UA-.NETStandard/Libraries/Opc.Ua.Client/Utils/AsyncManualResetEvent.cs

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// Copyright Stephen Cleary Nito.AsyncEx
// Original idea by Stephen Toub:
// http://blogs.msdn.com/b/pfxteam/archive/2012/02/11/10266920.aspx

using System.Threading;
using System.Threading.Tasks;

namespace Opc.Ua.Client
{
    /// <summary>
    /// An async-compatible manual-reset event.
    /// </summary>
    public sealed class AsyncManualResetEvent
    {
        /// <summary>
        /// Creates an async-compatible manual-reset event.
        /// </summary>
        /// <param name="set">Whether the manual-reset event is
        /// initially set or unset.</param>
        public AsyncManualResetEvent(bool set)
        {
            m_tcs = new TaskCompletionSource<object?>(
                 TaskCreationOptions.RunContinuationsAsynchronously);
            if (set)
            {
                m_tcs.TrySetResult(null);
            }
        }

        /// <summary>
        /// Creates an async-compatible manual-reset event
        /// that is initially unset.
        /// </summary>
        public AsyncManualResetEvent()
            : this(false)
        {
        }

        /// <summary>
        /// Whether this event is currently set. This member is seldom
        /// used; code using this member has a high possibility of race
        /// conditions.
        /// </summary>
        public bool IsSet
        {
            get
            {
                lock (m_lock)
                {
                    return m_tcs.Task.IsCompleted;
                }
            }
        }

        /// <summary>
        /// Asynchronously waits for this event to be set.
        /// </summary>
        public Task WaitAsync()
        {
            lock (m_lock)
            {
                return m_tcs.Task;
            }
        }

        /// <summary>
        /// Asynchronously waits for this event to be set or for the wait
        /// to be canceled.
        /// </summary>
        /// <param name="cancellationToken">The cancellation token used
        /// to cancel the wait. If this token is already canceled,
        /// this method will first check whether the event is set.</param>
        public Task WaitAsync(CancellationToken cancellationToken)
        {
            Task waitTask = WaitAsync();
            if (waitTask.IsCompleted)
            {
                return waitTask;
            }
            return waitTask.WaitAsync(cancellationToken);
        }

        /// <summary>
        /// Sets the event, atomically completing every task returned
        /// WaitAsync. If the event is already set, this method does
        /// nothing.
        /// </summary>
        public void Set()
        {
            lock (m_lock)
            {
                m_tcs.TrySetResult(null);
            }
        }

        /// <summary>
        /// Resets the event. If the event is already reset,
        /// this method does nothing.
        /// </summary>
        public void Reset()
        {
            lock (m_lock)
            {
                if (m_tcs.Task.IsCompleted)
                {
                    m_tcs = new TaskCompletionSource<object?>(
                        TaskCreationOptions.RunContinuationsAsynchronously);
                }
            }
        }

        private readonly Lock m_lock = new();
        private TaskCompletionSource<object?> m_tcs;
    }
}