Umbraco-CMS/src/Umbraco.Core/WaitHandleExtensions.cs

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

namespace Umbraco.Core
{
    internal static class WaitHandleExtensions
    {

        // http://stackoverflow.com/questions/25382583/waiting-on-a-named-semaphore-with-waitone100-vs-waitone0-task-delay100
        // http://blog.nerdbank.net/2011/07/c-await-for-waithandle.html
        // F# has a AwaitWaitHandle method that accepts a time out... and seems pretty complex...
        // version below should be OK

        public static Task WaitOneAsync(this WaitHandle handle, int millisecondsTimeout = Timeout.Infinite)
        {
            var tcs = new TaskCompletionSource<object>();
            var callbackHandleInitLock = new object();
            lock (callbackHandleInitLock)
            {
                RegisteredWaitHandle callbackHandle = null;
                // ReSharper disable once RedundantAssignment
                callbackHandle = ThreadPool.RegisterWaitForSingleObject(
                    handle,
                    (state, timedOut) =>
                    {
                        tcs.SetResult(null);

                        // we take a lock here to make sure the outer method has completed setting the local variable callbackHandle.
                        lock (callbackHandleInitLock)
                        {
                            // ReSharper disable once PossibleNullReferenceException
                            // ReSharper disable once AccessToModifiedClosure
                            callbackHandle.Unregister(null);
                        }
                    },
                    /*state:*/ null,
                    /*millisecondsTimeOutInterval:*/ millisecondsTimeout,
                    /*executeOnlyOnce:*/ true);
            }

            return tcs.Task;
        }
    }
}