• Jack Applegame (18/18) Mar 14 2013 What does mean attribute shared exactly for non global variables?
• John Colvin (11/29) Mar 14 2013 Without knowing what threads are running and which have access to
• Jack Applegame (1/1) Mar 14 2013 Thanks. I's much more clear now.

"Jack Applegame" <japplegame gmail.com> writes:

What does mean attribute shared exactly for non global variables? 
Is it safe to cast to/from shared?

For example, let us assume all data are synchronized properly. Is 
following code safe?

import core.atomic;

class A {
   int value;
}

struct B {
   A node;
}

void main() {
   shared B data;
   A node = new A;
   atomicStore(data, shared B(cast(shared) node));
   ...
   node = atomicLoad(data).node;
}

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 14 March 2013 at 10:39:11 UTC, Jack Applegame wrote:
 What does mean attribute shared exactly for non global 
 variables? Is it safe to cast to/from shared?

 For example, let us assume all data are synchronized properly. 
 Is following code safe?

 import core.atomic;

 class A {
   int value;
 }

 struct B {
   A node;
 }

 void main() {
   shared B data;
   A node = new A;
   atomicStore(data, shared B(cast(shared) node));
   ...
   node = atomicLoad(data).node;
 }

Without knowing what threads are running and which have access to 
which variables, it's hard to say much.

The store is safe as long as no one touches "node" during the 
construction of the temporary "shared B".

The load of "data" is safe, but the access of "node" is only safe 
if you can guarantee that no-one else can touch it during the 
read.


Shared is (in it's current form) a compiler enforced annotation 
and not much more. It is merely a way of saying "This data may be 
accessed from other threads, be careful".

"Jack Applegame" <japplegame gmail.com> writes:

Thanks. I's much more clear now.