cpu_usage.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-
require "webrick"
require "inline"
require "ruby-growl"

class Numeric
  def near?(with)
    (self - with).abs < 10
  end
end

class Array
  def average
    self.size > 0 ? self.inject{ |a,b| a+b } / self.size : 0
  end
end

module Processor
  class << self
    # http://d.hatena.ne.jp/harukasan/20080825#1219609683
    inline do |builder|
      builder.include '<mach/host_info.h>'
      builder.include '<mach/processor_info.h>'
      builder.c <<-EOF
    double usage(void) {
        mach_port_t host_port;
        host_cpu_load_info_data_t prev_cpu_load, cpu_load;
        mach_msg_type_number_t count = HOST_CPU_LOAD_INFO_COUNT;
        natural_t user, system, idle;
        double usage;
        host_port = mach_host_self();
        host_statistics(host_port, HOST_CPU_LOAD_INFO, (host_info_t)&prev_cpu_load, &count);
        sleep(1);
        host_statistics(host_port, HOST_CPU_LOAD_INFO, (host_info_t)&cpu_load, &count);
        user = cpu_load.cpu_ticks[CPU_STATE_USER] - prev_cpu_load.cpu_ticks[CPU_STATE_USER];
        system = cpu_load.cpu_ticks[CPU_STATE_SYSTEM] - prev_cpu_load.cpu_ticks[CPU_STATE_SYSTEM];
        idle = cpu_load.cpu_ticks[CPU_STATE_IDLE] - prev_cpu_load.cpu_ticks[CPU_STATE_IDLE];
        usage = (double)(user + system) / (system + user + idle) * 100.0;
        return usage;
    }
    EOF
    end
  end
end

history = []
about = Processor.usage
growl = Growl.new "127.0.0.1", "cpu-usage", ["message"]

WEBrick::Daemon.start do
  loop do
    history << Processor.usage
    history.shift if history.size > 4
    average = history.average
    if not average.near? about
      growl.notify "message", "CPU Usage",
        "%.1f%% (#{"+" if history.average > about}%.1f)" % [average, average - about]
      about = average
    end
  end
end