mem.rkt

#lang racket/base

(require racket/format)

(define (read-bytes/lazy n in [bufsize 4096])
  (define buf (make-bytes bufsize))
  (define offset
    (let loop ([offset 0])
      (define len
        (peek-bytes-avail! buf offset #f in))

      (cond
        [(eof-object? len) offset]
        [else
         (define offset* (+ offset len))
         (cond
           [(> offset* n) offset*]
           [else (loop offset*)])])))

  (cond
    [(zero? offset) eof]
    [else (read-bytes (min offset n) in)]))

(define-syntax-rule (mem e ...)
  (begin
    (collect-garbage)
    (define s (current-memory-use))
    (begin0 (begin e ...)
      (printf "mem delta: ~a\n" (~r (/ (- (current-memory-use) s)
                                       1024
                                       1024))))))

(define N (* 100 1024 1024))

(let ()
  (define-values (in out)
    (make-pipe))

  (define t1
    (thread
     (lambda _
       (mem
        (displayln "before")
        (printf "~v\n" (read-bytes/lazy N in))
        (displayln "after")))))

  (sleep 1)
  (displayln "hello" out)
  (displayln " how are you" out)
  (close-output-port out)
  (sync t1))


(let ()
  (define-values (in out)
    (make-pipe))

  (define t2
    (thread
     (lambda _
       (mem
        (displayln "before")
        (printf "~v\n" (read-bytes N in))
        (displayln "after")))))

  (sleep 1)
  (displayln "hello" out)
  (displayln " how are you" out)
  (close-output-port out)
  (sync t2))