Monotonic clock for more accurate timeouts.

lib/connection_pool/monotonic_time.rb

@@ -0,0 +1,66 @@
+# Global monotonic clock from Concurrent Ruby 1.0.
+# Copyright (c) Jerry D'Antonio -- released under the MIT license.
+# Slightly modified; used with permission.
+# https://github.com/ruby-concurrency/concurrent-ruby
+
+require 'thread'
+
+class ConnectionPool
+
+  class_definition = Class.new do
+
+    if defined?(Process::CLOCK_MONOTONIC)
+
+      # @!visibility private
+      def get_time
+        Process.clock_gettime(Process::CLOCK_MONOTONIC)
+      end
+
+    elsif defined?(RUBY_ENGINE) && RUBY_ENGINE == 'jruby'
+
+      # @!visibility private
+      def get_time
+        java.lang.System.nanoTime() / 1_000_000_000.0
+      end
+
+    else
+
+      # @!visibility private
+      def initialize
+        @mutex = Mutex.new
+        @last_time = Time.now.to_f
+      end
+
+      # @!visibility private
+      def get_time
+        @mutex.synchronize do
+          now = Time.now.to_f
+          if @last_time < now
+            @last_time = now
+          else # clock has moved back in time
+            @last_time += 0.000_001
+          end
+        end
+      end
+    end
+  end
+
+  ##
+  # Clock that cannot be set and represents monotonic time since
+  # some unspecified starting point.
+  #
+  # @!visibility private
+  GLOBAL_MONOTONIC_CLOCK = class_definition.new
+  private_constant :GLOBAL_MONOTONIC_CLOCK
+
+  class << self
+    ##
+    # Returns the current time a tracked by the application monotonic clock.
+    #
+    # @return [Float] The current monotonic time when `since` not given else
+    #   the elapsed monotonic time between `since` and the current time
+    def monotonic_time
+      GLOBAL_MONOTONIC_CLOCK.get_time
+    end
+  end
+end

lib/connection_pool/timed_stack.rb

@@ -1,5 +1,6 @@
 require 'thread'
 require 'timeout'
+require_relative 'monotonic_time'
 
 ##
 # Raised when you attempt to retrieve a connection from a pool that has been
@@ -72,7 +73,7 @@ class ConnectionPool::TimedStack
     options, timeout = timeout, 0.5 if Hash === timeout
     timeout = options.fetch :timeout, timeout
 
-    deadline = Time.now + timeout
+    deadline = ConnectionPool.monotonic_time + timeout
     @mutex.synchronize do
       loop do
         raise ConnectionPool::PoolShuttingDownError if @shutdown_block
@@ -81,7 +82,7 @@ class ConnectionPool::TimedStack
         connection = try_create(options)
         return connection if connection
 
-        to_wait = deadline - Time.now
+        to_wait = deadline - ConnectionPool.monotonic_time
         raise Timeout::Error, "Waited #{timeout} sec" if to_wait <= 0
         @resource.wait(@mutex, to_wait)
       end