eof performance

[JeffBezanson]

From Don MacMillen on julia-dev:

   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "help()" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.4.0-dev+147 (2014-08-14 22:04 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit 48eed79 (4 days old master)
|__/                   |  x86_64-linux-gnu

julia> io = open("ubuntu-14.04-desktop-amd64.iso")
IOStream(<file ubuntu-14.04-desktop-amd64.iso>)

julia> function readit(io)
           count = 0
           while !eof(io)
               ch = read(io, Uint8)
               count += 1
           end
           println("Bytes read: $count")
       end
readit (generic function with 1 method)

julia> @time readit(io)
Bytes read: 1010827264
elapsed time: 12.129340924 seconds (154348 bytes allocated)

julia> seekstart(io)
IOStream(<file ubuntu-14.04-desktop-amd64.iso>)

julia> @time readit(io)
Bytes read: 1010827264
elapsed time: 11.619949874 seconds (596 bytes allocated)

julia> seekstart(io)
IOStream(<file ubuntu-14.04-desktop-amd64.iso>)

julia> @time readit(io)
Bytes read: 1010827264
elapsed time: 11.881646789 seconds (596 bytes allocated)

julia> seekstart(io)
IOStream(<file ubuntu-14.04-desktop-amd64.iso>)

julia> function doread(io)
           count = 0
           fsize = getsize(io)
           while count < fsize
               ch = read(io, Uint8)
               count += 1
           end
           println("Bytes read: $count")
       end
doread (generic function with 1 method)

julia> function getsize(io)
           seekend(io)
           fsize = mark(io)
           seekstart(io)
           return fsize
       end
getsize (generic function with 1 method)

julia> @time doread(io)
Bytes read: 1010827264
elapsed time: 5.261891288 seconds (155772 bytes allocated)

julia> seekstart(io)
IOStream(<file ubuntu-14.04-desktop-amd64.iso>)

julia> @time doread(io)
Bytes read: 1010827264
elapsed time: 5.265442821 seconds (596 bytes allocated)

[JeffBezanson]

The times are much closer now. Beyond this I'm not sure it's possible to make eof as fast as integer comparison. Reading one byte at a time is not going to be super fast anyway.