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Yes, assigning a reference is an atomic operation.
ECMA-334 C# Language Specification:
"12.5 Atomicity of variable references
Reads and writes of the following data types shall be atomic: bool, char, byte, sbyte, short, ushort, uint, int, float, and reference types. In addition, reads and writes of enum types with an underlying type in the previous list shall also be atomic. Reads and writes of other types, including long, ulong, double, and decimal, as well as user-defined types, need not be atomic. Aside from the library functions designed for that purpose, there is no guarantee of atomic read-modify-write, such as in the case of increment or decrement."
Despite everything, the person most likely to be fooling you next is yourself.
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Great Guffa!
Question answered.
regards,
George
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Guffa wrote: Yes, assigning a reference is an atomic operation.
DANGER WILL ROBINSON! DANGER WILL ROBINSON!
An assignment of a reference type consists of an atomic read followed by an atomic write. The assignment as a whole is not atomic.
Assume var2 starts == 1.
Thread 1:
var1 = var2;
Thread2:
var2 = 2;
var1 = 3; If assignments were atomic, var1 might end up equal to 2 or 3, but it could not possibly end up equal to anything else (such as 1). Since they are not atomic, however, thead 1 decomposes as "temp = var2; var1 = temp;". The operations could thus be sequenced as "temp = var2 [1]; var2 = 2; var1 = 3; var1 = temp [1];"
It would be possible to write a generic class to support true atomic assignments. Given the existence of Interlocked.CompareExchange it could even be done without locks or spin-waits(*) in such a way that the total time required for any number of operations would be bounded (the time required for any particular operation would only be bounded if the number of other operations was limited).
(*) A thread may have to retry an operation up to 'n' times if other threads perform 'n' operations during its execution; it is never necessary, however, for a thread to wait for another thread to do something.
I don't know if there are any nice algorithms to synthesize atomic assignment given atomic compare-and-exchange. The best lock-free approach I can come up with is pretty nasty, but it would work.
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supercat9 wrote: An assignment of a reference type consists of an atomic read followed by an atomic write.
No, it doesn't. An assignment is only a write operation.
What you are talking about is a complete statement, which in this case is the evaluation of an expression and the assignment of the result. The complete statement is of course not an atomic operation.
Despite everything, the person most likely to be fooling you next is yourself.
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Guffa wrote: No, it doesn't. An assignment is only a write operation.
The original question was Is foo1 = foo2 atomic?. You answered in the affirmative, without giving any indication that "foo1 = foo2" represents two operations.
Guffa wrote: The complete statement is of course not an atomic operation.
Whether the complete statement is atomic or not depends on the implementation. Some microprocessors and microcontrollers do allow atomic memory-to-memory moves, at least in non-paged implementations (the 68020-68040 even allow it in paged implementations, though I doubt any compiler would use the CAS2 instruction for a normal assignment). Your statement could reasonably have been taken to suggest that the processors that run Windows will perform a statement like "foo1 = foo2" atomically. I think it's very important to point out clearly and unambiguously that they will not.
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As an addition to what Guffa said if you take for example:
Foo foo = new Foo();
you should know that first the right side of the assignment is evaluated. So that first the Foo object is constructed entirely and then assigned to foo. So this is also an atomic operation.
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Great Zoltan!
Question answered.
regards,
George
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I have two threads, one UI thread and one Background thread..
I want to keep a track of the background thread so that I may kill my UI thread (a tray icon) when the background thread has finished...
Please keep in mind mine is a console application.
Please review my code for more details..
class Program
{
static void Main(string[] args)
{
Thread[] threads = new Thread[2];
threads[0] = new Thread(new ThreadStart(UIMethod));
threads[1] = new Thread(new ThreadStart(BackGroundMethod));
threads[0].SetApartmentState(ApartmentState.STA);
threads[0].Start();
threads[1].Start();
}
public static void UIMethod()
{
Tray obj = new Tray();
obj.GenerateTrayIcon();
Application.Run();
}
public static void BackGroundMethod()
{
}
}
Any suggestions with some code would be highly appreciated..
Thanks.
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Either call Join() on the threads, or use signalling with WaitHandles.
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I dont know about them..
Could you post some sample code with respect to the code in my original code?
Thanks.
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Ok
Thread[] threads = new Thread[2];
threads[0] = new Thread(new ThreadStart(UIMethod));
threads[1] = new Thread(new ThreadStart(BackGroundMethod));
threads[0].SetApartmentState(ApartmentState.STA);
threads[0].Start();
threads[1].Start();
threads[1].Join();
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But this dosent server the purpose..
The UI thread still is waiting for user response although the background thread has finished.
I want to kill the UI thread when the background thread has finished executing..
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When you call Join() on the thread which executes background method, the current thread will be blocked until background method finishes executing. Just down to the Join() call, you can write code to kill the other one or kills the icon.
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If your goal is to have the user-interface thread run normally until the background thread dies, I would suggest having a 'quitNow' variable which is set by the background thread and polled in the main thread. The simplest approach to accomplishing that would be to have a timer that checks the 'quitNow' variable every 100ms or so. If you want to avoid the CPU overhead of doing that, you might be able to have the the timer disabled until the background thread enables it to signal its completion. I'm not sure if timer.enabled can be accessed between threads, though. If it can't, you may have to do something like:
Sub EnableKillMeTimer
If InvokeRequired then
BeginInvoke(New MethodInvoker(AddressOf EnableKillMeTimer))
Else
tmrKillMe.Enabled = True
Endif
End SubWhile an approach like the above could probably be used to have the main form execute me.close, using a timer could make things a little nicer in case the main form doesn't want to close quite instantly.
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Hey,
I have a Word 2003 Plug-in written in VS 2008.
In the plug-in startup method I create a button (or find it if it's already made) and assign an eventhandler to it:
m_SaveButton.Click += new Microsoft.Office.Core._CommandBarButtonEvents_ClickEventHandler(SaveDoc_Click);
m_SaveButton is a global variable (Office.CommandBarButton m_SaveButton;)
Everything works fine until I have opened a document, then the eventhandlers for my button is not called anymore. 
Any idea what's going on?
- Anders
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Suppose we got the following code snippet:
var a = new {i=1, j=2};
How to assign a value for the specific field of that variable? I mean, something like this:
a.i = 5;
thanks for help
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Yoyosch wrote: How to assign a value for the specific field of that variable?
You can't.
When you create an anonymous type the following code is generated:
private static void Main(string[] args)
{
var a;
a = new <>f__AnonymousType0<int, int>(1, 2);
return;
}
The special class <>f_AnonymousType0 looks like this:
[CompilerGenerated, DebuggerDisplay(@"\{ i = {i}, j = {j} }", Type="<Anonymous Type>")]
internal sealed class <>f__AnonymousType0<<i>j__TPar, <j>j__TPar>
{
[DebuggerBrowsable(0)]
private readonly <i>j__TPar <i>i__Field;
[DebuggerBrowsable(0)]
private readonly <j>j__TPar <j>i__Field;
[DebuggerHidden]
public <>f__AnonymousType0(<i>j__TPar i, <j>j__TPar j);
[DebuggerHidden]
public override bool Equals(object value);
[DebuggerHidden]
public override int GetHashCode();
[DebuggerHidden]
public override string ToString();
public <i>j__TPar i { get; }
public <j>j__TPar j { get; }
}
As you can see, there are no setters on any of those properties.
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Hello
i have used AxSHDocVw.AxWebBrowser in my application. i want to block popup windows for my code. How do i go about it.
i tried doing
private void axWebBrowser1_NewWindow2(object sender, AxSHDocVw.DWebBrowserEvents2_NewWindow2Event e)
{
e.ppDisp = null;
e.cancel = true;
}
But this is not helping
Can i get help over it?
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have you tried catching the NewWindow3 event?
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newWindow3 is used for Xp?
can i used in my code?
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static ISettings settings = null;
public static Categories Current
{
get
{
if (_categories == null)
{
LoadCategories();
}
return _categories;
}
}
private static void LoadCategories()
{
using (FileStream stream= settings.GetCategoryFileStream())
{
.....
}
}I am trying to test the Current property. It is calling LoadCategories method and this method is using an external file. So I am trying to mock the external file call. For doing this, I need to supply ISettings instance explicitly. How do I supply it in this scenario ?
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Your formatting is off - could you fix it so that I can see the rest of your message please?
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Pete O'Hanlon wrote: Your formatting is off
I can see that correctly. I have not pasted the entire code. Do you mean that ?
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