C# volatile field

[Water Cooler v2]

In this example, what would have happened, had the field "result" not
been declared "volatile"?

http://msdn.microsoft.com/library/de...pec_10_4_3.asp
The last few lines on the page tell us that but I do not understand.
Can someone please explain clearly?

[Jon Skeet [C# MVP]]

Water Cooler v2 <wt*****@yahoo.com> wrote:

In this example, what would have happened, had the field "result" not
been declared "volatile"?

http://msdn.microsoft.com/library/de...library/en-us/
csspec/html/vclrfcsharpspec_10_4_3.asp
The last few lines on the page tell us that but I do not understand.
Can someone please explain clearly?

See http://www.pobox.com/~skeet/csharp/t...latility.shtml

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[rossum]

On 3 Sep 2005 22:18:37 -0700, "Water Cooler v2" <wt*****@yahoo.com>
wrote:

In this example, what would have happened, had the field "result" not
been declared "volatile"?

http://msdn.microsoft.com/library/de...pec_10_4_3.asp
The last few lines on the page tell us that but I do not understand.
Can someone please explain clearly?

The example has two threads, Main and Thread2. Look at part of the
code in Main on its own:

finished = false;

for (;;) {
if (finished) {
Console.WriteLine("result = {0}", result);
return;
}
}

An optimising compiler might realise that the variable "finished" is
not changed and could be replaced by a literal:

for (;;) {
if (false) {
Console.WriteLine("result = {0}", result);
return;
}
}

If the code looked like this then it would never terminate as it could
be further optimised to:

for (;;) {
}
By declaring the variable "finished" as "volatile" you give notice to
the compiler that the variable "finished" might be changed at any time
by another thread, in this case Thread2. This means that the compiler
will not optimise away the variable, or do any other optimisations
that might prevent the code from working.

HTH

rossum
The ultimate truth is that there is no ultimate truth