Re: how to stop a variable from being optimized out

[Rory via Digitalmars-d-learn]

On Tuesday, 24 February 2015 at 06:48:26 UTC, ketmar wrote:
but why do you need this? just use `atomicLoad` to get shared 
variable

value, it will do the right caching.


Nice! Thanks. Tested atomicLoad and it is slightly faster for my 
non blocking queue.

Re: how to stop a variable from being optimized out

[ketmar via Digitalmars-d-learn]

On Tue, 24 Feb 2015 12:50:53 +, Rory wrote:

 On Tuesday, 24 February 2015 at 06:48:26 UTC, ketmar wrote:
 but why do you need this? just use `atomicLoad` to get shared variable
 value, it will do the right caching.
 
 Nice! Thanks. Tested atomicLoad and it is slightly faster for my non
 blocking queue.

just in case: by do the right caching i meant that this is memory 
barrier, so compiler will not optimise your `current` away. i.e. the only 
thing you have to change is this line:

  volatile auto current = payload; // payload is a shared variable

to:

  auto current = atomicLoad(payload);

i reread my answer and found that it may be not so obvious.

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Re: how to stop a variable from being optimized out

[ketmar via Digitalmars-d-learn]

On Tue, 24 Feb 2015 06:29:33 +, Rory wrote:

 Is there a way I can stop current from being optimized out without
 using volatile?

but why do you need this? just use `atomicLoad` to get shared variable 
value, it will do the right caching.

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how to stop a variable from being optimized out

[Rory via Digitalmars-d-learn]

Hi,


Is there a way I can stop current from being optimized out 
without using volatile?
The compiler is suggesting I replace volatile with 
synchronized but I don't want it synchronized?

Would a memory barrier work?

shared n = new int(value);
for (;;) {
  volatile auto current = payload; // payload is a shared variable
  if (current == payload) { // just to make sure we copied a 
complete value from

if (current is null) {
  if (cas(payload, current, n)) {
return true;
  }
}
  }
}


Thanks!
-Rory