add CrossPlatformProcessLock

src/MappedFileQueues/CrossPlatformProcessLock.cs

@@ -0,0 +1,133 @@
+using System.Runtime.InteropServices;
+using System.Security.Cryptography;
+
+namespace MappedFileQueues;
+
+/// <summary>
+/// A cross-platform process lock implementation. Only Windows and Linux are supported.
+/// On Windows, a named mutex is used. On Linux, a file lock is used. On other platforms, a no-op lock is used.
+/// </summary>
+internal sealed class CrossPlatformProcessLock : IDisposable
+{
+    private readonly IProcessLock _lock;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CrossPlatformProcessLock"/> class.
+    /// </summary>
+    /// <param name="name">The name of the process lock.</param>
+    /// <param name="storePath">The store path of the <see cref="MappedFileQueue{T}"/>.</param>
+    public CrossPlatformProcessLock(string name, string storePath)
+    {
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            var hashBytes = MD5.HashData(System.Text.Encoding.UTF8.GetBytes(storePath));
+            var hashString = Convert.ToHexString(hashBytes);
+            name = $"{name}_{hashString}";
+            _lock = new MutexProcessLock(name);
+        }
+        else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+        {
+            var lockFilePath = Path.Combine(storePath, $"{name}.lock");
+            _lock = new FileProcessLock(lockFilePath);
+        }
+        else
+        {
+            _lock = new EmptyProcessLock();
+        }
+    }
+
+    public void Acquire() => _lock.Acquire();
+    public void Release() => _lock.Release();
+
+    public void Dispose() => _lock.Dispose();
+
+    #region Process Lock Interface
+
+    private interface IProcessLock : IDisposable
+    {
+        void Acquire();
+        void Release();
+    }
+
+    #endregion
+
+    #region Windows Named Mutex Lock
+
+    private class MutexProcessLock(string name) : IProcessLock
+    {
+        private Mutex? _mutex;
+        // Global\ Make the mutex available across sessions
+        private readonly string _name = $@"Global\{name}";
+
+        public void Acquire()
+        {
+            _mutex = new Mutex(false, _name);
+            _mutex.WaitOne();
+        }
+
+        public void Release()
+        {
+            _mutex?.ReleaseMutex();
+            _mutex?.Dispose();
+        }
+
+        public void Dispose() => Release();
+    }
+
+    #endregion
+
+    #region Linux File Lock
+
+    private class FileProcessLock(string lockFilePath) : IProcessLock
+    {
+        private FileStream? _lockFileStream;
+
+        public void Acquire()
+        {
+            while (true)
+            {
+                try
+                {
+                    _lockFileStream = new FileStream(lockFilePath, FileMode.OpenOrCreate,
+                        FileAccess.ReadWrite, FileShare.ReadWrite);
+                    _lockFileStream.Lock(0, 0);
+                    return;
+                }
+                catch (IOException)
+                {
+                    // Lock is held by another process, wait and retry
+                    Thread.Sleep(200);
+                }
+            }
+        }
+
+        public void Release()
+        {
+            _lockFileStream?.Unlock(0, 0);
+            _lockFileStream?.Dispose();
+        }
+
+        public void Dispose() => Release();
+    }
+
+    #endregion
+
+    #region Empty Lock (for unsupported platforms)
+
+    private class EmptyProcessLock : IProcessLock
+    {
+        public void Acquire()
+        {
+        }
+
+        public void Release()
+        {
+        }
+
+        public void Dispose()
+        {
+        }
+    }
+
+    #endregion
+}

src/MappedFileQueues/MappedFileQueueT.cs

@@ -50,22 +50,10 @@ public void Dispose()
     // producer's offset to the position of the data that has been confirmed to be persisted.
     private void RecoverProducerOffsetIfNeeded()
     {
-        // On Windows, use "Global\" prefix to make the named semaphore visible across all user sessions (system-wide on this machine).
-        var semName = $"Global\\MappedFileQueueSem_{_options.StorePath.GetHashCode()}";
-        Semaphore? semaphore = null;
-        try
-        {
-            semaphore = new Semaphore(1, 1, semName);
-        }
-        catch (NotSupportedException)
-        {
-            // Named semaphores are not supported on this platform, use unnamed semaphore instead.
-            semaphore = new Semaphore(1, 1);
-        }
-
-        using var sem = semaphore;
+        var lockName = "recovery_lock";
+        using var processLock = new CrossPlatformProcessLock(lockName, _options.StorePath);
 
-        semaphore.WaitOne();
+        processLock.Acquire();
 
         try
         {
@@ -108,7 +96,7 @@ private void RecoverProducerOffsetIfNeeded()
             _producer = null;
             _consumer = null;
 
-            semaphore.Release();
+            processLock.Release();
         }
     }
 }

src/MappedFileQueues/OffsetMappedFile.cs

@@ -55,6 +55,7 @@ public void MoveTo(long offset, bool flushToDisk = false)
 
     public void Dispose()
     {
+        Flush();
         _fileStream.Dispose();
         _mmf.Dispose();
         _vierAccessor.Dispose();