# HG changeset patch
# User Franz Glasner <fzglas.hg@dom66.de>
# Date 1644353114 -3600
# Node ID 21d2589c96b9c1de12f15a360eb7f88c861ceae8
# Parent  b96d3585e8ced173aad281bcc94ce627745689e8
Use madvise if available to sequentially read a file

diff -r b96d3585e8ce -r 21d2589c96b9 shasum.py
--- a/shasum.py	Tue Feb 08 21:27:13 2022 +0100
+++ b/shasum.py	Tue Feb 08 21:45:14 2022 +0100
@@ -481,6 +481,10 @@
             # NOTE: On Windows mmapped files with length 0 are not supported.
             #       So ensure to not call mmap.mmap() if the file size is 0.
             #
+            try:
+                madvise = mmap.mmap.madvise
+            except AttributeError:
+                madvise = None
             if filesize < MAP_CHUNK_SIZE:
                 mapsize = filesize
             else:
@@ -492,6 +496,8 @@
                               mapsize,
                               access=mmap.ACCESS_READ,
                               offset=mapoffset)
+                if madvise:
+                    madvise(m, mmap.MADV_SEQUENTIAL)
                 try:
                     h.update(m)
                 finally: