并发与线程

探索 Racket 的线程、通道和并发编程模型。

线程基础

#lang racket

;; 创建线程
(thread
 (lambda ()
   (sleep 2)
   (displayln "Hello from thread!")))

(displayln "Main thread continues...")

线程通信——通道

;; 创建通道
(define ch (make-channel))

;; 发送线程
(thread
 (lambda ()
   (channel-put ch "message from worker")))

;; 接收
(channel-get ch)  ; => "message from worker"

线程邮箱

每个线程都有一个邮箱用于接收消息：

(define worker
  (thread
   (lambda ()
     (let loop ()
       (match (thread-receive)
         ['stop (void)]
         [msg   (displayln (format "Got: ~a" msg))
                (loop)])))))

(thread-send worker "hello")
(thread-send worker "world")
(thread-send worker 'stop)

同步事件

;; sync 等待多个事件中的第一个
(sync (handle-evt (alarm-evt 5)
                  (lambda (_) "timeout"))
      (handle-evt (thread-receive-evt)
                  (lambda (msg) msg)))

并行计算

;; places：共享内存的并行
(place p
  (channel-put p (heavy-computation)))

;; futures：自动并行
(future (lambda () (compute-primes 1000)))

小结

Racket 提供了多种并发原语。线程和通道适合协作式并发，sync/evt 适合事件驱动，places 和 futures 适合 CPU 密集型并行。