AsyncOperation.cs

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using System.Threading;
 
namespace System.ComponentModel;
 
public sealed class AsyncOperation
{
    private readonly SynchronizationContext _syncContext;
 
    private bool _alreadyCompleted;
 
    public object? UserSuppliedState { get; }
 
    public SynchronizationContext SynchronizationContext => _syncContext;
 
    private AsyncOperation(object userSuppliedState, SynchronizationContext syncContext)
    {
        UserSuppliedState = userSuppliedState;
        _syncContext = syncContext;
        _alreadyCompleted = false;
        _syncContext.OperationStarted();
    }
 
    ~AsyncOperation()
    {
        if (!_alreadyCompleted && _syncContext != null)
        {
            _syncContext.OperationCompleted();
        }
    }
 
    public void Post(SendOrPostCallback d, object? arg)
    {
        PostCore(d, arg, markCompleted: false);
    }
 
    public void PostOperationCompleted(SendOrPostCallback d, object? arg)
    {
        PostCore(d, arg, markCompleted: true);
        OperationCompletedCore();
    }
 
    public void OperationCompleted()
    {
        VerifyNotCompleted();
        _alreadyCompleted = true;
        OperationCompletedCore();
    }
 
    private void PostCore(SendOrPostCallback d, object arg, bool markCompleted)
    {
        VerifyNotCompleted();
        VerifyDelegateNotNull(d);
        if (markCompleted)
        {
            _alreadyCompleted = true;
        }
        _syncContext.Post(d, arg);
    }
 
    private void OperationCompletedCore()
    {
        try
        {
            _syncContext.OperationCompleted();
        }
        finally
        {
            GC.SuppressFinalize(this);
        }
    }
 
    private void VerifyNotCompleted()
    {
        if (_alreadyCompleted)
        {
            throw new InvalidOperationException(System.SR.Async_OperationAlreadyCompleted);
        }
    }
 
    private void VerifyDelegateNotNull(SendOrPostCallback d)
    {
        if (d == null)
        {
            throw new ArgumentNullException("d", System.SR.Async_NullDelegate);
        }
    }
 
    internal static AsyncOperation CreateOperation(object userSuppliedState, SynchronizationContext syncContext)
    {
        return new AsyncOperation(userSuppliedState, syncContext);
    }
}