Bug #2742: IO#read/gets can be very slow in doze
http://redmine.ruby-lang.org/issues/show/2742

Author: Roger Pack
Status: Open, Priority: Normal
ruby -v: ruby 1.9.2dev (2010-02-12 trunk 26649) [i386-mingw32]

this code

n = 100 * 1000 * 1000
puts "writing"
File.open("foo", 'wb'){|f| f.write(" " * n) }
puts "reading"
File.open("foo", 'r') do |io| 
 io.read
end

takes something like 700s in windows, most of the time is spent in rb_str_resize.  Cause seems to be that it is rb_str_resize'ing the string by 1024B at a time, so N^2 in the amount of time it takes to read it in because it has to keep copying it to the newly sized string.

The same thing happens for

File.open("foo", 'rb') do |io| 
 io.gets
end

except that it reads (and resizes) in 8K bytes.  Not sure why they're different sizes.  I'd imagine this problem exists in Linux, but without as much of a negative impact as it reads in larger sizes.


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