File I/O Metrics

Alan Ruttenberg alanruttenberg at
Tue Nov 1 01:33:00 UTC 2022

Here's an example of fast reading in ABCL. The implementation of certain
array types use java.nio buffers, which can be directly read into via the
java.nio functions.

(defun test-read (path)
  (let* ((f (new 'RandomAccessFile (namestring (truename path)) "r"))
         (channel (#"getChannel" f))
         (array (make-array (* 16 1024 1024) :element-type '(unsigned-byte
         (buffer (get-java-field array "elements" t)))
    (time (loop for count = (#"read" channel buffer)
                until (eql count -1)
                sum count
                do (#"position" buffer 0)

On my machine, for a 5G file, the SBCL code in an earlier post takes 2.4
seconds. This code takes 1.4 sec. It's fastest if I use 2M buffers - 1.1
seconds. SBCL is also marginally faster with smaller buffer sizes.

In the ABCL source code the files "SimpleArray_*.java" are the
implementations of the nio buffer backed array types. See
where the specific type of underlying array is chosen. There is a global
switch for array allocation choosing either direct allocation or
nio-buffers, with the default being nio buffers.

(get-java-field 'java$buffers "active" t)
-> #<org.armedbear.lisp.Java$Buffers$AllocationPolicy NIO {432E958E}>

I haven't looked into the :element-type 'character case.

Maybe someone who is familiar with the ABCL stream implementation is
interested in writing a fast path for read-sequence that uses the nio
calls? If so, shout. Otherwise I'll keep it on my
procrastinate-by-hacking-abcl list.

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