Variable modified by different threads.

[Andy Valencia]

On Monday, 2 December 2024 at 02:02:56 UTC, Ritina wrote:
> How can I implement a program where I have a global integer 
> variable g, and three threads: the first thread increments g by 
> 1, the second thread increments g by 2, and the third thread 
> increments g by 3? Additionally, while these threads are 
> running, I should be able to access the value of g both inside 
> and outside the threads.

Here's my own shared memory across multiple threads sample 
program,  It does a fine job of thrashing that cache line!

```
import core.atomic : atomicFetchAdd;
import std.concurrency : spawn;
import core.time : msecs;
import core.thread : Thread;
import core.memory : GC;

const uint NSWEPT = 100_000_000;
const uint NCPU = 4;

void
doadd(shared uint *buf)
{
     for (uint count = 0; count < NSWEPT/NCPU; ++count) {
         atomicFetchAdd(buf[0], 1);
     }
}

void
main()
{
     shared uint *buf =
         cast(shared uint *)GC.calloc(uint.sizeof * 1, 
GC.BlkAttr.NO_SCAN);

     for (uint x = 0; x < NCPU-1; ++x) {
         spawn(&doadd, buf);
     }
     doadd(buf);
     while (buf[0] != NSWEPT) {
         Thread.sleep(1.msecs);
     }
}
```