Parallel array append using std.parallelism?

[H. S. Teoh]

I have an array of input data that I'm looping over, and, based on some
condition, generate new items that are appended onto a target array
(which may already contain data). Since the creation of new items is
quite expensive, I'm thinking to parallelize it with parallel foreach.

To avoid data races, my thought is for each generated item to be
appended to thread-specific temporary arrays, that after the parallel
foreach get sequentially appended to the target array. Something like
this:

	Item[] targetArray = ...; // already contains data
	Item[][nThreads] tmp;
	foreach (elem; input.parallel) {
		if (condition(elem)) {
			auto output = expensiveComputation(elem);
			tmp[threadId] ~= output;
		}
	}
	foreach (a; tmp)
		targetArray ~= a;

Is there an easy way to achieve this with std.parallelism?  I looked
over the API but there doesn't seem to be any obvious way for a task to
know which thread it's running in, in order to know which tmp array it
should append to.  If possible I'd like to avoid having to manually
assign tasks to threads.


T

-- 
Questions are the beginning of intelligence, but the fear of God is the beginning of wisdom.