periodically print JVM memory usage and load

memory_monitor_daemon.rb

require 'logger'

Class.new do

  LOGGER = Logger.new(STDOUT)
  # Logger.new File.open('jmx.log', File::WRONLY | File::APPEND)

  def initialize; @done = nil end

  def start
    thread = Thread.new { log_usage while ! @done }
    Kernel.at_exit { @done = true; thread.join(1) }
  end

  def log_usage
    log_system_load_with_process
    log_heap_mem_usage
    log_perm_gen_usage

    sleep calc_sleep_time
  rescue => e
    LOGGER.warn "#{e.inspect}\n  #{(e.backtrace || []).join("\n  ")}"; @done = :error
  end

  def log_memory_usage
    log_heap_mem_usage
    log_perm_gen_usage

    sleep calc_sleep_time
  end

  def log_heap_mem_usage
    usage = get_heap_mem_usage
    percent = (usage.used / usage.max.to_f) * 100
    LOGGER.info "MM HeapMem: #{format_bytes(usage.used)} / #{format_bytes(usage.max)}" +
                "  #{sprintf('%#2d', percent)}%"
  end

  def log_perm_gen_usage
    return unless usage = get_perm_gen_usage
    percent = (usage.used / usage.max.to_f) * 100
    LOGGER.info "MM PermGen: #{format_bytes(usage.used)} / #{format_bytes(usage.max)}" +
                "  #{sprintf('%#2d', percent)}%"
  end

  def log_system_load
    return unless load = get_system_load_average
    LOGGER.info "OS LoadAvg: #{sprintf "%#9.4f", load.round(4)}"
  end

  def log_system_load_with_process
    return log_system_load unless pcs = get_process_load_percent
    return unless sys = get_system_load_average
    LOGGER.info "OS LoadAvg: #{sprintf "%#9.4f", sys.round(4)} - " +
                "JVM Using: #{sprintf('%#2d', ((pcs * 1000) / 10.0))}%"
  end

  protected

  def get_system_load_average
    mem_mx = java.lang.management.ManagementFactory.getOperatingSystemMXBean
    avg = mem_mx.getSystemLoadAverage; avg.to_i == -1 ? nil : avg
  end

  def get_process_load_percent
    name = javax.management.ObjectName.getInstance("java.lang:type=OperatingSystem")
    list = mbean_server.getAttributes name, ['ProcessCpuLoad']
    return nil if list.empty?
    list[0].value # ProcessCpuLoad is the % CPU of current JVM for the system
  end

  def get_heap_mem_usage
    mem_mx = java.lang.management.ManagementFactory.getMemoryMXBean
    mem_mx.getHeapMemoryUsage
  end

  def get_perm_gen_usage
    pool_mx = java.lang.management.ManagementFactory.getMemoryPoolMXBeans
    pool_mx = pool_mx.find { |pool| pool.name =~ /Perm.?Gen/ }
    pool_mx ? pool_mx.getUsage : nil # no Perm Gen on Java 8
  end

  def mbean_server
    java.lang.management.ManagementFactory.getPlatformMBeanServer
  end

  #

  def calc_sleep_time
    normal, three_quart, geting_full = 5, 3, 1.5 # seconds

    return normal unless usage = get_perm_gen_usage

    return geting_full if (usage.used / usage.max.to_f) >= 0.90
    return three_quart if (usage.used / usage.max.to_f) >= 0.75
    normal
  end

  private

  def format_bytes(count)
    sprintf "%#6.1f MB", (count / (1000 * 1024)).round(2)
  end

end.new.start if defined? JRUBY_VERSION