JDK 19 对反应式编程的批判

我们知道 JDK 19 引入了虚拟线程，实现了 JEP425 草案，https://openjdk.org/jeps/425 该案对反应式编程的批判可谓犀利：

Improving scalability with the asynchronous style

Some developers wishing to utilize hardware to its fullest have given up the thread-per-request style in favor of a thread-sharing style. Instead of handling a request on one thread from start to finish, request-handling code returns its thread to a pool when it waits for an I/O operation to complete so that the thread can service other requests. This fine-grained sharing of threads — in which code holds on to a thread only when it performs calculations, not when it waits for I/O — allows a high number of concurrent operations without consuming a high number of threads. While it removes the limitation on throughput imposed by the scarcity of OS threads, it comes at a high price: It requires what is known as an asynchronous programming style, employing a separate set of I/O methods that do not wait for I/O operations to complete but rather, later on, signal their completion to a callback. Without a dedicated thread, developers must break down their request-handling logic into small stages, typically written as lambda expressions, and then compose them into a sequential pipeline with an API (see CompletableFuture, for example, or so-called "reactive" frameworks). They thus forsake the language's basic sequential composition operators, such as loops and try/catch blocks.

In the asynchronous style, each stage of a request might execute on a different thread, and every thread runs stages belonging to different requests in an interleaved fashion. This has deep implications for understanding program behavior: Stack traces provide no usable context, debuggers cannot step through request-handling logic, and profilers cannot associate an operation's cost with its caller. Composing lambda expressions is manageable when using Java's stream API to process data in a short pipeline, but problematic when all of the request-handling code in an application must be written in this way. This programming style is at odds with the Java Platform because the application's unit of concurrency — the asynchronous pipeline — is no longer the platform's unit of concurrency.

在 golang 大行其道时 java 也算与时俱进了，愿 VirtualThread 的性能能不负所望。