A binding to the system mmap()
.
$ raco pkg install mmap
$ cat /tmp/x
111111111111111111111111111111111111111111111111111111111111111111111
$ racket
> (require mmap)
> (define bs (mmap "/tmp/x" #:length 20 #:prot '(PROT_READ PROT_WRITE) #:flags 'MAP_SHARED))
> bs
#"11111111111111111111"
> (bytes-set! bs 0 50)
> bs
#"21111111111111111111"
>
$ cat /tmp/x
211111111111111111111111111111111111111111111111111111111111111111111