Hi,
the following .NET 1.1 C#-program does not terminate (opposed to what I
would expect):
--------
using System;
using System.Threadin g;
public class Test {
static int i = 0;
public static void Main(string [] args) {
new Thread(new ThreadStart(t1) ).Start();
new Thread(new ThreadStart(t2) ).Start();
}
static void t1() {
int j = 0;
while(i == 0) {
j++;
}
}
static void t2() {
i = 1;
}
}
--------
A slight variation of the above program makes the strange behavior more
explicit:
--------
using System;
using System.Threadin g;
public class Test {
static int i1 = 0;
static int i2 = 0;
public static void Main(string [] args) {
new Thread(new ThreadStart(t1) ).Start();
new Thread(new ThreadStart(t2) ).Start();
}
static void t1() {
int j = 0;
i1 = 1;
while(i2 == 0) {
j++;
if(j + 1 < j) break;
}
Console.WriteLi ne(j);
}
static void t2() {
i2 = 1;
Console.WriteLi ne("t2: i1={0}, i2={0}", i1, i2);
}
}
--------
Output:
--------
t2: i1=1, i2=1
2147483647
--------
That means thread t2 sets the static variable i2=1, but thread t1 seems
to be unaware of this change of i2.
Can anyone reproduce this behavior in his environment with the above
programs (don't change a single line, because even slight variations
result in a different behavior)?
And what I'm interested more: Can anyone explain why these programs
behave in this way? Is this a bug in .NET/C#?
6  2515 
<kr*****@gmx.ne t> wrote: the following .NET 1.1 C#-program does not terminate (opposed to what I
would expect):
<snip>
That means thread t2 sets the static variable i2=1, but thread t1 seems
to be unaware of this change of i2.
Yup.
Can anyone reproduce this behavior in his environment with the above
programs (don't change a single line, because even slight variations
result in a different behavior)?
It doesn't happen on my box, but that's a single processor box - are
you by any chance running it on a multi-processor box?
And what I'm interested more: Can anyone explain why these programs
behave in this way? Is this a bug in .NET/C#?
No, it's not a bug in .NET. It's the way the .NET memory model works.
See http://www.pobox.com/~skeet/csharp/t...latility.shtml
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Inline
Willy.
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com... <kr*****@gmx.ne t> wrote: the following .NET 1.1 C#-program does not terminate (opposed to what I
would expect):
<snip>
That means thread t2 sets the static variable i2=1, but thread t1 seems
to be unaware of this change of i2.
Yup.
Can anyone reproduce this behavior in his environment with the above
programs (don't change a single line, because even slight variations
result in a different behavior)?
It doesn't happen on my box, but that's a single processor box - are
you by any chance running it on a multi-processor box?
The first sample won't terminate even on a single CPU when compiled with
full JIT optimization turned on (/o+ ), the static variable is register
allocated as opposed to heap allocated when not optimized (the default). And what I'm interested more: Can anyone explain why these programs
behave in this way? Is this a bug in .NET/C#?
No, it's not a bug in .NET. It's the way the .NET memory model works.
See http://www.pobox.com/~skeet/csharp/t...latility.shtml
--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Hi,
Jon wrote: It doesn't happen on my box, but that's a single processor box - are
you by any chance running it on a multi-processor box?
One Pentium-4 with hyperthreading turned off.
No, it's not a bug in .NET. It's the way the .NET memory model works.
See http://www.pobox.com/~skeet/csharp/t...latility.shtml
Thanks a lot for that URL. Declaring i and i2 as "volatile" helped!
Willy Denoyette [MVP] wrote: The first sample won't terminate even on a single CPU when compiled with
full JIT optimization turned on (/o+ ), the static variable is register
allocated as opposed to heap allocated when not optimized (the default).
"/o+" or "/o-" made no difference on my computer (first sample didn't
terminate in both cases).
<kr*****@gmx.ne t> wrote in message
news:11******** **************@ g43g2000cwa.goo glegroups.com.. . Hi,
Jon wrote: It doesn't happen on my box, but that's a single processor box - are
you by any chance running it on a multi-processor box?
One Pentium-4 with hyperthreading turned off.
No, it's not a bug in .NET. It's the way the .NET memory model works.
See http://www.pobox.com/~skeet/csharp/t...latility.shtml
Thanks a lot for that URL. Declaring i and i2 as "volatile" helped!
Willy Denoyette [MVP] wrote: The first sample won't terminate even on a single CPU when compiled with
full JIT optimization turned on (/o+ ), the static variable is register
allocated as opposed to heap allocated when not optimized (the default).
"/o+" or "/o-" made no difference on my computer (first sample didn't
terminate in both cases).
Try with /debug option on v1.1.4322, it should terminate. In this release
/o- is the default, and I guess it does register allocation per default
unless you have /debug specified.
Willy.
Willy Denoyette [MVP] <wi************ *@telenet.be> wrote: It doesn't happen on my box, but that's a single processor box - are
you by any chance running it on a multi-processor box?
The first sample won't terminate even on a single CPU when compiled with
full JIT optimization turned on (/o+ ), the static variable is register
allocated as opposed to heap allocated when not optimized (the default).
Ooh, indeed. That's great - a real sample I could include in my page,
which positively shows the dangers!
Cheers.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com... Willy Denoyette [MVP] <wi************ *@telenet.be> wrote: > It doesn't happen on my box, but that's a single processor box - are
> you by any chance running it on a multi-processor box?
The first sample won't terminate even on a single CPU when compiled with
full JIT optimization turned on (/o+ ), the static variable is register
allocated as opposed to heap allocated when not optimized (the default).
Ooh, indeed. That's great - a real sample I could include in my page,
which positively shows the dangers!
Sure it is, note that I'm experimenting a bit with these settings, and there
seem to be a minor difference between v1.1 and v2 (the beta). In v2.0 /o- ,
keeps the static heap allocated, while /o+ does register allocation (in this
particular sample!). In V1.1 /o+ or /o- both use a register for the
variable. Moreover, that I notice this behavior is processor type dependent,
that is AMD Athlon64 and Intel P4 behave differently.
You see reasons enough to lock your shared state.
Cheers.
--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
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