zhaolei
2020-11-20 921de2254ff5712a44ed8575ee8efe34252f6603
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using System;
using System.Collections.Generic;
using System.Threading;
 
namespace PetaPoco.Internal
{
    internal class Cache<TKey, TValue>
    {
        private ReaderWriterLockSlim _lock = new ReaderWriterLockSlim();
        private Dictionary<TKey, TValue> _map = new Dictionary<TKey, TValue>();
 
        public int Count
        {
            get { return _map.Count; }
        }
 
        public TValue Get(TKey key, Func<TValue> factory)
        {
            // Check cache
            _lock.EnterReadLock();
            TValue val;
            try
            {
                if (_map.TryGetValue(key, out val))
                    return val;
            }
            finally
            {
                _lock.ExitReadLock();
            }
 
            // Cache it
            _lock.EnterWriteLock();
            try
            {
                // Check again
                if (_map.TryGetValue(key, out val))
                    return val;
 
                // Create it
                val = factory();
 
                // Store it
                _map.Add(key, val);
 
                // Done
                return val;
            }
            finally
            {
                _lock.ExitWriteLock();
            }
        }
 
        public void Flush()
        {
            // Cache it
            _lock.EnterWriteLock();
            try
            {
                _map.Clear();
            }
            finally
            {
                _lock.ExitWriteLock();
            }
        }
    }
}