Using Parallel.ForEachAsync

December 6, 2021

I’m trying to run a Parallel.ForEachAsync() but I am getting these two errors

Error 1:
Argument 2: can not convert from System.Threading.Tasks.ParallelOptions to System.Threading.CancellationToken

Error 2:
Delegate Func<WC, CancellationToken, ValueTask> does not take 1 argument

and this is my code

Public async Task<List<DisplayDto>> GetData()
{
Var options = new ParallelOptions()
{
  MaxDegreeOfParallelism = 20;
};

  await Parallel.ForEachAsync(result, options, async OrderNumber => {
      //Do Stuff here. 
  });
}

what must be altered in order for this to work as I want?

>Solution :

Parallel.ForEachAsync expects Func<TSource,CancellationToken,ValueTask>
i.e. accepting 2 parameters (first one being an element of collection and second one – CancellationToken), not one. Usage can look like that:

public async Task<List<DisplayDto>> GetData()
{
    var options = new ParallelOptions()
    {
        MaxDegreeOfParallelism = 20
    };

    await Parallel.ForEachAsync(result, options, async (OrderNumber, ct) => {
        // do not forget to use CancellationToken (ct) where appropriate 
        // Do Stuff here. 
    });
 }

Example.