IoC 容器的對(duì)象生存期管理
如果你一直在使用 IoC 容器，你可能已經(jīng)使用過(guò)了一些對(duì)象生存期管理模型(Object Lifetime Management)。通過(guò)對(duì)對(duì)象生存期的管理，將使對(duì)象的復(fù)用成為可能。同時(shí)其使容器可以控制如何創(chuàng)建和管理對(duì)象實(shí)例。
Unity 提供的對(duì)象生存期管理模型是通過(guò)從抽象類 LifetimeManager 的派生類來(lái)完成。Unity 將為每個(gè)類型的注冊(cè)創(chuàng)建生存期管理器。每當(dāng) UnityContainer 需要?jiǎng)?chuàng)建一個(gè)新的對(duì)象實(shí)例時(shí)，將首先檢測(cè)該對(duì)象類型的生存期管理器，是否已有一個(gè)對(duì)象實(shí)例可用。如果沒(méi)有對(duì)象實(shí)例可用，則 UnityContainer 將基于配置的信息構(gòu)造該對(duì)象實(shí)例并將該對(duì)象交予對(duì)象生存期管理器。
LifetimeManager
LifetimeManager 是一個(gè)抽象類，其實(shí)現(xiàn)了 ILifetimePolicy 接口。該類被作為所有內(nèi)置或自定義的生存期管理器的父類。它定義了 3 個(gè)方法：
GetValue - 返回一個(gè)已經(jīng)存儲(chǔ)在生存期管理器中對(duì)象實(shí)例。
SetValue - 存儲(chǔ)一個(gè)新對(duì)象實(shí)例到生存期管理器中。
RemoveValue - 從生存期管理器中將已存儲(chǔ)的對(duì)象實(shí)例刪除。UnityContainer 的默認(rèn)實(shí)現(xiàn)將不會(huì)調(diào)用此方法，但可在定制的容器擴(kuò)展中調(diào)用。
Unity 內(nèi)置了 6 種生存期管理模型，其中有 2 種即負(fù)責(zé)對(duì)象實(shí)例的創(chuàng)建也負(fù)責(zé)對(duì)象實(shí)例的銷毀(Dispose)。
TransientLifetimeManager - 為每次請(qǐng)求生成新的類型對(duì)象實(shí)例。 (默認(rèn)行為)
ContainerControlledLifetimeManager - 實(shí)現(xiàn) Singleton 對(duì)象實(shí)例。 當(dāng)容器被 Disposed 后，對(duì)象實(shí)例也被 Disposed。
HierarchicalifetimeManager - 實(shí)現(xiàn) Singleton 對(duì)象實(shí)例。但子容器并不共享父容器實(shí)例，而是創(chuàng)建針對(duì)字容器的 Singleton 對(duì)象實(shí)例。當(dāng)容器被 Disposed 后，對(duì)象實(shí)例也被 Disposed。
ExternallyControlledLifetimeManager - 實(shí)現(xiàn) Singleton 對(duì)象實(shí)例，但容器僅持有該對(duì)象的弱引用(WeakReference)，所以該對(duì)象的生存期由外部引用控制。
PerThreadLifetimeManager - 為每個(gè)線程生成 Singleton 的對(duì)象實(shí)例，通過(guò) ThreadStatic 實(shí)現(xiàn)。
PerResolveLifetimeManager - 實(shí)現(xiàn)與 TransientLifetimeManager 類似的行為，為每次請(qǐng)求生成新的類型對(duì)象實(shí)例。不同之處在于對(duì)象實(shí)例在 BuildUp 過(guò)程中是可被重用的。
Code Double
public interface IExample : IDisposable
{
void SayHello();
}
public class Example : IExample
{
private bool _disposed = false;
private readonly Guid _key = Guid.NewGuid();
public void SayHello()
{
if (_disposed)
{
throw new ObjectDisposedException("Example",
string.Format("{0} is already disposed!", _key));
}
Console.WriteLine("{0} says hello in thread {1}!", _key,
Thread.CurrentThread.ManagedThreadId);
}
public void Dispose()
{
if (!_disposed)
{
_disposed = true;
}
}
}
TransientLifetimeManager
TransientLifetimeManager 是 Unity 默認(rèn)的生存期管理器。其內(nèi)部的實(shí)現(xiàn)都為空，這就意味著每次容器都會(huì)創(chuàng)建和返回一個(gè)新的對(duì)象實(shí)例，當(dāng)然容器也不負(fù)責(zé)存儲(chǔ)和銷毀該對(duì)象實(shí)例。
private static void TestTransientLifetimeManager()
{
IExample example;
using (IUnityContainer container = new UnityContainer())
{
container.RegisterType(typeof(IExample), typeof(Example),
new TransientLifetimeManager());
// each one gets its own instance
container.Resolve().SayHello();
example = container.Resolve();
}
// container is disposed but Example instance still lives
// all previously created instances weren't disposed!
example.SayHello();
Console.ReadKey();
}
ContainerControlledLifetimeManager
ContainerControlledLifetimeManager 將為 UnityContainer 及其子容器提供一個(gè) Singleton 的注冊(cè)類型對(duì)象實(shí)例。其只在第一次請(qǐng)求某注冊(cè)類型時(shí)創(chuàng)建一個(gè)新的對(duì)象實(shí)例，該對(duì)象實(shí)例將被存儲(chǔ)到生存期管理器中，并且一直被重用。當(dāng)容器析構(gòu)時(shí)，生存期管理器會(huì)調(diào)用 RemoveValue 將存儲(chǔ)的對(duì)象銷毀。
Singleton 對(duì)象實(shí)例對(duì)應(yīng)每個(gè)對(duì)象類型注冊(cè)，如果同一對(duì)象類型注冊(cè)多次，則將為每次注冊(cè)創(chuàng)建單一的實(shí)例。
private static void TestContainerControlledLifetimeManager()
{
IExample example;
using (IUnityContainer container = new UnityContainer())
{
container.RegisterType(typeof(IExample), typeof(Example),
new ContainerControlledLifetimeManager());
IUnityContainer firstSub = null;
IUnityContainer secondSub = null;
try
{
firstSub = container.CreateChildContainer();
secondSub = container.CreateChildContainer();
// all containers share same instance
// each resolve returns same instance
firstSub.Resolve().SayHello();
// run one resolving in other thread and still receive same instance
Thread thread = new Thread(
() => secondSub.Resolve().SayHello());
thread.Start();
container.Resolve().SayHello();
example = container.Resolve();
thread.Join();
}
finally
{
if (firstSub != null) firstSub.Dispose();
if (secondSub != null) secondSub.Dispose();
}
}
try
{
// exception - instance has been disposed with container
example.SayHello();
}
catch (ObjectDisposedException ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadKey();
}
HierarchicalLifetimeManager
HierarchicalLifetimeManager 類衍生自 ContainerControlledLifetimeManager，其繼承了父類的所有行為。與父類的不同之處在于子容器中的生存期管理器行為。ContainerControlledLifetimeManager 共享相同的對(duì)象實(shí)例，包括在子容器中。而 HierarchicalLifetimeManager 只在同一個(gè)容器內(nèi)共享，每個(gè)子容器都有其單獨(dú)的對(duì)象實(shí)例。
private static void TestHierarchicalLifetimeManager()
{
IExample example;
using (IUnityContainer container = new UnityContainer())
{
container.RegisterType(typeof(IExample), typeof(Example),
new HierarchicalLifetimeManager());
IUnityContainer firstSub = null;
IUnityContainer secondSub = null;
try
{
firstSub = container.CreateChildContainer();
secondSub = container.CreateChildContainer();
// each subcontainer has its own instance
firstSub.Resolve().SayHello();
secondSub.Resolve().SayHello();
container.Resolve().SayHello();
example = firstSub.Resolve();
}
finally
{
if (firstSub != null) firstSub.Dispose();
if (secondSub != null) secondSub.Dispose();
}
}
try
{
// exception - instance has been disposed with container
example.SayHello();
}
catch (ObjectDisposedException ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadKey();
}
ExternallyControlledLifetimeManager
ExternallyControlledLifetimeManager 中的對(duì)象實(shí)例的生存期限將有 UnityContainer 外部的實(shí)現(xiàn)控制。此生存期管理器內(nèi)部直存儲(chǔ)了所提供對(duì)象實(shí)例的一個(gè) WeakReference。所以如果 UnityContainer 容器外部實(shí)現(xiàn)中沒(méi)有對(duì)該對(duì)象實(shí)例的強(qiáng)引用，則該對(duì)象實(shí)例將被 GC 回收。再次請(qǐng)求該對(duì)象類型實(shí)例時(shí)，將會(huì)創(chuàng)建新的對(duì)象實(shí)例。
private static void TestExternallyControlledLifetimeManager()
{
IExample example;
using (IUnityContainer container = new UnityContainer())
{
container.RegisterType(typeof(IExample), typeof(Example),
new ExternallyControlledLifetimeManager());
// same instance is used in following
container.Resolve().SayHello();
container.Resolve().SayHello();
// run garbate collector. Stored Example instance will be released
// beacuse there is no reference for it and LifetimeManager holds
// only WeakReference
GC.Collect();
// object stored targeted by WeakReference was released
// new instance is created!
container.Resolve().SayHello();
example = container.Resolve();
}
example.SayHello();
Console.ReadKey();
}
需要注意，在 Debug 模式下，編譯器不會(huì)優(yōu)化本地變量，所以引用有可能還存在。而在 Release 模式下會(huì)優(yōu)化。
PerThreadLifetimeManager
PerThreadLifetimeManager 模型提供“每線程單實(shí)例”功能。所有的對(duì)象實(shí)例在內(nèi)部被存儲(chǔ)在 ThreadStatic 的集合。容器并不跟蹤對(duì)象實(shí)例的創(chuàng)建并且也不負(fù)責(zé) Dispose。
private static void TestPerThreadLifetimeManager()
{
IExample example;
using (IUnityContainer container = new UnityContainer())
{
container.RegisterType(typeof(IExample), typeof(Example),
new PerThreadLifetimeManager());
Actionaction = delegate(int sleep)
{
// both calls use same instance per thread
container.Resolve().SayHello();
Thread.Sleep(sleep);
container.Resolve().SayHello();
};
Thread thread1 = new Thread((a) => action.Invoke((int)a));
Thread thread2 = new Thread((a) => action.Invoke((int)a));
thread1.Start(50);
thread2.Start(50);
thread1.Join();
thread2.Join();
example = container.Resolve();
}
example.SayHello();
Console.ReadKey();
}
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