#region Apache License
//
// Licensed to the Apache Software Foundation (ASF) under one or more 
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership. 
// The ASF licenses this file to you under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with 
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System.Threading;

namespace log4net.Util;

/// <summary>
/// Defines a lock that supports single writers and multiple readers
/// </summary>
/// <remarks>
/// <para>
/// <see cref="ReaderWriterLock"/> is used to synchronize access to a resource. 
/// At any given time, it allows either concurrent read access for 
/// multiple threads, or write access for a single thread. In a 
/// situation where a resource is changed infrequently, a 
/// <see cref="ReaderWriterLock"/> provides better throughput than a simple 
/// one-at-a-time lock, such as <see cref="Monitor"/>.
/// </para>
/// <para>
/// If a platform does not support a <c>System.Threading.ReaderWriterLock</c> 
/// implementation then all readers and writers are serialized. Therefore 
/// the caller must not rely on multiple simultaneous readers.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
public sealed class ReaderWriterLock
{
  /// <summary>
  /// Acquires a reader lock
  /// </summary>
  /// <remarks>
  /// <para>
  /// <see cref="AcquireReaderLock"/> blocks if a different thread has the writer 
  /// lock, or if at least one thread is waiting for the writer lock.
  /// </para>
  /// </remarks>
  public void AcquireReaderLock()
  {
    // prevent ThreadAbort while updating state, see https://issues.apache.org/jira/browse/LOG4NET-443
    try { }
    finally
    {
      _readerWriterLock.EnterReadLock();
    }
  }

  /// <summary>
  /// Decrements the lock count
  /// </summary>
  /// <remarks>
  /// <para>
  /// <see cref="ReleaseReaderLock"/> decrements the lock count. When the count 
  /// reaches zero, the lock is released.
  /// </para>
  /// </remarks>
  public void ReleaseReaderLock() => _readerWriterLock.ExitReadLock();

  /// <summary>
  /// Acquires the writer lock
  /// </summary>
  /// <remarks>
  /// <para>
  /// This method blocks if another thread has a reader lock or writer lock.
  /// </para>
  /// </remarks>
  public void AcquireWriterLock()
  {
    // prevent ThreadAbort while updating state, see https://issues.apache.org/jira/browse/LOG4NET-443
    try { }
    finally
    {
      _readerWriterLock.EnterWriteLock();
    }
  }

  /// <summary>
  /// Decrements the lock count on the writer lock
  /// </summary>
  /// <remarks>
  /// <para>
  /// ReleaseWriterLock decrements the writer lock count. 
  /// When the count reaches zero, the writer lock is released.
  /// </para>
  /// </remarks>
  public void ReleaseWriterLock() => _readerWriterLock.ExitWriteLock();

  private readonly ReaderWriterLockSlim _readerWriterLock = new(LockRecursionPolicy.SupportsRecursion);
}
