//
//  Author: Carson Jones
//  Adapted from "Art of Multiprocessor Programming" by Herlihy and Shavit
//  CS6966
//

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace ReadWriteLock
{
    /// <summary>
    /// The main ReadWriteLock class.
    /// </summary>
    public class FifoReadWriteLock : IReadWriteLock
    {
        private static int readers;
        private static bool writer;
        static Mutex rwlock;
        private ILock readLock;
        private ILock writeLock;

        public FifoReadWriteLock()
        {
            writer = false;
            readers = 0;
            rwlock = new Mutex();
            readLock = new ReadLock();
            writeLock = new WriteLock();
        }
        public ILock GetReadLock()
        {
            return readLock;
        }
        public ILock GetWriteLock()
        {
            return writeLock;
        }

        /// <summary>
        /// Inner class for ReadLock.
        /// </summary>
        private class ReadLock : ILock
        {
            /// <summary>
            /// Locks the read lock.  If there is some writer writing, this method waits until the writer signals (pulses).
            /// </summary>
            public void Lock()
            {
                lock (rwlock)
                {
                    while (writer)
                    {
                        Monitor.Wait(rwlock);
                    }
                    readers++;
                }
                
            }
            /// <summary>
            /// Unlocks the read lock.  If there are no readers, this method will pulse the writer condition to let writers know they can proceed.
            /// </summary>
            public void Unlock()
            {
                lock (rwlock)
                {
                    readers--;
                    if (readers == 0)
                        Monitor.PulseAll(rwlock);
                }
                
            }
        }

        /// <summary>
        /// Inner class for WriteLock
        /// </summary>
        private class WriteLock : ILock
        {
            /// <summary>
            /// Locks the write lock.  If there are any readers, this method waits until they finish.
            /// </summary>
            public void Lock()
            {
                lock (rwlock)
                {
                    writer = true;
                    while (readers > 0)
                    {
                        Monitor.Wait(rwlock);
                    }
                }
                
            }
            /// <summary>
            /// Unlocks the write lock.  This method also pulses all waiting reader threads to signal them that data is available.
            /// </summary>
            public void Unlock()
            {
                lock (rwlock)
                {
                    writer = false;
                    Monitor.PulseAll(rwlock);
                }
                
            }
        }

    }
}