Question

I have a for loop that spawns threads… I want it to spawn 5 threads then wait until it drops down to 4 then spawn another one.

Basically, if I have 100 records, I want to to process 5 at a time. Which is the preferred approach?

Answer 1

The preferred approach would probably be to just use one of the built-in mechanisms for this.

For example, Parallel.ForEach has the option of specifying the MaxDegreeOfParallelism to use, which corresponds to the maximum number of threads used.

This would let you just write something like:

var options = new ParallelOptions { MaxDegreeOfParallelism = 5 };
Parallel.ForEach(records, options, rec =>
{
    ProcessRecord(rec);
});

If you’re “record processing” is a mapping or query operation, another good option is to use PLINQ’s WithDegreeOfParallelism to limit the parallelism:

var results = records.AsParallel().WithDegreeOfParallelism(5).Select(r => ProcessRecord(rec)).Where(result => result.Foo); // Some query...

I would choose the first option if you’re just “processing” each record (ie: ProcessRecord is a void method), and the second if you’re doing some type of mapping operation or query over the records, and returning results from the record processing.