use Process.clock_gettime instead of Time.now, resolves #13

CHANGELOG.markdown

@@ -2,6 +2,8 @@
 
 ## unreleased
 
+* Use `Process.clock_gettime` instead of `Time.now` which is faster and should give proper estimates even if sleeping in the middle [#13](https://github.com/toy/progress/issues/13) [@toy](https://github.com/toy)
+
 ## v3.5.2 (2019-07-14)
 
 * Remove deprecated `rubyforge_project` attribute from gemspec [rubygems/rubygems#2436](https://github.com/rubygems/rubygems/pull/2436) [@toy](https://github.com/toy)

lib/progress/class_methods.rb

@@ -1,6 +1,8 @@
 # encoding: UTF-8
 # frozen_string_literal: true
 
+require 'progress/elapsed_time'
+
 class Progress
   # Class methods of Progress
   module ClassMethods
@@ -165,14 +167,14 @@ def restart_beeper
     end
 
     def time_to_print?
-      !@next_time_to_print || @next_time_to_print <= Time.now
+      !@next_time_to_print || @next_time_to_print <= ElapsedTime.now
     end
 
     def print_message(options = {})
       force = options[:force]
       lock force do
         if force || time_to_print?
-          @next_time_to_print = Time.now + 0.3
+          @next_time_to_print = ElapsedTime.now + 0.3
           restart_beeper
           io << message_for_output(options)
         end

lib/progress/elapsed_time.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+class Progress
+  # Use Process.clock_gettime if available to get time more fitting to calculate elapsed time
+  module ElapsedTime
+    CLOCK_NAME = %w[
+      CLOCK_UPTIME_RAW
+      CLOCK_UPTIME
+      CLOCK_MONOTONIC_RAW
+      CLOCK_MONOTONIC
+      CLOCK_REALTIME
+    ].find{ |name| Process.const_defined?(name) }
+
+    CLOCK_ID = CLOCK_NAME && Process.const_get(CLOCK_NAME)
+
+  module_function
+
+    def now
+      if CLOCK_ID
+        Process.clock_gettime(CLOCK_ID)
+      else
+        Time.now.to_f
+      end
+    end
+  end
+end

lib/progress/eta.rb

@@ -1,10 +1,12 @@
 # frozen_string_literal: true
 
+require 'progress/elapsed_time'
+
 class Progress
   # Estimate time of arrival
   class Eta
     def initialize
-      @started_at = Time.now
+      @started_at = ElapsedTime.now
     end
 
     def left(completed)
@@ -15,7 +17,7 @@ def left(completed)
     end
 
     def elapsed
-      seconds_to_string(Time.now - @started_at)
+      seconds_to_string(ElapsedTime.now - @started_at)
     end
 
   private
@@ -36,7 +38,7 @@ def seconds_to_string(seconds)
     end
 
     def seconds_left(completed)
-      now = Time.now
+      now = ElapsedTime.now
       return unless completed > 0 && now - @started_at >= 1
 
       current_eta = @started_at + (now - @started_at) / completed

spec/elapsed_time_spec.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require 'progress/elapsed_time'
+
+describe Progress::ElapsedTime do
+  let(:timeout){ 0.01 }
+
+  describe '.now' do
+    it 'returns incrementing value' do
+      expect{ sleep timeout }.to change{ described_class.now }.by_at_least(timeout)
+    end
+  end
+end