JAVA NIO 中的 zerocopy 技术提高IO性能

「爱情、让人受尽委屈。」 2022-06-13 03:26 205阅读 0赞

关于一篇更详细更好的介绍 ZeroCopy技术的文章，可参考：[JAVA IO 以及 NIO 理解][JAVA IO _ NIO]

这篇文章介绍了 zerocopy技术来提高Linux平台上的IO密集型的JAVA应用程序的性能.

zerocopy技术能够避免中间缓冲区中的冗余数据复制以及减少Linux内核空间和用户空间上下文交换的次数。

适用场景：Many Web applications serve a significant amount of static content, which amounts to reading data off of a disk and writing the exact same data back to the response socket.

应用程序从本地磁盘读取数据，再将读取的数据原封不动地发送给Socket。

不采用zerocopy技术时的数据传输过程如下：

the kernel reads the data off of disk and pushes it across the kernel-user boundary to the application, and then the application pushes it back across the kernel-user boundary to be written out to the socket. In effect, the application serves as an inefficient intermediary that gets the data from the disk file to the socket.

数据先从本地磁盘读取到内核空间中，再通过缓冲区由用户程序得到，用户程序再通过缓冲区将数据发送到Socket。

![160942389072610.png][]

Each time data traverses the user-kernel boundary, it must be copied, which consumes CPU cycles and memory bandwidth. Fortunately, you can eliminate these copies through a technique called — appropriately enough — zero copy.

每次数据传输到 内核-用户 缓冲区时，必须进行复制，这消耗了CPU和内存，而通过 zerocopy技术 可以去掉复制操作。

Applications that use zero copy request that the kernel copy the data directly from the disk file to the socket, without going through the application.

用户程序通过zerocopy请求使得数据直接从内核发送到Socket。

JAVA类库通过`java.nio.channels.FileChannel`. `transferTo()``方法支持zerocopy技术。`

You can use the `transferTo()` method to transfer bytes directly from the channel on which it is invoked to another writable byte channel, without requiring data to flow through the application。

参考： [https://www.ibm.com/developerworks/linux/library/j-zerocopy/][https_www.ibm.com_developerworks_linux_library_j-zerocopy]

[JAVA IO _ NIO]: http://www.cnblogs.com/hapjin/p/5736188.html
[160942389072610.png]: /images/20220613/e75ac2f097174b1e8a962110f91588e1.png
[https_www.ibm.com_developerworks_linux_library_j-zerocopy]: https://www.ibm.com/developerworks/linux/library/j-zerocopy/