问题描述
我想编写一个同时写入多个文件的程序;认为通过使用非阻塞模式可以使用一个线程。但FileChannel不支持非阻塞模式。有人知道为什么吗？
I wanted to write a program which writes to multiple files simultaneously; thought it will be possible with one thread by using non-blocking mode. But FileChannel does not support non-blocking mode. Does anybody know why?
推荐答案
UNIX不支持文件的非阻塞I / O，请参阅。由于Java应该（至少尝试）在所有平台上提供相同的行为， FileChannel 不实现 SelectableChannel 。
UNIX does not support non-blocking I/O for files, see Non-blocking I/O with regular files. As Java should (at least try to) provide the same behaviour on all platforms, the FileChannel does not implement SelectableChannel.
然而，Java 7将包含一个新的类，支持异步文件I / O，这是一个不同的非阻塞I / O的机制。其中一个实现受益于Windows上的非阻塞I / O API（请参阅。
However Java 7 will include a new AsynchronousFileChannel class that supports asynchronous file I/O, which is a different mechanism to non-blocking I/O. One of its implementations WindowsAsynchronousFileChannelImpl benefits from non-blocking I/O API on Windows (see Asynchronous I/O in Windows).
在此期间，您可以使用多个线程来实现同样的效果。但这已经在可在所有操作系统中移植。
In the meantime, you could use multiple threads to achieve the same effect. But this is already implemented in SimpleAsynchronousFileChannelImpl which is portable across all operating systems.
一般只套接字和管道通过 select（）机制真正支持非阻塞I / O.
In general only sockets and pipes truly support non-blocking I/O via select() mechanism.
@Trying评论因此：
@Trying comments thus:
在我看来，异步I / O（使用例如 Future 或 CompletionHandler ）是一种非阻塞I / O.
To my mind, asynchronous I/O (using for example Future or a CompletionHandler) is a form of non-blocking I/O.
- 它不会阻止线程在通道上执行
读取（...）调用。 - 您可以使用
Future.isDone（）以避免以后阻止。
- It doesn't block the thread doing the
read(...)call on the channel. - You can use
Future.isDone()to avoid blocking later.
（A当然，使用 Selector 的I / O也可以是异步的...取决于你如何使用API。）
(And of course, I/O using a Selector can be asynchronous too ... depending on how you use the API.)
相比之下，如果您读取 FileChannel 并且当前没有可用的数据，则线程会阻塞...（通常）直到数据可用。
By contrast, if you read on a FileChannel and there is no data currently available, the thread blocks ... (typically) until data becomes available.
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