TaskPool.workerIndex

// Execute a loop that computes the greatest common
// divisor of every number from 0 through 999 with
// 42 in parallel.  Write the results out to
// a set of files, one for each thread.  This allows
// results to be written out without any synchronization.

import std.conv, std.range, std.numeric, std.stdio;

void main()
{
    auto filesHandles = new File[taskPool.size + 1];
    scope(exit) {
        foreach (ref handle; fileHandles)
        {
            handle.close();
        }
    }

    foreach (i, ref handle; fileHandles)
    {
        handle = File("workerResults" ~ to!string(i) ~ ".txt");
    }

    foreach (num; parallel(iota(1_000)))
    {
        auto outHandle = fileHandles[taskPool.workerIndex];
        outHandle.writeln(num, '\t', gcd(num, 42));
    }
}