SynchronizationContextAwaitTaskContinuation.cs

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using System.Diagnostics.Tracing;
using System.Runtime.CompilerServices;
 
namespace System.Threading.Tasks;
 
internal sealed class SynchronizationContextAwaitTaskContinuation : AwaitTaskContinuation
{
    private static readonly SendOrPostCallback s_postCallback = delegate(object state)
    {
        ((Action)state)();
    };
 
    private static ContextCallback s_postActionCallback;
 
    private readonly SynchronizationContext m_syncContext;
 
    internal SynchronizationContextAwaitTaskContinuation(SynchronizationContext context, Action action, bool flowExecutionContext)
        : base(action, flowExecutionContext)
    {
        m_syncContext = context;
    }
 
    internal sealed override void Run(Task task, bool canInlineContinuationTask)
    {
        if (canInlineContinuationTask && m_syncContext == SynchronizationContext.Current)
        {
            RunCallback(AwaitTaskContinuation.GetInvokeActionCallback(), m_action, ref Task.t_currentTask);
            return;
        }
        TplEventSource log = TplEventSource.Log;
        if (log.IsEnabled())
        {
            m_continuationId = Task.NewId();
            log.AwaitTaskContinuationScheduled((task.ExecutingTaskScheduler ?? TaskScheduler.Default).Id, task.Id, m_continuationId);
        }
        RunCallback(GetPostActionCallback(), this, ref Task.t_currentTask);
    }
 
    private static void PostAction(object state)
    {
        SynchronizationContextAwaitTaskContinuation synchronizationContextAwaitTaskContinuation = (SynchronizationContextAwaitTaskContinuation)state;
        TplEventSource log = TplEventSource.Log;
        if (log.IsEnabled() && log.TasksSetActivityIds && synchronizationContextAwaitTaskContinuation.m_continuationId != 0)
        {
            synchronizationContextAwaitTaskContinuation.m_syncContext.Post(s_postCallback, GetActionLogDelegate(synchronizationContextAwaitTaskContinuation.m_continuationId, synchronizationContextAwaitTaskContinuation.m_action));
        }
        else
        {
            synchronizationContextAwaitTaskContinuation.m_syncContext.Post(s_postCallback, synchronizationContextAwaitTaskContinuation.m_action);
        }
    }
 
    private static Action GetActionLogDelegate(int continuationId, Action action)
    {
        return delegate
        {
            Guid activityId = TplEventSource.CreateGuidForTaskID(continuationId);
            EventSource.SetCurrentThreadActivityId(activityId, out var oldActivityThatWillContinue);
            try
            {
                action();
            }
            finally
            {
                EventSource.SetCurrentThreadActivityId(oldActivityThatWillContinue);
            }
        };
    }
 
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static ContextCallback GetPostActionCallback()
    {
        return PostAction;
    }
}