java - 重用内存 MappedByteBuffer

Question

我将文件读入MappedByteBuffer:

MappedByteBuffer buffer = FileChannel.open(file, StandardOpenOption.READ)
    .map(FileChannel.MapMode.READ_ONLY, 0, Files.size(file))
    .load();

并将其写入OutputStream:

Channels.newChannel(getOutputStream())
    .write(buffer);

但是，我只能执行此操作，大概是因为 ByteBuffer“当前位置”位于缓冲区的末尾。

那么，处理我希望多个线程使用此内存映射文件这一事实的推荐方法是什么？

Answer 1

使用rewind() :

Rewinds this buffer. The position is set to zero and the mark is discarded.

Invoke this method before a sequence of channel-write or get operations, assuming that the limit has already been set appropriately.

Channels.newChannel(getOutputStream()).write(buffer);
buffer.rewind();
// ...
Channels.newChannel(getOutputStream()).write(buffer);
buffer.rewind();
// ...

请注意，ByteBuffer 不是线程安全的结构。

您最好的选择可能是为每个线程创建 ByteBuffer 的副本，以便可以同时读取它:

// in thread 1
ByteBuffer duplicate = buffer.duplicate();
// ...
// in thread 2
ByteBuffer duplicate = buffer.duplicate();
// ...