Graphical analysis of the underlying technology of NIO and NodeJS supporting Java

It is well known that in recent versions of Java, some support for Java NIO and NIO2 has been added. At the same time, one of the most praised advantages of the NodeJS technology stack is its high-performance IO. So the topic we want to discuss today is the underlying technology that supports these technologies.

A question to ask before starting is:

Why didn’t NodeJS and Java NIO2 appear earlier?

Answer: Personally, I think the underlying support technology is not yet mature.

So, what does the underlying technology refer to? Yes, I think many people have guessed that it is operating system technology. The two concepts proposed in this article, Java NIO2 and NodeJS, are without exception user-mode technologies or application layer technologies, and these application layer technologies run on the OS. At the same time, with the advancement of the operating system, they can support The Programming model is also richer. It can be said that these two technologies are completely evolved to apply the dividends brought by the advancement of operating systems. Generally speaking, the first technology to enjoy this benefit must be C\C++, because most of the latest improvements in OS are system calls, and C\C++ is the most convenient to apply these system calls, but it is also the most complex. In order to obtain the same performance, other platforms must continue to evolve and package so that users can take advantage of these bonuses. Once that platform stops updating, it is the time for this platform to decline. The more convenient the package is for users, the more user-friendly it is, and the more people may use it. Although many people can quickly write code based on these platforms, they often fail to understand the essence because they still do not understand the motivations and principles of these technologies. The technologies we discuss below are the underlying technologies related to these two technologies.

No matter which OS design, the following five IO models are essential.

• 1. blocking I/O

• 2. nonblocking I/O

• 3. I/O multiplexing (select, poll and epoll)

• 4. signal driven I/O (SIGIO)

• ##5. asynchronous I/ O (the POSIX aio_ functions)

1. blocking I/O

As shown in the figure, the advantage of this IO model is that it is simple to program and is also the earliest supported by the OS. One of the disadvantages of the IO model is that system calls block the execution of user dynamic threads, resulting in a waste of CPU time and low IO efficiency.

2. nonblocking I/O

As shown in the figure, an improvement of this IO model is that IO is non-blocking, but long polling is required , which also wastes CPU clock cycles.

3. I/O multiplexing (select, poll and epoll)

As shown in the figure, this IO model is the most stable provided by today’s OS Most mainstream applications are built based on this IO model, such as NodeJS, but these platforms often add a layer of encapsulation on top of this model to directly support AIO.

4. signal driven I/O (SIGIO)

As shown in the figure, the data records that this IO model has no performance advantage compared to model 3. At the same time, due to unstable system support, it is rarely used by designers.

5. asynchronous I/O (the POSIX aio_ functions)

As shown in the figure, this IO model is the most perfect AIO and programming model It is also the simplest, but there are very few OSs that can perfectly support this model. Online information shows that

Linux is making efforts in this area. Once the OS makes progress in this aspect, programmingframework ,The platform and programming model may still need ,to be simplified to a large extent.

Although this model is rarely supported by OS, it does not mean that there is no such AIO model now. Many frameworks have done work in this area and simulated AIO in user mode, so that users can do more Focus on business logic code.

6. Synchronous and asynchronous, blocking and non-blocking

Synchronization and asynchronous are for the interaction between the application and the kernel. Waiting until the data is read and then returning is synchronous, while returning directly is asynchronous. Blocking and non-blocking refer to processes and threads. In blocking mode, the reading or writing thread always waits. In non-blocking mode, the reading or writing thread immediately returns a

status value.

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