Fixed writing pages in the same thread that does EnqueuePage

LiteDB/Engine/Disk/DiskWriterQueue.cs

@@ -8,6 +8,8 @@
 
 namespace LiteDB.Engine
 {
+    using LiteDB.Utils.Extensions;
+
     /// <summary>
     /// Implement disk write queue and async writer thread - used only for write on LOG file
     /// [ThreadSafe]
@@ -23,7 +25,7 @@ internal class DiskWriterQueue : IDisposable
 
         private readonly ConcurrentQueue<PageBuffer> _queue = new ConcurrentQueue<PageBuffer>();
         private readonly object _queueSync = new object();
-        private readonly AsyncManualResetEvent _queueHasItems = new AsyncManualResetEvent();
+        private readonly ManualResetEventSlim _queueHasItems = new ManualResetEventSlim();
         private readonly ManualResetEventSlim _queueIsEmpty = new ManualResetEventSlim(true);
 
         private Exception _exception = null; // store last exception in async running task
@@ -100,7 +102,7 @@ private async Task ExecuteQueue()
 
                         _stream.FlushToDisk();
 
-                        await _queueHasItems.WaitAsync();
+                        await _queueHasItems.WaitHandle.WaitAsync().ConfigureAwait(false);
                     }
                 }
             }

LiteDB/LiteDB.csproj

@@ -29,7 +29,7 @@
     <AssemblyOriginatorKeyFile Condition="'$(Configuration)' == 'Release'">LiteDB.snk</AssemblyOriginatorKeyFile>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
-  
+
   <!--
   == All variables ==
   HAVE_APP_DOMAIN
@@ -64,8 +64,9 @@
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
     <PackageReference Include="System.Reflection.TypeExtensions" Version="4.5.1" />
     <PackageReference Include="System.Security.Cryptography.Algorithms" Version="4.3.1" />
+    <PackageReference Include="System.Threading.ThreadPool" Version="4.3.0" />
   </ItemGroup>
-  
+
   <!-- End References -->
 
 </Project>

LiteDB/Utils/Extensions/WaitHandleExtensions.cs

@@ -0,0 +1,33 @@
+namespace LiteDB.Utils.Extensions
+{
+    using System;
+    using System.Threading;
+    using System.Threading.Tasks;
+
+    internal static class WaitHandleExtensions
+    {
+        public static async Task<bool> WaitAsync(this WaitHandle handle)
+        {
+            var tcs = new TaskCompletionSource<bool>();
+
+            using (new ThreadPoolRegistration(handle, tcs))
+            {
+                return await tcs.Task.ConfigureAwait(false);
+            }
+        }
+
+        private sealed class ThreadPoolRegistration : IDisposable
+        {
+            private readonly RegisteredWaitHandle _registeredWaitHandle;
+
+            public ThreadPoolRegistration(WaitHandle handle, TaskCompletionSource<bool> tcs)
+            {
+                _registeredWaitHandle = ThreadPool.RegisterWaitForSingleObject(handle,
+                    (state, timedOut) => ((TaskCompletionSource<bool>)state).TrySetResult(!timedOut), tcs,
+                    Timeout.InfiniteTimeSpan, executeOnlyOnce: true);
+            }
+
+            void IDisposable.Dispose() => _registeredWaitHandle.Unregister(null);
+        }
+    }
+}