Hi,
I have created an array of Objects in a collection. I was wondering is there
a way to destroy the array to free up the space in the memory ? or they are
automatically destroyed and garbagge collected by .Net framework?
Sarfraz
Jul 21 '05
43  2738 
Cor Ligthert <no**********@p lanet.nl> wrote: Constructive quoting again from you, I once gave you a sample that more
people can do that however decent people do not do that.
Leaving the message from Scott out from this makes it the same as if Scott
was telling that the Tower Bridge was in Paris.
Sorry if you thought I was implying that - I certainly wasn't, and I
don't actually think anyone thought I was.
The message you give the same answer again as Scott was saying, while you
give the idea that he did not.
No, it didn't. It gave more information, notably that the GC is capable
of detecting variables after their last use within a method in most
situations - it *automatically* makes objects (where appropriate)
eligible for garbage collection before the end of the method. This is
not what Scott implied (in the way that Niki and I read it at least)
when Scott wrote:
"There are certain circumstances though, when you may want the object
in question to fall out of scope immediately, rather than waiting for
the end of a procedure."
To me, that suggests that unless you take the given action, the method
(procedure in Scott's terminology) has to end before the variable's
contents will be collected.
However, I suspect that this whole subthread isn't really about garbage
collection at all, and that you'd have praised Scott for adding extra
information if the posts had been the other way round... (And that if
it had been someone else replying to Scott, you wouldn't have posted at
all.)
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Is there anything equivalent to Erase in C#?
Sarfraz
"Brian Davis" <br***@knowdotn et.nospam.com> wrote in message
news:OL******** ******@TK2MSFTN GP11.phx.gbl... In addition, VB has an Erase statement, which should deallocate memory
used for the array's elements.
Brian Davis
http://www.knowdotnet.com
"Scott M." <s-***@nospam.nosp am> wrote in message
news:eS******** ********@TK2MSF TNGP09.phx.gbl. .. Everything in .NET is a type (either reference or value types). All
types are managed by the Garbage Collector. There is no need to "free up
memory" as this is the purpose of the GC. There are certain circumstances
though, when you may want the object in question to fall out of scope
immediately, rather than waiting for the end of a procedure. In this case you could
make the object = Nothing.
"Sarfraz Hooda" <sh****@iqueri. com> wrote in message
news:Od******** ******@TK2MSFTN GP09.phx.gbl... Hi,
I have created an array of Objects in a collection. I was wondering is
there a way to destroy the array to free up the space in the memory ? or
they are automatically destroyed and garbagge collected by .Net framework?
Sarfraz
Brian Davis <br***@knowdotn et.nospam.com> wrote: In addition, VB has an Erase statement, which should deallocate memory used
for the array's elements.
I don't *believe* it does, actually. It just sets each array element to
Nothing, which is the equivalent of calling Array.Clear. That's
different from actually deallocating the memory, which is the garbage
collector's job.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
I would tend to agree with you. What made me think otherwise is that the
MSDN documentation states that the Erase Statement is "Used to release array
variables and deallocate the memory used for their elements," so I am not
really sure. If I had to guess, I'd say that you are correct, and that MSDN
just means that it is marked as OK for deallocation by the GC rather than
actually deallocated.
As a side note, Erase isn't the same as calling Clear. Clear will set
elements of the array to Nothing, while Erase sets the array variable itself
to Nothing.
Either way, setting the array to Nothing should be functionally the same as
calling Erase, but, as you have pointed out in previous posts, that
shouldn't be necessary in most applications.
Brian Davis http://www.knowdotnet.com
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com... Brian Davis <br***@knowdotn et.nospam.com> wrote: In addition, VB has an Erase statement, which should deallocate memory
used for the array's elements.
I don't *believe* it does, actually. It just sets each array element to
Nothing, which is the equivalent of calling Array.Clear. That's
different from actually deallocating the memory, which is the garbage
collector's job.
--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Brian Davis <br***@knowdotn et.nospam.com> wrote: I would tend to agree with you. What made me think otherwise is that the
MSDN documentation states that the Erase Statement is "Used to release array
variables and deallocate the memory used for their elements," so I am not
really sure. If I had to guess, I'd say that you are correct, and that MSDN
just means that it is marked as OK for deallocation by the GC rather than
actually deallocated.
It wasn't even marking things as OK for deallocation in my (wrong)
understanding. It was just setting things to Nothing inside the array,
which may well not make them eligible for GC, as there could be other
references.
The MSDN is unfortunately not very clear (or, I believe, accurate) on
this. Looking at the IL generated, I believe it does just set the
variable to Nothing, which certainly doesn't fit in with the docs you
quoted. Odd.
So
Erase Foo, Bar Baz
is just the same as
Foo = Nothing
Bar = Nothing
Baz = Nothing
It seems relatively useless to me, to be honest. Maybe it was more
useful in VB6.
As a side note, Erase isn't the same as calling Clear. Clear will set
elements of the array to Nothing, while Erase sets the array variable itself
to Nothing.
Yup. You're absolutely right - I had completely misread the spec.
Sincere apologies for confusing things further :(
Either way, setting the array to Nothing should be functionally the same as
calling Erase, but, as you have pointed out in previous posts, that
shouldn't be necessary in most applications.
Yup.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Hi Jon,
I would have answered as well as someone else had written the message you
did, however they seldom do. (Probably the tone had been something different
because arguing between us is not something new, therefore I did leave out
the introduction.)
:-)
In my opinion Scott told it very clear. I did not read anything in your
message that would have given the OP more information when this arguing had
not been.
In my opinion there is a scene where setting an array to nothing can be good
and I do not believe that that is contradicting what Scott wrote.
In pseudo to make it language independent
Arraylist MyArray
Main
MakeNewArray
MakeNewArray
MyArray = New ArrayList
for i=0;i<5000000;i ++ Arraylist.add(m yobject)
Event Button1Click
MyArray = nothing
Event Button2Click
MakeNewArray
In my opinion I give the GC the change to clean up the old MyArrayObjects
before the program is ended.
Cor
Sarfraz Hooda <sh****@iqueri. com> wrote: Is there anything equivalent to Erase in C#?
There's an equivalent to what Erase *actually* does, which is just
setting the variable to null:
object[] foo = new object[100];
....
foo = null;
This is very rarely useful, as discussed elsewhere in the thread. (See
also http://blogs.msdn.com/csharpfaq/arch.../26/97229.aspx )
Of course, setting an instance or static variable to null is slightly
different - but for instance variables, I usually find that the array
is useful for exactly the same length of time as the object itself, so
again there's rarely a point in setting the variable to null.
Note that Erase doesn't automatically make an array eligible for
garbage collection - if there's another reference to the same array, it
can't be collected until that reference has changed (to null or to a
different array) or become eligible for garbage collection itself.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Cor Ligthert <no**********@p lanet.nl> wrote: In my opinion Scott told it very clear. I did not read anything in your
message that would have given the OP more information when this arguing had
not been.
Really. Having read only Scott's post, when would you believe Foo was
eligible for garbage collection in the Sub below?
Public Shared Sub Test()
Dim Foo(9) As Integer
Console.WriteLi ne(Foo(0))
Console.WriteLi ne("Hello")
MessageBox.Show ("Can it be collected now?")
End Sub
If I had just read Scott's post (and didn't know anything else) I would
expect the array not to be eligible for garbage collection until the
end of the Sub. In fact (in release mode), it's eligible for garbage
collection immediately after Foo(0) has been evaluated.
In my opinion there is a scene where setting an array to nothing can be good
and I do not believe that that is contradicting what Scott wrote.
No, and that's also not contradicting anything I wrote. I didn't
contradict what Scott wrote - I added to it.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Hi Jon, Really. Having read only Scott's post, when would you believe Foo was
eligible for garbage collection.
This is the message from Scott
Everything in .NET is a type (either reference or value types). All
types are managed by the Garbage Collector. There is no need to "free up
memory" as this is the purpose of the GC. There are certain circumstances
though, when you may want the object in question to fall out of scope
immediately, rather than waiting for the end of a procedure. In this case you could
make the object = Nothing.
Where Scott did write about the place it was eligible for the GC?
When the method falls out of scope, it does not always mean that an (in that
method created) object is collectable for the GC, however Scott did not
write that either.
This was your answerUsually that's unnecessary, however, as the garbage collector can tell
when a variable is last used in the IL. Unless you're in a particularly
special case (eg where a variable is used in the first iteration of a
long loop, and not thereafter) it's best not to clutter up your code
setting variables to null/Nothing.
It did, at that moment you wrote it, in my opinion Add nothing to the
question of the OP:
"How to destroy arrays", your message tells in a way where an array is
destroyed by the program (not for the system).
And that was for me already clear in the explanation from Scott. Why would
it be set to nothing at the end of the procedure (method)
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I have created an array of Objects in a collection. I was wondering is there
a way to destroy the array to free up the space in the memory ? or they are
automatically destroyed and garbagge collected by .Net framework?
Sarfraz
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