File.read的Ruby性能_Ruby_String_Performance_Io

File.read的Ruby性能

ruby string performance io

File.read的Ruby性能,ruby,string,performance,io,Ruby,String,Performance,Io,给定以下脚本： require 'rubygems' require 'open-uri' require 'benchmark' response = open('http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog') outside = Benchmark.measure do response_body = response.read 10000.times do response_body.sca

给定以下脚本：

require 'rubygems'
require 'open-uri'
require 'benchmark'

response = open('http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog')

outside = Benchmark.measure do
  response_body = response.read
  10000.times do
    response_body.scan(/dog/)
  end
end

inside = Benchmark.measure do
  10000.times do
    response.read.scan(/dog/)
  end
end

puts [outside, inside].map(&:utime).inspect

我得到以下结果：

[1.25, 0.06000000000000005]

为什么每次读取文件的性能会提高20倍

如果我的系统信息很重要：

ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.4.0]

这是因为在第一次测试之后，

response

被读取到最后，而在第二次测试的每次迭代中，

read

的结果都是微不足道的，这节省了时间，而且它也只返回空字符串。因此，

扫描也很快结束
irb> response.read.scan(/dog/)
=> ["dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog"]
irb> response.read.scan(/dog/)
=> []

这是因为在第一次测试之后，response
被读取到最后，而在第二次测试的每次迭代中，read
的结果都是微不足道的，这节省了时间，而且它也只返回空字符串。因此，扫描也很快结束
irb> response.read.scan(/dog/)
=> ["dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog"]
irb> response.read.scan(/dog/)
=> []

open（'http://gdata.youtube.com/feeds/api/videos?q=skateboarding+狗）。读取。扫描（/dog/）=>[“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“狗”、“，“dog”、“dog”、“dog”、“dog”、“dog”、“dog”]
@Kaleidoscope关键在于read
移动响应的读取指针（它充当流）。当您第二次调用read
时，它返回空字符串。open（'http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog'）.read.scan（/dog/）=>[“dog”狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗、狗
@Kaleidoscope关键是read
移动响应的读取指针（作为流）。当您第二次调用read
时，它返回空字符串。