Simplest multithreading example

[Ali Çehreli via Digitalmars-d-learn]

On 08/31/2017 06:59 PM, Brian wrote:
 > Hello, I am trying to get the most trivial example of multithreading
 > working, but can't seem to figure it out.
 > I want to split a task across threads, and wait for all those tasks to
 > finish before moving to the next line of code.
 >
 > The following 2 attempts have failed :
 >
 > -----------------------------------------------------
 > Trial 1 :
 > -----------------------------------------------------
 >
 > auto I = std.range.iota(0,500);
 > int [] X; // output
 > foreach (i; parallel(I) )
 >     X ~= i;
 > core.thread.thread_joinAll(); // Apparently no applicable here ?

As Michael Coulombe said, parallel() does that implicitly.

If the problem is to generate numbers in parallel, I restructured the 
code by letting each thread touch only its element of a results array 
that has already been resized for all the results (so that there is no 
race condition):

import std.stdio;
import std.parallelism;
import std.range;

void main() {
     auto arrs = new int[][](totalCPUs);
     const perWorker = 10;
     foreach (i, arr; parallel(arrs)) {
         const beg = cast(int)i * perWorker;
         const end = beg + perWorker;
         arrs[i] = std.range.iota(beg,end).array;
     }

     writeln(arrs);
}

If needed, std.algorithm.joiner can be used to make it a single sequence 
of ints:

     import std.algorithm;
     writeln(arrs.joiner);

Ali