FileDescriptor什么时候关闭？

问题描述

我的应用需要执行以下操作：

My app needs to do the following:

• 打开 FileInputStream ，并获取基础 FileDescriptor （通过 getFd（））


• 创建新的 FileInputStream 基于以上 FileDescriptor的对象

• Open a FileInputStream, and obtain the underlying FileDescriptor (via getFd())
• Create new FileInputStream objects based on the above FileDescriptor

到目前为止，我只需要一个 FileDescriptor ，所以我以前通过调用 close（）在原始流上（即在我调用的 getFd（）的流上）。我使用它是因为一些Android API方法有这样的参数。

So far, I only needed one FileDescriptor, so I used to close it by calling close() on the original stream (i.e. on the stream which getFd() I called). I use it because some Android API methods have such a parameter.

现在我将有更多的 FileInputStream 对象同时，何时关闭 FileDescriptor ？ （我猜：当所有 FileInputStream 对象都关闭？）

Now that I will have more FileInputStream objects at the same time, when will the FileDescriptor be closed? (My guess: when all FileInputStream objects are closed?)

推荐答案

我相信你是对的。一个小测试显示 FileDescriptor 在 FileInputStream 关闭后变为无效。请注意，对于相同 FileDescriptor 的多个 FileInputStream ， FileDescriptor 一旦第一个 FileInputStream 关闭就变为无效，即如果你先关闭 fis1 然后 fis2 或者相反：

I belive you are right. A small test shows that the FileDescriptor becomes invalid after its FileInputStream is closed. Note that, in case of more than one FileInputStream for the same FileDescriptor, the FileDescriptor becomes invalid as soon as its first FileInputStream is closed, i.e. it does not matter if you close first fis1 and then fis2 or the other way around:

FileInputStream fis1 = new FileInputStream("/tmp/adb.log");
FileDescriptor fd = fis1.getFD();
FileInputStream fis2 = new FileInputStream(fd);
System.out.println(fd.valid());
fis1.close();
System.out.println(fd.valid());
fis2.close();
System.out.println(fd.valid());

输出为：

true
false
false

别忘了在 finally 块中关闭流，以确保在I / O（读/写）错误的情况下也关闭它。

Do not forget to close the stream in a finally block, to make sure you close it also in case of an I/O (read/write) error.

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