atomicOp problem

[Heywood Floyd]

Interesting!
I get the same result, ie an infinite loop, with the CPU at 100%

Some things I noticed:
- Changing the for-loops to 100 or 10 doesn't help.
- Changing the atomicOp from "+=" to just "+" makes it work (although the account doesn't get changed)
- Adding a Thread.sleep(1000) in one of the for-loops, before the call to atomic-op, makes it all work with "+=" as well


By looking at the code in atomic.d it looks the "+="-operator ends up here:

            // L#131..:
            T get, set;            
            do
            {
                get = set = atomicLoad!(msync.raw)( val );
                mixin( "set " ~ op ~ " mod;" );
            } while( !cas( &val, get, set ) );
            return set;


And I suppose the cas()-function never returns true?

I don't know how atomic is supposed to work, so I'm not sure if it's a bug or not. I'm no expert with D, or threading for that matter, so I don't know.  (I'm just an expert guesser : ) 

I guess bug!


BR
/HF








Benjamin Thaut Wrote:

> I recently read the book "the D programming language" and wanted to try 
> out a few of the multithreaded examples pointed out in this book. I 
> tried to write a version of the bank account example using the atomicOp 
> from core.atomic. But when I compile it, it never finishes, it just gets 
> stuck in a endless loop inside atomic.d I think.
> Here is the code:
> 
> import std.stdio;
> import std.concurrency;
> 
> enum Messages {
> 	GO
> }
> 
> shared class Account {
> 	private float amount = 0;
> 		
> 	float getAmount() const {
> 		return amount;
> 	}
> 		
> 	void change(float change){
> 		atomicOp!"+="(amount,change);
> 	}
> }
> 
> shared Account bank = null;
> 	
> void otherThread(Tid father){
> 	send(father,Messages.GO);
> 	for(int i=0;i<1000;i++)
> 		bank.change(-100);
> }
> 
> void main(string[] args)
> {
> 	bank = new Account();
> 	spawn(&otherThread,thisTid);
> 	receiveOnly!(Messages)();
> 	for(int i=0;i<1000;i++)
> 		bank.change(+100);
> 	writefln("Program finished. Amount is %s",bank.getAmount());
> }
> 
> If you could please point out what I did wrong I would be very glad. If 
> I did not do anything wrong, I don't quite understand whats the exact 
> problem because the code inside atomic.d looks good (at least at my 
> level of understanding)
> 
> -- 
> Kind Regards
> Benjamin Thaut