BinaryReader.Dispose（BOOL处置）创建一个本地引用流。为什么？ [英] BinaryReader.Dispose(bool disposing) creates a local reference to stream. Why?

问题描述

我发现了整箱的代码不同寻常的样品

这是在System.IO.BinaryReader方式：

 受保护的虚拟无效的Dispose（BOOL处置）{
如果（处置）{
流copyOfStream = m_stream; 
 m_stream = NULL; 
如果（copyOfStream = NULL&放大器;！&安培;！m_leaveOpen）
 copyOfStream.Close（）; 
} 
 m_stream = NULL; 
 m_buffer = NULL; 
 m_decoder = NULL; 
 m_charBytes = NULL; 
 m_singleChar = NULL; 
 m_charBuffer = NULL; 
} 
  

在执行逻辑有什么影响copyOfStream？

解决方案

它的完成使m_stream将被设置为null即使 Stream.Close（）抛出异常。

在回应评论

什么样的​​异常可以在Stream.Close（）

筹集

当您关闭流，任何缓冲输出刷新，它可以抛出一个异常，如：由于网络故障。

我不知道，这是一个理由。通常我们调用Dispose在使用块，这意味着变量都不会使用反正

在上面的，如果Stream.Close （）抛出，然后m_stream就已经为空。以下替换，m_stream不会，如果Stream.Close（）抛出设置为空：

  m_stream.Close（） ; //< ==抛出
 m_stream = NULL; //<如果关闭（）抛出
 ==不执行 

不过，在这种情况下，如果我们谈论的是异常安全，有人可以重试调用Dispose方法和将面临的NullReferenceException

它赢得了 ŧ抛出NullReferenceException异常，因为它会检测空：

 如果（！copyOfStream = NULL&放大器;&安培; m_leaveOpen）
 copyOfStream.Close（）; 
  

I found an unusual sample in FCL code.

This is method in System.IO.BinaryReader:

    protected virtual void Dispose(bool disposing) { 
        if (disposing) { 
            Stream copyOfStream = m_stream;
            m_stream = null; 
            if (copyOfStream != null && !m_leaveOpen)
                copyOfStream.Close();
        }
        m_stream = null; 
        m_buffer = null;
        m_decoder = null; 
        m_charBytes = null; 
        m_singleChar = null;
        m_charBuffer = null; 
    }

What impact on the execution logic has 'copyOfStream'?

解决方案

It's done so that m_stream will be set to null even if Stream.Close() throws an exception.

In response to comments

what kind of exception can be raised on Stream.Close()

When you close a stream, any buffered output is flushed, which can throw an exception, e.g. due to a network failure.

I'm not sure that this is a rationale. Usually we're calling Dispose in using block, and this means that variable will never used anyway

In the above, if Stream.Close() throws, then m_stream will already be null. With the following alternative, m_stream won't be set to null if Stream.Close() throws:

m_stream.Close(); // <== throws
m_stream = null;  // <== not executed if Close() throws

But in this case if we're talking about exception-safety, someone can retry call to Dispose method and will face NullReferenceException

It won't throw a NullReferenceException because it tests for null:

if (copyOfStream != null && !m_leaveOpen)
        copyOfStream.Close();

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