naive jstat proof-of-concept for ruby

ruby_live_gc_stats.rb

Thread.new do
  GC::Profiler.enable
  current_message = ""
  epoch           = Time.now
  total_time      = 0
  gc_events       = 0
  heap_use        = 0
  heap_size       = 0
  fmt             = "%7s %5s %15s %15s %10s"

  Thread.new do
    loop do
      # TODO: Could drop GC events added between accessing them and clearing.
      total_time += GC::Profiler.total_time
      GC::Profiler.raw_data.each do |gc_event|
        heap_use  = gc_event[:HEAP_USE_SIZE]
        heap_size = gc_event[:HEAP_TOTAL_SIZE]
        gc_events += 1
      end
      GC::Profiler.clear
      current_message = fmt % [
        "%.2f" % (Time.now - epoch),
        gc_events,
        "%.2f" % (heap_use / 1024.0 / 1024),
        "%.2f" % (heap_size / 1024.0 / 1024),
        "%.3f" % total_time
      ]
      sleep 0.5
    end
  end

  server = TCPServer.new 8787
  loop do
    Thread.start(server.accept) do |client|
      begin
        client.puts fmt % [
          "Time",
          "#",
          "Heap Use (mb)",
          "Heap Size (mb)",
          "GC Time (s)"
        ]

        loop do
          client.puts current_message
          sleep 0.5
        end
      rescue Errno::EPIPE
      end
    end
  end
end

sample_output

   > telnet localhost 8787
   Time     #   Heap Use (mb)  Heap Size (mb) GC Time (s)
   0.50     7            2.22            2.25      0.002
   1.00    61            3.06            3.09      0.003
   1.50   139            3.91            3.94      0.006
   2.00   194            4.76            4.80      0.007
   2.50   248            5.60            5.64      0.008
   3.01   302            6.44            6.47      0.009
   3.51   390            7.11            7.14      0.012
   4.01   445            7.96            8.00      0.013
   4.51   500            8.81            8.85      0.014
   5.01   554            9.65            9.69      0.015
   5.51   608           10.49           10.53      0.016
   6.02   662           11.34           11.38      0.018
   6.52   717           12.20           12.23      0.019
   7.02   834           12.43           12.45      0.021
   7.52   943           12.43           12.45      0.022
   8.02  1052           12.43           12.45      0.023
   8.52  1162           12.43           12.45      0.024
   9.02  1271           12.43           12.45      0.025
   9.52  1399            9.22           12.45      0.026
  10.03  1513            9.22           12.45      0.028
  10.53  1622            9.22           12.45      0.029
  11.03  1733            9.22           12.45      0.030
  11.53  1841            9.22           12.45      0.031
  12.03  1957            9.20           12.45      0.032

server.rb

require 'socket'
require './ruby_live_gc_stats'

loop do
  1000.times do
    Object.new
  end
  sleep 0.01
end