Parallel LINQ (PLINQ)

2022-02-20

0. What is PLINQ?

a parallel version of LINQ
whether it’s going to be parallel will be determined by the PLINQ’s internal analysis on the query
- therefore, performance gain is not guaranteed
you can force parallelism but it’s not recommended
using PLINQ has overhead, so don’t overuse it
make sure to use lock properly along with PLINQ

1. Example

AsParallel (use PLINQ)
AsSequential (not using parallel)
AsOrdered (maintain order)
ForAll (parallel iteration)

void Main()
{
	var stopwatch = new Stopwatch();
	stopwatch.Start();

	var result = Enumerable.Range(0,100)
					.AsParallel() // use PLINQ
					.Select(Compute)
					.Sum();
					
	Console.WriteLine(result);
	
	"------------------------".Dump();

	var result2 = Enumerable.Range(0, 100)
				.AsParallel() // use PLINQ
				.Select(Compute)
				.Take(10);

	foreach (var r in result2)
	{
		Console.WriteLine(r); // not ordered
	}
	
	"------------------------".Dump();

	var result3 = Enumerable.Range(0, 100)
			.AsParallel() // use PLINQ
			.AsOrdered() // ordered (will add overhead)
			.Select(Compute)
			.Take(10);

	foreach (var r in result3)
	{
		Console.WriteLine(r); // ordered
	}

    "------------------------".Dump();

    result3.ForAll(Console.WriteLine); // parallel

	Console.WriteLine($"It took: {stopwatch.ElapsedMilliseconds}ms to run");
}

static Random random = new Random();
static int Compute(int value)
{
	var randomMilliseconds = random.Next(10, 50);
	var end = DateTime.Now + TimeSpan.FromMilliseconds(randomMilliseconds);

	while (DateTime.Now < end) { }

	return value + 100;
}