为什么有些人使用Finalize方法而不是Dispose方法?
在什么情况下你会使用Finalize方法而不是Dispose方法,反之亦然?
为什么有些人使用Finalize方法而不是Dispose方法?
在什么情况下你会使用Finalize方法而不是Dispose方法,反之亦然?
当前回答
99%的情况下,你都不需要担心。但是,如果你的对象持有对非托管资源的引用(例如,窗口句柄,文件句柄),你需要为托管对象提供一种释放这些资源的方法。Finalize对释放资源进行隐式控制。它由垃圾回收器调用。Dispose是一种对资源释放进行显式控制的方法,可以直接调用。
关于垃圾收集的主题还有很多很多需要学习,但这只是一个开始。
其他回答
以下是MCSD认证工具包(考试70-483)第193页中的一些关键信息:
析构函数≈(几乎等于)base.Finalize(),析构函数被转换为Finalize方法的重写版本,该方法执行析构函数的代码,然后调用基类的Finalize方法。这是完全不确定的,你不知道什么时候会被调用,因为这取决于GC。
如果一个类不包含托管资源和非托管资源,它就不应该实现IDisposable或具有析构函数。
如果类只有托管资源,它应该实现IDisposable,但不应该有析构函数。(当析构函数执行时,您仍然不能确定托管对象 所以你不能调用它们的Dispose()方法。)
如果类只有非托管资源,则需要实现IDisposable,并需要析构函数以防程序不调用Dispose()。
Dispose()方法必须能够安全地运行多次。您可以通过使用一个变量来跟踪它以前是否运行过来实现这一点。
Dispose()应该同时释放托管和非托管资源。
析构函数应该只释放非托管资源。当析构函数执行时,您 不能确定托管对象是否仍然存在,因此无论如何都不能调用它们的Dispose方法。这是通过使用规范的受保护的void Dispose(bool Dispose)模式获得的,其中只有在Dispose == true时才释放(Dispose)托管资源。
释放资源后,Dispose()应该调用GC。SuppressFinalize,这样对象就可以 跳过结束队列。
一个具有非托管资源和托管资源的类的实现示例:
using System;
class DisposableClass : IDisposable
{
// A name to keep track of the object.
public string Name = "";
// Free managed and unmanaged resources.
public void Dispose()
{
FreeResources(true);
// We don't need the destructor because
// our resources are already freed.
GC.SuppressFinalize(this);
}
// Destructor to clean up unmanaged resources
// but not managed resources.
~DisposableClass()
{
FreeResources(false);
}
// Keep track if whether resources are already freed.
private bool ResourcesAreFreed = false;
// Free resources.
private void FreeResources(bool freeManagedResources)
{
Console.WriteLine(Name + ": FreeResources");
if (!ResourcesAreFreed)
{
// Dispose of managed resources if appropriate.
if (freeManagedResources)
{
// Dispose of managed resources here.
Console.WriteLine(Name + ": Dispose of managed resources");
}
// Dispose of unmanaged resources here.
Console.WriteLine(Name + ": Dispose of unmanaged resources");
// Remember that we have disposed of resources.
ResourcesAreFreed = true;
}
}
}
finalizer方法在对象被垃圾收集时被调用,并且您无法保证何时会发生这种情况(您可以强制执行,但这会影响性能)。
另一方面,Dispose方法应该由创建类的代码调用,以便在代码处理完对象后立即清理和释放已获得的任何资源(非托管数据、数据库连接、文件句柄等)。
标准实践是实现IDisposable和Dispose,这样就可以在using语句中使用对象。例如使用(var foo = new MyObject()){}。在终结器中,你调用Dispose,以防调用代码忘记释放你。
99%的情况下,你都不需要担心。但是,如果你的对象持有对非托管资源的引用(例如,窗口句柄,文件句柄),你需要为托管对象提供一种释放这些资源的方法。Finalize对释放资源进行隐式控制。它由垃圾回收器调用。Dispose是一种对资源释放进行显式控制的方法,可以直接调用。
关于垃圾收集的主题还有很多很多需要学习,但这只是一个开始。
完成
Finalizers should always be protected, not public or private so that the method cannot be called from the application's code directly and at the same time, it can make a call to the base.Finalize method Finalizers should release unmanaged resources only. The framework does not guarantee that a finalizer will execute at all on any given instance. Never allocate memory in finalizers or call virtual methods from finalizers. Avoid synchronization and raising unhandled exceptions in the finalizers. The execution order of finalizers is non-deterministic—in other words, you can't rely on another object still being available within your finalizer. Do not define finalizers on value types. Don't create empty destructors. In other words, you should never explicitly define a destructor unless your class needs to clean up unmanaged resources and if you do define one, it should do some work. If, later, you no longer need to clean up unmanaged resources in the destructor, remove it altogether.
拥有
Implement IDisposable on every type that has a finalizer Ensure that an object is made unusable after making a call to the Dispose method. In other words, avoid using an object after the Dispose method has been called on it. Call Dispose on all IDisposable types once you are done with them Allow Dispose to be called multiple times without raising errors. Suppress later calls to the finalizer from within the Dispose method using the GC.SuppressFinalize method Avoid creating disposable value types Avoid throwing exceptions from within Dispose methods
处理/确定模式
Microsoft recommends that you implement both Dispose and Finalize when working with unmanaged resources. The Finalize implementation would run and the resources would still be released when the object is garbage collected even if a developer neglected to call the Dispose method explicitly. Cleanup the unmanaged resources in the Finalize method as well as Dispose method. Additionally call the Dispose method for any .NET objects that you have as components inside that class(having unmanaged resources as their member) from the Dispose method.
Dispose和Finalize之间的主要区别是:
Dispose通常由代码调用。当您调用它时,资源立即被释放。人们忘记调用这个方法,所以使用(){}语句被发明出来。当您的程序完成{}内代码的执行时,它将自动调用Dispose方法。
您的代码不会调用Finalize。它意味着由垃圾收集器(GC)调用。这意味着在将来的任何时候,只要GC决定这样做,就可以释放资源。当GC工作时,它将通过许多Finalize方法。如果你在这里面有沉重的逻辑,它会使过程变慢。这可能会导致程序的性能问题。所以小心你放进去的东西。
我个人会在Dispose中编写大部分销毁逻辑。希望这能消除困惑。