How can I merge two Linq IEnumerable<T> queries without running them?
- by makerofthings7
How do I merge a List<T> of TPL-based tasks for later execution?
public async IEnumerable<Task<string>> CreateTasks(){ /* stuff*/ }
My assumption is .Concat() but that doesn't seem to work:
void MainTestApp() // Full sample available upon request.
{
List<string> nothingList = new List<string>();
nothingList.Add("whatever");
cts = new CancellationTokenSource();
delayedExecution =
from str in nothingList
select AccessTheWebAsync("", cts.Token);
delayedExecution2 =
from str in nothingList
select AccessTheWebAsync("1", cts.Token);
delayedExecution = delayedExecution.Concat(delayedExecution2);
}
/// SNIP
async Task AccessTheWebAsync(string nothing, CancellationToken ct)
{
// return a Task
}
I want to make sure that this won't spawn any task or evaluate anything. In fact, I suppose I'm asking "what logically executes an IQueryable to something that returns data"?
Background
Since I'm doing recursion and I don't want to execute this until the correct time, what is the correct way to merge the results if called multiple times?
If it matters I'm thinking of running this command to launch all the tasks var AllRunningDataTasks = results.ToList(); followed by this code:
while (AllRunningDataTasks.Count > 0)
{
// Identify the first task that completes.
Task<TableResult> firstFinishedTask = await Task.WhenAny(AllRunningDataTasks);
// ***Remove the selected task from the list so that you don't
// process it more than once.
AllRunningDataTasks.Remove(firstFinishedTask);
// TODO: Await the completed task.
var taskOfTableResult = await firstFinishedTask;
// Todo: (doen't work)
TrustState thisState = (TrustState)firstFinishedTask.AsyncState;
// TODO: Update the concurrent dictionary with data
// thisState.QueryStartPoint + thisState.ThingToSearchFor
Interlocked.Decrement(ref thisState.RunningDirectQueries);
Interlocked.Increment(ref thisState.CompletedDirectQueries);
if (thisState.RunningDirectQueries == 0)
{
thisState.TimeCompleted = DateTime.UtcNow;
}
}
