Support in-process named mutexes in managed implementation

src/libraries/System.IO.IsolatedStorage/tests/AssemblyInfo.cs

@@ -8,5 +8,4 @@
 // create unique identities for every test to allow every test to have
 // it's own store.
 [assembly: CollectionBehavior(CollectionBehavior.CollectionPerAssembly, DisableTestParallelization = true)]
-[assembly: ActiveIssue("https://github.com/dotnet/runtime/issues/48720", TestPlatforms.AnyUnix, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
 [assembly: SkipOnPlatform(TestPlatforms.Browser, "System.IO.IsolatedStorage is not supported on Browser")]

src/libraries/System.Private.CoreLib/src/System/Threading/Mutex.Unix.cs

@@ -12,10 +12,15 @@ public sealed partial class Mutex
     {
         private void CreateMutexCore(bool initiallyOwned, string? name, out bool createdNew)
         {
-            // See https://github.com/dotnet/runtime/issues/48720
             if (name != null)
             {
-                throw new PlatformNotSupportedException(SR.PlatformNotSupported_NamedSynchronizationPrimitives);
+                SafeWaitHandle? safeWaitHandle = WaitSubsystem.CreateNamedMutex(initiallyOwned, name, out createdNew);
+                if (safeWaitHandle == null)
+                {
+                    throw new WaitHandleCannotBeOpenedException(SR.Format(SR.Threading_WaitHandleCannotBeOpenedException_InvalidHandle, name));
+                }
+                SafeWaitHandle = safeWaitHandle;
+                return;
             }
 
             SafeWaitHandle = WaitSubsystem.NewMutex(initiallyOwned);
@@ -24,7 +29,9 @@ private void CreateMutexCore(bool initiallyOwned, string? name, out bool created
 
         private static OpenExistingResult OpenExistingWorker(string name, out Mutex? result)
         {
-            throw new PlatformNotSupportedException(SR.PlatformNotSupported_NamedSynchronizationPrimitives);
+            OpenExistingResult status = WaitSubsystem.OpenNamedMutex(name, out SafeWaitHandle? safeWaitHandle);
+            result = status == OpenExistingResult.Success ? new Mutex(safeWaitHandle!) : null;
+            return status;
         }
 
         public void ReleaseMutex()

src/libraries/System.Private.CoreLib/src/System/Threading/WaitSubsystem.Unix.cs

@@ -166,6 +166,53 @@ public static SafeWaitHandle NewMutex(bool initiallyOwned)
             return safeWaitHandle;
         }
 
+        public static SafeWaitHandle? CreateNamedMutex(bool initiallyOwned, string name, out bool createdNew)
+        {
+            // For initially owned, newly created named mutexes, there is a potential race
+            // between adding the mutex to the named object table and initially acquiring it.
+            // To avoid the possibility of another thread retrieving the mutex via its name
+            // before we managed to acquire it, we perform both steps while holding s_lock.
+            s_lock.Acquire();
+            bool holdingLock = true;
+            try
+            {
+                WaitableObject? waitableObject = WaitableObject.CreateNamedMutex_Locked(name, out createdNew);
+                if (waitableObject == null)
+                {
+                    return null;
+                }
+                SafeWaitHandle safeWaitHandle = NewHandle(waitableObject);
+                if (!initiallyOwned || !createdNew)
+                {
+                    return safeWaitHandle;
+                }
+
+                // Acquire the mutex. A thread's <see cref="ThreadWaitInfo"/> has a reference to all <see cref="Mutex"/>es locked
+                // by the thread. See <see cref="ThreadWaitInfo.LockedMutexesHead"/>. So, acquire the lock only after all
+                // possibilities for exceptions have been exhausted.
+                ThreadWaitInfo waitInfo = Thread.CurrentThread.WaitInfo;
+                int status = waitableObject.Wait_Locked(waitInfo, timeoutMilliseconds: 0, interruptible: false, prioritize: false);
+                Debug.Assert(status == 0);
+                // Wait_Locked has already released s_lock, so we no longer hold it here.
+                holdingLock = false;
+                return safeWaitHandle;
+            }
+            finally
+            {
+                if (holdingLock)
+                {
+                    s_lock.Release();
+                }
+            }
+        }
+
+        public static OpenExistingResult OpenNamedMutex(string name, out SafeWaitHandle? result)
+        {
+            OpenExistingResult status = WaitableObject.OpenNamedMutex(name, out WaitableObject? mutex);
+            result = status == OpenExistingResult.Success ? NewHandle(mutex!) : null;
+            return status;
+        }
+
         public static void DeleteHandle(IntPtr handle)
         {
             HandleManager.DeleteHandle(handle);

src/libraries/System.Private.CoreLib/src/System/Threading/WaitSubsystem.WaitableObject.Unix.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections.Generic;
 using System.Diagnostics;
 
 namespace System.Threading
@@ -14,9 +15,17 @@ internal static partial class WaitSubsystem
         /// </summary>
         public sealed class WaitableObject
         {
+            /// <summary>
+            /// Dictionary to look up named waitable objects.  This implementation only supports in-process
+            /// named waitable objects.  Currently only named mutexes are supported.
+            /// </summary>
+            private static Dictionary<string, WaitableObject>? s_namedObjects;
+
             private readonly WaitableObjectType _type;
             private int _signalCount;
             private readonly int _maximumSignalCount;
+            private int _referenceCount;
+            private readonly string? _name;
 
             /// <summary>
             /// Only <see cref="Mutex"/> has a thread ownership requirement, and it's a less common type to be used, so
@@ -33,6 +42,7 @@ private WaitableObject(
                 WaitableObjectType type,
                 int initialSignalCount,
                 int maximumSignalCount,
+                string? name,
                 OwnershipInfo? ownershipInfo)
             {
                 Debug.Assert(initialSignalCount >= 0);
@@ -42,6 +52,8 @@ private WaitableObject(
                 _type = type;
                 _signalCount = initialSignalCount;
                 _maximumSignalCount = maximumSignalCount;
+                _referenceCount = 1;
+                _name = name;
                 _ownershipInfo = ownershipInfo;
             }
 
@@ -56,24 +68,87 @@ public static WaitableObject NewEvent(bool initiallySignaled, EventResetMode res
                             : WaitableObjectType.AutoResetEvent,
                         initiallySignaled ? 1 : 0,
                         1,
+                        null,
                         null);
             }
 
             public static WaitableObject NewSemaphore(int initialSignalCount, int maximumSignalCount)
             {
-                return new WaitableObject(WaitableObjectType.Semaphore, initialSignalCount, maximumSignalCount, null);
+                return new WaitableObject(WaitableObjectType.Semaphore, initialSignalCount, maximumSignalCount, null, null);
             }
 
             public static WaitableObject NewMutex()
             {
-                return new WaitableObject(WaitableObjectType.Mutex, 1, 1, new OwnershipInfo());
+                return new WaitableObject(WaitableObjectType.Mutex, 1, 1, null, new OwnershipInfo());
+            }
+
+            public static WaitableObject? CreateNamedMutex_Locked(string name, out bool createdNew)
+            {
+                s_lock.VerifyIsLocked();
+
+                s_namedObjects ??= new Dictionary<string, WaitableObject>();
+
+                if (s_namedObjects.TryGetValue(name, out WaitableObject? result))
+                {
+                    createdNew = false;
+                    if (!result.IsMutex)
+                    {
+                        return null;
+                    }
+                    result._referenceCount++;
+                }
+                else
+                {
+                    createdNew = true;
+                    result = new WaitableObject(WaitableObjectType.Mutex, 1, 1, name, new OwnershipInfo());
+                    s_namedObjects.Add(name, result);
+                }
+
+                return result;
+            }
+
+            public static OpenExistingResult OpenNamedMutex(string name, out WaitableObject? result)
+            {
+                s_lock.Acquire();
+                try
+                {
+                    if (s_namedObjects == null || !s_namedObjects.TryGetValue(name, out result))
+                    {
+                        result = null;
+                        return OpenExistingResult.NameNotFound;
+                    }
+                    if (!result.IsMutex)
+                    {
+                        result = null;
+                        return OpenExistingResult.NameInvalid;
+                    }
+                    result._referenceCount++;
+                    return OpenExistingResult.Success;
+                }
+                finally
+                {
+                    s_lock.Release();
+                }
             }
 
             public void OnDeleteHandle()
             {
                 s_lock.Acquire();
                 try
                 {
+                    // Multiple handles may refer to the same named object.  Make sure the object
+                    // is only abandoned once the last handle to it is deleted.  Also, remove the
+                    // object from the named objects dictionary at this point.
+                    _referenceCount--;
+                    if (_referenceCount > 0)
+                    {
+                        return;
+                    }
+                    if (_name != null)
+                    {
+                        s_namedObjects!.Remove(_name);
+                    }
+
                     if (IsMutex && !IsSignaled)
                     {
                         // A thread has a reference to all <see cref="Mutex"/>es locked by it, see

src/libraries/System.Threading/tests/MutexTests.cs

@@ -45,7 +45,6 @@ public void Ctor_InvalidNames_Unix()
         }
 
         [Theory]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/48720", TestPlatforms.AnyUnix, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         [MemberData(nameof(GetValidNames))]
         public void Ctor_ValidName(string name)
         {
@@ -97,7 +96,6 @@ public void Ctor_TryCreateGlobalMutexTest_Uwp()
         }
 
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/48720", TestPlatforms.AnyUnix, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         [MemberData(nameof(GetValidNames))]
         public void OpenExisting(string name)
         {
@@ -132,7 +130,6 @@ public void OpenExisting_InvalidNames()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/48720", TestPlatforms.AnyUnix, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         public void OpenExisting_UnavailableName()
         {
             string name = Guid.NewGuid().ToString("N");
@@ -228,7 +225,6 @@ public static IEnumerable<object[]> AbandonExisting_MemberData()
         }
 
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/48720", TestPlatforms.AnyUnix, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         [MemberData(nameof(AbandonExisting_MemberData))]
         public void AbandonExisting(
             string name,
@@ -469,7 +465,6 @@ private static void IncrementValueInFileNTimes(Mutex mutex, string fileName, int
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/48720", TestPlatforms.AnyUnix, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         public void NamedMutex_ThreadExitDisposeRaceTest()
         {
             var mutexName = Guid.NewGuid().ToString("N");
@@ -530,7 +525,6 @@ public void NamedMutex_ThreadExitDisposeRaceTest()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/48720", TestPlatforms.AnyUnix, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         public void NamedMutex_DisposeWhenLockedRaceTest()
         {
             var mutexName = Guid.NewGuid().ToString("N");