egonSchiele · May 16, 2013 18:20 · May 16, 2013
diff --git a/dining_with_waiter.rb b/dining_with_waiter.rb
@@ -0,0 +1,92 @@
+require 'thread'
+
+class Waiter
+  def initialize
+    @mutex = Mutex.new
+  end
+
+  def can_eat? philosopher
+    left = philosopher.left_fork
+    right = philosopher.right_fork
+    @mutex.synchronize do
+      if !left.used && !right.used
+        left.used = true
+        right.used = true
+        return true
+      else
+        return false
+      end
+    end
+  end
+
+  def stop_eating philosopher
+    @mutex.synchronize do
+      philosopher.left_fork.used = false
+      philosopher.right_fork.used = false
+    end
+  end
+end
+
+class Philosopher
+  attr_accessor :left_fork, :right_fork
+  def initialize(name, left_fork, right_fork, waiter)
+    @name = name
+    @left_fork = left_fork
+    @right_fork = right_fork
+    @waiter = waiter
+    think
+  end
+
+  def think
+    puts "Philosopher #@name is thinking..."
+    sleep(rand())
+    puts "Philosopher #@name is hungry..."
+    dine
+  end
+
+  def dine
+    while !@waiter.can_eat?(self)
+      think
+    end
+    puts "Philosopher #@name eats..."
+    sleep(rand())
+    puts "Philosopher #@name belches"
+    @waiter.stop_eating(self)
+    think
+  end
+end
+
+n = 5
+
+forks = []
+
+class Fork
+  attr_accessor :used
+  def initialize
+    @used = false
+  end
+end
+
+(1..n).each do |i|
+  forks << Fork.new
+end
+
+threads = []
+waiter = Waiter.new
+
+(1..n).each do |i|
+  threads << Thread.new do
+    if i < n
+      left_fork = forks[i]
+      right_fork = forks[i+1]
+    else
+      # special case for philosopher #5 because he gets forks #5 and #1
+      # and the left fork is always the lower id because that's the one we try first.
+      left_fork = forks[0]
+      right_fork = forks[n]
+    end
+    Philosopher.new(i, left_fork, right_fork, waiter)
+  end
+end
+
+threads.each {|thread| thread.join}