1 files changed, 296 insertions, 0 deletions
diff --git a/src/Jellyfin.Database/Jellyfin.Database.Implementations/Locking/PessimisticLockBehavior.cs b/src/Jellyfin.Database/Jellyfin.Database.Implementations/Locking/PessimisticLockBehavior.cs
new file mode 100644
index 000000000..2d6bc6902
--- /dev/null
+++ b/src/Jellyfin.Database/Jellyfin.Database.Implementations/Locking/PessimisticLockBehavior.cs
@@ -0,0 +1,296 @@
+#pragma warning disable MT1013 // Releasing lock without guarantee of execution
+#pragma warning disable MT1012 // Acquiring lock without guarantee of releasing
+
+using System;
+using System.Data;
+using System.Data.Common;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Diagnostics;
+using Microsoft.Extensions.Logging;
+
+namespace Jellyfin.Database.Implementations.Locking;
+
+/// <summary>
+/// A locking behavior that will always block any operation while a write is requested. Mimicks the old SqliteRepository behavior.
+/// </summary>
+public class PessimisticLockBehavior : IEntityFrameworkCoreLockingBehavior
+{
+    private readonly ILogger<PessimisticLockBehavior> _logger;
+    private readonly ILoggerFactory _loggerFactory;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="PessimisticLockBehavior"/> class.
+    /// </summary>
+    /// <param name="logger">The application logger.</param>
+    /// <param name="loggerFactory">The logger factory.</param>
+    public PessimisticLockBehavior(ILogger<PessimisticLockBehavior> logger, ILoggerFactory loggerFactory)
+    {
+        _logger = logger;
+        _loggerFactory = loggerFactory;
+    }
+
+    private static ReaderWriterLockSlim DatabaseLock { get; } = new(LockRecursionPolicy.SupportsRecursion);
+
+    /// <inheritdoc/>
+    public void OnSaveChanges(JellyfinDbContext context, Action saveChanges)
+    {
+        using (DbLock.EnterWrite(_logger))
+        {
+            saveChanges();
+        }
+    }
+
+    /// <inheritdoc/>
+    public void Initialise(DbContextOptionsBuilder optionsBuilder)
+    {
+        _logger.LogInformation("The database locking mode has been set to: Pessimistic.");
+        optionsBuilder.AddInterceptors(new CommandLockingInterceptor(_loggerFactory.CreateLogger<CommandLockingInterceptor>()));
+        optionsBuilder.AddInterceptors(new TransactionLockingInterceptor(_loggerFactory.CreateLogger<TransactionLockingInterceptor>()));
+    }
+
+    /// <inheritdoc/>
+    public async Task OnSaveChangesAsync(JellyfinDbContext context, Func<Task> saveChanges)
+    {
+        using (DbLock.EnterWrite(_logger))
+        {
+            await saveChanges().ConfigureAwait(false);
+        }
+    }
+
+    private sealed class TransactionLockingInterceptor : DbTransactionInterceptor
+    {
+        private readonly ILogger _logger;
+
+        public TransactionLockingInterceptor(ILogger logger)
+        {
+            _logger = logger;
+        }
+
+        public override InterceptionResult<DbTransaction> TransactionStarting(DbConnection connection, TransactionStartingEventData eventData, InterceptionResult<DbTransaction> result)
+        {
+            DbLock.BeginWriteLock(_logger);
+
+            return base.TransactionStarting(connection, eventData, result);
+        }
+
+        public override ValueTask<InterceptionResult<DbTransaction>> TransactionStartingAsync(DbConnection connection, TransactionStartingEventData eventData, InterceptionResult<DbTransaction> result, CancellationToken cancellationToken = default)
+        {
+            DbLock.BeginWriteLock(_logger);
+
+            return base.TransactionStartingAsync(connection, eventData, result, cancellationToken);
+        }
+
+        public override void TransactionCommitted(DbTransaction transaction, TransactionEndEventData eventData)
+        {
+            DbLock.EndWriteLock(_logger);
+
+            base.TransactionCommitted(transaction, eventData);
+        }
+
+        public override Task TransactionCommittedAsync(DbTransaction transaction, TransactionEndEventData eventData, CancellationToken cancellationToken = default)
+        {
+            DbLock.EndWriteLock(_logger);
+
+            return base.TransactionCommittedAsync(transaction, eventData, cancellationToken);
+        }
+
+        public override void TransactionFailed(DbTransaction transaction, TransactionErrorEventData eventData)
+        {
+            DbLock.EndWriteLock(_logger);
+
+            base.TransactionFailed(transaction, eventData);
+        }
+
+        public override Task TransactionFailedAsync(DbTransaction transaction, TransactionErrorEventData eventData, CancellationToken cancellationToken = default)
+        {
+            DbLock.EndWriteLock(_logger);
+
+            return base.TransactionFailedAsync(transaction, eventData, cancellationToken);
+        }
+
+        public override void TransactionRolledBack(DbTransaction transaction, TransactionEndEventData eventData)
+        {
+            DbLock.EndWriteLock(_logger);
+
+            base.TransactionRolledBack(transaction, eventData);
+        }
+
+        public override Task TransactionRolledBackAsync(DbTransaction transaction, TransactionEndEventData eventData, CancellationToken cancellationToken = default)
+        {
+            DbLock.EndWriteLock(_logger);
+
+            return base.TransactionRolledBackAsync(transaction, eventData, cancellationToken);
+        }
+    }
+
+    /// <summary>
+    /// Adds strict read/write locking.
+    /// </summary>
+    private sealed class CommandLockingInterceptor : DbCommandInterceptor
+    {
+        private readonly ILogger _logger;
+
+        public CommandLockingInterceptor(ILogger logger)
+        {
+            _logger = logger;
+        }
+
+        public override InterceptionResult<int> NonQueryExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<int> result)
+        {
+            using (DbLock.EnterWrite(_logger, command))
+            {
+                return InterceptionResult<int>.SuppressWithResult(command.ExecuteNonQuery());
+            }
+        }
+
+        public override async ValueTask<InterceptionResult<int>> NonQueryExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<int> result, CancellationToken cancellationToken = default)
+        {
+            using (DbLock.EnterWrite(_logger, command))
+            {
+                return InterceptionResult<int>.SuppressWithResult(await command.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false));
+            }
+        }
+
+        public override InterceptionResult<object> ScalarExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<object> result)
+        {
+            using (DbLock.EnterRead(_logger))
+            {
+                return InterceptionResult<object>.SuppressWithResult(command.ExecuteScalar()!);
+            }
+        }
+
+        public override async ValueTask<InterceptionResult<object>> ScalarExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<object> result, CancellationToken cancellationToken = default)
+        {
+            using (DbLock.EnterRead(_logger))
+            {
+                return InterceptionResult<object>.SuppressWithResult((await command.ExecuteScalarAsync(cancellationToken).ConfigureAwait(false))!);
+            }
+        }
+
+        public override InterceptionResult<DbDataReader> ReaderExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result)
+        {
+            using (DbLock.EnterRead(_logger))
+            {
+                return InterceptionResult<DbDataReader>.SuppressWithResult(command.ExecuteReader()!);
+            }
+        }
+
+        public override async ValueTask<InterceptionResult<DbDataReader>> ReaderExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result, CancellationToken cancellationToken = default)
+        {
+            using (DbLock.EnterRead(_logger))
+            {
+                return InterceptionResult<DbDataReader>.SuppressWithResult(await command.ExecuteReaderAsync(cancellationToken).ConfigureAwait(false));
+            }
+        }
+    }
+
+    private sealed class DbLock : IDisposable
+    {
+        private readonly Action? _action;
+        private bool _disposed;
+
+        private static readonly IDisposable _noLock = new DbLock(null) { _disposed = true };
+        private static (string Command, Guid Id, DateTimeOffset QueryDate, bool Printed) _blockQuery;
+
+        public DbLock(Action? action = null)
+        {
+            _action = action;
+        }
+
+#pragma warning disable IDISP015 // Member should not return created and cached instance
+        public static IDisposable EnterWrite(ILogger logger, IDbCommand? command = null, [CallerMemberName] string? callerMemberName = null, [CallerLineNumber] int? callerNo = null)
+#pragma warning restore IDISP015 // Member should not return created and cached instance
+        {
+            logger.LogTrace("Enter Write for {Caller}:{Line}", callerMemberName, callerNo);
+            if (DatabaseLock.IsWriteLockHeld)
+            {
+                logger.LogTrace("Write Held {Caller}:{Line}", callerMemberName, callerNo);
+                return _noLock;
+            }
+
+            BeginWriteLock(logger, command, callerMemberName, callerNo);
+            return new DbLock(() =>
+            {
+                EndWriteLock(logger, callerMemberName, callerNo);
+            });
+        }
+
+#pragma warning disable IDISP015 // Member should not return created and cached instance
+        public static IDisposable EnterRead(ILogger logger, [CallerMemberName] string? callerMemberName = null, [CallerLineNumber] int? callerNo = null)
+#pragma warning restore IDISP015 // Member should not return created and cached instance
+        {
+            logger.LogTrace("Enter Read {Caller}:{Line}", callerMemberName, callerNo);
+            if (DatabaseLock.IsWriteLockHeld)
+            {
+                logger.LogTrace("Write Held {Caller}:{Line}", callerMemberName, callerNo);
+                return _noLock;
+            }
+
+            BeginReadLock(logger, callerMemberName, callerNo);
+            return new DbLock(() =>
+            {
+                ExitReadLock(logger, callerMemberName, callerNo);
+            });
+        }
+
+        public static void BeginWriteLock(ILogger logger, IDbCommand? command = null, [CallerMemberName] string? callerMemberName = null, [CallerLineNumber] int? callerNo = null)
+        {
+            logger.LogTrace("Aquire Write {Caller}:{Line}", callerMemberName, callerNo);
+            if (!DatabaseLock.TryEnterWriteLock(TimeSpan.FromMilliseconds(1000)))
+            {
+                var blockingQuery = _blockQuery;
+                if (!blockingQuery.Printed)
+                {
+                    _blockQuery = (blockingQuery.Command, blockingQuery.Id, blockingQuery.QueryDate, true);
+                    logger.LogInformation("QueryLock: {Id} --- {Query}", blockingQuery.Id, blockingQuery.Command);
+                }
+
+                logger.LogInformation("Query congestion detected: '{Id}' since '{Date}'", blockingQuery.Id, blockingQuery.QueryDate);
+
+                DatabaseLock.EnterWriteLock();
+
+                logger.LogInformation("Query congestion cleared: '{Id}' for '{Date}'", blockingQuery.Id, DateTimeOffset.Now - blockingQuery.QueryDate);
+            }
+
+            _blockQuery = (command?.CommandText ?? "Transaction", Guid.NewGuid(), DateTimeOffset.Now, false);
+
+            logger.LogTrace("Write Aquired {Caller}:{Line}", callerMemberName, callerNo);
+        }
+
+        public static void BeginReadLock(ILogger logger, [CallerMemberName] string? callerMemberName = null, [CallerLineNumber] int? callerNo = null)
+        {
+            logger.LogTrace("Aquire Write {Caller}:{Line}", callerMemberName, callerNo);
+            DatabaseLock.EnterReadLock();
+            logger.LogTrace("Read Aquired {Caller}:{Line}", callerMemberName, callerNo);
+        }
+
+        public static void EndWriteLock(ILogger logger, [CallerMemberName] string? callerMemberName = null, [CallerLineNumber] int? callerNo = null)
+        {
+            logger.LogTrace("Release Write {Caller}:{Line}", callerMemberName, callerNo);
+            DatabaseLock.ExitWriteLock();
+        }
+
+        public static void ExitReadLock(ILogger logger, [CallerMemberName] string? callerMemberName = null, [CallerLineNumber] int? callerNo = null)
+        {
+            logger.LogTrace("Release Read {Caller}:{Line}", callerMemberName, callerNo);
+            DatabaseLock.ExitReadLock();
+        }
+
+        public void Dispose()
+        {
+            if (_disposed)
+            {
+                return;
+            }
+
+            _disposed = true;
+            if (_action is not null)
+            {
+                _action();
+            }
+        }
+    }
+}