C# 对象池的实现(能限制最大实例数量，类似于WCF的MaxInstanceCount功能)

对象池服务可以减少从头创建每个对象的系统开销。在激活对象时，它从池中提取。在停用对象时，它放回池中，等待下一个请求。
我们来看下主线程中，如何与对象池打交道：

static void Main(string[] args)        {            InstancePoolResolver.Register<OrderQueryServiceInterface, OrderQueryService>();            while (true)            {                Thread.Sleep(2000);                Console.Clear();                for (int i = 0; i < 20;i++ )                {                    ThreadPool.QueueUserWorkItem(new WaitCallback(ConsumeObject));                }            }        }        private static void ConsumeObject(object state)        {            OrderQueryServiceInterface srv = null;            try            {                using (srv = InstancePoolResolver.Resolve<OrderQueryServiceInterface>())  //从对象池中取得对象，没有可用对象则throw exception                {                    Console.WriteLine("Object ID--->" + srv.GetHashCode());                    Thread.Sleep(1000);  //故意长时间占用对象                }            }            catch (Exception ex)            {                Console.WriteLine(ex.Message);            }            finally            {                if (srv != null)                    srv.Dispose();            }        }

 运行效果：

最多只有2个instance，那在哪里设置这个数量呢？请看

是通过Attribute打tag上去的

下面来看看最核心的InstancePoolResolver类

public sealed class InstancePoolResolver    {        private static Dictionary<Type, Type> typeMappers = new Dictionary<Type, Type>();        private static Dictionary<Type, int> typeMappersMaxInstanceCount = new Dictionary<Type, int>();        private static Dictionary<Type, List<PoolableObject>> typeInstances = new Dictionary<Type, List<PoolableObject>>();        private static object o4lock = new object();        public static void Register<T, TProvider>()            where TProvider : class, new()        {            if (typeMappers.ContainsKey(typeof(T)))                throw new Exception("Key existed");                        lock (o4lock)            {                Type t = typeof(T);                typeMappers.Add(t, typeof(TProvider));                typeInstances.Add(t, new List<PoolableObject>());                InstanceSettingAttribute setting = GetInstanceSettingAttribute(typeof(TProvider));                typeMappersMaxInstanceCount.Add(t, setting.MaxInstanceGlobal);            }        }        public static T Resolve<T>()            where T: PoolableObject        {            Type t = typeof(T);            if (!typeMappers.ContainsKey(t) || !typeInstances.ContainsKey(t))                throw new Exception("Key empty, register please");            lock (o4lock)            {                List<PoolableObject> instances = typeInstances[t];                if (instances == null)                {                    instances = new List<PoolableObject>();                    typeInstances[t] = instances;                }                foreach (PoolableObject o in instances)//是否已经存在已有闲置对象                {                    if (o.IsInPool)                    {                        o.IsInPool = false;                        return (T)o;                    }                }                if (instances.Count < typeMappersMaxInstanceCount[t])//new新对象到对象池中                {                    Type type = typeMappers[t];                    PoolableObject obj = (PoolableObject)Activator.CreateInstance(type);                    instances.Add(obj);                    obj.IsInPool = false;                    return (T)obj;                }            }            throw new Exception("Object Pool fulled!"); //没有多余的资源        }        private static InstanceSettingAttribute GetInstanceSettingAttribute(Type type)        {            object[] attrs = type.GetCustomAttributes(typeof(InstanceSettingAttribute), false);            if (attrs == null || attrs.Count() == 0)                return new InstanceSettingAttribute() {  MaxInstanceGlobal=10};            return (InstanceSettingAttribute)attrs[0];        }    }

 

其实很简单，只是多了个获取Attribute的函数