LINQ to SQL Transformation: Examples and Source Code

using System;
using System.Collections.Generic;
using System.Threading;

namespace LinqToSql {
    
    public class ThreadSafeCache<TKey, TValue> {

        private readonly Dictionary<TKey, TValue> theDictionary = new Dictionary<TKey, TValue>();
        private readonly ReaderWriterLock rwl = new ReaderWriterLock();
        private readonly TimeSpan readerLockTimeout = TimeSpan.FromSeconds(1);
        private readonly TimeSpan writerLockTimeout = TimeSpan.FromSeconds(2);

        public ThreadSafeCache() {
        }

        public TValue this[TKey key] {
            get {
                try {
                    rwl.AcquireReaderLock(readerLockTimeout);
                    return theDictionary[key];
                }
                finally {
                    rwl.ReleaseReaderLock();
                }
            }
        }

        public ICollection<TKey> Keys {
            get {
                try {
                    rwl.AcquireReaderLock(readerLockTimeout);
                    return theDictionary.Keys;
                }
                finally {
                    rwl.ReleaseReaderLock();
                }
            }
        }

        public Dictionary<TKey, TValue>.ValueCollection Values {
            get {
                try {
                    rwl.AcquireReaderLock(readerLockTimeout);
                    return theDictionary.Values;
                }
                finally {
                    rwl.ReleaseReaderLock();
                }
            }
        }

        public bool ContainsKey(TKey key) {

            try {
                rwl.AcquireReaderLock(readerLockTimeout);
                return theDictionary.ContainsKey(key);
            }
            finally {
                rwl.ReleaseReaderLock();
            }
        }

        public bool Remove(TKey key) {
            try {
                rwl.AcquireWriterLock(writerLockTimeout);
                return theDictionary.Remove(key);
            }
            finally {
                rwl.ReleaseWriterLock();
            }
        }

        public bool TryGetValue(TKey key, out TValue value) {
            try {
                rwl.AcquireReaderLock(readerLockTimeout);
                return theDictionary.TryGetValue(key, out value);
            }
            finally {
                rwl.ReleaseReaderLock();
            }
        }

        public bool TryAdd(TKey key, TValue value) {
            try {
                rwl.AcquireWriterLock(writerLockTimeout);

                if (theDictionary.ContainsKey(key)) {
                    return false;
                }

                theDictionary.Add(key, value);
                return true;
            }
            finally {
                rwl.ReleaseWriterLock();
            }
        }

        public void Clear() {
            try {
                rwl.AcquireWriterLock(writerLockTimeout);
                theDictionary.Clear();
            }
            finally {
                rwl.ReleaseWriterLock();
            }
        }

        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() {

            foreach (KeyValuePair<TKey, TValue> pair in theDictionary) {
                yield return pair;
            }
        }
    }
}