c# - 如何在 C# 中的 Dispose() 方法中处理托管资源？

Question

我知道 Dispose() 是为非托管资源设计的，当资源不再需要时应该被释放，而不用等待垃圾收集器完成对象。

但是，在处置对象时，它会抑制垃圾收集器的终结(在下面的代码中为 GC.SuppressFinalize(this);)。这意味着如果对象包含托管资源，我们也必须处理它，因为垃圾收集器不会清理它。

在下面的示例代码中(来自 MSDN)，“Component”是一个托管资源，我们为此资源调用了 dispose() (component.Dispose())。我的问题是，我们如何为托管资源的组件类实现这个方法？我们是否应该使用像 Collect() 这样的东西来戳垃圾收集器来清理这部分？

任何想法将不胜感激。谢谢。

下面是我正在查看的来自 MSDN 的代码:

using System;
using System.ComponentModel;

// The following example demonstrates how to create
// a resource class that implements the IDisposable interface
// and the IDisposable.Dispose method.

public class DisposeExample
{
// A base class that implements IDisposable.
// By implementing IDisposable, you are announcing that
// instances of this type allocate scarce resources.
public class MyResource: IDisposable
{
    // Pointer to an external unmanaged resource.
    private IntPtr handle;
    // Other managed resource this class uses.
    private Component component = new Component();
    // Track whether Dispose has been called.
    private bool disposed = false;

    // The class constructor.
    public MyResource(IntPtr handle)
    {
        this.handle = handle;
    }

    // Implement IDisposable.
    // Do not make this method virtual.
    // A derived class should not be able to override this method.
    public void Dispose()
    {
        Dispose(true);
        // This object will be cleaned up by the Dispose method.
        // Therefore, you should call GC.SupressFinalize to
        // take this object off the finalization queue
        // and prevent finalization code for this object
        // from executing a second time.
        GC.SuppressFinalize(this);
    }

    // Dispose(bool disposing) executes in two distinct scenarios.
    // If disposing equals true, the method has been called directly
    // or indirectly by a user's code. Managed and unmanaged resources
    // can be disposed.
    // If disposing equals false, the method has been called by the
    // runtime from inside the finalizer and you should not reference
    // other objects. Only unmanaged resources can be disposed.
    private void Dispose(bool disposing)
    {
        // Check to see if Dispose has already been called.
        if(!this.disposed)
        {
            // If disposing equals true, dispose all managed
            // and unmanaged resources.
            if(disposing)
            {
                // Dispose managed resources.
                component.Dispose();
            }

            // Call the appropriate methods to clean up
            // unmanaged resources here.
            // If disposing is false,
            // only the following code is executed.
            CloseHandle(handle);
            handle = IntPtr.Zero;

            // Note disposing has been done.
            disposed = true;

        }
    }

    // Use interop to call the method necessary
    // to clean up the unmanaged resource.
    [System.Runtime.InteropServices.DllImport("Kernel32")]
    private extern static Boolean CloseHandle(IntPtr handle);

    // Use C# destructor syntax for finalization code.
    // This destructor will run only if the Dispose method
    // does not get called.
    // It gives your base class the opportunity to finalize.
    // Do not provide destructors in types derived from this class.
    ~MyResource()
    {
        // Do not re-create Dispose clean-up code here.
        // Calling Dispose(false) is optimal in terms of
        // readability and maintainability.
        Dispose(false);
    }
}
public static void Main()
{
    // Insert code here to create
    // and use the MyResource object.
}
}

Answer 1

那个一次性模式是confusing .这是 a better way实现它:

第 1 步。 创建一个一次性类来封装您拥有的每个非托管资源。这应该是非常罕见的，大多数人没有非托管资源需要清理。本课only cares (pdf)关于它的非托管资源，并且应该有一个终结器。实现看起来像这样:

public class NativeDisposable : IDisposable {

  public void Dispose() {
    CleanUpNativeResource();
    GC.SuppressFinalize(this);
  }

  protected virtual void CleanUpNativeResource() {
    // ...
  }

  ~NativeDisposable() {
    CleanUpNativeResource();
  }

  // ...

  IntPtr _nativeResource;

}

第 2 步。 当类(class)举办其他一次性类(class)时，创建一个一次性类(class)。这很容易实现，你不需要终结器。在您的 Dispose 方法中，只需对其他一次性用品调用 Dispose。在这种情况下，您不关心非托管资源:

public class ManagedDisposable : IDisposable {

  // ...

  public virtual void Dispose() {
    _otherDisposable.Dispose();
  }

  IDisposable _otherDisposable;

}

示例中的“组件”可能是其中之一，具体取决于它是封装了非托管资源还是仅由其他一次性资源组成。

另请注意，抑制终结并不意味着您抑制垃圾收集器清理您的实例；这只是意味着当垃圾收集器在您的实例中运行时，它不会调用为其定义的终结器。