BB 0.3.5-SNAPSHOT - Memory mapping

binf_bb_mmap.clj

;; Test should fail because it requires `java.nio.DirectByteBufferR`

(require '[babashka.deps :as deps])
(deps/add-deps '{:deps {io.helins/binf {:mvn/version "1.0.0-beta1"}}})

(ns helins.binf.example.mmap-file

  "Using BinF for writing and reading to a memory-mapped file on the JVM.

   BinF protocols are implemented for ByteBuffer, parent of MappedByteBuffer."

  ;; We shall reuse our functions for writing and reading a date.
  ;;
  (:require [helins.binf         :as binf])
  (:import java.io.RandomAccessFile
           java.nio.channels.FileChannel$MapMode))

(defn rr-date

  [view]

  [(binf/rr-u16 view)
   (binf/rr-u8 view)
   (binf/rr-u8 view)])

(defn wr-date

  [view year month day]

  (-> view
      (binf/wr-b16 year)
      (binf/wr-b8 month)
      (binf/wr-b8 day)))

(= [2021 3 16]

   (with-open [file (RandomAccessFile. "/tmp/binf-example.dat"
                                       "rw")]
     (let [view (-> file
                    .getChannel
                    (.map FileChannel$MapMode/READ_WRITE
                          ;; From byte 0 in the file
                          0
                          ;; A size in bytes, we know a date is 4 bytes
                          4)
                    .load)]
       (-> view
           ;; Writing date
           (wr-date 2021
                    3
                    16)
           ;; Ensuring changes are persisted on disk
           .force
           ;; Reading it back from the start of the file
           (binf/seek 0)
           rr-date))))

Error:

Type:     java.lang.IllegalArgumentException
Message:  No matching method load found taking 0 args for class java.nio.DirectByteBufferR