Add AsyncMutex class

src/Microsoft.VisualStudio.Threading/AsyncMutex.cs

@@ -0,0 +1,189 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Concurrent;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.VisualStudio.Threading;
+
+/// <summary>
+/// A mutex that can be entered asynchronously.
+/// </summary>
+/// <remarks>
+/// <para>
+/// This mutex utilizes an OS synchronization primitive which is fundamentally thread-affinitized and requires synchronously blocking the thread that will own the mutex.
+/// This makes a native mutex unsuitable for use in async methods, where the thread that enters the mutex may not be the same thread that exits it.
+/// This class solves that problem by using a private dedicated thread to enter and release the mutex, but otherwise allows its owner to execute async code, switch threads, etc.
+/// </para>
+/// </remarks>
+public class AsyncMutex : IDisposable
+{
+#pragma warning disable SA1310 // Field names should not contain underscore
+    private const int STATE_READY = 0;
+    private const int STATE_HELD_OR_WAITING = 1;
+    private const int STATE_DISPOSED = 2;
+#pragma warning restore SA1310 // Field names should not contain underscore
+
+    private static readonly Action ExitSentinel = new Action(() => { });
+    private readonly Thread namedMutexOwner;
+    private readonly BlockingCollection<Action> mutexWorkQueue = new();
+    private readonly Mutex mutex;
+    private int state;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AsyncMutex"/> class.
+    /// </summary>
+    /// <param name="name"><inheritdoc cref="Mutex(bool, string)" path="/param[@name='name']"/></param>
+    /// <remarks>
+    /// See the help docs on the underlying <see cref="Mutex"/> class for more information on the <paramref name="name"/> parameter.
+    /// Consider when reading that the <c>initiallyOwned</c> parameter for that constructor is always <see langword="false"/> for this class.
+    /// </remarks>
+    public AsyncMutex(string? name)
+    {
+        this.namedMutexOwner = new Thread(this.MutexOwnerThread, 100 * 1024)
+        {
+            Name = $"{nameof(AsyncMutex)}-{name}",
+        };
+        this.mutex = new Mutex(false, name);
+        this.namedMutexOwner.Start();
+        this.Name = name;
+    }
+
+    /// <summary>
+    /// Gets the name of the mutex.
+    /// </summary>
+    public string? Name { get; }
+
+    /// <summary>
+    /// Disposes of the underlying native objects.
+    /// </summary>
+    public void Dispose()
+    {
+        int priorState = Interlocked.Exchange(ref this.state, STATE_DISPOSED);
+        if (priorState != STATE_DISPOSED)
+        {
+            this.mutexWorkQueue.Add(ExitSentinel);
+            this.mutexWorkQueue.CompleteAdding();
+        }
+    }
+
+    /// <inheritdoc cref="EnterAsync(TimeSpan)"/>
+    public ValueTask<LockReleaser> EnterAsync() => this.EnterAsync(Timeout.InfiniteTimeSpan);
+
+    /// <summary>
+    /// Acquires the mutex asynchronously.
+    /// </summary>
+    /// <param name="timeout">The maximum time to wait before timing out. Use <see cref="Timeout.InfiniteTimeSpan"/> for no timeout, or <see cref="TimeSpan.Zero"/> to acquire the mutex only if it is immediately available.</param>
+    /// <returns>A value whose disposal will release the mutex.</returns>
+    /// <exception cref="TimeoutException">Thrown from the awaited result if the mutex could not be acquired within the specified timeout.</exception>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown from the awaited result if the <paramref name="timeout"/> is a negative number other than -1 milliseconds, which represents an infinite timeout.</exception>
+    /// <exception cref="InvalidOperationException">Thrown if called before a prior call to this method has completed, with its releaser disposed if the mutex was entered.</exception>
+    public async ValueTask<LockReleaser> EnterAsync(TimeSpan timeout) => await this.TryEnterAsync(timeout) ?? throw new TimeoutException();
+
+    /// <summary>
+    /// Acquires the mutex asynchronously, allowing for timeouts without throwing exceptions.
+    /// </summary>
+    /// <param name="timeout">The maximum time to wait before timing out. Use <see cref="Timeout.InfiniteTimeSpan"/> for no timeout, or <see cref="TimeSpan.Zero"/> to acquire the mutex only if it is immediately available.</param>
+    /// <returns>
+    /// If the mutex was acquired, the result is a value whose disposal will release the mutex.
+    /// In the event of a timeout, the result in a <see langword="null" /> value.
+    /// </returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown from the awaited result if the <paramref name="timeout"/> is a negative number other than -1 milliseconds, which represents an infinite timeout.</exception>
+    /// <exception cref="InvalidOperationException">Thrown if called before a prior call to this method has completed, with its releaser disposed if the mutex was entered.</exception>
+    public ValueTask<LockReleaser?> TryEnterAsync(TimeSpan timeout)
+    {
+        int priorState = Interlocked.CompareExchange(ref this.state, STATE_HELD_OR_WAITING, STATE_READY);
+        switch (priorState)
+        {
+            case STATE_HELD_OR_WAITING:
+                throw new InvalidOperationException();
+            case STATE_DISPOSED:
+                throw new ObjectDisposedException(this.GetType().FullName);
+        }
+
+        TaskCompletionSource<LockReleaser?> tcs = new();
+        this.mutexWorkQueue.Add(delegate
+        {
+            try
+            {
+                if (this.mutex.WaitOne(timeout))
+                {
+                    tcs.SetResult(new LockReleaser(this));
+                }
+                else
+                {
+                    Assumes.True(Interlocked.CompareExchange(ref this.state, STATE_READY, STATE_HELD_OR_WAITING) == STATE_HELD_OR_WAITING);
+                    tcs.SetResult(null);
+                }
+            }
+            catch (AbandonedMutexException)
+            {
+                tcs.SetResult(new LockReleaser(this, abandoned: true));
+            }
+            catch (Exception ex)
+            {
+                Assumes.True(Interlocked.CompareExchange(ref this.state, STATE_READY, STATE_HELD_OR_WAITING) == STATE_HELD_OR_WAITING);
+                tcs.SetException(ex);
+            }
+        });
+
+        return new ValueTask<LockReleaser?>(tcs.Task);
+    }
+
+    private void Release()
+    {
+        Assumes.True(Interlocked.CompareExchange(ref this.state, STATE_READY, STATE_HELD_OR_WAITING) == STATE_HELD_OR_WAITING);
+        this.mutexWorkQueue.Add(this.mutex.ReleaseMutex);
+    }
+
+    private void MutexOwnerThread()
+    {
+        try
+        {
+            while (!this.mutexWorkQueue.IsCompleted)
+            {
+                Action work = this.mutexWorkQueue.Take();
+                if (work == ExitSentinel)
+                {
+                    // We use an exit sentinel to avoid an exception having to be thrown and caught on disposal when we call Take() and CompleteAdding() is called.
+                    break;
+                }
+
+                work();
+            }
+        }
+        finally
+        {
+            this.mutex.Dispose();
+        }
+    }
+
+    /// <summary>
+    /// The value returned from <see cref="EnterAsync(TimeSpan)"/> that must be disposed to release the mutex.
+    /// </summary>
+    public struct LockReleaser : IDisposable
+    {
+        private AsyncMutex? owner;
+
+        internal LockReleaser(AsyncMutex mutex, bool abandoned = false)
+        {
+            this.owner = mutex;
+            this.IsAbandoned = abandoned;
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether the mutex was abandoned by its previous owner.
+        /// </summary>
+        public bool IsAbandoned { get; }
+
+        /// <summary>
+        /// Releases the named mutex.
+        /// </summary>
+        public void Dispose()
+        {
+            Interlocked.Exchange(ref this.owner, null)?.Release();
+        }
+    }
+}

src/Microsoft.VisualStudio.Threading/net472/PublicAPI.Unshipped.txt

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+Microsoft.VisualStudio.Threading.AsyncMutex
+Microsoft.VisualStudio.Threading.AsyncMutex.AsyncMutex(string? name) -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync() -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.IsAbandoned.get -> bool
+Microsoft.VisualStudio.Threading.AsyncMutex.Name.get -> string?
+Microsoft.VisualStudio.Threading.AsyncMutex.TryEnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser?>

src/Microsoft.VisualStudio.Threading/net6.0-windows/PublicAPI.Unshipped.txt

@@ -0,0 +1,10 @@
+Microsoft.VisualStudio.Threading.AsyncMutex
+Microsoft.VisualStudio.Threading.AsyncMutex.AsyncMutex(string? name) -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync() -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.IsAbandoned.get -> bool
+Microsoft.VisualStudio.Threading.AsyncMutex.Name.get -> string?
+Microsoft.VisualStudio.Threading.AsyncMutex.TryEnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser?>

src/Microsoft.VisualStudio.Threading/net6.0/PublicAPI.Unshipped.txt

@@ -0,0 +1,10 @@
+Microsoft.VisualStudio.Threading.AsyncMutex
+Microsoft.VisualStudio.Threading.AsyncMutex.AsyncMutex(string? name) -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync() -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.IsAbandoned.get -> bool
+Microsoft.VisualStudio.Threading.AsyncMutex.Name.get -> string?
+Microsoft.VisualStudio.Threading.AsyncMutex.TryEnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser?>

src/Microsoft.VisualStudio.Threading/netstandard2.0/PublicAPI.Unshipped.txt

@@ -0,0 +1,10 @@
+Microsoft.VisualStudio.Threading.AsyncMutex
+Microsoft.VisualStudio.Threading.AsyncMutex.AsyncMutex(string? name) -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync() -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.EnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser>
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.Dispose() -> void
+Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser.IsAbandoned.get -> bool
+Microsoft.VisualStudio.Threading.AsyncMutex.Name.get -> string?
+Microsoft.VisualStudio.Threading.AsyncMutex.TryEnterAsync(System.TimeSpan timeout) -> System.Threading.Tasks.ValueTask<Microsoft.VisualStudio.Threading.AsyncMutex.LockReleaser?>