c# - BinaryReader.Dispose(bool disposing) 创建流的本地引用。为什么？

Question

我在 FCL 代码中发现了一个不寻常的样本。

这是 System.IO.BinaryReader 中的方法:

    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; 
    }

“copyOfStream”对执行逻辑有什么影响？

Answer 1

这样即使 Stream.Close() 抛出异常，m_stream 也会被设置为 null。

回应评论

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

当你关闭一个流时，任何缓冲的输出都会被刷新，这可能会抛出异常，例如由于网络故障。

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

在上面，如果 Stream.Close() 抛出异常，则 m_stream 已经为空。使用以下替代方案，如果 Stream.Close() 抛出，则 m_stream 不会设置为 null:

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

它不会抛出 NullReferenceException 因为它测试 null:

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