Make UseWriterLockAsync thread-safe

Author: usercode

src/AsyncKeyLock.Tests/AsyncLockTest.cs

@@ -34,7 +34,7 @@ public async Task ThreeParallelReadersClosed()
             using var r1 = await lockEntity.ReaderLockAsync();
             using var r2 = await lockEntity.ReaderLockAsync();
             using var r3 = await lockEntity.ReaderLockAsync();
-        }
+        }        
 
         Assert.Equal(0, lockEntity.CountRunningReaders);
     }

src/AsyncKeyLock/AsyncLock.cs

@@ -11,7 +11,7 @@ public sealed class AsyncLock
 {
     public AsyncLock()
     {
-        _syncObj = _waitingWriters;
+        SyncObj = _waitingWriters;
 
         _readerReleaserTask = Task.FromResult(new ReaderReleaser(this, true));
         _writerReleaserTask = Task.FromResult(new WriterReleaser(this, true));
@@ -20,10 +20,10 @@ public AsyncLock()
     internal AsyncLock(object syncObject)
         : this()
     {
-        _syncObj = syncObject;
+        SyncObj = syncObject;
     }
 
-    private readonly object _syncObj;
+    internal readonly object SyncObj;
 
     private readonly Queue<TaskCompletionSource<ReaderReleaser>> _waitingReaders = new Queue<TaskCompletionSource<ReaderReleaser>>();
     private readonly Queue<TaskCompletionSource<WriterReleaser>> _waitingWriters = new Queue<TaskCompletionSource<WriterReleaser>>();
@@ -86,7 +86,7 @@ public Task<ReaderReleaser> ReaderLockAsync(CancellationToken cancellation = def
             return Task.FromCanceled<ReaderReleaser>(cancellation);
         }
 
-        lock (_syncObj)
+        lock (SyncObj)
         {
             //no running or waiting write lock?
             if (_isWriterRunning == false && _waitingWriters.Count == 0)
@@ -110,7 +110,7 @@ public Task<WriterReleaser> WriterLockAsync(CancellationToken cancellation = def
             return Task.FromCanceled<WriterReleaser>(cancellation);
         }
 
-        lock (_syncObj)
+        lock (SyncObj)
         {
             if (_isWriterRunning == false && _readersRunning == 0)
             {
@@ -126,9 +126,9 @@ public Task<WriterReleaser> WriterLockAsync(CancellationToken cancellation = def
         }
     }
 
-    internal void Release(AsyncLockType type)
+    internal void Release(AsyncLockType type, bool sendReleaseEvent = true)
     {
-        lock (_syncObj)
+        lock (SyncObj)
         {
             try
             {
@@ -143,7 +143,7 @@ internal void Release(AsyncLockType type)
             }
             finally
             {
-                if (State == AsyncLockState.Idle)
+                if (sendReleaseEvent && State == AsyncLockState.Idle)
                 {
                     Released?.Invoke(this);
                 }

src/AsyncKeyLock/Releaser/ReaderReleaser.cs

@@ -29,21 +29,41 @@ public async Task UseWriterLockAsync(Func<Task> func, CancellationToken cancella
     {
         cancellation.ThrowIfCancellationRequested();
 
-        //release reader lock
-        AsyncLock.Release(AsyncLockType.Read);
+        Task<WriterReleaser> taskWriter;
+        WriterReleaser? writerReleaser = null;
+
+        lock (AsyncLock.SyncObj)
+        {
+            //release reader lock
+            AsyncLock.Release(AsyncLockType.Read, false);
+
+            taskWriter = AsyncLock.WriterLockAsync(cancellation);
+        }
 
         try
         {
             //create new writer lock
-            using (await AsyncLock.WriterLockAsync(cancellation))
-            {
-                await func();
-            }
+            writerReleaser = await taskWriter;
+            
+            await func();
+            
         }
         finally
         {
-            //restore reader lock
-            await AsyncLock.ReaderLockAsync();
+            Task<ReaderReleaser> taskReader;
+
+            lock (AsyncLock.SyncObj)
+            {
+                if (writerReleaser != null)
+                {
+                    AsyncLock.Release(AsyncLockType.Write, false);
+                }
+
+                //restore reader lock
+                taskReader = AsyncLock.ReaderLockAsync();
+            }
+
+            await taskReader;
         }
     }