Not axactly a memory leak but can be bad

[Zeng]

I finally narrowed down my code to this situation, quite a few (not all) of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and they
all share one stance of another class that I don't have enough memory hold
more than a just a few in the memory. Notice that the finalizaer the my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist. The interesting thing is if I run the page again,
the old dangling ones got destroyed and the new ones become dangling. Am I
missing something about the GC? Do I need to explicitly implement and call
dispose for these classes instead of relying on GC to promptly collect it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text ); ++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Jon Shemitz]

the finalizaer the my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist.

Actually, the finalizer is the problem. When the GC detects that an
object with a finalizer is garbage, it "resurrects" it and puts it on
a finalization queue, to be finalized by a background thread. When the
finalization thread actually gets to call finalize and remove your
object from the queue, the object is again available for collection.
Of course, it's (probably) now been bumped a generation, and so will
stick around for a while.

// Jon, who's procrastinating a bit today ....

 

[Willy Denoyette [MVP]]

I finally narrowed down my code to this situation, quite a few (not all)
of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and
they
all share one stance of another class that I don't have enough memory hold
more than a just a few in the memory. Notice that the finalizaer the my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist.

Why do you have a finalizer in the first place, classes having finalizers
need at least two sweeps to be collected.

Willy.

 

[Guest]

Why do you have a finalizer in the first place, classes having finalizers
need at least two sweeps to be collected.

The main reason IMO is CYA when unmanaged resources are involved. The
intent should always be to use Dispose to clean them up asap but if you
forget, or the person who has to maintain your code a year after you've left
doesn't realize he needs to, finalize will make sure it's cleaned up
eventually.

 

[Willy Denoyette [MVP]]

The main reason IMO is CYA when unmanaged resources are involved. The
intent should always be to use Dispose to clean them up asap but if you
forget, or the person who has to maintain your code a year after you've
left
doesn't realize he needs to, finalize will make sure it's cleaned up
eventually.

I know, but in this case the CMyClass class doesn't implement IDisposable,
doesn't hold any unmanaged resouces and has a completely redundant empty
Finalizer.

Willy.

 

[Zeng]

Is there a way to force the collection on those objects with a finalizer?
From all the documentation I've been reading (not enough reading)
GS.Collect() would do it, then I found some place that calling Collect()
then call WaitForPendingFinalizers() then Collect() again would do it, now I
found that it doesn't do it either. Disposing would just help freeing memory
from unmanaged resources, if all the stuff that occupy memory are in the
managed classes, it would be a problem w/o a way to force collection.

 

[Jon Shemitz]

Is there a way to force the collection on those objects with a finalizer?

Why do you want to? (Fwiw, we usually want to avoid finalization,
because resurrection (and memory use that's higher than necessary for
longer than necessary) is not free. This is the point of IDisposable
and the "using" statement. Write a finalizer to do any necessary
cleanup, in case someone forgets to call Dispose; and call
GC.SuppressFinalize in the Dispose() routine, to avoid finalization
costs.)

if all the stuff that occupy memory are in the
managed classes, it would be a problem w/o a way to force collection.

"Would be"? Or "is"? Some very bright people worked very hard on the
garbage collector - it works awfully well, and you almost never need
to "force" it to do anything.

 

[Zeng]

I wouldn't need to force it if I know for sure that they will be collected
before the asp.net process gets recycled because it reaches maximum % of
memory in the system (the default is 60%). Does anybody know for sure?
thanks!

 

[Willy Denoyette [MVP]]

I wouldn't need to force it if I know for sure that they will be collected
before the asp.net process gets recycled because it reaches maximum % of
memory in the system (the default is 60%). Does anybody know for sure?
thanks!

Yes, for sure the GC runs more often that you ever imagine.

Willy.

 

[Guest]

and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you try to
force the VM to run garbage collection, it will still run at it's earliest
convenience.

During compilation, your code is injected with "safe points" whereby the GC
can hijack the thread and take control to do its work. Now, when you call
GC.Collect() your code might not be in a stable enough state for the GC to
run, and the only way that the GC can know that it is safe to run is if it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you will
inadvertantly interrupt a perfectly (or near to) working system, and you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is going
on (for maintenance reasons, or whatever), however, designing our classes
"off centre" just in case, the next developer doesn't know as much as us is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk

I finally narrowed down my code to this situation, quite a few (not all) of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and they
all share one stance of another class that I don't have enough memory hold
more than a just a few in the memory. Notice that the finalizaer the my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist. The interesting thing is if I run the page again,
the old dangling ones got destroyed and the new ones become dangling. Am I
missing something about the GC? Do I need to explicitly implement and call
dispose for these classes instead of relying on GC to promptly collect it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text ); ++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Zeng]

Relying on IDisposable won't work easily in the multi-threading scenarios.
Since the memory required for each object is big, I have put them on static
variable to share it among the servicing threads. Think of CMyClass is a
spell-grammar-checker that helps looking up things and provide suggestions
for correction for many users create their documents online. In this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer knows
what he/she needs to be done but can't change its behavior (which is very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system to be
done with collection and there is a safe point in that method? And is there
a safe point in the component that checks for memory usage and recycle the
aspnet process when 60%(default) is reached?

and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you try to
force the VM to run garbage collection, it will still run at it's earliest
convenience.

During compilation, your code is injected with "safe points" whereby the GC
can hijack the thread and take control to do its work. Now, when you call
GC.Collect() your code might not be in a stable enough state for the GC to
run, and the only way that the GC can know that it is safe to run is if it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you will
inadvertantly interrupt a perfectly (or near to) working system, and you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is going
on (for maintenance reasons, or whatever), however, designing our classes
"off centre" just in case, the next developer doesn't know as much as us is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk

I finally narrowed down my code to this situation, quite a few (not all) of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and they
all share one stance of another class that I don't have enough memory hold
more than a just a few in the memory. Notice that the finalizaer the my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist. The interesting thing is if I run the page again,
the old dangling ones got destroyed and the new ones become dangling. Am I
missing something about the GC? Do I need to explicitly implement and call
dispose for these classes instead of relying on GC to promptly collect it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text ); ++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Willy Denoyette [MVP]]

Again, you don't have to implement IDisposable when you don't deal with
managed resources. What do you expect to do in your Dispose method? And No
there is no documentation available on Safe points, because they don't apply
here (at least not in the code snip you've posted).
I'm also not clear on what you mean with recycling the asp.net process, is
this something you intend to do or is it something that you are expecting to
be done automatically, anyway before the asp.net process recycles, all
application domains get unloaded, and this implies a GC run and a finalizer
run, so all objects (still referenced too) will be collected , but even when
some objects aren't collected, all memory once allocated for the process
will return to the OS when the process ends. So what are you afraid of?


Willy.

Relying on IDisposable won't work easily in the multi-threading scenarios.
Since the memory required for each object is big, I have put them on
static
variable to share it among the servicing threads. Think of CMyClass is a
spell-grammar-checker that helps looking up things and provide suggestions
for correction for many users create their documents online. In this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer knows
what he/she needs to be done but can't change its behavior (which is very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system to be
done with collection and there is a safe point in that method? And is
there
a safe point in the component that checks for memory usage and recycle the
aspnet process when 60%(default) is reached?

and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you try to
force the VM to run garbage collection, it will still run at it's
earliest
convenience.

During compilation, your code is injected with "safe points" whereby the GC
can hijack the thread and take control to do its work. Now, when you call
GC.Collect() your code might not be in a stable enough state for the GC
to
run, and the only way that the GC can know that it is safe to run is if
it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you
will
inadvertantly interrupt a perfectly (or near to) working system, and you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to
implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is going
on (for maintenance reasons, or whatever), however, designing our classes
"off centre" just in case, the next developer doesn't know as much as us is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk

I finally narrowed down my code to this situation, quite a few (not
all) of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and they
all share one stance of another class that I don't have enough memory hold
more than a just a few in the memory. Notice that the finalizaer the my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist. The interesting thing is if I run the page again,
the old dangling ones got destroyed and the new ones become dangling.
Am I
missing something about the GC? Do I need to explicitly implement and call
dispose for these classes instead of relying on GC to promptly collect it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and
help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text ); ++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Zeng]

I'm not sure on what you mean by "there is no documentation
available...because they don't apply here...". The existance of a document
doesn't depend on what part of version of my code was posted. I appreciate
your help looking into this for me, many people would just ignore posts and
move on even they know the answer or have some comments, but I don't think
we are going anywhere with it. My response was to BillR who proposes that I
should be implementing the IDisposable.

It's the production environment, if the process get recycled, all my cache
in the memory will have to be reloaded when it goes back up. That would
cause delay to the service that we want to provide. Sounds like you are not
familiar with the processModel entry with attribute memoryLimit="60" as
default, it's in the machine.config file. thanks!

Again, you don't have to implement IDisposable when you don't deal with
managed resources. What do you expect to do in your Dispose method? And No
there is no documentation available on Safe points, because they don't apply
here (at least not in the code snip you've posted).
I'm also not clear on what you mean with recycling the asp.net process, is
this something you intend to do or is it something that you are expecting to
be done automatically, anyway before the asp.net process recycles, all
application domains get unloaded, and this implies a GC run and a finalizer
run, so all objects (still referenced too) will be collected , but even when
some objects aren't collected, all memory once allocated for the process
will return to the OS when the process ends. So what are you afraid of?


Willy.

Relying on IDisposable won't work easily in the multi-threading scenarios.
Since the memory required for each object is big, I have put them on
static
variable to share it among the servicing threads. Think of CMyClass is a
spell-grammar-checker that helps looking up things and provide suggestions
for correction for many users create their documents online. In this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer knows
what he/she needs to be done but can't change its behavior (which is very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system to be
done with collection and there is a safe point in that method? And is
there
a safe point in the component that checks for memory usage and recycle the
aspnet process when 60%(default) is reached?

and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you

try
to

force the VM to run garbage collection, it will still run at it's
earliest
convenience.

During compilation, your code is injected with "safe points" whereby

the
GC

can hijack the thread and take control to do its work. Now, when you call
GC.Collect() your code might not be in a stable enough state for the GC
to
run, and the only way that the GC can know that it is safe to run is if
it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you
will
inadvertantly interrupt a perfectly (or near to) working system, and you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to
implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is going
on (for maintenance reasons, or whatever), however, designing our classes
"off centre" just in case, the next developer doesn't know as much as

us
is a

pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk


:


I finally narrowed down my code to this situation, quite a few (not
all) of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory

and
they

all share one stance of another class that I don't have enough memory hold
more than a just a few in the memory. Notice that the finalizaer

the
my

CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist. The interesting thing is if I run the page again,
the old dangling ones got destroyed and the new ones become dangling.
Am I
missing something about the GC? Do I need to explicitly implement and call
dispose for these classes instead of relying on GC to promptly

collect
it?

Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and
help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text ); ++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Willy Denoyette [MVP]]

Sorry what I meant was ""there is no documentation ... AND they don't apply
here". If you need more info on GC safe points I'm afraid you'll have to
look in the source code files of the CLR if you happen to have a Source Code
License. Anyway, when your code calls GC.Collect it's always at a safe GC
point, it's only when a GC is "induced" that it might get postponed when
your code is not at a GC safe point.
What Billr proposed makes little sense in your case because your class don't
own unmanaged resources, like DB connections, unmanaged memory OS handles
etc..., it only consumes managed heap memory which is taken care of by the
GC, there is no need to force collections by calling GC.Collect yourself.
But if you really think you have to implement IDisposable, go ahead, but
please tell us what you will do in your Dispose method.

I guess I'm more familiar with the process model than you might think. The
asp.net hosting process recycles when it's Working Set exceeds the
memoryLimit% of total available memory, but the hosting process will try to
survive first by forcing a full GC run, followed by an attempt to reduce the
working set, then and ONLY when it's WS still exceeds the MemoryLimit% it
will recycle, else it simply continues to run.
In case the WS could not be reduced it's simply because an application
hosted in asp.net allocates too much memory or as a result of heap
fragmentation (take care when allocating many large objects (>85Kb)), or as
a result of a design error.
When it happens on a production system, it must be considered an application
error , because the memoryLimit%, available system memory, number of active
clients etc.. should have been defined during staging, when you performed
your load/stress testing and your workload modeling.

Willy.

I'm not sure on what you mean by "there is no documentation
available...because they don't apply here...". The existance of a
document
doesn't depend on what part of version of my code was posted. I
appreciate
your help looking into this for me, many people would just ignore posts
and
move on even they know the answer or have some comments, but I don't think
we are going anywhere with it. My response was to BillR who proposes that
I
should be implementing the IDisposable.

It's the production environment, if the process get recycled, all my cache
in the memory will have to be reloaded when it goes back up. That would
cause delay to the service that we want to provide. Sounds like you are
not
familiar with the processModel entry with attribute memoryLimit="60" as
default, it's in the machine.config file. thanks!

Again, you don't have to implement IDisposable when you don't deal with
managed resources. What do you expect to do in your Dispose method? And
No
there is no documentation available on Safe points, because they don't apply
here (at least not in the code snip you've posted).
I'm also not clear on what you mean with recycling the asp.net process, is
this something you intend to do or is it something that you are expecting to
be done automatically, anyway before the asp.net process recycles, all
application domains get unloaded, and this implies a GC run and a finalizer
run, so all objects (still referenced too) will be collected , but even when
some objects aren't collected, all memory once allocated for the process
will return to the OS when the process ends. So what are you afraid of?


Willy.

Relying on IDisposable won't work easily in the multi-threading scenarios.
Since the memory required for each object is big, I have put them on
static
variable to share it among the servicing threads. Think of CMyClass is
a
spell-grammar-checker that helps looking up things and provide suggestions
for correction for many users create their documents online. In this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer knows
what he/she needs to be done but can't change its behavior (which is very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system to be
done with collection and there is a safe point in that method? And is
there
a safe point in the component that checks for memory usage and recycle the
aspnet process when 60%(default) is reached?



and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you try
to
force the VM to run garbage collection, it will still run at it's
earliest
convenience.

During compilation, your code is injected with "safe points" whereby the
GC
can hijack the thread and take control to do its work. Now, when you call
GC.Collect() your code might not be in a stable enough state for the
GC
to
run, and the only way that the GC can know that it is safe to run is
if
it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you
will
inadvertantly interrupt a perfectly (or near to) working system, and you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to
implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is
going
on (for maintenance reasons, or whatever), however, designing our classes
"off centre" just in case, the next developer doesn't know as much as us
is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk


:


I finally narrowed down my code to this situation, quite a few (not
all)
of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows
that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and
they
all share one stance of another class that I don't have enough
memory
hold
more than a just a few in the memory. Notice that the finalizaer the
my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist. The interesting thing is if I run the page
again,
the old dangling ones got destroyed and the new ones become
dangling.
Am
I
missing something about the GC? Do I need to explicitly implement
and
call
dispose for these classes instead of relying on GC to promptly collect
it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and
help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text );
++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Zeng]

From what I understand, Dispose method doesn't help freeing manage
resources, and that's consistent with what you are saying.

About the hosting process tries to do a full GC run before it recycles based
on MemoryLimit%; I don't believe it at this point, if there is such thing as
full GC and it's doing what we expect, then it should have been exposed so
we - developers - can call it when we need to bring down the heap size
immediately (of course we don't need this if full GC is actually possible
privately to the framework, but I don't believe it). How many times should
I try to call GC.Collect to free the dangling objects in my demo code? And
if GC.Collect doesn't do what "Collect" means, what is its use? Purely
advertising?

Imagine somebody sell you a cabinet and there is knob on it, and he tells
you that yes that's a knob but don't use it, you NEVER need or want to use
it. If you actually never need to use it then it should be only for
decoration but that was only a speculation - and one day you decide to
pull or turn it, and it doesn't do anything ... hahaha who is more insane,
the person tries to use the knob or the person put the knob on the cabinet
and didn't think it's for decoration??

Sorry what I meant was ""there is no documentation ... AND they don't apply
here". If you need more info on GC safe points I'm afraid you'll have to
look in the source code files of the CLR if you happen to have a Source Code
License. Anyway, when your code calls GC.Collect it's always at a safe GC
point, it's only when a GC is "induced" that it might get postponed when
your code is not at a GC safe point.
What Billr proposed makes little sense in your case because your class don't
own unmanaged resources, like DB connections, unmanaged memory OS handles
etc..., it only consumes managed heap memory which is taken care of by the
GC, there is no need to force collections by calling GC.Collect yourself.
But if you really think you have to implement IDisposable, go ahead, but
please tell us what you will do in your Dispose method.

I guess I'm more familiar with the process model than you might think. The
asp.net hosting process recycles when it's Working Set exceeds the
memoryLimit% of total available memory, but the hosting process will try to
survive first by forcing a full GC run, followed by an attempt to reduce the
working set, then and ONLY when it's WS still exceeds the MemoryLimit% it
will recycle, else it simply continues to run.
In case the WS could not be reduced it's simply because an application
hosted in asp.net allocates too much memory or as a result of heap
fragmentation (take care when allocating many large objects (>85Kb)), or as
a result of a design error.
When it happens on a production system, it must be considered an application
error , because the memoryLimit%, available system memory, number of active
clients etc.. should have been defined during staging, when you performed
your load/stress testing and your workload modeling.

Willy.

I'm not sure on what you mean by "there is no documentation
available...because they don't apply here...". The existance of a
document
doesn't depend on what part of version of my code was posted. I
appreciate
your help looking into this for me, many people would just ignore posts
and
move on even they know the answer or have some comments, but I don't think
we are going anywhere with it. My response was to BillR who proposes that
I
should be implementing the IDisposable.

It's the production environment, if the process get recycled, all my cache
in the memory will have to be reloaded when it goes back up. That would
cause delay to the service that we want to provide. Sounds like you are
not
familiar with the processModel entry with attribute memoryLimit="60" as
default, it's in the machine.config file. thanks!

Again, you don't have to implement IDisposable when you don't deal with
managed resources. What do you expect to do in your Dispose method? And
No
there is no documentation available on Safe points, because they don't apply
here (at least not in the code snip you've posted).
I'm also not clear on what you mean with recycling the asp.net

process,
is

this something you intend to do or is it something that you are

expecting
to

be done automatically, anyway before the asp.net process recycles, all
application domains get unloaded, and this implies a GC run and a finalizer
run, so all objects (still referenced too) will be collected , but even when
some objects aren't collected, all memory once allocated for the process
will return to the OS when the process ends. So what are you afraid of?


Willy.

Relying on IDisposable won't work easily in the multi-threading scenarios.
Since the memory required for each object is big, I have put them on
static
variable to share it among the servicing threads. Think of CMyClass is
a
spell-grammar-checker that helps looking up things and provide suggestions
for correction for many users create their documents online. In this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer knows
what he/she needs to be done but can't change its behavior (which is very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system

to
be

done with collection and there is a safe point in that method? And is
there
a safe point in the component that checks for memory usage and

recycle
the

aspnet process when 60%(default) is reached?



and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when

you
try

to
force the VM to run garbage collection, it will still run at it's
earliest
convenience.

During compilation, your code is injected with "safe points" whereby the
GC
can hijack the thread and take control to do its work. Now, when you call
GC.Collect() your code might not be in a stable enough state for the
GC
to
run, and the only way that the GC can know that it is safe to run is
if
it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you
will
inadvertantly interrupt a perfectly (or near to) working system, and you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to
implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is
going
on (for maintenance reasons, or whatever), however, designing our classes
"off centre" just in case, the next developer doesn't know as much

as
us

is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk


:


I finally narrowed down my code to this situation, quite a few (not
all)
of
my CMyClass objects got hold up after each run of this function

via
the

simple webpage that shows NumberEd editbox. My memory profile shows
that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and
they
all share one stance of another class that I don't have enough
memory
hold
more than a just a few in the memory. Notice that the finalizaer the
my
CMyClass makes a big difference in demonstrating this issue, w/o

it
the

problem doesn't exist. The interesting thing is if I run the page
again,
the old dangling ones got destroyed and the new ones become
dangling.
Am
I
missing something about the GC? Do I need to explicitly implement
and
call
dispose for these classes instead of relying on GC to promptly collect
it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and
help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text );
++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Guest]

I guess it's time for me to make my apologies. The point of my mentioning
Safe Points was to illustrate the workings of the GC.

Safe Points are points in the code that have been identified as it being
safe for the GC to suspend ALL threads in order to do its thing.

A problem faced by the GC is that when compacting the heap it must make sure
that it does not change the structure of the object graphs (internal
tree-like structures used for determining reachable/non-reachable objects
i.e. referenced/non-referenced objects), nor should it change the structure
of the heap. In order to achieve this, the GC is responsible for maintaining
object references (i.e. adjusting references within objects contained within
the graphs), because of course, when an object is moved in the heap, any
existing references to that object will be invalid. The only safe way to cope
with this is to suspend all application threads during garbage collection. It
is for this reason that the JIT compiler inserts Safe Points into the code,
i.e. points in the execution path that are safe for thread suspension.

Garbage collection occurs by the GC effectively "hijacking" the thread by
inserting a different return address from the safe point. When GC is
complete, .NET sends the thread back to its original return address and
normal execution continues.

Garbage collection is triggered in .NET either by application shutdown, heap
exhaustion, or an explicit call GC.Collect(). With the exception of
application shutdown, however, garbage collection only occurs when the
execution path reaches a safe point.

IMPORTANT NOTE :
================

When the GC has determined that an object is in fact garbage, the first
thing it does is check the object's metadata, and if the object implements
Finalize(), instead of destroying the object, it is marked as reachable
(which is not what you want if you want your object to be destroyed
immediately) and is moved from its original graph to another graph called the
"finalized queue". A seperate thread then iterates over the finalized queue
invoking Finalize() on all objects contained therein; then -and only then-
are the objects removed from the queue and destroyed, hence freeing up its
heap space.

So, essentially, when you implement Finalize() you are telling the GC that
when the object is no longer referenced it is NOT SAFE for deletion YET, and
Finalize() must first be invoked, which means that the object is not
destroyed for approximately two runs of garbage collection. It is for this
reason that deterministic finalization is recommended.

EXPLICIT garbage collection is not recommended becuase it is an expensive
operation involving scanning object graphs, thread suspension and resumption,
thread context switches, and EXTENSIVE use of reflection to read the objects'
metadata.

I hope that that clears up the confusion I might have injected into the
discussion, also, I hope it clears up why you should not declare a finalizer,
even if there is no body. The simple act of declaring a finalizer ensures
that the object lives for longer than you might actually intend/require.



--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk

I'm not sure on what you mean by "there is no documentation
available...because they don't apply here...". The existance of a document
doesn't depend on what part of version of my code was posted. I appreciate
your help looking into this for me, many people would just ignore posts and
move on even they know the answer or have some comments, but I don't think
we are going anywhere with it. My response was to BillR who proposes that I
should be implementing the IDisposable.

It's the production environment, if the process get recycled, all my cache
in the memory will have to be reloaded when it goes back up. That would
cause delay to the service that we want to provide. Sounds like you are not
familiar with the processModel entry with attribute memoryLimit="60" as
default, it's in the machine.config file. thanks!

Again, you don't have to implement IDisposable when you don't deal with
managed resources. What do you expect to do in your Dispose method? And No
there is no documentation available on Safe points, because they don't apply
here (at least not in the code snip you've posted).
I'm also not clear on what you mean with recycling the asp.net process, is
this something you intend to do or is it something that you are expecting to
be done automatically, anyway before the asp.net process recycles, all
application domains get unloaded, and this implies a GC run and a finalizer
run, so all objects (still referenced too) will be collected , but even when
some objects aren't collected, all memory once allocated for the process
will return to the OS when the process ends. So what are you afraid of?


Willy.

Relying on IDisposable won't work easily in the multi-threading scenarios.
Since the memory required for each object is big, I have put them on
static
variable to share it among the servicing threads. Think of CMyClass is a
spell-grammar-checker that helps looking up things and provide suggestions
for correction for many users create their documents online. In this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer knows
what he/she needs to be done but can't change its behavior (which is very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system to be
done with collection and there is a safe point in that method? And is
there
a safe point in the component that checks for memory usage and recycle the
aspnet process when 60%(default) is reached?



and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you try
to
force the VM to run garbage collection, it will still run at it's
earliest
convenience.

During compilation, your code is injected with "safe points" whereby the
GC
can hijack the thread and take control to do its work. Now, when you call
GC.Collect() your code might not be in a stable enough state for the GC
to
run, and the only way that the GC can know that it is safe to run is if
it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you
will
inadvertantly interrupt a perfectly (or near to) working system, and you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to
implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is
going
on (for maintenance reasons, or whatever), however, designing our classes
"off centre" just in case, the next developer doesn't know as much as us
is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk


:


I finally narrowed down my code to this situation, quite a few (not
all)
of
my CMyClass objects got hold up after each run of this function via the
simple webpage that shows NumberEd editbox. My memory profile shows
that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory and
they
all share one stance of another class that I don't have enough memory
hold
more than a just a few in the memory. Notice that the finalizaer the
my
CMyClass makes a big difference in demonstrating this issue, w/o it the
problem doesn't exist. The interesting thing is if I run the page
again,
the old dangling ones got destroyed and the new ones become dangling.
Am
I
missing something about the GC? Do I need to explicitly implement and
call
dispose for these classes instead of relying on GC to promptly collect
it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and
help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text ); ++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Guest]

GC.Collect() does do what it says on the packet, i.e. it does cause the GC to
run; however, it will only run at its next convenient opportunity -which
might or might not be the next time it was going to run anyway.

You can use GC.Collect(), and I didn't mean to imply that you cannot,
however, it should be considered that this does entail additional overhead,
and garbage collection will not necessarily run as soon as you have made the
call.

I completely agree with your analogy, however, I think that it does not
really apply here, and maybe my original post should have been a little
clearer on this point.

The method is supplied so that you can call it, but under normal operating
conditions, you really shouldn't NEED to make the call.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk

From what I understand, Dispose method doesn't help freeing manage
resources, and that's consistent with what you are saying.

About the hosting process tries to do a full GC run before it recycles based
on MemoryLimit%; I don't believe it at this point, if there is such thing as
full GC and it's doing what we expect, then it should have been exposed so
we - developers - can call it when we need to bring down the heap size
immediately (of course we don't need this if full GC is actually possible
privately to the framework, but I don't believe it). How many times should
I try to call GC.Collect to free the dangling objects in my demo code? And
if GC.Collect doesn't do what "Collect" means, what is its use? Purely
advertising?

Imagine somebody sell you a cabinet and there is knob on it, and he tells
you that yes that's a knob but don't use it, you NEVER need or want to use
it. If you actually never need to use it then it should be only for
decoration but that was only a speculation - and one day you decide to
pull or turn it, and it doesn't do anything ... hahaha who is more insane,
the person tries to use the knob or the person put the knob on the cabinet
and didn't think it's for decoration??

Sorry what I meant was ""there is no documentation ... AND they don't apply
here". If you need more info on GC safe points I'm afraid you'll have to
look in the source code files of the CLR if you happen to have a Source Code
License. Anyway, when your code calls GC.Collect it's always at a safe GC
point, it's only when a GC is "induced" that it might get postponed when
your code is not at a GC safe point.
What Billr proposed makes little sense in your case because your class don't
own unmanaged resources, like DB connections, unmanaged memory OS handles
etc..., it only consumes managed heap memory which is taken care of by the
GC, there is no need to force collections by calling GC.Collect yourself.
But if you really think you have to implement IDisposable, go ahead, but
please tell us what you will do in your Dispose method.

I guess I'm more familiar with the process model than you might think. The
asp.net hosting process recycles when it's Working Set exceeds the
memoryLimit% of total available memory, but the hosting process will try to
survive first by forcing a full GC run, followed by an attempt to reduce the
working set, then and ONLY when it's WS still exceeds the MemoryLimit% it
will recycle, else it simply continues to run.
In case the WS could not be reduced it's simply because an application
hosted in asp.net allocates too much memory or as a result of heap
fragmentation (take care when allocating many large objects (>85Kb)), or as
a result of a design error.
When it happens on a production system, it must be considered an application
error , because the memoryLimit%, available system memory, number of active
clients etc.. should have been defined during staging, when you performed
your load/stress testing and your workload modeling.

Willy.

I'm not sure on what you mean by "there is no documentation
available...because they don't apply here...". The existance of a
document
doesn't depend on what part of version of my code was posted. I
appreciate
your help looking into this for me, many people would just ignore posts
and
move on even they know the answer or have some comments, but I don't think
we are going anywhere with it. My response was to BillR who proposes that
I
should be implementing the IDisposable.

It's the production environment, if the process get recycled, all my cache
in the memory will have to be reloaded when it goes back up. That would
cause delay to the service that we want to provide. Sounds like you are
not
familiar with the processModel entry with attribute memoryLimit="60" as
default, it's in the machine.config file. thanks!


Again, you don't have to implement IDisposable when you don't deal with
managed resources. What do you expect to do in your Dispose method? And
No
there is no documentation available on Safe points, because they don't
apply
here (at least not in the code snip you've posted).
I'm also not clear on what you mean with recycling the asp.net process,
is
this something you intend to do or is it something that you are expecting
to
be done automatically, anyway before the asp.net process recycles, all
application domains get unloaded, and this implies a GC run and a
finalizer
run, so all objects (still referenced too) will be collected , but even
when
some objects aren't collected, all memory once allocated for the process
will return to the OS when the process ends. So what are you afraid of?


Willy.

Relying on IDisposable won't work easily in the multi-threading
scenarios.
Since the memory required for each object is big, I have put them on
static
variable to share it among the servicing threads. Think of CMyClass is
a
spell-grammar-checker that helps looking up things and provide
suggestions
for correction for many users create their documents online. In this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are
done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer
knows
what he/she needs to be done but can't change its behavior (which is
very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system to
be
done with collection and there is a safe point in that method? And is
there
a safe point in the component that checks for memory usage and recycle
the
aspnet process when 60%(default) is reached?



and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you
try
to
force the VM to run garbage collection, it will still run at it's
earliest
convenience.

During compilation, your code is injected with "safe points" whereby
the
GC
can hijack the thread and take control to do its work. Now, when you
call
GC.Collect() your code might not be in a stable enough state for the
GC
to
run, and the only way that the GC can know that it is safe to run is
if
it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you
will
inadvertantly interrupt a perfectly (or near to) working system, and
you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to
implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is
going
on (for maintenance reasons, or whatever), however, designing our
classes
"off centre" just in case, the next developer doesn't know as much as
us
is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk


:


I finally narrowed down my code to this situation, quite a few (not
all)
of
my CMyClass objects got hold up after each run of this function via
the
simple webpage that shows NumberEd editbox. My memory profile shows
that
those instances survive 3 rounds of GC collections - it's not what I
expected. In my real code, CMyClass occupies big amount of memory
and
they
all share one stance of another class that I don't have enough
memory
hold
more than a just a few in the memory. Notice that the finalizaer
the
my
CMyClass makes a big difference in demonstrating this issue, w/o it
the
problem doesn't exist. The interesting thing is if I run the page
again,
the old dangling ones got destroyed and the new ones become
dangling.
Am
I
missing something about the GC? Do I need to explicitly implement
and
call
dispose for these classes instead of relying on GC to promptly
collect
it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment and
help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text );
++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )

 

[Willy Denoyette [MVP]]

Seems like you have a fundamental mis-understanding on what the GC is meant
for and how it's actually performing.
The GC's task is, to collect the memory space occupied by non-reachable
objects and compact the generation it is actually collecting, so that a
contiguous free space remains in the heap to add new objects.
A full GC is a GC run that collects all generations, the current version of
the CLR has 3 generational logical heaps plus a separate large object heap
(LOH), from code you can ask for a GC run by calling GC.Collect(n) where n
indicates the generation to end with, a collection always starts with
generation 0.
GC.Collect() collects all generations plus the LOH, that's why it's called a
full collect.

However, it's NOT the task of the GC to bring down the heap size, that's the
task of the CLR memory manager , or the hosting process memory manager (if
any) in close cooperation with the OS.

Your code sample needs at least two GC.Collect() calls, that's because you
have a Finalizer (destructor in C# parlance).
When an instance of a finalizable object gets instantiated, it's registered
as finalizable.
When it is no longer rooted at the next GC run, it will be moved to the
finalizable queue, where it stays until after the finalizer has run, after
which it's removed from the finalizer queue and it becomes eligible for
collection.
Note that it's possible that not all finalizables are immediately finalized,
all depends on the load of the system and the time the finalizer thread
spends finalizing objects. The finalizer thread can be suspended before all
finalizer have run, that's why we say at LEAST 2 GC runs, and why we suggest
against destructors in C#.

Willy.

PS I suggest you start reading these (somewhat outdated) articles , before
you start arguing about a subject you don't seem to fully understand.
http://msdn.microsoft.com/msdnmag/issues/1100/GCI/default.aspx
http://msdn.microsoft.com/msdnmag/issues/1200/GCI2/default.aspx

From what I understand, Dispose method doesn't help freeing manage
resources, and that's consistent with what you are saying.

About the hosting process tries to do a full GC run before it recycles
based
on MemoryLimit%; I don't believe it at this point, if there is such thing
as
full GC and it's doing what we expect, then it should have been exposed so
we - developers - can call it when we need to bring down the heap size
immediately (of course we don't need this if full GC is actually possible
privately to the framework, but I don't believe it). How many times
should
I try to call GC.Collect to free the dangling objects in my demo code?
And
if GC.Collect doesn't do what "Collect" means, what is its use? Purely
advertising?

Imagine somebody sell you a cabinet and there is knob on it, and he tells
you that yes that's a knob but don't use it, you NEVER need or want to use
it. If you actually never need to use it then it should be only for
decoration but that was only a speculation - and one day you decide to
pull or turn it, and it doesn't do anything ... hahaha who is more insane,
the person tries to use the knob or the person put the knob on the cabinet
and didn't think it's for decoration??

Sorry what I meant was ""there is no documentation ... AND they don't apply
here". If you need more info on GC safe points I'm afraid you'll have to
look in the source code files of the CLR if you happen to have a Source Code
License. Anyway, when your code calls GC.Collect it's always at a safe GC
point, it's only when a GC is "induced" that it might get postponed when
your code is not at a GC safe point.
What Billr proposed makes little sense in your case because your class don't
own unmanaged resources, like DB connections, unmanaged memory OS handles
etc..., it only consumes managed heap memory which is taken care of by
the
GC, there is no need to force collections by calling GC.Collect yourself.
But if you really think you have to implement IDisposable, go ahead, but
please tell us what you will do in your Dispose method.

I guess I'm more familiar with the process model than you might think.
The
asp.net hosting process recycles when it's Working Set exceeds the
memoryLimit% of total available memory, but the hosting process will try to
survive first by forcing a full GC run, followed by an attempt to reduce the
working set, then and ONLY when it's WS still exceeds the MemoryLimit% it
will recycle, else it simply continues to run.
In case the WS could not be reduced it's simply because an application
hosted in asp.net allocates too much memory or as a result of heap
fragmentation (take care when allocating many large objects (>85Kb)), or as
a result of a design error.
When it happens on a production system, it must be considered an application
error , because the memoryLimit%, available system memory, number of active
clients etc.. should have been defined during staging, when you performed
your load/stress testing and your workload modeling.

Willy.

I'm not sure on what you mean by "there is no documentation
available...because they don't apply here...". The existance of a
document
doesn't depend on what part of version of my code was posted. I
appreciate
your help looking into this for me, many people would just ignore posts
and
move on even they know the answer or have some comments, but I don't think
we are going anywhere with it. My response was to BillR who proposes that
I
should be implementing the IDisposable.

It's the production environment, if the process get recycled, all my cache
in the memory will have to be reloaded when it goes back up. That
would
cause delay to the service that we want to provide. Sounds like you
are
not
familiar with the processModel entry with attribute memoryLimit="60" as
default, it's in the machine.config file. thanks!


Again, you don't have to implement IDisposable when you don't deal
with
managed resources. What do you expect to do in your Dispose method?
And
No
there is no documentation available on Safe points, because they don't
apply
here (at least not in the code snip you've posted).
I'm also not clear on what you mean with recycling the asp.net process,
is
this something you intend to do or is it something that you are expecting
to
be done automatically, anyway before the asp.net process recycles,
all
application domains get unloaded, and this implies a GC run and a
finalizer
run, so all objects (still referenced too) will be collected , but
even
when
some objects aren't collected, all memory once allocated for the process
will return to the OS when the process ends. So what are you afraid
of?


Willy.

Relying on IDisposable won't work easily in the multi-threading
scenarios.
Since the memory required for each object is big, I have put them on
static
variable to share it among the servicing threads. Think of CMyClass is
a
spell-grammar-checker that helps looking up things and provide
suggestions
for correction for many users create their documents online. In
this
scenario, looks like there is the only choice
--> Make CMyClass disposable and create managing component (internal or
external to the class) just to coordinate when and which objects are
done
just to call Dispose. This sounds like the intensive plumbing and
error-prone approach that I was so used to with C++

Conceptually, this is the drawback of a smart system, the programmer
knows
what he/she needs to be done but can't change its behavior (which is
very
very smart most of the time)

By the way, where can I find a documentation about the safe-points?
Wouldn't that be better that there is a call to wait for the system to
be
done with collection and there is a safe point in that method? And
is
there
a safe point in the component that checks for memory usage and recycle
the
aspnet process when 60%(default) is reached?



and just to add my two pennies worth ...

Although you may call GC.Collect(), much the same as in Java when you
try
to
force the VM to run garbage collection, it will still run at it's
earliest
convenience.

During compilation, your code is injected with "safe points"
whereby
the
GC
can hijack the thread and take control to do its work. Now, when
you
call
GC.Collect() your code might not be in a stable enough state for
the
GC
to
run, and the only way that the GC can know that it is safe to run
is
if
it
has reached a "safe point".

Generally speaking, it is bad practice to call GC.Collect() since you
will
inadvertantly interrupt a perfectly (or near to) working system,
and
you
yourself can cause all sorts of naughtiness to occur.

My choice of preference (as it is for a lot of developers) is to
implement
IDisposable.

AND, yes, our code should be easily readable and left in a state that
renders it possible for future devlopers to look at it and see what is
going
on (for maintenance reasons, or whatever), however, designing our
classes
"off centre" just in case, the next developer doesn't know as much as
us
is a
pretty poor choice IMHO.

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk


:


I finally narrowed down my code to this situation, quite a few (not
all)
of
my CMyClass objects got hold up after each run of this function via
the
simple webpage that shows NumberEd editbox. My memory profile shows
that
those instances survive 3 rounds of GC collections - it's not
what I
expected. In my real code, CMyClass occupies big amount of
memory
and
they
all share one stance of another class that I don't have enough
memory
hold
more than a just a few in the memory. Notice that the
finalizaer
the
my
CMyClass makes a big difference in demonstrating this issue, w/o it
the
problem doesn't exist. The interesting thing is if I run the
page
again,
the old dangling ones got destroyed and the new ones become
dangling.
Am
I
missing something about the GC? Do I need to explicitly implement
and
call
dispose for these classes instead of relying on GC to promptly
collect
it?
Apparently somehow these objects can survive the automatic
collections...disposing it would help. Thanks for your comment
and
help.

internal class CMyClass
{
ArrayList m_array = new ArrayList( 50000 );
private string m_idStr;
private Guid m_guid;
internal CMyClass( int n )
{
for( int i = 0; i < n; ++i )
m_array.Add( Guid.NewGuid() );

m_guid = Guid.NewGuid();
m_idStr = m_guid.ToString();
}

internal Guid id
{
get{ return (Guid ) m_array[ 0 ]; }
}

~CMyClass()
{
// Trace.Write( m_guid, m_idStr );
}

}
private void RunBtn_Click(object sender, System.EventArgs e)
{
ResultEd.Text = "";
try
{

for( int i = 0; i < int.Parse( NumberEd.Text );
++i )
{

Hashtable table = new Hashtable( 100 );
ArrayList ids = new ArrayList( 10 );
for( int j = 0; j < 10; ++j )
{
Guid id = Guid.NewGuid();
table[ id ] = null;
ids.Add( id );
}


for( int k=0; k < 10; ++k )
{
foreach( Guid id in ids )
{
table[ id ] = new CMyClass( 10 );
}

CMyClass myobj;
foreach( Guid id in ids )
{
myobj = (CMyClass) table[ id ];
myobj.id.ToString();
}
} // for k
} // for
}
catch( Exception ex )
{
ResultEd.Text = ex.Message + "...CallSTack:" +
ex.StackTrace;
}

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

GC.WaitForPendingFinalizers();
GC.Collect();

ResultEd.Text = "Done";
}

 

[Willy Denoyette [MVP]]

Garbage collection is triggered in .NET either by application shutdown,
heap
exhaustion, or an explicit call GC.Collect(). With the exception of
application shutdown, however, garbage collection only occurs when the
execution path reaches a safe point.

To be precise a GC run can be "induced" by the CLR when the gen0 has reached
a certain threshold, not when the heap is exhausted. This gen0 threshold
starts with a fixed value depending on a number of system (the size of the
Level2 cache, GC flavor, etc...), but is dynamically adjusted during
run-time using GC statistics (allocation pattern and frequency).
Also the GC is 'induced' when all threads are at a safe point to be
suspended, unsafe points are 'signaled' by the JIT, but also by the EE
itself. A flag is set when it's not safe to collect and the EE checks this
flag before it suspends the threads and starts a GC sweep using one of the
suspended threads. Note however that unsafe points are rare, so most of the
time a GC can be initiated.

Willy.

 

[Guest]

Thanks for that little extra info Willy.


--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk