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Memory Leak in .NET 1.1

I've detected memory leaks in our huge .NET 1.1 C# application but
couldn't localize them directly. So I've reduced the code to the
following console application:

using System;
using System.IO;

namespace MemLeak
{
class MemLeak
{
[STAThread]
static void Main(string[] args)
{
try
{
throw new NullReferenceEx ception();
}
catch
{
}

for(int i=0; i<1000; i++)
{
using(StreamWri ter newMasterfile =
new StreamWriter(@" c:\XXX.tmp"))
{
newMasterfile.C lose();
}
}

Console.ReadLin e();
}
}
}

Also you have to create an "App.config " file which is distributed by
VS2003 into the application directory with the name of the application
followed by ".config". There may be any content, the file can be empty
too - this will not influence our result.

Compile the "Release" configuration and you'll see with a tool like
"NetMemoryProfi ler" that there are almost 1000 StreamWriter reserved at
"Console.ReadLi ne". You can wait as long as you want - they'll never be
freed. If you don't have such a tool: increase the number of loops.
Then you can use the task manager to see how the memory grows (look at
the virtual memory!). With an endless loop there will be an "Out of
virtual memory" error at the end.

This problem is not only bounded to StreamWriter. We've seen this for
database objects, simple strings and other.

We have tested this with several Windows XP SP2 Systems with different
configurations. Also with the latest fixes for Windows and .NET.

The funny thing: there will be no leaks when you use the "Debug"
configuration. Also you can omit the exception or the "App.config "
file. In these cases the memory will be freed correctly. But we will
comile in "Release" configuration, use the "App.config " and Exceptions
can't be avoided.

The last option is to switch the attribute "[STAThread]" to
"[MTAThread]". The memory is ok in the small example (why?) and also in
our huge application. But I'm not sure with the COM-components we use.
So I prefer the "[STAThread]" attribute.

There are some methods which you can tell the gabage collector to clean
up: "GC.GetTotalMem ory(...)", "GC.WaitForPend ingFinalizers() " and
"GC.Collect ()". You can find combinations in the small example to get
rid of the memory. But this is very unreliable and will not work
correctly in our huge application where late binding and remoting is
used.

After some days of trial and error, I am really at my wits' end over
this problem. So is there anybody who can help me?

Many thanks in advance
Martin Gaus

May 28 '06
30 4714
Willy Denoyette [MVP] <wi************ *@telenet.be> wrote:

<snip>
1. The only point in time a GC can occur is when objects are being created
on the GC heap, when waiting on a ReadLine(), no more objects are getting
instantiated, so, no GC can ever occur as long as you are waiting for a
keybord input.


That's not quite true, IMO. I believe GC will kick in when there's
memory pressure, too. Here are two programs which demonstrate it
between them:

Test.cs:
using System;

class Test
{
~Test()
{
Console.WriteLi ne ("Finalizer" );
}

static void Main()
{
Test t = new Test();
Console.WriteLi ne ("Created");
Console.ReadLin e();
}
}
UseMemory.cs:
using System.Collecti ons;

class UseMemory
{
static void Main()
{
ArrayList list = new ArrayList();
while (true)
{
list.Add (new byte[10000]);
}
}
}

From one console, compile and run Test.cs. You'll see (or may see)
"Created" on its own. You can then leave that console alone for a
couple of minutes, and nothing is printed.

Then compile and run UseMemory.cs. Shortly, you should see "Finalizer"
being printed in the original console window - at least, that's what
happens on my box.

While this isn't absolute proof (due to finalizers and GC being
different things) it's at least extremely suggestive.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too
May 28 '06 #11
True, when there is physical memory pressure (high memory threshold) and you
are running on XP or higher, the OS will notify the CLR who will start to
trim it's working set, but before doing this, the CLR will trigger a full
collection, that means it will trigger the GC at the next allocation request
or whenever the program enters the CLR (or returns from unmanaged), but in
your case (unless you run a server GC), the GC cannot run as it's main
thread blocked in unmanaged code (result of the ReadLine()), so the CLR
proceeds by starting the finalizer thread (running on it's own thread), this
is exactly what you noticed when running your code.

I didn't want to complicate things any further by introducing "external
triggers", so I didn't mention these, I didn't count on you to come back on
this, I should have known better ;-).

Willy.

"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...
| Willy Denoyette [MVP] <wi************ *@telenet.be> wrote:
|
| <snip>
|
| > 1. The only point in time a GC can occur is when objects are being
created
| > on the GC heap, when waiting on a ReadLine(), no more objects are
getting
| > instantiated, so, no GC can ever occur as long as you are waiting for a
| > keybord input.
|
| That's not quite true, IMO. I believe GC will kick in when there's
| memory pressure, too. Here are two programs which demonstrate it
| between them:
|
| Test.cs:
| using System;
|
| class Test
| {
| ~Test()
| {
| Console.WriteLi ne ("Finalizer" );
| }
|
| static void Main()
| {
| Test t = new Test();
| Console.WriteLi ne ("Created");
| Console.ReadLin e();
| }
| }
|
|
| UseMemory.cs:
| using System.Collecti ons;
|
| class UseMemory
| {
| static void Main()
| {
| ArrayList list = new ArrayList();
| while (true)
| {
| list.Add (new byte[10000]);
| }
| }
| }
|
| From one console, compile and run Test.cs. You'll see (or may see)
| "Created" on its own. You can then leave that console alone for a
| couple of minutes, and nothing is printed.
|
| Then compile and run UseMemory.cs. Shortly, you should see "Finalizer"
| being printed in the original console window - at least, that's what
| happens on my box.
|
| While this isn't absolute proof (due to finalizers and GC being
| different things) it's at least extremely suggestive.
|
| --
| Jon Skeet - <sk***@pobox.co m>
| http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
| If replying to the group, please do not mail me too
May 28 '06 #12
Thats all fine. But why do I ran out of virtual memory when I have an
endless loop?

....
while(true)
{
using(StreamWri ter newMasterfile =
new StreamWriter(@" c:\XXX.tmp"))
{
newMasterfile.C lose();
}
}
....

May 28 '06 #13
Martin <MA*****@gmx.ne t> wrote:
Thats all fine. But why do I ran out of virtual memory when I have an
endless loop?

...
while(true)
{
using(StreamWri ter newMasterfile =
new StreamWriter(@" c:\XXX.tmp"))
{
newMasterfile.C lose();
}
}


That I don't know - I can't reproduce it. How quickly do you leak
memory? Should I be able to easily see it in task manager?

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too
May 28 '06 #14
I think so.
About 10MB per minute.
Intel P4 mobile, 2 GHz.

May 28 '06 #15

"Martin" <MA*****@gmx.ne t> wrote in message
news:11******** **************@ y43g2000cwc.goo glegroups.com.. .
| Thats all fine. But why do I ran out of virtual memory when I have an
| endless loop?
|
| ...
| while(true)
| {
| using(StreamWri ter newMasterfile =
| new StreamWriter(@" c:\XXX.tmp"))
| {
| newMasterfile.C lose();
| }
| }
| ...
|

Don't know, it doesn't happen when I run your code, are you sure you are
running the exact same code as you posted?

Willy.

May 28 '06 #16
Why post you exact solution and we can check it out? The code posted at
present when brought here (with or without an app.config does not seem to
have any problems)

Cheers,

Greg Young
MVP - C#
"Martin" <MA*****@gmx.ne t> wrote in message
news:11******** **************@ y43g2000cwc.goo glegroups.com.. .
Thats all fine. But why do I ran out of virtual memory when I have an
endless loop?

...
while(true)
{
using(StreamWri ter newMasterfile =
new StreamWriter(@" c:\XXX.tmp"))
{
newMasterfile.C lose();
}
}
...

May 28 '06 #17
Please give me a place where I can upload a zip file with the solution.

May 28 '06 #18
There are lots of free services such as http://www.savefile.com/ which offer
this exact functionality.

Cheers,

Greg Young
"Martin" <MA*****@gmx.ne t> wrote in message
news:11******** **************@ i39g2000cwa.goo glegroups.com.. .
Please give me a place where I can upload a zip file with the solution.

May 28 '06 #19
Good morning and thank you Greg!

you'll find the files there:
http://savefile.com/projects/831693

There are 2 files:
- MemoryLeak1: File with the original problem as described
- MemoryLeak2: A threading test with free main thread

Just start the compiled release.
Is there anyone who can reproduce my problem?

Martin

May 29 '06 #20

This thread has been closed and replies have been disabled. Please start a new discussion.

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