Bug #2742: IO#read/gets can be very slow in doze

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 1.9.2dev (2010-02-12 trunk 26649) [i386-mingw32]

[rogerdpack (Roger Pack)]

=begin
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.
=end

[rogerdpack (Roger Pack)]

=begin
This seems to help, though I'm not sure if it's the best way.

Index: io.c

--- io.c (revision 26655)
+++ io.c (working copy)
@@ -1170,7 +1170,7 @@
if (fptr->rbuf == NULL) {
fptr->rbuf_off = 0;
fptr->rbuf_len = 0;

•    fptr->rbuf_capa = 8192;
  

•    fptr->rbuf_capa = 64*1024;
     fptr->rbuf = ALLOC_N(char, fptr->rbuf_capa);
  

  }
  if (fptr->rbuf_len == 0) {
  @@ -1583,7 +1583,7 @@
  rb_exc_raise(rb_econv_open_exc(sname, dname, ecflags));
  fptr->cbuf_off = 0;
  fptr->cbuf_len = 0;

•    fptr->cbuf_capa = size < 1024 ? 1024 : size;
  

•    fptr->cbuf_capa = size < (64*1024) ? (64*1024) : size;
     fptr->cbuf = ALLOC_N(char, fptr->cbuf_capa);
  

  }
  }

=end

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

=begin
This issue was solved with changeset r26997.
Roger, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

=end