ThreadPoolTaskScheduler.cs

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using System.Collections.Generic;
 
namespace System.Threading.Tasks;
 
internal sealed class ThreadPoolTaskScheduler : TaskScheduler
{
    private static readonly ParameterizedThreadStart s_longRunningThreadWork = delegate(object s)
    {
        ((Task)s).ExecuteEntryUnsafe(null);
    };
 
    internal ThreadPoolTaskScheduler()
    {
        _ = base.Id;
    }
 
    protected internal override void QueueTask(Task task)
    {
        TaskCreationOptions options = task.Options;
        _ = Thread.IsThreadStartSupported;
        if ((options & TaskCreationOptions.LongRunning) != 0)
        {
            Thread thread = new Thread(s_longRunningThreadWork);
            thread.IsBackground = true;
            thread.Name = ".NET Long Running Task";
            thread.UnsafeStart(task);
        }
        else
        {
            ThreadPool.UnsafeQueueUserWorkItemInternal(task, (options & TaskCreationOptions.PreferFairness) == 0);
        }
    }
 
    protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
    {
        if (taskWasPreviouslyQueued && !ThreadPool.TryPopCustomWorkItem(task))
        {
            return false;
        }
        try
        {
            task.ExecuteEntryUnsafe(null);
        }
        finally
        {
            if (taskWasPreviouslyQueued)
            {
                NotifyWorkItemProgress();
            }
        }
        return true;
    }
 
    protected internal override bool TryDequeue(Task task)
    {
        return ThreadPool.TryPopCustomWorkItem(task);
    }
 
    protected override IEnumerable<Task> GetScheduledTasks()
    {
        return FilterTasksFromWorkItems(ThreadPool.GetQueuedWorkItems());
    }
 
    private static IEnumerable<Task> FilterTasksFromWorkItems(IEnumerable<object> tpwItems)
    {
        foreach (object tpwItem in tpwItems)
        {
            if (tpwItem is Task task)
            {
                yield return task;
            }
        }
    }
 
    internal override void NotifyWorkItemProgress()
    {
        ThreadPool.NotifyWorkItemProgress();
    }
}