effects.

b and c are not modified inside of the loop and also not inside
of the operator. That is certain.

Well, without the operator code I couldn't (and still can't) see this, but
you'll have
to excuse me for looking for the straightforward explanations first. A
demonstrable
example would be the ideal, but I gather that isn't going to happen...

Since finalizers are involved, and since we have (seemingly) exhausted the
simple
options, then it is possible that you are racing the GC; does this article
help any?

http://blogs.msdn.com/cbrumme/archiv.../19/51365.aspx

Marc

[Willy Denoyette [MVP]]

Re: Expressions in C#...


"Atmapuri" <dip@community. nospamwrote in message
news:%23WzWGGD0 GHA.1252@TK2MSF TNGP04.phx.gbl. ..
| Hi!
|
| Could it be a problem if I call GC.Collect from inside a
| class constructor?
|

Please post your code, it makes no sense to ask further questions you only
can answer.

Willy.